:Not only can energy have mass, most of the mass you deal with day-to-day is energy. The mass of protons and neutrons are much greater (by about [[Mass_of_proton#Quarks_and_the_mass_of_the_proton|eighty times]]) than the summed masses of the constituent quarks. It's the energy associated with bringing the quarks together that accounts for the rest. Most of the mass of protons and neutrons (and by extension of most things) is due to energy, rather than (rest) mass of fundamental particles. -- [[Special:Contributions/174.21.229.4|174.21.229.4]] ([[User talk:174.21.229.4|talk]]) 18:50, 22 January 2011 (UTC)
:Not only can energy have mass, most of the mass you deal with day-to-day is energy. The mass of protons and neutrons are much greater (by about [[Mass_of_proton#Quarks_and_the_mass_of_the_proton|eighty times]]) than the summed masses of the constituent quarks. It's the energy associated with bringing the quarks together that accounts for the rest. Most of the mass of protons and neutrons (and by extension of most things) is due to energy, rather than (rest) mass of fundamental particles. -- [[Special:Contributions/174.21.229.4|174.21.229.4]] ([[User talk:174.21.229.4|talk]]) 18:50, 22 January 2011 (UTC)
[[User:Count Iblis/Speed of light|See here for another perspective]] [[User:Count Iblis|Count Iblis]] ([[User talk:Count Iblis|talk]]) 22:56, 22 January 2011 (UTC)
== Discovery of link between food and energy ==
== Discovery of link between food and energy ==
Revision as of 22:56, 22 January 2011
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
What causes a (metal) cooking pot (no handle) to rock from side-to-side when on a stove burner (electric in my case) just as the water is about to boil? This motion can be halted temporarily by grasping the pot briefly. When released, the rocking resumes.--Koosharem (talk) 01:20, 18 January 2011 (UTC)[reply]
Even before proper boiling, bubbles form in the water. These bubbles can exert forces on the walls of the pot. It could also be from Cavitation, which is the net effect of lots of tiny shock waves created by tiny bubbles collapsing. --Jayron32 03:03, 18 January 2011 (UTC)[reply]
Short, uncomplicated answer - The water is moving. Roger (talk) 07:43, 18 January 2011 (UTC)[reply]
undetectable viral load risk
how risky is it for those that have unprotected sex with someone that is hiv+ but has an undetectable viral load? I know that most people get HIV from other people that have just gotten it because those people have the highest amounts of replicas of the virus in their bloodstream. I know it is less likely that you would get hiv from someone on antiretrovirals or that is undetectable but is it nearly safe sex or not? Are there any statistics on this? Where would I find the answer to this question?Thisbites (talk) 01:29, 18 January 2011 (UTC)[reply]
How do I access a previously asked question.eg Jan 8 2011? —Preceding unsigned comment added by 118.208.117.68 (talk) 02:01, 18 January 2011 (UTC)[reply]
Arthur C Clarke and others have postulated "Gossamer thin sails" for interstellar travel using light presure.Since light by definition is massless how can it exert pressure to 'fill' the sails?
John Cowell118.208.117.68 (talk) 02:15, 18 January 2011 (UTC)[reply]
Photons (light) have momentum even though they have no mass. In modern physics, relativistic momentum is more complicated than just the simple "mass × velocity" relationship; in fact, momentum is related to the mass, velocity, and energy of the particle, according to a Lorentz transform. (So, even zero-mass photons can have non-zero momentum). This was formalized by Einstein as part of the theory of Special Relativity. Nimur (talk) 02:25, 18 January 2011 (UTC)[reply]
Photons have no rest mass. However, they clearly have energy and energy is mass, so anything which has energy can also exert a force. The photoelectric effect, not-so-coincidentally also described by Einstein at the same time he explained special relativity is an atomic-scale example of a massless photon moving a massed particle (the electron). It works just as well on solar sails. --Jayron32 03:00, 18 January 2011 (UTC)[reply]
Photons are not massless. They have no rest mass (or to put it another way, at rest they don't exist), but while in transit they do have mass. Ariel. (talk) 03:01, 18 January 2011 (UTC)[reply]
There's no disagreement about the physics here - this is strictly a matter of semantics and terminology. I use the term "mass" to specifically refer to rest mass - as do many physicists. An equally-valid but different definition of the unqualified term "mass" refers to the sum of the rest mass plus the normalized kinetic energy, per mass-energy equivalence. Photons have an exactly-zero rest mass. Many physicists (myself included) thus say "it has no mass." Many other physicists dislike this terminology, and always use "mass" to refer to relativistic mass. I don't think we need to devolve in to word-mungling pedantry over this, because we're all in agreement about the actual phenomena. See the mass article, the terminology section, and the list of reference texts and papers for a bunch of different opinions about which definition is "better." Nimur (talk) 04:08, 18 January 2011 (UTC)[reply]
I wasn't arguing with you (not sure if you thought I was), it was a reply to the OP. I prefer to assign the word mass to relativistic mass because that's the one you need to use for calculations - momentum, gravity, inertia, etc. The trouble with doing so is that relativistic mass is not a constant (because it depends on who you are comparing it with), so I understand the arguments for assigning it to rest mass. Ariel. (talk) 04:22, 18 January 2011 (UTC)[reply]
Energy in a magnet.
For more than 20 years I used a 3 inch magnet on a daily basis.It was so strong it would fly out of my hand if I got too close steel and the only way to release it from the deck of my truck was to slide it to the edge and carefuly remove.As a tool of trade for a scrap metal buyer it even exerted a 'pull' on 304 and 316 stainless steel.It was used for holding steel for welding,holding spring doors open etc.It would have lifted the equivalent of hundreds of tons over the years without diminishing in strength.
How can so much potential energy be incorporated in something so small,how is it stored and calculated,and surely there must be a multitude more practical uses for such a mini powerpack other than computers and maybe speakers?
John Cowell118.208.117.68 (talk) 03:07, 18 January 2011 (UTC)[reply]
The nutshell answer is that a magnet exerts force, which is neither energy nor work. Work, rather, is force acting over a distance. When the magnet leaps from your hand to the steel, it's done some work, because it's moved. However, it's then stuck to the steel and does no further work. For it to move again, you've got to do work of your own (counteracting the work the magnet did) to get it back away from the steel. As for other practical uses (I'll leave aside whether they're more practical, as computers are way up there), magnets are essential to electric motors, generators, transformers, and medical devices. — Lomn 05:14, 18 January 2011 (UTC)[reply]
I was thinking about this the other day again because magnet questions are quite common on the ref desk. Maybe someone has used this analogy before but I thought a spring analogy might be good at illustrating the difference between force and energy. A loaded spring exerts a strong force, try holding a strong spring closed just with your arms for a long time! It can take a lot of energy on YOUR part. But a spring can only do an amount of work relative to its length and force it was loaded with to begin with. Once a spring is "unloaded" that's it, no more force. Same as a magnet. Vespine (talk) 05:48, 18 January 2011 (UTC)[reply]
OP, This is by no means the first time a human has had this thought! :) Magnets are quite baffling until you understand how they work. It's the mystery of magnets that has led men on life-long fruitless and often fraudulent attempts at gaining "free" energy/money (Steorn, for example). Until a material is discovered that can block magnetic fields, no "work" can be done by them, just simple attraction. They are still fun to play with thoughZzubnik (talk) —Preceding undated comment added 12:39, 18 January 2011 (UTC).[reply]
This work has some interesting things to say regarding the science behind magnets. --Jayron32 14:43, 18 January 2011 (UTC)[reply]
For those of you wondering, the song in the link Jayron gave is the source of the "Fucking magnets, how do they work?" Internet meme (which may not really be a meme, the talk page argues...). Also, I never realized people got hung up about the use of the word "miracles" in that song :rolleyes: TomorrowTime (talk) 15:16, 18 January 2011 (UTC)[reply]
I'd like to point out the enormous work I do every day by exerting a force of mumble Newton with by behind to the seat of my chair - not to mention the nightly work quota I exert on my bed. ;-) --Stephan Schulz (talk) 17:32, 18 January 2011 (UTC)[reply]
The Tesla is not actually a unit of energy, so you can't say how much energy it takes to make a magnet of a certain strength. And yet, it would be interesting to know how much actual energy it takes to turn a non-magnetic chunk of metal or rare earth into a powerful magnet like the one described; and conversely whether there is any theoretical way by which the entropy of the magnet as it degrades from perfect order could be used to drive a thermodynamic process that produces work. Hmmm - is this the same as a measurement of any excess thermal energy released if the magnet is pulverized under a powerful ram? I would think that the amount of energy needed to create two magnets of opposite polarity must exceed the amount of energy they release by coming forcefully together - I suspect that this is by some large factor - I wonder what physical factor describes this necessary limitation on the ease with which permanent magnetism can be induced in a material. Wnt (talk) 06:10, 19 January 2011 (UTC)[reply]
I suspect that the 'crushing' process would actually be endothermic, not exothermic. Ordered, aligned spins in a ferromagnetic material have a lower energy than randomly oriented spins; you have to put in energy to break the alignment. At the Curie temperature, a phase transition occurs when you move from aligned to random spins; this shows up as a measurable endothermic bump by differential thermal analysis. Similarly, if you just pull aligned-spin particles or domains apart without jumbling their orientations, that costs you energy as well — the energy of aligned spins is lower than the energy of the free or separated particles. TenOfAllTrades(talk) 14:30, 19 January 2011 (UTC)[reply]
Well, I have to admit, you're right about that. My intuitive feeling was that a pile of powdered magnet shouldn't spontaneously assemble into a powerful magnet ball - I wonder if that was also false. Wnt (talk) 18:07, 19 January 2011 (UTC)[reply]
Will an object past the event horizon of a black hole inevitably reach the singularity?
An object around a gravitational body like the Earth can orbit indefinitely if its velocity is sufficiently high, but is it possible for an object to remain stationary within a black hole? Likewise, can an observer past the event horizon perceive other objects? By definition, light can not escape the horizon, so would it be impossible for photons to reach the observer from further within the black hole? —Preceding unsigned comment added by 68.40.57.1 (talk) 03:27, 18 January 2011 (UTC)[reply]
Yes, in case of Schwarzschild black hole, object that crosses event horizon reaches the singularity sooner or later. All the paths inside of event horizon lead to singularity. So harder it tries to avoid, sooner it reaches singularity. For other types of black holes (charged or rotating black holes), there is possibility of avoiding singularity. I am doubtful whether an object can remain stationary within a black hole. About your last question, are you asking whether photons from within black hole can reach observer who is outside event horizon? No, photons cannot escape from black hole. Or, are you asking whether observer within the black hole can observe photons? Yes, observer falling inside black hole continues to observer things according to his clock, he cannot determine whether he has reached event horizon or has crossed it. - manya (talk) 04:21, 18 January 2011 (UTC)[reply]
To clarify, I was asking whether the observer within the event horizon can detect photons from further inside the black hole. Also, your statement regarding the observer not being able to determine whether he has reached the event horizon is in contradiction of the article on it. --68.40.57.1 (talk) 04:34, 18 January 2011 (UTC)[reply]
No, it is exactlyt confirmed by the event horizon article. Let me quote it for you. "An observer crossing a black hole event horizon can calculate the moment they've crossed it, but will not actually see or feel anything special happen at that moment." --Jayron32 04:40, 18 January 2011 (UTC)[reply]
I presume you meant to say "within the event horizon", not "within the singularity". Yes, for a while an observer inside the event horizon will be able to see an object that's further inside the black hole, that fell in shortly before the observer. However, the object will rapidly move further away from the observer, due to the extreme tidal forces, and the object's image will become red shifted, to the point where the observer soon won't be able to see it at all. In other words, the appearance of the object will qualitatively appear very similar to the appearance of an infalling object as seen from an observer that's outside the event horizon. Red Act (talk) 06:16, 18 January 2011 (UTC)[reply]
You have to be specific about what you mean by "further inside", because black hole spacetimes are nothing like the ordinary flat space where concepts like "inside" are normally defined and make sense. The most obvious thing you might mean by "further inside" is that the Schwarzschild r coordinate is smaller. Outside the event horizon, that coordinate measures distance from the center of the hole, more or less. Inside the event horizon, though, it measures time. The singularity is in the future, not in a particular place, and "further inside", in this sense, would really be "later in time". You can't see the future, even inside a black hole. You can, however, see objects that crossed the event horizon before you did. The easiest way to understand how this works is to look at a diagram like the one to the right. Ignore everything but the upper right quadrant. The straight diagonal line is the event horizon; below and to the right of that is the outside world; above and to the left is the black hole interior. The singularity is the boundary of the grey region. The grey region itself is nothing (it's not part of the solution). The past is down, the future is up. Light travels along 45° diagonal lines. You can only cross the event horizon from right to left, since you're limited by the speed of light. If you draw two sub-light worldlines crossing the horizon, it's easy to see that light from the first one will reach the second, so you can see someone who crossed the horizon before you did. You will hit the singularity before you see them hit the singularity, though. The animated blue lines are lines of constant Schwarzschild r. -- BenRG (talk) 07:25, 18 January 2011 (UTC)[reply]
Ticklish sensation near forehead
If an object is brought close to my forehead, but does not touch it, my forehead becomes sensitive and starts tingling and becoming very "ticklish", for lack of a better term. For several years, I've asked certain people if they've had the same sensation, and I've only met one girl who did. I have unsuccessfully tried testing the sensation with my eyes closed. As the object (any object) is brought closer to the forehead, the sensation deepens. It used to be really bad when I was a child, but now as an adult, I hardly even think about it anymore. It just popped into my head a minute ago and I decided to ask about it :)Reflectionsinglass (talk) 03:56, 18 January 2011 (UTC)[reply]
You are not alone.[1] -- I'm particularly interested in this comment from DocCathode:
"Nothing supernatural about it. It's a mixture of a sense of danger/discomfort, the urge to move away, and the repression of that urge.
"To prove this, you need a friend who trusts you and follows instructions. Tell them to stay still, and to open and close their eyes when you tell them. Begin approaching with finger about two feet away. Tell them to close their eyes. Move the finger foot closer and tell them to open their eyes. Tell them to close their eyes. Move the finger to six inches away. Tell them to open their eyes. Tell them to close their eyes. Move the finger to three inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to two inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to an inch. Tell them to open their eyes. Tell them to close their eyes. Move the the finger to half an inch from their forhead. Tell them to open their eyes. Tell them to close their eyes. Slowly and quietly move your arm away from them. Tell them to open their eyes.
"The tingling sensation is most intense the last time, despite the fact the no object is near their forehead."
Please try that and let us know what happens. 71.198.176.22 (talk) 05:57, 18 January 2011 (UTC)[reply]
what killed Dinosaurs
I read an article that had say something about the death of mamots in 35000years ago that may be general for last happening for dinosoros 0 the radiation of any supper nova can kill dinosoros
in some million years ago. A.mohammadzade jan 18 iran —Preceding unsigned comment added by 78.38.28.3 (talk) 04:23, 18 January 2011 (UTC)[reply]
I'm not sure I understand your question properly. Dinosaurs became extinct during the Cretaceous–Tertiary extinction event. There are various theories about what caused this to happen. The most popular theories have to do with an asteroid (or asteroids) hitting the earth. You may also find the simple wikipedia article or the farsi wikipedia article on this topic to be helpful. Calliopejen1 (talk) 04:55, 18 January 2011 (UTC)[reply]
3500 years ago? Are you thinking about Noah's flood (Nuh in Islam)? According to the (Christian) Ussher chronology this occurred 2348 BCE. Modern science places the dinosaurs extinction to the Cretaceous–Tertiary event 65.5 million years ago (as Calliopejen1 noted), and woolly mammoths to about 10 thousand years ago. BTW, several web-browsers have spell-checkers for their text-entry boxes; you should consider installing one for all the languages you speak. CS Miller (talk) 05:36, 18 January 2011 (UTC)[reply]
Actually, the OP said 35,000 years ago, not 3,500 - no need to drag young earth creationism into this. As you note, mammoths were still alive and well at that point, so it's a curious date to bring up. Our article on 35,000 BC No, we don't really have an article on that date, but it is a nice redirect... doesn't mention anything particularly germane. 15:08, 18 January 2011 (UTC)
Ooops. My apologies. I can only think the lack of punctuation made me not see one of the zeros, and conflate the OP's timescale with that of YECs. CS Miller (talk) 17:05, 18 January 2011 (UTC)[reply]
There is really no question that the asteroid killed the dinos. Headline writers and popular science in general will never tire of stirring up controversies, but a panel of 41 international experts have met and agreed that there is consensus on the cause. This is mentioned in the articles. Imagine Reason (talk) 00:00, 19 January 2011 (UTC)[reply]
Actually, I killed the dinosaurs. It was a time travel mistake, sorry, but when you gotta sneeze, you gotta sneeze. I take no responsibility for the mammoths, though. I think Baseball Bugs did them in. --Ludwigs2 00:04, 19 January 2011 (UTC)[reply]
I thought Tezuka killed the dinosaurs. — DanielLC 06:02, 19 January 2011 (UTC)[reply]
What is the fastest growing, soil erosion preventing, preferably edible plant suitable for San Francisco's climate? 71.198.176.22 (talk) 05:47, 18 January 2011 (UTC)[reply]
Lespedeza are commonly used in the Southeastern U.S. and meet all of your requirements except edibility. Not sure if it will grow in the Bay area, however. --Jayron32 05:53, 18 January 2011 (UTC)[reply]
never say death star for pulsars
the crab nebula is sending several rays and is alive there in space . the heart of the star is sending palses so we ought never say the super nova has died . a. mohammad zade iran --78.38.28.3 (talk) 06:06, 18 January 2011 (UTC)[reply]
There is no question that the crab nebula article uses the term "dead" only when citing [2]. 71.198.176.22 (talk) 06:03, 18 January 2011 (UTC)[reply]
when the earth was shining
i think that the earth was shining for some million years . if you want to know why then that will explain with my new theory a. mohammad zade
Why don't you ask whether your theory is consistent with the evidence so we can critique it for you? To do so, you would have to explain it. It is true that the elements heavier than iron came from supernovae in the Earth's distant past. 71.198.176.22 (talk) 06:06, 18 January 2011 (UTC)[reply]
thanks for giving commnets .i will soon write my theory hear i have some problems in safe evaluation andpublishing . so i save it such as patent . it will wrote here as soon as i published .--78.38.28.3 (talk) 06:13, 18 January 2011 (UTC)[reply]
Wikipedia is not the right place for people to develop their new theories. See our WP:Original Research policy. Comet Tuttle (talk) 18:38, 18 January 2011 (UTC)[reply]
Pre-existing conditions and Medical Insurance
I really don't understand why people who have a pre-existing conditions are making SUCH a big deal out of having to pay more for insurance. I understand they get mad if they are denied, but they should have to pay more. It's the same way I have to pay more for auto insurance because I am younger and have had several speeding tickets in the past few years, I am a greater risk. Many (not all, but many) CHOOSE to have these pre-existing conditions. Many people who are obese, choose to have several other related problems, many people who high cholesterol choose to have it, same with so many other conditions. Is there a flaw in my thinking? I'm already paying over $200 a month for insurance when I don't ever use it because of all these abusers, when I am perfectly healthy, take care of myself, follow a healthy diet, and go to the gym 5 days a week. If everyone was covered, it would just make the problem worse and more expensive for everyone. —Preceding unsigned comment added by 76.169.33.234 (talk) 07:44, 18 January 2011 (UTC)[reply]
What country are you from? People there might be grateful they don't live here in Australia. Here, if you have a pre-existing condition, you can be denied any benefits for treatment of that condition for 12 months after taking out the insurance; but after that, you're fully covered like everybody else. There's no alteration to premiums, though; that's strictly outlawed. -- Jack of Oz[your turn] 08:00, 18 January 2011 (UTC)[reply]
USA. I don't know how people think in Australia or in other countries, but I work in a pharmacy and my customers think just because they are taking a cholesterol medication, they can eat whatever they want. My customer was joking about it the other day. —Preceding unsigned comment added by 76.169.33.234 (talk) 08:04, 18 January 2011 (UTC)[reply]
Yes, insurance companies have to discriminate, but it's sometimes hard to be tough on those with self-inflicted conditions while being fair to those whose ailments are innocently gained. HiLo48 (talk) 08:09, 18 January 2011 (UTC)[reply]
No, insurance companies don't have to discriminate, but only if you run a system of compulsary insurance. This is what happens, in one form or another, across most of the developed world: compulsary insurance with a ban on discrimination. Physchim62(talk) 12:39, 18 January 2011 (UTC)[reply]
I'm actually kind of struck by your first sentence. My fiancee, in trying to get private coverage, has been rejected by every insurer in California due to a pre-existing condition, which we're told will continue to be the case for another couple years. This is not a matter of paying more - she's not even allowed in the existing high-risk pools. I hate to think where she'd be if neither she nor I had a job. HIPAA and COBRA (expensive) do ignore pre-existing conditions, but they are not available to everyone. As for whether people choose to have a pre-existing condition, I have no comment. Someguy1221 (talk) 08:15, 18 January 2011 (UTC)[reply]
HIPAA is a health information privacy act, not an insurance company. COBRA is Federally mandated insurance coverage for those who recently left employment. I do not see how those apply in the context you are using. -- kainaw™ 17:28, 18 January 2011 (UTC)[reply]
Further, California has a state managed program specifically for high-risk patients who have been denied insurance. It is explained here. -- kainaw™ 17:31, 18 January 2011 (UTC)[reply]
I wasn't even aware of that plan, thanks (but thankfully she has a job, and I don't even want to know how much that costs). I was referring to HIPAA health plans, by the way. I was using both that and COBRA as examples of coverage potentially available to individuals with pre-existing conditions who do not get such coverage through their current employer, or who are unemployed. Someguy1221 (talk) 00:04, 19 January 2011 (UTC)[reply]
Really it is a question of what costs we think are fair to spread across society, and which we don't. If you happen to be develop a terribly expensive health condition, through no fault of your own, should society bear this cost, or should you? Thinking from a position behind the veil of ignorance, one might prefer to spread such costs across society. Also, you note that some health conditions are in part caused by deliberate choices. This may be true, but most health conditions are not, and what sort of surveillance regime would be necessary to monitor which people this applies to? Such surveillance would likely be prohibitively expensive, as well as intrusive on privacy. Thinking forward into the future, as genetic health data becomes more readily available, it is plausible that insurance companies could very easily calculate your health risks to a much greater precision. (Assuming this were legal.) Is this something you would want? It is essentially just an extension of your principle of paying a premium that reflects your health risks. It would assign costs much more precisely to the individual, but it would change the nature of health insurance as we know it. Now, health insurance effectively insures against the risk that you will get Alzheimer's, for example. In the future, perhaps it would already be known that you will get Alzheimer's (even now, there are some genetic markers identified that are highly correlated with it). Then, since your premiums would already reflect your future disease, you would bear the cost for your Alzheimer's treatment, and your insurance would only be effective against risks such as being hit by a car and needing emergency surgery. Would this be preferable? To me, probably not. YMMV. Calliopejen1 (talk) 11:11, 18 January 2011 (UTC)[reply]
What does this have to do with science? thx1138 (talk) 13:01, 18 January 2011 (UTC)[reply]
Generally this is misplaced, although the degree to which disease is a "choice" could be more scientific. After all, obesity and even high cholesterol are controlled by genetic and other propensities (I suspect that there should be a dramatic role for epigenetics here...) I feel that nothing but prejudice controls what people like the OP pick out as a "choice" - after all, the commuter who suffers injuries in a traffic accident also made a choice, right? The skier who leaves his testes with a buried pole on the slopes, likewise. The HIV victim, few would disagree, but what about the victim of flu or rotavirus or meningitis or malaria, who could have avoided it all just by staying inside his front door?
It may be more for the humanities desk to answer what the point is of having insurance if suffering a diagnosis means being denied insurance. Why not just keep your money and pay as you go, with no private bureaucrats pretending to serve you by driving up costs? The problem is, no one wants to be diagnosed with anything, and as they are servants only of corporations and government the doctors are trusted far less than Mafia bookies, so preventative care becomes a pretty myth. Wnt (talk) 15:30, 18 January 2011 (UTC)[reply]
"Why should society pay for the consequences of someone's bad choices?" begs the question of bad things happening to people who have in no way brought it on themselves. It is a reasonable question whether a society should spread the medical costs across all members, or have a "Every man for himself and the devil take the hindmost" lifeboat ethic. A person can be bopping along, healthy as a horse at 20 and at 30, and at 40, never took a sick day, eating right, not smoking, exercising regularly, then suddenly they have some crippling injury or ailment, like a debilitating and persistent and ineradicable infection, or a crippling injury, or cancer, or heart disease, or insulin dependent diabetes, with little hope of getting individual health insurance from a for-profit insurer. Many Americans live in a fantasy world where they will always have a policy from work. If the hospitalization means you can't work, and you don't have or lose your employer-provided insurance, you are just out of luck when you need surgery or hospitalization which might cost $100,000. Figure on losing the home and spending every dollar of retirement savings. "Move in with the folks" is not an option when they are dead and gone. Even if someone with severely impaired health found a private insurer, it would cost more per month than they could pay, especially if they are not healthy and can only work part time or a lesser pay level than their previous fine career allowed. "Paying more for insurance because of a preexisting condition" may mean paying an extra $12,000 a year more than the basic insurance, or even more than that, which the unwell person simply cannot afford. According to a report, "80 percent of people with diabetes were uninsured after they lost health insurance coverage due to loss of a job or job change, divorce, change in income or health status, or a move. " It is not presently affordable for them. Over 50 million Americans have no health insurance, so that if they do go to see a doctor or have tests, they must pay "list price," typically several times what the cost is for those with insurance, since Blue Cross et al reduce the price to a fraction of what the doctor, hospital or lab says it should cost. For instance, Xrays that the insurer writes down to $100, and which cost me $15 out of pocket, would have cost the uninsured $350. An EKG that would have cost the uninsured $1100 got written down by the insurer to under $300 (and only cost me under $30). Edison (talk) 16:59, 18 January 2011 (UTC)[reply]
Fom a european persepective the "devil take the hindermost" American health care system, or lack of it, is scandalous. Add that to guns being used freely, with gun-murders being 100 times more common per capita. They are not good adverts for the US. 92.24.183.183 (talk) 14:42, 19 January 2011 (UTC)[reply]
While I agree with all that you said (in particular, many medical conditions are not or not fully the result of irresponsible choices), there is also another aspect: It might be cheaper to pay for the effect of someones bad choices. Sick people typically can contribute less to society - imagine Stephen Hawking without universal health care. Similarly, desperate people will do desperate deeds. Would you rather pay for someones cancer treatment via a social insurance system, or pay for more police to keep desperate husbands, wives, or parents from robbing banks to pay for treatment? --Stephan Schulz (talk) 17:24, 18 January 2011 (UTC)[reply]
This is a valid point, but it really doesn't go far enough. Society has prevented disaster by various back-door ways of paying for health care for the poor, such as hospitals providing care and then just not getting paid for it, then working the costs into care for other patients. But hospitals have become more and more commercialized, with less profitable sites even shutting down, and if political efforts to correct the situation are rebuffed, then you're left with a situation where a segment of the population denied access to health care would begin to turn on it as an enemy. The effect of even a single ambulance bomb would be devastating (and how do you apply security precautions?). The effect of three or four simultaneous attacks against all remaining hospitals of a metropolitan area would essentially put major health care out of commission for a hundred miles in any direction - even if such a homegrown al Qaida didn't manage to get their hands on the radiation sources inside the hospital ... Wnt (talk) 05:12, 19 January 2011 (UTC)[reply]
I have a concise answer: The argument (that people with pre-existing conditions should just suck it up and pay a lot more for their medical insurance) makes complete sense from an actuarial point of view, but it collides with many people's belief that a society should take care of its sick, even though this makes insurance more costly for the more-healthy. Comet Tuttle (talk) 18:37, 18 January 2011 (UTC)[reply]
Yes. Once we have decided we will not let people simply die on the street, then we must assess the cost of emergency treatment and conclude that an ounce (or penny) of prevention is worth a pound (dollar) of cure, therefore the next step is to try to fund preventative care. Because whether through taxes or insurance premiums, you still have to pay for the sick, so might as well pay less for better results. SamuelRiv (talk) 22:10, 18 January 2011 (UTC)[reply]
This isn't really a science issue and is OT on the RD anyway but that probably applies to most of this discussion. The above is one of the arguments for measures to tackle obesity, smoking and other problems as well as encouraging healthy eating, exercise etc in countries with some sort of socialised medical care. Of course depending on the measures this can lead to claims of nanny state, food police, sin tax and whatever else and measuring the efficacy of such measures is generally difficult at best. And I've seen it argued smokers at least actually cost the system less in the long run, particularly where there are other costs (e.g. in NZ where a government funded pension is something most citizens past a certain age are entitled) due to the shorter lifespan even with their added medical bills. (Of course you then get in to complicated issues like whether they contribute less.) Unrelated to this but related to the earlier point you also get the complex issue of how much should be spent on treating people with a given expected outcome. For example, is it worth spending $100k on treatment that may increase the chance of living past 5 years from 5% to 10%? (Very simplistic of course, the outcome of many treatments come in things like improved quality of life which are generally subjective.) Ironically this was seen to some extent in the US with the recent debates when the death camps nonsense came up. Nil Einne (talk) 22:46, 18 January 2011 (UTC)[reply]
Most of the others have hit the main points here, but I just want to point out that insurance that covers you when you are healthy, but not when you are sick, is not really insurance. That's just a series of subsidized physical exams. The entire point of insurance is that you pool the resources of many so that when others are in hard times, they have resources as well. It is a sign of how screwed up the American medical system has become that the basic notion of insurance has been completely forgotten by most Americans, who just understand it as "the way I pay for routine checkups and prescriptions." It's about spreading the risk, plain and simple. --Mr.98 (talk) 03:30, 19 January 2011 (UTC)[reply]
The deal with paying for routine checkups is that's how the insurance companies manage their own risk. The costs of dealing with tragic diseases goes up considerably the later they are treated; insurance companies actually save themselves money by making sure you go to the doctor regularly to for physicals, and to get even "nuisance" issues checked (like the non-specific and usually benign but occasionally deadly "Flu-like symptoms"). The ideal "deal" between insurance companies and their customers is something like "You agree to get checked by doctors more often, and we'll cover it when shit goes really bad". Same deal with prescription coverage; people would forgo necessary medicine if it's too expensive, and on the bulk these people will end up costing the insurance companies much more if you end up in the hospital getting treated for something your medicine could have prevented. This is not a defense of the American insurance industry at all; they've basically dropped the ball with regards to their fiduciary responsibility towards their clients. But in theory, the system is supposed to work as I describe. --Jayron32 05:26, 19 January 2011 (UTC)[reply]
Isn't it the insurance company's fiduciary duty to do the bare minimum to brand the sick person with a permanent record of poor health, and help their client (the employer) to get rid of the problem before it amounts to a major expense? Wnt (talk) 18:11, 19 January 2011 (UTC)[reply]
Thank god for the National Health Service. It has made me disinclined to emigrate to a sunnier cheaper or less crowded country as I would not have the piece of mind of knowing that I would get unlimited free health care if I needed it. See also Universal health care. 92.24.183.183 (talk) 13:17, 19 January 2011 (UTC)[reply]
I am the OP, sorry it took me so long to get back to this post....
Edison, you are really sucked into the idea that obesity and high cholesterol is almost all about genetics, when it has little to do with it. The issue here is that for a genetic defect (not sure if this would be the right word) to be present, it would require the proper environment. Almost every single obese person eats horribly and that is a choice. Same with many people with high cholesterol. You can be thin and have high cholesterol, but if you really take a look at it, almost every single person with high cholesterol is overweight, many of them even obese. If you look at both groups, neither one in almost every consumes a "healthy" or a low calorie diet (low cholesterol diet in the high cholesterol patient) and they almost never exercise if they do at all. Most these people "think" they know how to diet, but they have no clue, they think 3000 calories a day or more is a diet. They think exercising is walking around the block or taking the stairs instead of taking the elevator. Try going into the gym and pounding the weights for an hour and then doing 45 minutes of hardcore cardio 5 days a week and then lets see if you still have high cholesterol or are obese after a year doing that and consuming a low calorie diet. I can guarantee you over 90% of the people will be cured as long as they keep it up.
Now lets discuss choices in life. Everything you do is a "choice." Many or all of them involve some degree of risk. Everyone knows that driving a car involves risk, you can get into an accident. Some people choose to take that risk and some paranoid people or people that have been in very bad accidents that have not recovered emotionally choose to not take that risk. So is it a choice? Yes, it is. At my age, I choose to take the risk of maxing my car out to see how fast it goes on the freeway. I know there is more risk involved going very fast, but if I had children, I would not take that risk. Same with skiing, there is a risk involved. An example that may be more clear would be weight lifting, there is a great deal of risk involved. Personally, I choose not to do some exercises at the gym because of the risk involved. And yes, even with sex and contracting HIV there is a risk. Have you not heard of getting tested yourself and having your partner tested before you have unprotected sex? Do you think its a good idea to have sex with a woman or a male that has had 50 partners in the past? Would you take that risk? Some people would, some people wouldn't. That is called a choice. There is a distinction between acceptable risk and unacceptable risk.
The real issue here is that many diseases are preventable. Look at most people with type 2 diabetes. If they lose the damn weight and exercise, most of them would be cured. I work with one of them, he has either Jack in the Box, Kentucky fried chicken, or McDonalds every single day. Then he has 2 snickers and peanut M&Ms on top of it. He has high cholesterol and is overweight because of all that junk too. He never goes to the gym and has no interest at all in dieting. His blood sugar was dangerously high before he found out (at work by the way). As previously mentioned, going to the doctor for preventative care can reduce the chances of contracting several diseases or at least you can cut down costs to treat the disease if you catch it early. Most people don't even do that and it costs us healthy people tons of money. Some older women don't get mammograms as often as they should, others don't get them at all. Some older people don't get colonoscopies. Other people don't get their yearly physicals and dont people don't want to pay for their medication and think they know better than their doctor. In the end, it costs us money. It just hurts my wallet and others when I take good care of myself, eat healthy, exercise, and get regular checkups and do everything necessary to stay healthy and other people don't and I have to pay for it. There is no reason why I should have to. ALSO, let me add something to what I originally said. I don't have an issue with supporting people who are disabled and cannot work, I don't have a problem paying for their healthcare. I'm also kind of OK supporting some people who's income is around the poverty level, but then again, I do believe if they really wanted to, they could somehow, someway, come up with the money. I mean just imagine, the last time you really wanted something you could not really afford, didn't you figure out a way to come up with the money? I always do and so do many other people. —Preceding unsigned comment added by 76.169.33.234 (talk) 09:34, 20 January 2011 (UTC)[reply]
I'm gonna skip all the non-sense rant about having to burden the expenses of other people's choices (Welcome to life in society. Go be an hermit if you don't like it) and go directly to the only point of your post worth commenting on. YOU SHOULDN'T SPEED IN THE FREEWAY JUST FOR THE FUN OF IT. I sincerely hope that you get caught next time you do it, making the freeways safer for the rest of us. Dauto (talk) 16:27, 20 January 2011 (UTC)[reply]
To all the "Blame the victim" ranters: Heart disease, strokes, type 1 diabetes, (and even type 2 diabetes) and cancer, not to mention infections and injuries, happen all the time to those who take good care of their bodies. Some diseases are more prevalent among those who eat greasy food 10 times a day , smoke and never exercise, but you could still fill any number of hospital beds with those victims who are "blameless." Edison (talk) 22:35, 21 January 2011 (UTC)[reply]
You have two formulas under the section "Timescale"
Two different science textbooks are quoted for the source of these formula:
B. Gladman et al. (1996). "Synchronous Locking of Tidally Evolving Satellites". Icarus 122: 166. doi:10.1006/icar.1996.0117. (See pages 169-170 of this article.
Formula (9) is quoted here, which comes from S.J. Peale, Rotation histories of the natural satellites, in J.A. Burns, ed (1977). Planetary Satellites. Tucson: University of Arizona Press. pp. 87–112.)
Do both formulas come from the same publication?PaulNethercott (talk) 09:25, 18 January 2011 (UTC)[reply]
I fixed the link for you, and placed a link on the doi from the reference. Hopefully someone has access to read the article and can check for you. Ariel. (talk) 10:49, 18 January 2011 (UTC)[reply]
The article is available online here (PDF). It gives the first formula and cites to Peale. I didn't look thoroughly for the second formula - maybe someone else can do that? (Note that the Wikipedia article does not cite the second formula to this journal article specifically, though perhaps it also comes from here.) Peale does not seem to be available online anywhere. (I searched in google books using a variety of ISBNs that seem to be associated with the book, and I didn't get any results.) If you are interested in verifying the formula in the original source, the Burns book seems to be available in many university libraries and large cities' public libraries,[3] or you can buy it through Barnes & Noble for $1.99.[4]Calliopejen1 (talk) 10:54, 18 January 2011 (UTC)[reply]
An object hanging on a string
On this page: http://www.croomphysics.com/notes/app_hewitt/chapter2.pdf (page 11) I found an answer to a question that confuses me: "Consider what would happen if you suspended a 10-N object midway along a very tight, horizontally stretched guitar string. Is it possible for the string to remain horizontal without a slight sag at the point of suspension?"
Answer: "No way! If the 10-N load is to hang in equilibrium, there must be a supporting 10-N upward resultant. The tension in each half of the guitar string must form a parallelogram with a vertically upward 10-N resultant."
I understand this for a guitar string and a 10-N load, but what if the string is replaced by a strong rope, and the load is only 1 N. Surely it must be possible to pull at both ends of the rope with enough force to make it remain horizontal without a sag??? Actually, I tried this myself with a piece of rope that I pulled apart and a pair of scissors, and there was no perceptible sag. My reasoning is that a stretched rope must be able to exert an upward directed normal force in the same way as a table exerts an upward directed normal force. Am I correct?? Lova Falktalk 13:05, 18 January 2011 (UTC)[reply]
No. Your rope cannot exert a force at right-angles to itself. The only way it can hold something up is if it is pulling up at the point of the suspended object (to cancel the object's gravitational downward pull). If it's pulling up, it must have a vertical component to its direction, which means it's distorted down from perfectly horizontal. Once you recognize "one mass, one string", there's no basis for making a cutoff "only if the mass is less than a certain amount" or "only if the string has certain elasticity". For a very light mass on a very stiff string, the deflection is just very small (because the mass is light, doesn't require much upward pull, and that can be accomplished without much deflection because the string is so non-stretchy). DMacks (talk) 13:13, 18 January 2011 (UTC)[reply]
(edit conflict) No, there should always be a sag, but the sag may not be perceptible under certain parameters. A non-ridged string should always sag in the middle if supported only at the ends, regardless of how hard you pull it. What your eye defines for you as "horizontal" may have a higher tolerance than a true horizontal. In fact, horizontal is one of the least stable positions for such an arrangement, if you look at something like bridges; all rope bridges sag in the middle; if you try to make them not sag, then you end up putting so much force on the ropes as to make them too close to the breaking point for safety. In Suspension bridges, you often engineer the roadway to sort-of "reverse sag", that is many such bridges actually have a hill in the middle, in effect redirecting the stress into the ground anchors on either side of the bridge. --Jayron32 13:16, 18 January 2011 (UTC)[reply]
Indeed, the rope will sag under its own weight, even if you don't have any additional suspended mass. If the rope's mass is uniformly distributed along its length, it will form what is known as a catenary curve. TenOfAllTrades(talk) 15:12, 18 January 2011 (UTC)[reply]
Another perspective: in physics problems, 'rope' is often modeled as a mass-less object that has tensile strength but no compressive strength. Real ropes DO have compressive strength, especially large diameter ropes of short length. A short length of thick rope (~6" diam X 3' long), anchored at both ends can support an upright load-bearing catenary like the gateway arch. This would not usually be considered 'sagging'. SemanticMantis (talk) 17:37, 18 January 2011 (UTC)[reply]
I seem to recall an unintentional verse in a book by a distinguished scientist:
as you can see here. Of course, he's talking about the weight of the cord itself, but the sentences just before that are about the case of a weight hanging from a cord whose own weight is negligible. According to Martin Gardner in a Mathematical Games column reprinted in Martin Gardner's Sixth Book of Mathematical Games from Scientific American, Whewell was annoyed to learn about the "poem" and had the wording changed in the next edition. Gardner misquotes the "poem" slightly, though. --Anonymous, 05:10 UTC, January 20/11.
Even the ground will sag if enough weight is put on it. Compressive strength means only that the material resists sagging, not that it avoids it entirely. Wnt (talk) 18:42, 19 January 2011 (UTC)[reply]
Sure, I just wanted to point out the limitations of the way string is often modeled for simple problems. In particular, a string modeled with no compressive strength cannot take the shape of an upright catenary, but a real rope can. This may help explain some of the confusion between real-world problems and physics 101 type stuff. SemanticMantis (talk) 20:59, 19 January 2011 (UTC)[reply]
What if both ends of the string are attached to spherical cows? --Jayron32 00:57, 20 January 2011 (UTC)[reply]
This basically translates into "the absolute smallest a thing can be and still physically exist", right? HalfShadow 18:23, 18 January 2011 (UTC)[reply]
Not really. It's a really, really small distance, so there are some theories that it's the fundamental granularity of the universe, but none of the well-accepted, well-proven physics theories hold that there is anything special about that length. It's just the length unit you get if you attempt to scale units such that major physical constants come out to unity ("natural units"). Keep in mind that the mass unit you get when you do that (the Planck mass, is 2.2 x 10-9 kg, about the size of a human egg cell (see Orders of magnitude (mass). -- 140.142.20.229 (talk) 18:46, 18 January 2011 (UTC)[reply]
As it says in Planck length: "In some theories or forms of quantum gravity, it is the length scale at which the structure of spacetime becomes dominated by quantum effects, giving it a discrete or foamy structure, but other theories of quantum gravity predict no such effects." Basically, we don't know what happens at such small scales. --Tango (talk) 21:56, 18 January 2011 (UTC)[reply]
I think you might fairly say that it's the absolute smallest a black hole that can exist. Any smaller, and the Compton wavelength gets bigger; but the Schwartzschild radius gets smaller. Which means that the hole is too fuzzy to fit in the hole, so to speak. So if you have a black hole that is evaporating by Hawking radiation, something ought to give out at least mathematically around this time; the Heisenberg principle says you're not supposed to know where the black hole is that precisely, but how is it going to get away? You can play a merry chase through Planck mass, Planck length, Planck momentum, Matter wave to figure this out, but one word of caution - I initially looked up de Broglie wavelength to see how the math worked out and had a curious disagreement by a factor of 2 pi (on the Planck momentum; with the de Broglie wavelength you can't say a mass has a given wavelength without giving it some arbitrary velocity). It turns out that there's a distinction between the "reduced" and "non-reduced" Compton wavelength as explained in that article. A distinction which I don't understand... you'll need a real physicist for that... :( Wnt (talk) 05:02, 19 January 2011 (UTC)[reply]
Coal mining efficiency
I saw on a TV show this gigantic drilling machine many hundreds of feet below the surface around Pittsburgh, PA and started thinking about the massive amount of energy that must be needed to turn the thing's huge and undoubtedly heavy drill bits against the resistance of the earth it was drilling through, and the energy needed to move the thing forward, along with all the energy used for the other trolley cars, lights, ventilation systems, and of course the energy expenditures to raise the mined material back to the surface, and I wonder roughly how much energy quantified as an amount of coal (I know the machines don't take coal for fuel, but I want to know the figure in terms of coal) the average coal mining plant expends in all the actions it takes to extract 100 tons of coal? Just a very ballpark estimate is all I'm after here. For instance, do they use about a ton of coal's worth of energy to get 100 tons? Do they use over 50 tons' worth? Thanks. 20.137.18.50 (talk) 18:38, 18 January 2011 (UTC)[reply]
This is a very important and valuable analytic tool: it is formally known as EROEI (energy returned on energy invested). It is heavily studied by economists, business analysts, and geoscientists and engineers in the mining and production industries. I know quite a bit about the ballpark numbers for the oil industry, but unfortunately not for coal; I imagine coal mining experts know similar metrics for coal mining. I have heard reputable petrophysicists claim that the EROI for tar sands is dramatically and dangerously approaching 1.0 in the long run; this means that it is economically unsustainable (in other words, you must use one full barrel of oil to power the extraction of one barrel of oil). Coal mining is different from petroleum, because the energy to extract coal comes from many sources: electricity (... from coal); chemical energy (from explosives... and you could trace the energy budget farther back to the factory, to electricity, and again, ...to coal); and petroleum (...imported from the oil industry). The oil industry, on the other hand, powers almost all of its field operational energy budget using energy derived from oil - so the budget is easier to balance. (Machines, drills, motors, trucks, and so on, are all diesel or even fuel-oil powered). As discussed in the article I just linked, the EROI is very difficult to measure exactly. Nonetheless, the EROIE definitely does impact the business model of large-scale energy extraction. Here is an OilDrum node on the EROI of coal. Let me know if you need help deciphering the energy-budget numbers in there. ("Lower-" and "Higher-" heating values, and so on, are all "engineering adjustments" that cloud the nice, pure theoretical thermodynamic analysis of "how many pounds of coal did we burn?") And, as one post anecdotally claims, if you still live in an area where coal can be mined with a pick and shovel, (like Indonesia), you burn zero pounds of coal to extract 1 pound of coal - a net EROI of "infinity." I would posit, based on comparative prices between coal and oil in BBOE, that coal extraction is significantly more energy-efficient than oil - let's say, 1 ton of coal burned to extract 10 tons of coal (in a developed, mechanized, American Wyoming strip mine). In the spirit of providing solid, numerical references, there's no substitute for the cold, hard economic and production statistics collected by the United States Department of Energy, and made available at no charge to the public through the Energy Information Administration website. Nimur (talk) 20:57, 18 January 2011 (UTC)[reply]
Stability
Did first-rateships of the line such as the HMS Victory have any stability problems? It looks very top-heavy. Did it go a long way under the water? And does anyone have a picture of a model of it out of water? --T H F S W (T·C·E) 18:46, 18 January 2011 (UTC)[reply]
Some of your questions are obliquely answered in the article Ship of the line. In the earliest era of European warship building when trial-and-error and guesstimation ruled, stability was indeed a problem, as witnessed by the fates of HMS Mary Rose (1509) and Sweden's Vasa, but by Victory's era Naval architects worked by well-established scientific laws. Some of the more basic means of achieving stability are ballast below the waterline and the 'tumblehome' or inward angling of the upper decks, which significantly improved weight distribution. 87.81.230.195 (talk) 19:25, 18 January 2011 (UTC)[reply]
And does anyone have a picture of what the Victory would look like out of water? --T H F S W (T·C·E) 19:30, 18 January 2011 (UTC)[reply]
Well seeing as the Victory has been "out of the water"/in dry-dock for almost a century, I'd expect that most photographs that exist of the hull are "out of the water". Roger (talk) 20:12, 18 January 2011 (UTC)[reply]
My mistake, I thought it was in the water. Still, that doesn't answer my question: does anyone know where I could find a picture of the whole thing, or an accurate model? I mostly want to see the bottom. --T H F S W (T·C·E) 20:53, 18 January 2011 (UTC)[reply]
I think this site might be helpful. There are a number of reasonably good photos of what appears to be an accurate scale model, particularly this one. Karenjc 21:55, 18 January 2011 (UTC)[reply]
Out of water? Drink rum! Arrrrhhhh. Clarityfiend (talk) 07:37, 19 January 2011 (UTC)[reply]
A centreboard is a useful addition for stability. Trouble is, that article doesn't give much history. I'm personally aware of them being used on some sailing ships of the nineteenth century. HiLo48 (talk) 22:07, 18 January 2011 (UTC)[reply]
Personally aware? How old are you? DuncanHill (talk) 00:06, 19 January 2011 (UTC)[reply]
A centreboard or keel, as I learned earlier here, is mostly to keep the ship in a straight line. Anyways, thank you, the site Karenjc pointed out is exactly what I was looking for. --T H F S W (T·C·E) 00:37, 19 January 2011 (UTC)[reply]
Actually, a centerboard is mostly to keep a ship from drifting sideways with the wind. As a side effect, it does reduce rolling, but it adds little if anything to improve real stability, as it does not significantly change metacentric height. A keel can serve either or both purposes, drift reduction and increasing stability. --Stephan Schulz (talk) 19:35, 19 January 2011 (UTC)[reply]
Here's a picture of the Victory; there's no centreboard. The keel was also the main structural member of any wooden ship. Alansplodge (talk) 23:48, 20 January 2011 (UTC)[reply]
January 19
Volume (sound)
How did it come to be that Volume became associated with loudness?Smallman12q (talk) 00:09, 19 January 2011 (UTC)[reply]
According to the OED, the first use of the word "volume" to mean loudness of sound occurs in Byron's Werner, 1822: "I heard‥, Distinct and keener far upon my ear Than the late cannon's volume, this word—‘Werner!’". And it was defined in a musical dictionary as early as 1786 to refer to "the compass of a voice from grave to acute: also to its tone, or power". WikiDao☯ 00:40, 19 January 2011 (UTC)[reply]
Recently, a friend had me watch a video of someone putting a candle in a microwave oven and turning it on. This produced some neat effects, supposedly creating "plasma". (The video was not made by professionals.) My question(s) are: Is this actually plasma? And regardless whether it is or not, what exactly is happening?
Avicennasis @ 07:19, 14 Shevat 5771 / 19 January 2011 (UTC)
I have seen such experiments in reality. a flame is already very slightly ionized. Apparently, the microwaves transfer energy to the plasma, ionizing it further and enlarging it, though I don't know the exact mechanism by which this happens. 157.193.175.207 (talk) 07:47, 19 January 2011 (UTC)[reply]
Is there a video online of this anywhere please? 92.24.183.183 (talk) 13:23, 19 January 2011 (UTC)[reply]
It's even more impressive when you do it with a grape. 90.193.232.5 (talk) 14:20, 19 January 2011 (UTC)[reply]
There are many such videos on YouTube. If you can name it, someone has microwaved it, with comic effect. "Coconut in a microwave" isn't as impressive as you'd think, but I remember when I looked for it, I found it.
There is a wide subset of videos about "ball lightning" in a microwave. I think that this is overly promoted - it is simply that fire is conductive and absorbs more energy, and sometimes the gasses continue to glow a moment after they escape from a hole, etc. that has been built for this purpose. I don't think that the sort of energy or structure present in real ball lightning is actually duplicated --- but if someone disagrees, by all means let us know! Wnt (talk) 17:55, 19 January 2011 (UTC)[reply]
Where does the bigger flame come from? My guess is that the heat from the microwave heats up the candle and/or wick, so that more fuel is available to be consumed by the flame. I do not believe that the energy for the bigger flame comes from the microwaving directly, as microwaves do not burn all by themselves. 92.29.123.151 (talk) 23:40, 20 January 2011 (UTC)[reply]
It really is a plasma, and is very high energy. Part of the flame of a candle is made of ionized atoms. Ionized atoms are very good conductors. Microwaves will induce large currents in conductors. Thats why they tell you not to put metal objects in a microwave. In the tiny plasma of the flame, suddenly about a kilowatt of power is injected. This greatly heats the plasma, which heats the air around it, and ionizes it, and causes the plasma to grow, which causes it to heat more, which causes it to grow more and in a moment, you have a large ball of plasma at several thousand degrees in your microwave. It will literally destroy the oven if allowed to form for too long. It also stresses the electronics in the oven due to the large currents generated. Once you open the door though, the power maintaining the plasma's temperature disappears and the plasma disappears. Though the melted roof of your microwave oven will remain. 24.127.93.76 (talk) 07:51, 23 January 2011 (UTC)[reply]
Need a Formula
i need information the formula 10extera abrasive becuse used oxalic acid —Preceding unsigned comment added by 85.185.25.251 (talk) 07:30, 19 January 2011 (UTC)[reply]
I think you need to make your question a little clearer. --ColinFine (talk) 08:48, 19 January 2011 (UTC)[reply]
It's not just the brand, but this is the kind of products I'm wondering about.[5] How are they nutrition-wise? Thanks. Imagine Reason (talk) 12:58, 19 January 2011 (UTC)[reply]
I understand the process of freezing damages the cell-structure (water/liquid expanding as it freezes), and then means that when cooked they lose some of their flavour (I know, I've worded that terribly, but have a quick read of the Frozen vegetables article, and I'll have a look for some bette source)... this extract points to the difference in texture between frozen and fresh veg.this source argues that frozen veg are higher in nutritional value than fresh (or, as the case may be, not entirely fresh vegetables). this source also argues that frozen veg are less at risk from contamination, as long as they are not frozen, defrosted and then refrozen - Although, having said that, I am sure that I have seen other sources before that argue that frozen veg in bags that have not been properly sealed are at risk from contamination. Darigan (talk) 13:16, 19 January 2011 (UTC)[reply]
It could also be related to the way they are cooked after being frozen -- are you boiling them in water? I've always found that makes veggies taste a lot more bland. -- JSBillings 13:48, 19 January 2011 (UTC)[reply]
OR answer here: I have found that frozen vegetables taste better when steamed than when boiled; the "steam in the bag they came in" varieties are particularly close to their fresh cousins. Some vegetables take to freezing better than others. I find frozen carrots and frozen corn-on-the-cob to be pale comparisons to their fresh versions, while green beans (haricots) and garden peas are usually fairly comparable. I'm not much of a fan of many cruciferous vegetables in any form, so I can't comment on frozen vs. fresh broccoli or cauliflower or brussel sprouts. --Jayron32 15:48, 19 January 2011 (UTC)[reply]
With peas, it's vastly superior to freeze (or can, though I find canned peas unappetizing) them rather than shipping them "fresh" to a supermarket: the sugar in peas breaks down incredibly rapidly, making it nearly impossible to get good fresh peas, other than by growing them yourself. This is mentioned in Pea#Use, though I'm surprised we don't have anything more on this. I think typically, peas need to be blanched and preserved within a couple of hours of being picked. Buddy431 (talk) 17:15, 19 January 2011 (UTC)[reply]
I think your example of corn is illustrative of a few things. Really fresh corn (as in, you put the pot on to boil while you run out to pick the ears) is unbelievably good; it barely even needs a blanching, you just want to warm it up for the butter. Within a day, it's good, but not nearly the same kind of thing. If you IQF freeze it at that point, you'll get a pretty decent product - good enough that it's better than the so-called fresh corn you find in grocery stores that's already 2-3 days old, if not more. Canned corn is pretty abysmal. So you've got a weird sort of graph where really fresh is best, but frozen is better than just about anything else. The trouble with many vegetables, particularly carrots and peas, is that freezing them wrecks the crispness; the flavour might not change much, but the mouth feel is completely different. Matt Deres (talk) 19:00, 19 January 2011 (UTC)[reply]
IQF seems to mean individually quick frozen in this context - it stops the corn/peas etc from sticking together. CS Miller (talk) 19:37, 19 January 2011 (UTC)[reply]
That's the problem I have with frozen corn: it loses the snappy mouthfeel that makes fresh corn-on-the-cob so tasty. I usually buy my corn at the local farmer's market the day I plan to use it; when it is in season it's usually picked within 24 hours before I buy it. I find all canned vegetables taste more like can than vegetable, so I avoid them pretty much at all cost. --Jayron32 19:23, 19 January 2011 (UTC)[reply]
Wouldn't the vegetables that are used by the frozen vegetables processors be those most manageable for that process? There are lots of varieties of a vegetable. Those destined for freezing are likely to be those that have the handling characteristics that best lend them to mechanical manipulation—from the field to the packaged and frozen product. If any tradeoffs have to be made, taste might get sacrificed in favor of the ease of large scale mechanized agriculture. Even the nonorganic but fresh vegetables on the supermarket shelf might tend to be those varieties of a given vegetable that don't require those qualities that lend themselves so well to the highly mechanized freezing (and harvesting) process but may instead retain some of those qualities that made them desirable in times gone by. Bus stop (talk) 22:23, 19 January 2011 (UTC)[reply]
The one exception, I think, is tomatoes, where the canned ones can have better flavor than either fresh or frozen. Freezing destroys them, and even farmer's markets can't usually handle them at the peak of flavor -- canners, however, can process them directly out of the field. Looie496 (talk) 00:12, 20 January 2011 (UTC)[reply]
I'll second that; canning tomatoes also has the practical effect of concentrating the flavor components. I find good canned tomatoes to be more intensely "tomatoey" than even fresh-off-the-vine-minutes-before tomatoes. Which is not to say that fresh tomatoes don't have their place; canned tomatoes make a better sauce than fresh, but I wouldn't ever use them in a salad. --Jayron32 01:27, 20 January 2011 (UTC)[reply]
O.R.: Food processing companies such as Green Giant, who have contracts with farmers, pick and process crops (for freezing or canning) at the absolute perfect state of development. If they get a few days behind, they skip the crops which would be post-mature and go on to the next perfect batch. If you buy "fresh" corn or peas, there is no such guarantee that they were picked on the very best day of maturation and presented for your purchase with no delay. The damage due to freezing is likely offset by the benefit of picking at the peak of quality, compared to picking too late, or picking early and shipping of "fresh" vegetables. Of course, you could grow your own produce and guard the crop at night to stave off marauding raccoons, who can detect ripening corn (maize to Brits) from miles away. Edison (talk) 02:19, 22 January 2011 (UTC)[reply]
Electrical
Hi I have some basic doubts in electrical I am an electrical student please help me
1)Why we maintain voltage as constant not current?
2)In producing AC there comes both +ve AND -ve voltage in both the ends (slip rings) but in power line only phase has while neutral remain null.
3)Is human body a conductor?
4)If a coil connected to power supply produces magnetic flux will that flux link on that same coil and induce a emf?
5)Fan is an inductive load thus on using it there should be 90° phase out b/w Amps and Volt if so won't it affect Transformer?
6)If a bulb excited by AC what happen when it changed to DC of same rms value of volt and current?Kanniyappan (talk) 14:08, 19 January 2011 (UTC)[reply]
Regarding #3, everything is a conductor under sufficient voltage. The human body, being basically a giant bag of salt water (an electrolyte) is actually a pretty decent conductor, even under moderate voltages. Regarding #4, in order to produce an emf through the coil, you must move the coil in relation to the magnet (or visa-versa). Regarding #6, my understanding is that light bulbs (and resistance heaters, and other similar devices) behave roughly the same under AC and DC conditions, as the effects of resistive heating are the same regardless of the direction of the current; in other words the AC or DC nature of the current does not play into Joule's first law. I will let someone who actually knows about this answer the rest (and correct my mistakes). --Jayron32 15:42, 19 January 2011 (UTC)[reply]
It is not possible to maintain a constant current except under carefully controlled conditions. "Voltage" is another name for "electro-motive force" (EMF) which you can compare with "pressure" in water pipes. The supply of both electrical and water services aims to maintain a constant "pressure" so that the amount of electricity or water that flows when something is turned on can be reliably predicted. In the case of water, it is usually the tap that controls how much water flows, but, for electricity, it is usually the resistance or reactance of the appliance that determines how much current flows (though dimmer switches work like taps).
AC supply does not have positive and negative. Usually one side of the supply is connected to earth and for this reason is called "neutral", but it doesn't really matter whether this is done or not except for safety reasons. Both "live" and "neutral" wires behave in exactly the same way (except when one is shorted to earth), so there is really no difference between them if they are isolated from "earth". Three phase supply is generated and transmitted with three "lives", each one being 120 degrees out of phase with each of the others. Sometimes there is no "neutral" (delta configuration), and power can be transmitted without any other conductor. More often, each of the phases is generated at a fixed voltage to a common wire "3-phase neutral" which is usually connected to earth. The three main wires for the three phases still carry the main current because the three currents in the three phases will cancel each other out if they are equal, but the common neutral serves to carry any residual current if the phases are not balanced.
Just one minor addition to Jayron's answer to #4: If AC is connected to a coil, then the flux does indeed produce an induced EMF in the same coil becuase the current is constantly changing. See autotransformer. Dbfirs 18:24, 19 January 2011 (UTC)[reply]
As far as I know, single-wire earth return is never used in the UK. (I've tried it, unofficially, but probably illegally.) Dbfirs 22:17, 19 January 2011 (UTC)[reply]
A/C can have potential on both sides of circuit (although obviously not positive/negative, since it's A/C). Voltage can only be measured as a difference - there is no such thing as an absolute voltage. A/C in households is designed so that the earth is one side of the circuit, and since we stand on the earth, to us the feels like neutral. But it doesn't have to be that way. If you isolate your A/C generator completely from the Earth, then both sides "have" potential (although of course that's meaningless since you need two sides to measure anything). An interesting side effect of this kind of isolation is that you can't get shocked by touching just one wire - you need two to get shocked. Unless of course two different people happen to each touch one wire at the same time and you complete the circuit through both of them via the Earth. You can also make D/C with one side hot and the other neutral - you just need to attach one side to the earth. Ariel. (talk) 22:35, 19 January 2011 (UTC)[reply]
Well if you want to be pedantic, AC does have positive and negative on both sides, it just changes 100 or 120 times each second, so I meant that you can't label either conductor positive or negative. Good point that DC can have "live" and "neutral". Is it often supplied this way (other than in motor vehicles)? Dbfirs 23:09, 19 January 2011 (UTC)[reply]
Most circuit diagrams have a source and ground, rather that a positive and negative. Computer power supplies are also wired this way - a common ground for everything, and different wires for various voltages/rails/polarities. Ariel. (talk) 00:17, 20 January 2011 (UTC)[reply]
Yes, good point, though voltages are quoted positive or negative with respect to the "ground". Is this just because the mains supply is grounded? My laptop just has 19v DC with no ground, but the circuitry probably has an artificial "ground", possibly connected to mains "earth" (I haven't checked). Did early wet and dry battery circuits also have a "ground"? (I was really meaning long-range supply of DC, but this is relatively rare.)Dbfirs 13:05, 21 January 2011 (UTC)[reply]
Real mains fans have some corrective circuitry to bring the current much closer in phase to the voltage. See power factor. Dbfirs 18:37, 19 January 2011 (UTC)[reply]
Mains supplies provide a constant voltage so that any number of appliances can be connected and disconnected without affecting one another. Each receives the standard voltage and only the total current varies. A constant current mains supply is impractical because the current to an appliance would change every time another appliance was connected, and dangerously high voltage will be delivered if no appliance is connected.
A basic two-wire or "single-phase" AC supply usually has one wire called neutral connected to earth which we may call 0V. The voltage on the other wire alternates between +ve and -ve voltages.
The human body is a conductor. See the article Electric shock.
An emf is induced in a wire in a changing magnetic field. A coil is an example of an inductive load. When a coil is connected to a DC power supply, the current in the coil grows slowly because it produces an increasing magnetic field that induces an emf that opposes the supply voltage. For the same reason, when a coil is connected to an AC supply the current is slow to follow the voltage changes. The time delay can be expressed in degrees where a full alternating cycle is 360. If the coil has no resistance, the current lags the AC voltage by 90.
A fan motor is an inductive load. When the fan shaft rotates the motor is also a generator of emf that opposes the supply voltage.
The filament of a lamp bulb glows because of the heating effect of current flowing through its resistance. The heating power is proportional to the voltage squared (so both positive and negative voltages give heating). An AC supply with rms (root mean square) voltage equal to the voltage of a DC supply has the same heating power as the DC supply. So there will be no change in the lamp brightness if one switches between the two supplies. Actually the brightness flickers at double the frequency of the AC cycles but you cannot see this because mains supply frequency is too high. Cuddlyable3 (talk) 22:59, 19 January 2011 (UTC)[reply]
On question 6: Similar light bulbs connected to DC or to AC of the same RMS voltage will produce similar light and heat, and consume similar power initially. However a bulb connected to DC may show a light streak, like an inverse shadow, behind the leg of the filament connected to the positive supply. This "shadow" led todiscovery ofThermionic emission, the basis for Vacuum tubes and electronics. I suppose an AC powered bulb might display a less distinct shadow in line with each filament leg, since each in turn has each polarity. If the frequency of the AC is low enough, many people can see objectionable flicker. I have seen this in bulbs of street cars powered by 25 cycle electricity. This slight flicker at twice the mains frequency can also produce a slight strobe effect when viewing a vibrating or rotating object. If there is a magnet or magnetic field near the bulb, the filament may vibrate quite a bit when powered by AC, depending on the construction and how the filament is supported. If powered by DC, it could move in one direction and stay there as long as the field and current continue. This was very clearly visible with early carbon filament lamps: See [6]. Edison (talk) 22:04, 21 January 2011 (UTC)[reply]
Rephrased: relaxing voices
Sorry to the board, it wasn't supposed to be a medical question. I will attempt to rephrase the question. Why do some voices, e.g., Bob Ross's, cause people to relax? I've read on other forums that people will watch his show to help them fall asleep. Thank you very much! Reflectionsinglass (talk) 18:54, 19 January 2011 (UTC)[reply]
To answer a question with a question, why is some music relaxing and other music exciting? Why do some people find traffic noises soothing, and others find it irritating? Ariel. (talk) 22:37, 19 January 2011 (UTC)[reply]
Ice expanding, minimum density
It is my understanding that when water is cooled (at standard pressure), it reaches a maximum density at 4°C (due to hydrogen bonds, and then starts to expand as it is cooled further. As it transitions to Ice Ih it expands by about 9%, and then continues to expand as it cools further. At what temperature does ice reach its minimum density? I did a quick websearch and found [7] which indicates that it is at 70K. Is the minimum density really this cold? — Preceding unsigned comment added by Csmiller (talk • contribs) 20:10, 19 January 2011 (UTC)[reply]
Under Ice#Characteristics it says: "The density of ice is 0.9167 g/cm³ at 0°C [...] Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).", quite the opposite of your statement. But it doesn't say what ice does on further cooling or where minima/maxima of density are. Another image on commons ([8]) also implies that density rises when ice is cooled. Oh, just read through your link again, and as I understand it, ice increases its density when heated up starting from 0K to 70K, then it apparently decreases again--178.26.171.11 (talk) 21:03, 19 January 2011 (UTC)EDIT: The minimum density should be at 0°C then (unless there's a way of "superheating" ice above that without melting it at standard pressure.--178.26.171.11 (talk) 21:05, 19 January 2011 (UTC)[reply]
A very similar question was asked a couple weeks ago.[9]Red Act (talk) 23:23, 19 January 2011 (UTC)[reply]
Allergen
I'm trying to pin down whether an item would be a high risk to cause an allergic reaction. The ingredients listed on the website for it are: Water, denatured alcohol (<5%), sodium iminodisuccinate (<1%), zinc diricinoleate (<1%), cocamidopropyl betaine (<1%), menthol (<1%), microorganisms (<1%), citric acid (<1%), polydimethylsiloxane emulsion (<1%). The microorganisms in this product are non-genetically modified, naturally sourced, non-pathogenic (i.e. do not cause disease) dormant bacteria, and are the primary “active ingredients” in this formulation. They work by eating up all of the accumulated dander, dead dust mites, and dust mite fecal matter that has accumulated in your mattress/ pillows/ furniture/ car upholstery over time, eventually converting those allergens into carbon dioxide and water.
Obviously, people can be allergic to just about anything, but do any of these items seem like likely candidates? Their use of "naturally sourced" bacteria kind of raised my eyebrow, for one thing. I've heard of cleansers touting their "enzymatic action!" before, but not bacterial. Anything else on there look weird? Matt Deres (talk) 20:37, 19 January 2011 (UTC)[reply]
Wow. That's like an ingredient list that includes "...chemicals. All our chemicals are safe, trust us..." To give a parallel example with a more defined set of natural microorganisms, consider the regulation of raw-milk cheeses by the U.S. and Australia. Wnt (talk) 20:52, 19 January 2011 (UTC)[reply]
You also may take interest in the zinc diricinoleate (the basic component there is ricinoleic acid, with two conjugated to zinc. See [10][11][12] for some leads. (It is widely used, but I'd like to know who puts castor oil in chocolate? Remind me to avoid that brand...) Wnt (talk) 21:03, 19 January 2011 (UTC)[reply]
Apparently this is being done by Hershey's, Nestle, and Mars, Incorporated, as part of a campaign to sell cocoa butter to the cosmetics industry and replace it with cheap substitutes in chocolate.[13] Which is just one small reason why American chocolate doesn't taste like chocolate. And people wonder why this country keeps running record trade deficits... Wnt (talk) 04:18, 20 January 2011 (UTC)[reply]
This site: http://www.cosmeticsdatabase.com/ is pretty good for that kind of thing. You can either look up individual ingredients, or register an account and enter all the ingredients of a product and it will give you a grade. (Not just allergies, any kind of potential risk.) Ariel. (talk) 22:52, 19 January 2011 (UTC)[reply]
That site looks helpful - thanks; I'll give it a look when I get some time to play around. I don't know if it matters, but the substance in question isn't a cosmetic, it's for spraying on beds and other furniture to reduce dust mite allergens and odour. Matt Deres (talk) 23:12, 19 January 2011 (UTC)[reply]
Water and brick question
My daughter has a science project in 5th grade this week. I was watching the discovery channel last night and the segament was about taking a 5gal. water jug,filling it a 1/4 with wate, connecting a hose to it,then connecting the end to a hot water bottle.Then take 5 blocks and put them on top of the water bottle.Once that is complete,turn the 5gal. jug upside down about 4ft. high ,then the water should fill the bottle and knock off the bricks. What is the topic of this project? — Preceding unsigned comment added by Jeffryan777 (talk • contribs) 22:01, 19 January 2011 (UTC)[reply]
Can't you ask your daugher? (I added a header) SmartSE (talk) 22:37, 19 January 2011 (UTC)[reply]
The topic appears to be pressure, in that the head of water in the hose is sufficient to lift the bricks. --Tagishsimon(talk) 22:41, 19 January 2011 (UTC)[reply]
You could also discuss conservation of energy. Lifting the 5 gallon jug takes work (in the literal and technical sense of the word). That work is transferred, via the hydraulic pressure, to lift the blocks. One useful property of hydraulic machines is that they can multiply force - so it can be possible to lift some pretty heavy cinder-blocks (which requires a large force), by exerting a smaller force over a large distance to lift the water (hence, to pressurize the fluid). (The force is increased, but the energy is conserved). Nimur (talk) 23:33, 19 January 2011 (UTC)[reply]
And because of this force multiplying, hydraulic systems similar to the one described can act like many types of levers, pulleys and other simple machines. SemanticMantis (talk) 00:02, 20 January 2011 (UTC)[reply]
"Radiation therapy may lower testosterone to the low-normal range in some men" source - so yes. (That could be worked out a lot quicker by googling "radiation lower testosterone") SmartSE (talk) 22:35, 19 January 2011 (UTC)[reply]
Radiation could increase free testosterone but our article on Testicular Cancer does not mention this. Could someone please expand this, as I'm not sure of certain details.--Aspro (talk) 22:38, 19 January 2011 (UTC)[reply]
It depends on what type of radiation, how it was applied, where it was applied, and so on. A lot of research has been performed to study the effects of localized radiation applied to the testes or to the prostate as part of a cancer treatment. Here are some relevant papers on that topic that were found using this Google Scholar search: Effect of Graded Doses of Ionizing Radiation on the Human Testis, Serum testosterone levels after external beam radiation for clinically localized prostate cancer, and so on. If you are trying to evaluate medical options, you should consult a physician. Significant other research has studied the effects of environmental radiation (like if you work in a room or laboratory near radioisotopes, or near a uranium mine, or if you have a radon gas problem in your home); for example, Environmental endocrine disruption: an effects assessment and analysis. We can point you to better resources, and provide better answers if you can specify your question a little more clearly. "Radiation" is a very broad term for a lot of different kinds of energetic effects from a lot of different places: nuclear radioisotopes; strong electromagnetic sources (like mobile phones); and even ultraviolet radiation from overexposure to the Sun or tanning booths. Nimur (talk) 23:45, 19 January 2011 (UTC)[reply]
January 20
Plant hardiness - temperature versus sunlight volume
It's about -20C outside these days, though my apartment (apart from near windows) is around 20 degrees at all times. I have a Creeping Charlie that was placed too close to a window and began to die. However, the ambient temperature was never at or below freezing.
This made me wonder about plant hardiness and why some plants cannot tolerate super-freezing temperatures. If a tropical plant like a banana tree was given ample, full-spectrum artificial light but kept at an ambient temperature of 5~10C, would it still die? If yes, why? There wouldn't be any cell damage from freezing... The Masked Booby (talk) 01:14, 20 January 2011 (UTC)[reply]
I don't know, but a conjecture is that different enzymes work best at different temperatures. Perhaps the plants that like warmth have enzymes that only function at those temperatures. Ariel. (talk) 06:16, 20 January 2011 (UTC)[reply]
Yes, it's basically the same reason why humans die if their body temperature is to far away from 37°C (without freezing). The physiology of most life forms is tuned (by evolution) to certain ranges of environmental and internal variables, and if you cross the thresholds, the processes in the cells don't work anymore as they should. That's the same principle for plants, animals and even single celled organisms (some bacteria that thrive in warm shallow sea water won't grow at all or even die in cold shallow sea water, for example). --TheMaster17 (talk) 10:33, 20 January 2011 (UTC)[reply]
This previous question covers some of the relevant points (I was posting as 131.111). Chilling can damage plants because it disrupts the cell membranes by making them solid, instead of fluid which then makes them leaky, allowing all the parts of cells to mix, whcih is not good news at all. A banana plant will certainly die at 5-10C because they have never evolved to cope with those temperatures. Ariel's point about enzymes is probably partially true, but the disrupting of cell membranes is more of an issue - unlike us, plants have to cope with a wide range of temperatures and so they have enzymes which function over wider ranges, or will have isozymes for different temperatures. As to how some plants survive super-freezing, it's pretty complicted! There are some details at Ecophysiology#Temperature (unfortunately unreferenced, but I can vouch for its accuracy as I wrote it from lecture notes - I will try to reference it some day!) and combined these allow trees like larch in Siberia to survive liquid nitrogen, because the cells are placed in suspended animation. If you want a paper discussing this, this one might be a good start. SmartSE (talk) 15:43, 20 January 2011 (UTC)[reply]
Pregnancy and radiation-blocking smocks...
Here in China pregnant women wear smocks with a thin lead liner in the workplace. I can understand the need for such clothing if someone worked in an area with serious radiation potential, like an x-ray equipment factory or something. However, 99% of these women only ever sit in front of a computer doing routine tasks. I suspect this practice, like many medical habits in China, is based on no real proven science. Is there anything to gain from such clothing? I didn't see any indications in the Electromagnetic radiation and health article... The Masked Booby (talk) 01:17, 20 January 2011 (UTC)[reply]
Well, considering that lead doesn't even block EMF I don't know what they're trying to achieve. I would be much more worried about exposure to lead! Even if it is sealed, what if a section becomes exposed due to wear or tear? Lead rubs of extremely easily onto hands or clothes, even just touching it and then handling food or inadvertently touching your mouth sounds like a much higher risk then sitting in front of a computer or monitor. Vespine (talk) 03:35, 20 January 2011 (UTC)[reply]
I'd hesitate to concur -- while lead doesn't attenuate all forms of electromagnetic radiation well, it does do a great job for x-rays, for example. This may not relate to the circumstances posed in a positive fashion (it may reveal the ignorance of Chinese women and/or their husbands), but your blanket statement is certainly incorrect on the whole. DRosenbach(Talk | Contribs) 05:02, 20 January 2011 (UTC)[reply]
EMF |= electromagnetic radiation. I didn't think computers and lcd monitors are significant sources of EMR, unless you have a wifi or bluetooth transmitter or something. It's hard to find reliable sources to look this up because of all the fear mongering but my guess is there would be small amounts of things like radio waves and stuff coming out of a normal computer, but there's certainly no ionizing EMR coming out of your computer. Vespine (talk) 05:24, 20 January 2011 (UTC)[reply]
It could have started with ladies worried about the X-Rays emitted from older model CRTs (Which, for all I know might still be in wide use in China.). Once these sorts of things start they usually become divorced from their rational underpinnings pretty quickly, so it's not hard to imagine that some ladies would still wear them even if they never use anything that emits anything dangerous. APL (talk) 15:30, 20 January 2011 (UTC)[reply]
Yes, but you said, "lead doesn't even block EMF." DRosenbach(Talk | Contribs) 16:09, 21 January 2011 (UTC)[reply]
I'm confused, why are you saying "but you said"? Yes I did say it, and? Is the confusion because a lot of the internet seem to use the terms EMF and EMR interchangeably? They are not the same thing. However both are blamed for adverse health effects by the alt med crowd. Vespine (talk) 00:42, 22 January 2011 (UTC)[reply]
Biology vs. the Cosmetics Industry
(My last question of the day...) My wife, like many women, spends a fair bit of money on facial cleansers and moisturizers, always used in conjunction. She also makes a big stink about my need to have empty pores on my face in order to be "clean". I am skeptical of this entire process. I've read Cleanser, Sweat gland, Acid mantle, and Sebaceous gland and have not been able to definitively confirm or refute my contention that: stripping oil from your face with cleansers and then applying moisturizer is equivalent to doing nothing at all and letting your skin regulate itself, it just costs loads more. But again, none of those articles directly say whether this is truly necessary or not. Can anyone shed some scientific light on this? The Masked Booby (talk) 01:28, 20 January 2011 (UTC)[reply]
We have a refdesk rule about medical diagnoses, do we need one about marital harmony? Ariel. (talk) 01:33, 20 January 2011 (UTC)[reply]
This is not a medical diagnosis request. This is a question about the biological/chemical function of the face and the utility of cosmetics. I am inherently distrustful of the cosmetics industry given their proven non-sense like conditioner making your hair "healthier" and would like to know if facial cleanser/moisturizers fall into the same sphere. I included the bit about my wife for color, not because I'm going to print out your replies and wave them in her face and say SEE! WIKIPEDIA SAID SO! The Masked Booby (talk) 01:38, 20 January 2011 (UTC)[reply]
Stuff in small print is usually for more light hearted (or off topic) comments. Ariel. (talk) 01:42, 20 January 2011 (UTC)[reply]
You aren't just stripping the oil off of your face, you are stripping all of the stuff that tends to get stuck to the oil, like dead skin cells, dirt, (for many women) makeup, etc. It may be quite difficult to remove, for example, dead skin cells from pores with just soap, while an astringent cleanser which dissolves the oil the skin cells are stuck to will make it much easier to get them out. Bacteria like to feed on these dead skin cells; this can be a primary cause of acne. The deal is, since you just removed all that oil, you need to replace it to prevent your skin from drying out, hence the moisturizer. In summation, it isn't the skin oils per se that need removing, its all of the stuff that is in the oil. --Jayron32 01:37, 20 January 2011 (UTC)[reply]
I guess the question is, Does that stuff really need removing? Where is the science behind it? (PS: Agree with comment about marital harmony.) HiLo48 (talk) 02:52, 20 January 2011 (UTC)[reply]
Which is a fair question. I'm more familiar with the argument against shampoo-conditioning, which is a somewhat similar arrangement: the hair is cleaned of oil (and the attached dirt) and then has a moisturizer (hair conditioner) added back on. Our article on that argument can be found at the humorously titled "no poo", though it's a pretty poor article. Western habits (and obviously Chinese ones as well) on cleanliness are hugely influenced by social expectations, to the point where the "necessity" of having to shower multiple times a day, for example, borders more on ritual purification than anything to do with an increase in health or other objective goal. As with anything else, moderation is probably the sensible option. Matt Deres (talk) 03:02, 20 January 2011 (UTC) Quick aside - I got a chuckle by reading that our article on cleanliness has been flagged for "cleanup" for seven months... [reply]
@HiLo48 for some people, probably not, but for others definately. I am a life-long sufferer of acne (I basically have the exact same skin problems at 34 that I had at 14); through years of trial and error I have found that some products work for me, and some do not, and I use those that do. Clearly, for people who have acne, skincare can be tricky business. It's one of those "if you don't have the problem, you just don't understand" sort of deals. For people without acne problems, washing daily with the bar soap they use for the rest of their body works fine. For others, however, it just doesn't cut it. --Jayron32 03:35, 20 January 2011 (UTC)[reply]
I seem to remember discussing something similar about washing hair too, but can't find an archive link. If you're correct, it almost certainly has something to do with differences in skin flora. I found this which says "soap may reduce the normal skin flora, leading to an increased colonization of the skin with coagulase-negative staphylococci; this effect has been linked to the shift in skin pH caused by soaps. Lastly, it has been found that applying agents that specifically inhibit gram-positive cocci, such as antibacterial soap, generally increases gram-negative rods." and this paper tells a similar story. I think it's probably difficult to give you a definitive answer and as everyone else is ORing so will I - I think that cleansers + moisturisers change the balance of skin flora and that if you then stop using them, your skin condition detiorates because the equilibrium was being maintained by the products. For those of us who don't use such products (myself included) our skin flora is in equilibrium, and generally speaking we don't suffer from unhealthy skin. Carrying on, we obviously evolved in a world without soap, and our skin produces oils for a reason, I see no reason why you would need to replace this with something else. (Maybe you can experiment with your wife's face, only letting her clean + moisturise one side and come back with photos in a few months) Interestingly, I don't think anyone has done any metagenomic studies of skin flora, which would be a very interesting thing to do, when comparing you and your wife. SmartSE (talk) 16:12, 20 January 2011 (UTC)[reply]
What about situations where skin flora is "off" in the absense of products, but correctly balanced with them, before such products were used by the person? I had acne before I started using products... Your explanation isn't consistant in that skin problems exist in absense of even the existance of skin care products. It would only make sense if skin problems didn't exist prior to people using skin care products. However, that is demonstratably false. --Jayron32 16:29, 20 January 2011 (UTC)[reply]
I don't think anyone is suggesting that corrective action is never a good thing - at least, that's not what I'm saying. If you've got a busted leg, wearing a cast is probably a good idea, but when it seems that virtually everyone is wearing one, I think it's justifiable to say "Look, there are negatives to wearing these things." Such comments aren't really directed at the people with broken legs, they're just reminders of the "If it ain't broke, don't fix it" adage. Matt Deres (talk) 19:50, 20 January 2011 (UTC)[reply]
Fair enough. I actually agree with you on that; many people use uneccessary or even harmful products under the misbegotten notion of retaining a "youthful appearence" whatever that means. Much of the skincare industry hinges on the fact that people believe they can avoid looking their age by smearing some gunk or another on their face. Sometimes, however, that gunk does actually help people with a real problem. It's not the gunk, per se, that's the problem...--Jayron32 20:13, 20 January 2011 (UTC)[reply]
WP:OR Face wash products work well. They just include sticky substance which once applied to your face you must wash your face thoroughly with lot of water to remove it, and any other dirt/oil on your face, if any, also washes out along with the water :) - manya (talk) 04:10, 20 January 2011 (UTC)[reply]
Calcium oxide reaction
calcium oxide reaction with water —Preceding unsigned comment added by 125.99.5.139 (talk) 09:08, 20 January 2011 (UTC)[reply]
Welcome to Wikipedia. You can easily look up this topic yourself. Please see calcium oxide. For future questions, try using the search box at the top left of the screen. It's much quicker, and you will probably find a clearer answer. If you still don't understand, add a further question below by clicking the "edit" button to the right of your question title. . DMacks (talk) 11:04, 20 January 2011 (UTC)[reply]
Is there anybody to reply me positively
1.Is a photon massless?
If yes,then why does it has particle nature as a particle has a must property of mass and it also has momentum?
If no,then why it cannot be proved?
2. Is a vacuum really vacuum or not?
If yes,then why does there exist a dark energy as energy cannot be held without any medium?
If no,then what does there exist?
3. Does a string really exist?
If yes,then what is the matter the string made of?
If no,then what is the cause of producing charge in an electron?
4. Do the photons carry the energy from one place to another?
If yes,then why does the intensity of radiation decrease gradually and if an electro magnetic radiation is one kind of transverse wave,then the main property of this kind of radiation should be transfer of energy not the particle and it definitely needs a medium to traverse?
5.What is the situation before the Big Bang? Is it a cyclic process?
6. What is the way to transfer energy from one place to another?
If it is vibration of different mode which produce different kind of energy,then is it possible to construct the T.O.E. equation?
(I think I have some definite reasons to explain those things stated above. But I need a definite person to explain these mathematically. 117.194.164.185 (talk) 14:35, 20 January 2011 (UTC)[reply]
You asked a lot of very hard questions, so it is impossible to answer them all here. You should look at the articles on Wikipedia and ask if you have specific questions.
1. A photon has no rest mass, though it does have momentum. Who says that particles must have mass? It's perfectly possible to conceive a massless particle.
2. Vacuum#In_quantum_mechanics and Vacuum energy explain this better than I could. The exact nature of a vacuum is complex - however it is quite well defined in quantum theory. The idea that energy cannot be held without a medium is just a hypothesis and may not be true.
3. String theory is still a matter of debate, and it's not clear if any version of it is true. Therefore nobody is certain what the strings are made of, or even if it makes sense to ask if they are made of anything (just as Einsteinian space-time is not made of anything, and electrons are, in standard models, made of electron without any internal structure).
4. Photons do indeed carry energy. Intensity of radiation decreases with distance from the source because photons spread out as they travel and the further from the source you are, the fewer photons hit you (see inverse-square law).
(edit conflict)Almost identical to previous response, but I've written it now and don't want to discard it.
1. If you mean "does a photon have zero rest mass ?" then the answer is yes, although the question is somewhat meaningless as a photon is never observed at rest. This does not prevent a photon being a particle.
2. If you mean "is the vacuum empty" then the answer is no - any vacuum in our universe will contain the electromagnetic field, its quanta (photons), a large number of passing neutrinos and a "sea" of virtual particles.
3. If you mean the strings in string theory then we don't know whether they really exist.
4. Yes, photons carry energy. The intensity of radiation decreases with distance because the flux of photons per unit area decreases as the area over which the photons are spread increases. For large photon fluxes the intensity appears to follow a continuous curve; for small photon fluxes the continuous model breaks down and individual photons are observed. You can recover the continuous model by averaging the photon flux over a long enough period of time.
5. We don't know what was before the Big Bang. We don't even know if this question makes any sense.
6. In quantum field theory, you can think of energy as being carried by waves in quantum fields or by the momenta of particles associated with those fields. These are dual models - "reality" is both, not one or the other. A field does not need a medium. Gandalf61 (talk) 15:40, 20 January 2011 (UTC)[reply]
@OP: Regarding 3: What does "really exist" mean? String theory is a model just like many other models. It is useful insofar as it matches observations, and has a useful predictive power. Is an electron a little ball, a standing wave, a probability distribution? It is all of these, depending on which model you use. None of this is wrong, though some models better match observation, and some are more useful in certain applications. Is light a wave or a particle? Neither, it is just light, but we have wave-based models of light which are useful in some explanations (see diffraction, refraction, etc) and we have particle-based models of light useful in others (see photoelectric effect). If you commit yourself to "The Truth" rather than "Consistent with observations" you miss the point of science. It is perfectly fine and consistant to have multiple, accepted models of the same phenomenon, and each of these models is "real" insofar as any can be. So, stop worrying about if strings "exist" or what they are "made of" and instead focus on what the model teaches us about how the universe works. --Jayron32 16:00, 20 January 2011 (UTC)[reply]
It remains to be seen whether or not string theory is a useful model of reality capable of offering testable predictions. In this context, showing that string theory is capable of making new verifiable predictions is basically the same as showing that strings "really exist". Dragons flight (talk) 16:28, 20 January 2011 (UTC)[reply]
That's kinda the point; though it would be better to say that "really exist" misses the boat in that it implies only a single "right" answer; after all if strings really exist, than other models which do not contain strings, really don't exist. Having a paradigm that searches for the One Right Answer completely misses the point of science. Lets go back to the light example. Does light really and truly exist as a particle or does it really and truly exist as a wave? If you commit yourself to that mindset, you are left with three very unsatisfying results:
Light is only one or only the other (observationally inconsistent; light clearly behaves like a particle in some situations, and like a wave in others)
Light is both at the same time (logically inconsistent; a little ball and a mode of movement don't occupy the same class of nouns even. It's akin to claiming that something smells like the color red. It has a poetic appeal, but it doesn't make any logical sense)
Light switches between the two modes, depending on the type of observation (seems better at first, but it begs the question about what light is doing when it isn't being watched.)
People have grappled with this concept for a very long time, the only satisfying result comes when you come to realize that there is a difference between reality and perception, and most importantly reality is not observable at all at the most fundemental level. All you can say is that your mind perceives an object or phenomena to be real, but you have no way to confirm that. Look at your keyboard. How can you confirm your keyboard exists, as an entity seperate from your internal, mind-created construct of what it is. At some point, you need to accept that as true. But that's still an unproven (and unprovable) proposition. When we deal with scientific concepts which are only observable in the second or third order, where we are further removed from the observable properties of it, these sort of problems become manifest in the situation. Back to light, rather than trying to decide what light "really" looks like, and "really is", change your paradigm to just accept that light is what it is, and is fundementally unconcievable apart from the models we make to describe it. Accept that, while light exists and is consistent, our models being by definition imperfect representations, can never fully capture what it means to be light, and let yourself be OK with that. Understand that the two competing and mutually exclusive models of light work in their own domains, are uncontradicted by other models, and so are as close to "real" as we can get, insofar as anything is "real". On that level, string theory may be "real", but also be willing to accept other, competing, and apparently mutually exclusive models as equally "real" insofar as they contradict neither logic nor observations. --Jayron32 16:48, 20 January 2011 (UTC)[reply]
... and if you were claiming that electro-magnetic radiation "definitely needs a medium to traverse", then the claim is mistaken. Dbfirs 21:43, 20 January 2011 (UTC)[reply]
Electron proton collision
What happens in general when an electron collides with a proton? My understanding is a neutron and a neutrino are produced, but where is a good reference for the dynamics prior to the moment of collision? Also, in particular, how does the electron's de Broglie wave shape change as it transitions from free to collided? 71.198.176.22 (talk) 21:10, 20 January 2011 (UTC)[reply]
In general, nothing happens when an electron collides with a proton. They pass clear through each other. Electrons in s orbitals have a (locally) maximal probability to be found right at the nucleus, and don't appear to suffer any wear and tear from that.
In order to something interesting to happen between an electron and a proton, either the electron must spontaneously break into a neutrino and a W- boson, and the W- must then hit the proton and convert it to a neutron, or the proton must turn into a neutron and a W+ which combines with the electron to form a neutrino. Both of these possibilities are energetically disfavored and so happen extremely seldomly, except if the proton really wants to be a neutron, in which case see electron capture.
De Broglie waves are not really a good model for describing particles that turn into other kinds of particles. You'll need a quantum field theory for that. –Henning Makholm (talk) 01:59, 21 January 2011 (UTC)[reply]
Actually, electron-proton collisions (and resulting inverse beta decay into a neutron) happen when a neutron star is formed. At densities such as those of a white dwarf, it is the electron degeneracy pressure (the statistically-favorable Pauli exclusion principle) that holds the dead star up from further gravitational collapse. But when the mass is great enough that this pressure is overcome, the electrons will literally collide with protons to form neutrons (and neutrinos), which is seen as neutron-degenerate matter (that last article has a more-complete explanation). SamuelRiv (talk) 03:18, 21 January 2011 (UTC)[reply]
Hm, yes. I didn't consider that case. However, I don't that it should actually be understood kinematically as the electrons being pushed into the protons by the pressure of the collapsing star. In the (slightly facetious) language I'm using above, it would not be a case of "the proton really wanting to be a neutron" (because the proton is in a high-energy shell within the nucleus), but "the electron really wanting to become a neutrino" (because the electron is in a high-energy state within the degenerate electron gas).
But I am now puzzled why the expression for Chandrasekhar's limit appears to be completely independent of the mass of a neutron (and in particular to the difference in mass between a neutron and a proton, which ought to be important for when electron capture becomes favorable) –Henning Makholm (talk) 08:57, 21 January 2011 (UTC)[reply]
Research of Light-Dependent reactions as an energy source
Is anyone researching the Light-Dependent reactions as an alternate energy source? Albacore (talk) 21:13, 20 January 2011 (UTC)[reply]
How do you mean? --Jayron32 21:30, 20 January 2011 (UTC)[reply]
If that's the case, the answer is "cut down the tree and burn it". Plants are already a very efficient way of storing energy from the sun; I'm not sure we can do it better in a laboratory outside of the plant than plants are already doing it on their own. There are actually some pretty advanced ideas on how to use photosyntheis to generate energy for us, but they all involve letting plants do the actual hard bits. Biofuel in general is all produced via photosynthesis, albeit indirectly. There is also the use of Algae fuel produced in Photobioreactors. There's some really interesting stuff being done in the field of Biological hydrogen production which uses photosynthesis by plants to produce hydrogen for use in fuel cells. --Jayron32 21:53, 20 January 2011 (UTC)[reply]
Though plants are pretty efficient at photosynthesis, there are indeed people who are working on artificial light dependent chemical reactions: see Artificial photosynthesis. Buddy431 (talk) 22:56, 20 January 2011 (UTC)[reply]
A perfect opportunity to advertise our department: do you mean something like this? There should be a lot about the project in english, but couldn't find it just now... Albval (talk) 20:03, 22 January 2011 (UTC)[reply]
January 21
S2O32-
Why is S2O32- impossible as a molecule? So far I've found its 3D structure is a very unstable zig-zag shape, but is there a better reason? THanks. EDIT: I am actually going from a Lewis drawing which I have written the formula for, unaware that there is actually a differently shaped molecule thiosulphate for the formula. I will try to describe it: the Oxygen and Sulfur form a chain, with oxygen on both ends. They are all covalently bonded on both side (obviously excluding the end atoms). The two electrons are added to both end oxygen to fill the outer level. 24.92.70.160 (talk) 03:32, 21 January 2011 (UTC)[reply]
What do you mean it is impossible? Have you read Thiosulfate? --Jayron32 04:01, 21 January 2011 (UTC)[reply]
To answer why your molecule doesn't work: the short answer is that the thiosulfate arrangement is most stable; your arrangement may end up with a very unbalanced formal charge distribution (and indicator of an unlikely structure) or it may have an unstable molecular orbital arangement. Incidentally, Molecular orbital theory has a much better predictive power for molecular structures than Lewis Theory does. The deal is, it is much more complex than Lewis theory, but it gets the "right" answer more times than Lewis theory; for example MOT correctly predicts that the oxygen molecule is a diradical, something impossible to draw in a Lewis structure and still maintain symmetry and a double bond. MOT is capable of describing a symetrical, doubly bonded, diradical oxygen which more closely matches the actual structure. --Jayron32 04:06, 21 January 2011 (UTC)[reply]
In general, sulfur is rather amenable to long chains S-S-S-S etc. (S8 for example: see allotropes of sulfur). But any attempt to do this with oxygen fails. Tetraoxygen almost but not quite has the potential to exist, and other forms of solid oxygen go a different path. I remember asking about this before and hearing something about the extra orbitals in the outer shells of sulfur coming into play, but I'm afraid I didn't quite understand how it worked then, so... Wnt (talk) 05:11, 21 January 2011 (UTC)[reply]
Another thing to consider is that 5-atom molecules tend to (almost) universally assume a Tetrahedral molecular geometry. If you've got 5 atoms to try to fit into a structure, start there. Early chemistry students have a hard time thinking "three dimensionally" so don't often see the symmetry and stability of that shape; and often what results is all sorts of strange arangements, either linear or cyclical in nature. Always start with one of the basic molecular geometries (180 degrees, 120 degrees, or 109.5 degrees) and only go on to more complex structures if those don't work. --Jayron32 05:31, 21 January 2011 (UTC)[reply]
The Ethiopian mountain Erta Ale is in the historical land of Punt at the fringes of ancient Egyptian influence. (see File:Egypt_NK_edit.svg) It superficially resembles a traditional notion of Mount Horeb. To me it would seem to make sense that Moses might have scouted the location before settling on the equally remote region to the east of the river Jordan as a place to which to withdraw. In modern times it is a continually active volcano, with a pool of lava that has been stable and accessible for the past hundred years. Which raises some questions in my mind...
Was Erta Ale similarly active near the end of the Eighteenth dynasty of Egypt a bit more than three millennia ago? Or could other volcanoes along the Rift Valley have been similar then?
Does the outgassing from a volcano like this create a usable reservoir of water to which a nomadic tribe might expect to come to drink? Is it reasonable that hammering into the rock could do something useful to release it if the level is low?
Suppose you have a thick rope and a large ceramic bucket. Is it possible to fill the bucket from a lava pool like that pictured, and pour it into a mold or work on while molten, in such a way to create tablets which could be presented as "inscribed by the finger of God" (and recognizably not by any method known to skilled craftsman of ancient Egypt)? Wnt (talk) 04:12, 21 January 2011 (UTC)[reply]
Except that it doesn't match other parts of the Exodus narrative. If other scholarly consensus is to be believed, the Crossing the Red Sea occurred at either the Gulf of Suez or "Lake Timsah", a freshwater body just to the north of the northern tip of the Gulf of Suez. The Stations of the Exodus lays out a pretty consistent route, and none of it ends up anywhere NEAR Ethiopia. Furthermore, the Biblical Mount Sinai (usually identified as identical to Horeb), while its location is unknown, is generally placed either in or near the Sinai proper. While many of the stations lack modern locales with certainty, Ezion-Geber is well attested to and it is also nowhere near Ethiopia. Exodus 19 makes it clear that it took 3 months to get to Mount Sinai. How they got from the Gulf of Suez to Ethiopia in 3 months is beyond me, especially as the only route takes them back through Egypt; probably not the best way to go. --Jayron32 04:36, 21 January 2011 (UTC)[reply]
(ec)I don't want to start a huge humanities detour - I doubt I would hold my own in a proper archaeological and biblical debate about this. Generally I'm going by the idea that Moses is described as going to Horeb in Exodus 3, then returning to Egypt [14] so (at least at the first mention it need not necessarily be en route. I don't know for sure that Mount Horeb is truly a place, or has some more general status (like "Air Force One", which is not a literal single aircraft). I was mostly giving the idea behind this as an explanation for the rather peculiar questions about Erta Ale. Wnt (talk) 04:51, 21 January 2011 (UTC)[reply]
Is this by any chance a Ron Wyatt-inspired question...? WikiDao☯ 04:49, 21 January 2011 (UTC)[reply]
No, never heard of him. I see he placed Mount Sinai in Saudi Arabia... in general, it's hard to prove any unconventional idea based on historical evidence, since the evidence necessarily points at the conventional interpretation. But it is all too easy to propose one. That's why I want to take this from the other end and say, if I were at Erta Ale, could I strike the rock and make water come out of cracks in the rock? Could I scoop up some lava and make some impressive looking non-carved words in stone tablets? And if so, then is Erta Ale the only such place, or are there others? Wnt (talk) 04:56, 21 January 2011 (UTC)[reply]
No I don't think you can make/find water that way (without God's help of course :) Water usually flows from springs that are below the water table, but a volcano rises above it. Plus water from a volcano is mixed with sulfur and other chemicals and is not drinkable (water is frequently mixed with lava and a steam explosion is a common cause of an eruption). Lava would make a very poor casting material. It has a very coarse texture, and would show shapes very poorly. Plus it doesn't match the description of the tablets which were extremely heavy (and lava rock is very light), and were sapphire blue. Ariel. (talk) 07:58, 21 January 2011 (UTC)[reply]
Where's the praline That quality (coarse and light) depends on the volcano, surely. Pumice is crumbly and floats, but obsidian is perfectly smooth and quite heavy, and basalt I think varies. 81.131.65.219 (talk) 17:38, 21 January 2011 (UTC)[reply]
Obsidian is smooth and heavy, yes, but it is essentially glass. For a quick comparison, take a chunk of glass and try chiselling something into it and let us know how you make out. :-) It makes outstanding points, but it's not something I would ever try to carve into with a metal implement. Matt Deres (talk) 18:00, 21 January 2011 (UTC)[reply]
Wnt is suggesting casting it, though - or casting dense basalt, judging by the below remarks. 81.131.65.219 (talk) 18:13, 21 January 2011 (UTC)[reply]
The difficulty in chiseling it is actually crucial to the plan. The point is, master stonemasons who build great obelisks as a matter of routine should have been able to look at the tablets and (unaware that lava is molten rock) declare that it is physically impossible for the hand of man to make them. Wnt (talk) 19:18, 21 January 2011 (UTC)[reply]
Check out the Portland Vase, though, an awesome piece of glassware made in a year somewhere between 5 and 25, the decorations done, I think, by chiseling. I also see in Ancient Egyptian technology#Glassworking that cast glass is a very old technique. So presumably a high-level craftsman would not be taken in, whereas a low-level craftsman could be convinced if you just made the tablets out of clay with a bit of sand thrown at it. I wonder whether investigative skeptics abounded, anyway. 81.131.65.219 (talk) 20:08, 21 January 2011 (UTC)[reply]
(ec/outdent)I know that the water begins mixed with chemicals, but if it emerges as a column of steam, there should be places nearby where it condenses as distilled water ... I think.
I found a rather convoluted explanation of why the tablets are said to be made out of sapphire online,[15] but compare "The LORD said to Moses, “Chisel out two stone tablets like the first ones..."[16] I'm not sure a blue color is strictly required. Now I know that obsidian can present a very smooth surface, and there are many such smooth lava flows. But a description of Ethiopian volcanoes mentions obsidian flows from some other volcanoes in the area, but describes Erta Ale as basaltic.[17] I don't know if a stone like tachylite (from rapidly cooled basaltic lava) would give a usable surface, but if it did, the stone is described as being very brittle, which seems consistent with the smashing of the tablets. Wnt (talk) 17:48, 21 January 2011 (UTC)[reply]
To go back to some of the original questions, this or a similar volcano is likely to have been active at the time. Obsidian is unlikely from the volcanoes of the northern Ethiopian rift, I would think, but basalt can certainly be pretty glassy. I wouldn't expect to find significant water on an active volcano in an arid environment (although I recall that things may have been different a few thousand years ago climatically). As to the rope and bucket - the bucket might survive, but the rope wouldn't, that molten lava is at 700°C minimum, never mind the protection that the people trying to get the lava out would need. Mikenorton (talk) 18:17, 21 January 2011 (UTC)[reply]
It sounds feasible to me but technically tricky, and would require Moses to hang around the volcano for a month or so secretly designing and manufacturing different kinds of buckets. 81.131.65.219 (talk) 18:36, 21 January 2011 (UTC)[reply]
Forty days and forty nights?[18] Admittedly, the rope is a clear vulnerability - though in the current caldera it looks like there is a cooled crust and fairly good airflow, reducing the direct and convective heating, and of course you can always soak it in water before lowering. Wnt (talk) 19:18, 21 January 2011 (UTC)[reply]
I figured rather than a bucket you'd want a long-handled ladle, which could also be used to manipulate the lava from a safe distance once it's hauled up, and tie the rope to that. Not sure whether the necessary length is within the bounds of practicality. The bowl of the ladle would be pivoting, like a bucket on a handle. 81.131.65.219 (talk) 19:56, 21 January 2011 (UTC)[reply]
Sorry, I was glossing over the bucket part because I figured they could work out something. But to give an example, take an amphora and suspend it by ropes through the handles and around the neck, and smash out a hole a little way up one side for the lava to flow into. Maybe tie a weight around the neck to help the bottom make it into the lava. Wnt (talk) 20:02, 21 January 2011 (UTC)[reply]
scroll down - you'll discover "medical terrorism" instead of "medical tourism". This has been edited on 20/1 (yesterday). —Preceding unsigned comment added by 132.72.226.107 (talk) 06:39, 21 January 2011 (UTC)[reply]
Already edited myself and changed it back to tourism. Only problem is that the links are still pointing to wrong articles.. This I cannot change. —Preceding unsigned comment added by 132.72.226.107 (talk) 07:19, 21 January 2011 (UTC)[reply]
This is the wrong place for this, but I checked history of the article and reverted it back to before the vandalism. But I don't understand what you mean by "links are still pointing to wrong articles" - can you explain? Ariel. (talk) 07:35, 21 January 2011 (UTC)[reply]
Ok, I'm not touching it again.. just tried to change it and you reverted my changes :-).
so just try to follow the links and see for yourself. If they point to the articles they claim to be pointing to, than everything is all right. check it.
btw, what is the right place for this? —Preceding unsigned comment added by 132.72.226.107 (talk) 07:38, 21 January 2011 (UTC)[reply]
Here: Wikipedia:Administrator intervention against vandalism to request a ban, but before going there the user needs to be warned (but he has been). Normally go here: Wikipedia:Abuse response. The links were not changed by the vandal - it looks like Haaretz changed their site. This is not uncommon. It would be great if you could search their site and find the new location of those articles. Don't just remove the references like you did, find the new url for them. Ariel. (talk) 07:51, 21 January 2011 (UTC)[reply]
10x for the help. About finding pro-Israeli articles at Haaretz site - yeah right.. why don't you have a go :-). Well, have a nice weekend. gotta go. —Preceding unsigned comment added by 132.72.226.107 (talk) 07:58, 21 January 2011 (UTC)[reply]
I'm not sure what you're referring to since no one else discussed pro-Israeli articles at Haaretz. I can't find any sign of the article on Haaretz but as Ariel has said, speaking generally it's hardly uncommon the articles disappear in site reorganisations or whatever. Some websites don't even bother to keep articles for that long trying to encourage subscriptions to archives etc. In any case, I doubt Haaretz removed the article because it was "pro-Israeli". It was on Haaretz at one stage as proven by this archive.org[19] archive which I added to the article. Nil Einne (talk) 09:47, 21 January 2011 (UTC)[reply]
trusting science?
I'm not sure if it's a scientific question or not; but I have a religious friend who says:"Science can't be trusted because it's always changing and scientists always make mistakes.".I do trust science, but is this some kind of faith? Is it a good reason not to trust science at all? do we have enough reasons to do so?--Sina-chemo (talk) 11:40, 21 January 2011 (UTC)[reply]
Without modern science, life expectancy would be far lower. Travel, communication, technology would not exist as they do. Without science, we would be living in the middle-ages. Science definitely makes mistakes, but the beauty of it is that science is free-form, and constantly updating itself, constantly challenging ideas in the search for truth. Your friend has been (struggling not to say brainwashed) given somebody else's opinion. Besides, I bet this "science hater", uses products developed by "science" all day every day, and is, as such, a hypocrite.Zzubnik (talk) 11:58, 21 January 2011 (UTC)[reply]
Heh, Scientists will say that's exactly why you should trust them, because they are willing to correct mistakes. But really science isn't meant to be taken on trust, the entire point of it is that anyone can duplicate the results for themself. You need to distinguish the different sciences though, some are far more definitive than others. In some fields (physics, chemistry) you can do a direct experiment to answer a question - you should trust those. But in others you only get your info by doing a statistical analysis (some aspects of biology), and those are less reliable. Scientists know this, and do the best they can. Also, there are some fields where the info comes from modeling (climate, cosmology), or basically educated guesses (archeology). Those are the least reliable IMO, because you can't actually do an experiment. That doesn't make them automatically wrong of course, but nothing beats an actual experiment. I hope I don't get in trouble for listing specific fields. But I will note that when physics depends on statistics, it requires a much much higher confidence for experiments than biology does. Ariel. (talk) 12:07, 21 January 2011 (UTC)[reply]
Organisations that refuse to consider that they make mistakes go whacko. Every organisation makes mistakes: quality organisations openly put them right when they become apparant, but bad organisations cover them up to avoid losing face. Correcting mistakes is part of the process of adapting to a changing environment. If they will not adapt, they die. 92.15.25.92 (talk) 12:11, 21 January 2011 (UTC)[reply]
@Sina-chemo: Here's the deal with science and why you can trust it: Humanity arrives at knowledge multiple ways, but we can reduce it down to a few basic methods, broadly speaking:
We can use our senses to observe the world around us, and we can use logic and reason to connect our observations together and draw conclusions about what we observe
We can make it all up
Science does #1. You decide which method is more trustworthy to you. --Jayron32 13:33, 21 January 2011 (UTC)[reply]
I'll note that that was a positivistic (not to mistake with 'positive') view of things. That is, it's not the only one out there. As for the initial question. According to what we were taught in University, all scientific theories do have inconsistencies and blank spots on the field of explainable experimental data. From purely scientific point of view, certain theories are being applied, are used not because they are true, but because they're the ones that are best at the moment at the explaining experimental ovservations and predicting outcomes of planned experiments. I really was amused at the hydrodynamics and heat exchange theories. They have formulae of such beauty, where basically everything is multiplied by each other with degrees like 0.89, 0.43, and then the result is said to be expected to have ~30 % accuracy. Some examples can be seen in Nusselt number. The Nusselt number is one of the things used for calculating heat-transfer processes parameters. And, there are industrial processes which utilize heat exchangers, which exchangers are neither chosen randomly nor have thousands of percent of efficiency reserve. They are built according to calculations. But if existing views were just wrong, heat-exchangers would go hay-wire en masse, in some cases most likely leading to casualties. At the same time I don't think that even a scientism freak would believe that all those numbers are catching the essence of nature and are therefore "true" or absolutely "trustworthy". Still, those numbers are science. And it is because an idea of 'no universal criteria exist' applies to the degrees of trustworthiness as well, original poster's friend has his right to adhere to his own opinion. He's adding to the variety, so I'd approve, but share his views I'd not. If I were to argue with him, I'd push for the point that he doesn't have a thing to trust among his means of physical sustenance then. :) Which may be true, but so what? Physically, nothing has changed after such a declaration. Legate of Skai (talk) 16:11, 21 January 2011 (UTC)[reply]
If you read up about 5 sections, you'll see that I leave a long explanation where I have pre-agreed with everything you have said regarding the nature of "truth" and its irrelevence to scientific thought, even before you said it. The indeterminability of the One Right Answer, and the fact that science is simply unconcerned with such matters is still 100% compatible with the statement I made with regards to the utility of science in acquiring knowledge. --Jayron32 16:18, 21 January 2011 (UTC)[reply]
Is it that hard to fathom what original poster's friend would say to the–in my opinion–crude dichotomy provided as an answer option?.. Such things wouldn't help with "Is that your best?" sort of confusion when confronting sophists. Legate of Skai (talk) 19:21, 21 January 2011 (UTC)[reply]
One does have a form of "faith" in science, as one does not actually re-perform experiments and even practicing scientists cannot possibly know the entire literature at once. But what you are having "faith" in is a system that on the aggregate does review and re-test and challenge its tenets in a systematic way. The goal is to get reliable knowledge about the natural world, plain and simple. The models of science have so far provided a far more reliable model of the natural world than those formed by simply interpreting and re-interpreting the Bible. That does not mean that science is all-knowing or that the conclusions of every study should be trusted blindly. There is a lot of science which is tremendously unsettled at this point, and even entire fields have practices that I think are going to be seen as colossal methodological goofs in future years. Still, science gets us things which definitely "work" — like airplanes, satellites, GPS, computers, and nuclear reactors. If the underlying theories on these technologies were not essentially correct (and they are not intuitive—GPS would not work without General Relativity, modern computers use a good deal of quantum mechanics, and nuclear reactors rely on very specific models for how atoms work), then they would simply fail from the beginning. That's a better track record than any other knowledge system I've ever heard. --Mr.98 (talk) 13:40, 21 January 2011 (UTC)[reply]
One thing to remember is that scientists are still humans, and thus are capable of both errors in understanding, errors in judgement, and outright deception. You can expect to find these character traits in scientists roughly as often as you find them in the rest of the human population. So, while it is true that some scientists (see Andrew Wakefield) lie and cheat and produce deliberately fraudulant statements, that is also true of religious leaders (see Jim Bakker) and politicians (see Richard Nixon) and any other group of people. The question is not whether you can trust every single scientist down to the last person; you can't ask that of any group of people in all of humanity. You need to ask if you can trust science as a process to produce reliable results. If your inclined to such cynicism that you can trust no person about anything, then no one is going to convince you that you should trust science. Insofar as you can place your trust in any human endeavor, even in light of the fact that some humans are not trustworthy, science is a pretty good bet. --Jayron32 13:47, 21 January 2011 (UTC)[reply]
The answer all depends on how you define "trust", and also "science". If you get in an automobile, you "trust science" in that you assume it's not going to explode and kill you; even if you don't go by the engineering but simply see that other people's cars don't usually blow up, that is still a sort of scientific observation, subject to the usual caveats (do your neighbors have Pintos..?). But science doesn't define trust, and it defines science only by providing a theory, which you may or may not know. Ordinary day to day life involves a vast amount of unspoken philosophy, and few if anyone can tell if it is correct. Wnt (talk) 19:42, 21 January 2011 (UTC)[reply]
Scientists are always aiming to get closer to the correct explanation for everything they investigate. Religious folk think they already know. HiLo48 (talk) 23:02, 21 January 2011 (UTC)[reply]
Volume of subatomic particles?
the diameter of the nucleus in the atom is 1fm.Does it mean that the protons and neutrons have a certain diameter(or volume Or even shape, spherical, for example)too? what about other subatomic particles? are particle just some small dots with extended properties such as elecric fields? or they have some sort of a size or volume?--Sina-chemo (talk) 11:57, 21 January 2011 (UTC)[reply]
You can define the the radius of an object as the length scale associated with the energy required to probe its structure. So far we know that baryons and mesons do also have internal structure, and thus a finite radius, but other particles, like leptons, quarks, gauge bosons and neutrinos, have, in the energies accessible to modern science, no discernible structure. Thus, to our knowledge, they are point particles. —Preceding unsigned comment added by 129.67.37.227 (talk) 13:36, 21 January 2011 (UTC)[reply]
(edit conflict)At the fundemental level in the atom (electrons and quarks) concepts like "volume" make little sense. If we consider them to be particulate at all, then they are true "point particle"s with no volume. But its not even necessary to consider such entities to be "particles" in the "little ball" sense. In some cases, it makes perfect sense to think of an electron as a standing wave occupying the space of its defined orbital, for example. When an object, like you, has volume, such volume is purely the consequence of, as you put it, the "extended properties" of the many fundemental particles that make it up. Another way to look at it is that volume only exists where fundemental particles interact with other fundemental particles; the volume of an proton is therefore defined by the distances at which the strong nuclear force works in keeping the quarks together. --Jayron32 13:41, 21 January 2011 (UTC)[reply]
The volume of the proton also has an effect in its interaction with the electron in a hydrogen atom, causing (extremely small) shifts in the the allowed energy levels of the electron, and hence of the frequencies of the lines in the atomic spectrum of hydrogen. Having said that, the proton is not a hard sphere, but rather something which is a bit fuzzy with no firmly defined edge – atoms are similar in this respect. The usual measurement of the "size" of a proton is called the "rms charge radius", which is 0.877 fm. So 1 fm for the diameter of an atomic nucleus is a bit small – a few femtometres would be a more accurate description (depending on the nucleus, of course). Physchim62(talk) 14:02, 21 January 2011 (UTC)[reply]
Decaffeination
I (in the US) recently bought some Taster's Choice decaffeinated coffee and notice a distinct taste difference from regular, and after reading the decaffeination article, see how it's a challenge to remove the caffeine but leave all the other molecules that provide the original coffee taste. Does anyone know of a US instant decaffeinated coffee that tastes closer to regular than Taster's Choice, because it's almost not even worth it for me to drink this. DRosenbach(Talk | Contribs) 14:18, 21 January 2011 (UTC)[reply]
insofar as its worth it to drink any slightly bitter, brown water which doesn't wake you up?As in, there's a reason to drink preground, canned coffee that isn't related to its caffeine content. --Jayron32 14:23, 21 January 2011 (UTC)[reply]
Some people swear by sanka as the best decaf. In general the swiss water process mentioned in the decaf article is probably best at leaving flavour intact, though it can be hard to tell which method a certain brand uses. In a completely different direction, many people enjoy the naturally caffeine-free postum wish postum still existed. SemanticMantis (talk) 15:03, 21 January 2011 (UTC)[reply]
While postum may not be availible, many people drink chicory root as a coffee substitute, either by itself or mixed 50/50 with coffee. I believe that chicory root has no caffeine in it. --Jayron32 15:58, 21 January 2011 (UTC)[reply]
Yes, if you like chicory, it will make up for some of the flavor lost by decaffeinating. the brand Luzianne sells decaf with chicory. SemanticMantis (talk) 17:03, 21 January 2011 (UTC)[reply]
Radius of Black Hole
If "You can define the the radius of an object as the length scale associated with the energy required to probe its structure. So far we know that baryons and mesons do also have internal structure, and thus a finite radius, but other particles, like leptons, quarks, gauge bosons and neutrinos, have, in the energies accessible to modern science, no discernible structure. Thus, to our knowledge, they are point particles." Then can't we apply this argument to black hole radii in that the event horizon is the radius. I mean the black hole as a point particle or singularity argument is simply a result of our inability to properly measure something with no free space inside it like the sub atomic point particles that we know of? —Preceding unsigned comment added by 165.212.189.187 (talk) 14:59, 21 January 2011 (UTC)[reply]
Defining the radius of particles in this way makes sense, as it highlights the 'radius' as the crossover from one regime to another (for example when within the radius of a proton, modelling it as a point electric charge completely fails to describe the effects that are found. This is no different to say modelling a billiard ball as a hard sphere, if you are operating on atomic scales, or with energies capable of smashing the ball, you will find that your experiments do not detect something that behaves like a hard sphere). The reason that a Black Hole has radius is slightly different, the event horizon instead describes a radius within which no information can escape. The black holes existence and dynamics have their origins in the distortion of the universe's geometry, rather than in the properties of the objects that make it up. —Preceding unsigned comment added by 129.67.37.227 (talk) 15:20, 21 January 2011 (UTC)[reply]
So that would suggest that a black hole is not a singularity as in the size of a point particle but rather a singularity because the "measurable" distance from one point on the event horizon to the opposite point is zero, as a result of our inability to accurately measure that distance, right? —Preceding unsigned comment added by 165.212.189.187 (talk) 15:42, 21 January 2011 (UTC)[reply]
No, it's more complex than that. The measurable distance inside the event horizon from one side to the other is zero. The measurable distance across the event horizon as measured by a stationary observer outside of is a finite, measurable distance. But the equivalent measurement taken inside of the event horizon would be exactly zero; that is the singularity being refered to. Its not as simple that there is some point at the center of the event horizon which around which the event horizon is projected like a sort of cloud. It can be modeled that way to an external observer (that is, we tend to think of a black hole in those terms), but the gravitational distortions in terms of the effect of the black hole on spacetime is such that the internal structure is literally a singularity. The reason this is different from, say, quarks or electrons as "point particles" is that, from an external observer, electrons really are a point with no dimensions. For an external observer of a black hole, the "event horzion" has apparent dimensions and an apparent volume. --Jayron32 15:53, 21 January 2011 (UTC)[reply]
No, that is wrong. There is spacetime between the event horizon and the singularity, and this spacetime looks (locally) just like any other spacetime -- there are lots of different points/events inside, separated by positive time and space intervals. It is not true that an observer inside the horizon cannot measure any distance, for example. All the horizon means is that he cannot tell anybody outside of it about his measurement, and that he has limited time to enjoy his knowledge before he splats into the singularity. –Henning Makholm (talk) 20:01, 21 January 2011 (UTC)[reply]
So then the black hole's radius is the event horizon or very close to it, and not infinitely small, right? —Preceding unsigned comment added by 165.212.189.187 (talk) 18:22, 21 January 2011 (UTC)
But black holes and point particles are similar in that they both cannot be measured due to the fact that there is no free space inside them. —Preceding unsigned comment added by 165.212.189.187 (talk) 18:37, 21 January 2011 (UTC)[reply]
Scientists who study black holes would rarely use the term "radius" because that word is ambiguous. They would use the term event horizon. When defining the geometry, they would use an Einstein tensor in 4-space. By definition, a "radius" is a one-dimensional measurement. Thorough, rigorous, and correct analysis of a black hole requires general relativity, and it is atypical (if not impossible) to construct general relativistic gravity field equations in one dimension. (The geometry described by relativity just isn't one-dimensional). So, if you want to communicate about black holes in an unambiguous way, you will not describe a "radius." You will present a 4x4 tensor, and demonstrate that this results in a singularity along a surface, called an event horizon. It so happens that if you project this surface in to a Cartesian space and "ignore" the singularity for a moment, you'll look like you are describing a sphere with a radius; but that's going to give rise to logical conundrums as described above (for example, the size of the measured radius is different, depending on whether you are inside or outside the sphere). Nimur (talk) 19:25, 21 January 2011 (UTC)[reply]
The event horizon is not a singularity. It is a hypersurface that surrounds a particular region of spacetime; the surrounded region contains a singularity, which is different and distinct from the horizon. –Henning Makholm (talk) 20:01, 21 January 2011 (UTC)[reply]
No, but behavior around the event horizon is very, um, strange. For an observer falling towards a black hole, neither the observer themselves, nor anyone watching the observer from afar, will see the observer "cross" the event horizon. The observer sees no change at all in their environment, and falls, from their point of view, for an infinite amount of time, or until tidal forces spagettifi them. An external observer will watch the faller decelerate and become arbitrarily close to the event horizon, without ever crossing it. One can calculate the exact moment where one should cross the the event horizon, but no observation ever shows this occuring, because of the effects of gravitational time dilation. The event horizon is not the singularity itself, but every point inside of the event horizon is the singularity... --Jayron32 20:21, 21 January 2011 (UTC)[reply]
No, that is just wrong, almost all of it. An observer falling into the hole can calculate when he crosses the horizon if he knows the geometry of the hole (he will have to calculate it because nothing particularly momentous will happen to him at that time). After crossing the horizon, he experiences a finite amount of time before he necessarily reaches the singularity, (ignoring the fact that he will be spaghettified first). The horizon crossing happens at a definite time and place in spacetime. Just because light from the horizon-crossing event never reaches the outside observer, that doesn't mean that this observer is going to conclude that the horizon was never crossed. To the contrary, knowing the spacetime metric he has no trouble compute when each of the bits of light he does eventually receive must have left the infalling object. He can easily plot these results and find that they converge towards a particular point in spacetime, and can infer that at that point, the object crossed the horizon. In particular he will not conclude that the faller ever decelerates, unless he is stupid or careless enough to fail to correct his data for the increasing lightspeed delay between something happening and him seeing it. Finally, as I have said before, there are plenty of points in spacetime that are inside the horizon yet different from the singularity. –Henning Makholm (talk) 22:11, 21 January 2011 (UTC)[reply]
Thank you Henning for adding detail to the discussion. As I stated below, I was sketchy on some details. If your description of black holes is more correct than mine, then could you perhaps also correct the article Black hole, which contains the following statements. "Due to this effect, known as gravitational time dilation, an object falling into a black hole appears to slow down as it approaches the event horizon, taking an infinite time to reach it." That is plainly wrong, and I would appreciate it if you could fix it. As far as what happens inside of the black hole, I readily admitted below that my mathematical background was not strong enough to derive the geometry. Thank you for clearing it up for me as far as that goes. --Jayron32 23:09, 21 January 2011 (UTC)[reply]
There isn't necessarily an inconsistency between what the article says, and what Henning is saying. It all really boils down to the difference between "appears to" and "concludes that".
The article is correct, assuming I understand black holes correctly. As an object gets very close to an event horizon, it does "appear to" a distant observer to slow down, in that: A) If the object is between the observer and the black hole, the angle subtended by the object as seen by the observer will decrease more slowly than does the angle of an object traveling away at constant speed in empty space, and indeed, the angle subtended approaches a finite limit instead of zero. And B) If the object is approaching the black hole from what appears to the observer to be the side of the black hole, the pixels per frame that the object's image in the observer's video camera moves decreases with time, and the object's image approaches a fixed position in the frame, corresponding to where the event horizon is, without ever actually quite reaching that position.
I guess Henning's point is that it would be "stupid" or "careless" to conclude from those observations that the object was really decelerating, because those observations alone don't take the finite speed of light into account at all. From a general relativity perspective, the object is neither decelerating or accelerating (assuming it isn't using thrusters or something). Like all objects in free fall, the proper acceleration of the object is zero. And any other kind of acceleration is just a coordinate "acceleration", that depends entirely on one's choice of coordinates, and isn't a real, physical acceleration at all.
The above might give the impression that the outside observer will be able to see the infalling object forever, hanging just outside the event horizon. That's not really true. The object's image will very rapidly get red shifted to the point where the wavelengths of light that came from the object are too huge for the light to be detected by any method. Red Act (talk) 02:31, 22 January 2011 (UTC)[reply]
As an addendum, I think the scale length of a black hole, as measured from inside the black hole, is ∞ (not zero). If you are inside the event horizon, and want to move to any other point, it will take an infinite time to traverse (and hence to exit), no matter what speed you travel at. But I would also point out that in certain geometries, zero and infinity are congruent. The simplest case of this is the projective space (which, while a nice mind-bender of a geometric space, is not a solution to general relativity). Again, we can't really expect logical continuity when we are using the wrong geometry to describe a black-hole. Nimur (talk) 19:31, 21 January 2011 (UTC)[reply]
Correct me if I am wrong, because my math in this area is nonexistant, but my understanding about the internal geometry of a black hole as being "zero volume" comes from the fact that, from the point of view inside, all points are "compressed" into the singularity, and thus occupy the same location in 4D spacetime, and are thus identical in location. Two points that occupy the same exact location have zero distance between them, n'est ce pas? --Jayron32 19:39, 21 January 2011 (UTC)[reply]
I'll second that, pointing out that as I understand it, the singularity is in the future of those falling into the hole. Not in the sense that they'll reach it in the future, but that it is the future, because their light cones point at it. Wnt (talk) 19:45, 21 January 2011 (UTC)[reply]
Thanks that was helpful, but with all this focus on black holes, the actual question about their similarity to point particles was ignored. Could someone please address this observation? Additionally, could black holes be a giant atom like "blackholeum" with a giant nucleus and an electron cloud(event horizon)? —Preceding unsigned comment added by 165.212.189.187 (talk) 20:14, 21 January 2011 (UTC)[reply]
There is no similarity to point particles. Black holes have an inside, which has no internal volume. Point particles have neither an inside, nor a volume. --Jayron32 20:23, 21 January 2011 (UTC)[reply]
Could you please expand on the difference between no internal volume and no volume (point particle)? —Preceding unsigned comment added by 165.212.189.187 (talk) 20:31, 21 January 2011 (UTC)[reply]
Sure, I explained this above at least once, but we'll try again. To an observer from outside a black hole, the event horizon occupies (surrounds) an apparent volume of space. You can fly around one, take measurements, and calculate an apparent volume that the event horizon would encase, if, for example, it were an ordinary star. However, because of the warping of spacetime by the singularity inside of the event horizon, the black hole itself compresses all of the space that would appear to be inside of the event horizon into the exact same location. By definition, any two points that occupy the same location have no distance between them; so there is no volume. By contrast, a point particle has no apparent volume to any observer. If you look at a point particle, it does not appear to occupy any amount of spacetime, unlike a black hole, where you can measure the dimmensions of it from a vantage point outside of the event horizon. You cannot measure any dimensions of a point particle from any vantage point. --Jayron32 20:57, 21 January 2011 (UTC)\[reply]
Most of these claims about black holes are wrong. See above. –Henning Makholm (talk) 22:11, 21 January 2011 (UTC)[reply]
See above. Could you fix the Black hole article then so that we can stop telling people wrong things? Thanks! --Jayron32 23:09, 21 January 2011 (UTC)[reply]
What you said about the apparent volume enclosed by the event horizon is correct, and that is how the quantity called "black hole radius" is defined. But "the black hole itself compresses all of the space that would appear to be inside of the event horizon into the exact same location" is wrong, or at least I don't understand what you mean by it. There is no sudden change in the structure of spacetime at the event horizon. -- BenRG (talk) 01:33, 22 January 2011 (UTC)[reply]
Black holes have variable mass, whereas all particles of a given type have the same rest mass. (Then again, is the mass of a black hole a rest mass?) I suppose every different mass of black hole would be a different "particle", in a sense, which interacts with other particles by eating them and becoming a higher-order black hole?
We should ask whether the mass, charge, and spin of black holes are quantized. I don't think there is any doubt that the charge will vary in the usual increments. The spin should also, one would think - a black hole should eat or emit photons with angular momentum hbar. Now whether a black hole is a boson or a fermion (can it be absolutely without spin or only plus or minus hbar/2) - I'll let someone else work on that a while. But the mass, well, a black hole can eat all sorts of particles, and we're aware of no underlying common denominator of their masses, so what kind of quantization scheme describes a black hole's mass? Wnt (talk) 20:55, 21 January 2011 (UTC)[reply]
Jay, could you rephrase this "You cannot measure any dimensions of a point particle from any vantage point." to include "yet" or "with our current tech." at the end, since that sound like the famous last words of some physicist in the 1800s?. —Preceding unsigned comment added by 165.212.189.187 (talk) 21:15, 21 January 2011 (UTC)[reply]
It's not a technological limitation; it's a definition. If there were any way to measure a dimension, then the particle would not be a point particle at all. That's what being a point particle means. –Henning Makholm (talk) 22:11, 21 January 2011 (UTC)[reply]
The quantity called "the radius of a black hole" is the reduced circumference of the event horizon. The "reduced circumference" is simply the circumference divided by 2π, i.e., the radius that a circle with that circumference would have in ordinary flat space. Obviously, practical experiments on black holes are difficult—for one thing, we don't have any to experiment on—but in principle you could build some kind of wire-frame structure just outside the event horizon that encloses it on all sides, then disassemble it and reassemble it somewhere else, and the result will be a sphere whose (now directly measurable) radius equals the radius of the black hole. That radius doesn't have any literal meaning when applied to the black hole itself, but that doesn't mean there's no space inside the black hole. The inside is very similar to the outside, according to the theory at least.
There is probably a close relationship between black holes and elementary particles in quantum gravity (this is just personal prejudice, really, but it's a fairly common prejudice among particles physicists, I think). For starters, you can't really have point particles in general relativity because they're too dense—they ought to collapse into black holes. If elementary particles were black holes, you would expect them to radiate away their excess mass and evaporate—and that's what they do, conservation laws permitting, except that it's called particle decay. So it's quite appealing to think of the world as consisting entirely of black holes in vacuum, with the funny low-energy fermion spectrum (electrons and whatnot) resulting from some kind of small-scale tweaking of the rules of general relativity. If you're wondering why this hasn't been developed into a working theory of quantum gravity, it's because it doesn't actually work very well. One big problem is that black hole electric charges have to satisfy |q| < m, in natural units, and electrons violate that bound by a factor of about 1021 (this is one aspect of the hierarchy problem). One way of solving that is to introduce large extra dimensions, and that's a big part of the reason many particle physicists were/are hoping for evidence of large extra dimensions at the LHC. I think the LHC has already ruled out some versions of this idea, but I don't know the details. -- BenRG (talk) 01:33, 22 January 2011 (UTC)[reply]
Oklo reactor and the fine-structure constant
The articles say that the isotope ratios are consistent with alpha actually staying constant, but The Disappearing Spoon by Sam Kean points out that the isotopes of samarium are in the wrong proportion. --J4\/4 <talk> 17:19, 21 January 2011 (UTC)[reply]
Cells
As I understand it, aging is caused by cell replication being imperfect. Cells are copied from copies of copies and over time this results in degradation, like photocopying a photocopy over and over. So the solution would seem to be; introduce cells which have not suffered degradation into the body for the replication process to use. Is this biologically possible? What would be the limits of doing this? Could a person theoretically live forever using this method? 149bbac79bf1bc39671cee9d04cfb7d2—Preceding unsigned comment added by 188.163.48.105 (talk) 19:40, 21 January 2011 (UTC)[reply]
The brain. You could theoretically replace any part of your body after it degenerates other than the brain - once that is gone, there's no getting it back, at least not in the shape yours was. From the brain cells article: "Neurons of the adult brain do not generally undergo cell division, and usually cannot be replaced after being lost, although there are a few known exceptions." TomorrowTime (talk) 19:49, 21 January 2011 (UTC)[reply]
I second the statements by TomorrowTime. Note also that most neuroscientists believe that memories are stored in the connections between brain cells, so if you somehow managed to replace all the brain cells with new ones, you would presumably lose all your memories in the process. Looie496 (talk) 02:03, 22 January 2011 (UTC)[reply]
I think that the brain has more regenerative capacity than it's given credit for. I was just reading that Jim Brady actually has made a substantial recovery over the past 30 years. And a shortage of neuroblasts seems to be associated with depression. While it may be that complete replacement of all the brain's cells and regrowth from scratch would be a reset, it also appears that memories are constantly being recalled and rewritten, so if cells gradually turn over, it doesn't necessarily mean a loss of all the information. Wnt (talk) 06:07, 22 January 2011 (UTC)[reply]
Proton target fusion
Yesterday I saw Dr. Vince Teofilo speak at Lockheed's Advanced Technology Center[20] about inertial electrostatic confinement (IEC) for boron-11 + proton fusion, which avoids the problem of neutron activation creating nuclear waste from D-T fusion, but there are questions as to whether it can break even. However, Dr. Teofilo was very optimistic about non-maxwellian plasma, beam-beam type fusion which has recently been achieved in IEC devices. I asked about bombarding solid 11B with a proton beam. Dr. Teofilo said to look at Wikipedia's Proton target fusion article, but there isn't one and I can't find anything about it. Does the energy at which protons must be accelerated in order to fuse with a solid boron target exceed the resulting output energy? The boron article says 0.5 MeV in for 8.7 MeV out, but does that assume the boron is already ionized, and what if it isn't; can the necessary energy be front-loaded into the proton's momentum? 71.198.176.22 (talk) 20:01, 21 January 2011 (UTC)[reply]
The phrase "proton target fusion" barely appears on the web at all, but we do have an article on aneutronic fusion, which looks like the topic of his talk from the blurb. I can't answer your more specific questions as I am not smart. --Sean 20:17, 21 January 2011 (UTC)[reply]
Most people don't know what aneutronic fusion is, so you are smart. Keep trying to achieve your desired level. 71.198.176.22 (talk) 00:06, 22 January 2011 (UTC)[reply]
Related question: What would happen if a proton with 0.5 MeV plus the Boron-11 atom's ionization energy collided with a Boron-11 atom held in place by a crystal structure? 71.198.176.22 (talk) 00:19, 22 January 2011 (UTC)[reply]
January 22
Interstellar travel using asteroid rubble for shielding
One of the steepest obstacles to interstellar travel, whether by generation ship or vitrification freezer based sleeper ship colonization, is exposure to baryon and electromagnetic radiation for which shielding is more economical to take from the rubble of a spherical (loosely gravitationally bound) asteroid, because it is very expensive to launch fabricated shielding from the Earth's surface to space. Therefore, early successful interstellar craft will likely look like spherical asteroids themselves, with habitat modules burrowed under their rough surfaces. Comet fluid propellant tanks, for example mylar balloon based and/or rigid tanks (possibly formed from asteroid rubble) would also need to be shielded from baryons. Why do all the designs in the Interstellar travel article assume that asteroid-based shielding would not be necessary, sufficient, and the most economical shielding solution? 71.198.176.22 (talk) 00:17, 22 January 2011 (UTC)[reply]
Your question seems to be based on certain assumptions: (i) it is focused on something hypothetical = interstellar human travel; (ii) if/when interstellar human travel becomes a reality, we will know nothing new about economical radiation shielding; and (iii) the authors of existing WP articles considered and dismissed your proposed solution. If you have evidence to the contrary, please be more clear. I'm not convinced of any of these, but if you'd like to try improving the Interstellar travel article based on reliable sources, please do so. Talk:Interstellar travel would be a great place to discuss that article's content and propose significant changes. -- Scray (talk) 01:45, 22 January 2011 (UTC)[reply]
I haven't checked the article but isn't the normal assumption that most of the construction will in fact be done in space with the materials possibly coming from the moon or yes even an asteroid so the cost of launching fabricated shielding from earth may not be relevant anyway? Nil Einne (talk) 04:01, 22 January 2011 (UTC)[reply]
Probably, but in practice the ISS wasn't constructed in space so much as assembled from modules constructed on Earth. I don't see any reason to believe that will not continue to be the most economical solution. Fabricating fancy smooth hulls in space from asteroid fragments would be orders of magnitude more expensive than placing habitat and propellant tank modules inside such fragments and fastening them together. 71.198.176.22 (talk) 08:43, 22 January 2011 (UTC)[reply]
Well the ISS is orders of magnitudes away from capable of interstellar travel let alone being a generation ship. And we don't have any sort of base on the moon. (From what I've seen the general assumption is we won't still be stuck on earth by the time we begin to seriously consider a generation ship.) So perhaps not the best comparisons... You should perhaps consider where/how you are going to get these asteroid fragments of the right mass for your purposes, what difficulties using something which isn't optimised for the purpose is going to create (e.g. in extra fuel and engine capabilities needed) since this seems to be something you've ignored. In fact you seem to be mainly pointing out albeit indirectly the obvious, that we are still decades, probably centuries away from this being capable of construction such a ship whatever your starting point so this is all very highly speculative and going by our current capabilities a bit flawed. Nil Einne (talk) 12:32, 22 January 2011 (UTC)[reply]
Fabricating fancy smooth hulls in space . . . ." Why would you bother to do that with a vessel that will only operate in a vacuum and doesn't therefore require any kind of streamlining? 87.81.230.195 (talk) 13:48, 22 January 2011 (UTC)[reply]
The Wikipedia article is, like any other Wikipedia article, based on what is written in reliable sources. There are lots of reliable sources that describe ideas for interstellar vessels that don't involve lots of shielding. There are also some that describe ideas that do - the idea of hollowing out an asteroid and adding an engine is well known (although it doesn't seem to be mentioned in our article - probably an oversight).
However, shielding is only a big issue for fast interstellar vessels (at relativistic velocities, interstellar dust is a big issue). For slower vessels (sleeper ships and generation ships), shielding shouldn't be a big issue. Radiation in interstellar space is much less than near stars, so even over long timescales you don't need to worry too much. A couple of inches of titanium should be sufficient hull. A generation ship would, be neccessity, be very large so you would get a lot of shielding just from the air inside (assuming people don't spend too much time in the outer sections - make sure the living quarters are near the middle). --Tango (talk) 13:44, 22 January 2011 (UTC)[reply]
... and by the time that these vessels are carrying humans, we will probably have developed "USS Enterprise" style of "shields" that deflect all harmful particles, dust, and even larger debris away from the inner hull. Dbfirs 14:16, 22 January 2011 (UTC)[reply]
It's possible. Our current understanding of science doesn't include anything that could be used to make a force field, though. We can deflect charged particles, that's easy, but neutral ones are a problem. --Tango (talk) 15:17, 22 January 2011 (UTC)[reply]
Yes, good point! I've watched so many episodes of Star Trek that I've started to believe its pseudo-science! Dbfirs 21:10, 22 January 2011 (UTC)[reply]
"AD is a terminal illness with the cause of death typically being an external factor such as infection of pressure ulcers or pneumonia, not the disease itself."
Does this mean that the disease itself kills people occasionally; and if so, how does this happen? I don't have access to the source for this statement. Nyttend (talk) 01:22, 22 January 2011 (UTC)[reply]
The last paragraph of the source states:
After the clinical diagnosis of AD, life expectancy is reduced by one third (Heymen et al. 1987). A long persistence
of symptoms, the severity of illness, old age, male sex, and physical disease are major risk factors for mortality in AD (Bowen et al. 1996; Burns et al. 1991; Kurz and Greschniok 1994). Pneumonia followed by myocardial infarction and septicaemia are the most frequent causes of death in AD (Förstl and Hewer 1993).
Having sadly watched a few people die with Alzheimer's, I'd suggest that some such people just lose interest in all the things to do with healthy living, including eating at all. OK, they can be semi-force fed in an institution, but I suspect that sometimes they are just allowed to pass on. HiLo48 (talk) 01:59, 22 January 2011 (UTC)[reply]
Hazelnuts
Why do hazelnuts taste so much better than other kinds of nuts? Do they have some special chemical that other nuts don't have? If so, what is it? --75.15.161.185 (talk) 01:23, 22 January 2011 (UTC)[reply]
Apparently there are a number of relevant compounds, and the most important ones depend on heat to be produced (raw hazelnuts are far less flavorful than roasted ones). This paper gives some information, if you can make any use of it. Looie496 (talk) 02:00, 22 January 2011 (UTC)[reply]
All nuts contain somewhat different combinations of "chemicals", and all people have somewhat different tastes. I think brazils taste best.--Shantavira|feed me 07:31, 22 January 2011 (UTC)[reply]
No, sorry, it's pistachios that taste the best. Richard Avery (talk) 09:03, 22 January 2011 (UTC)[reply]
You are all mistaken. Pecans taste best, followed by walnuts and then almonds. — Preceding unsigned comment added by Roberto75780 (talk • contribs) 18:28, 22 January 2011 (UTC)[reply]
Cashews are best. Scary the way they have to get them for you, though. They get one tiny nut out of a whole false-fruit-true-fruit complex, the only part of which not filled with poison oak poison being the nut itself. Stopped complaining about the cost when I found that out. --Trovatore (talk) 21:17, 22 January 2011 (UTC)[reply]
After reviewing the article, I guess it's not quite that bad. One part, the "cashew apple", is apparently edible. Still, it sounds like nasty work for someone getting the nuts out. --Trovatore (talk) 21:46, 22 January 2011 (UTC)[reply]
gravity waves
i am A.mohammadzade and have some difficulties in understanding gravity waves . and based on
my studies i know there is some paradoxes in formulation of that .i reach some of this paradoxes
and will list them here . jan 22 2011 --78.38.28.3 (talk) 06:55, 22 January 2011 (UTC) —Preceding unsigned comment added by 78.38.28.3 (talk) 06:48, 22 January 2011 (UTC)[reply]
22 January 2011 (UTC)
my questions are about the diagravity and paragravity matters . if there is gravity wave
in universe then we ought to have diagravity paragravity matters and so reducing the speed
of such wave .and after laying three matters in straight line what will happen . and when
we got the central mass such as sun what will happen for waves ... {{ i do apologies these
are new words and i have aim of this words diagravity paragravity}}--78.38.28.3 (talk) 08:54,
22 January 2011 (UTC) a. mohammadzade iran 2011
Diagravity and paragravity seem to be terms used by those who study magnetic levitation, or even by those who think that gravity is a form of magnetic field.
I recall attending a lecture by one such "crank" many years ago. He had his arguments well-marshalled, and it was difficult to find chinks in his armour of conviction.
Mr Mohammadzade, please don't take this as a comment on the respectability of your studies (of which I know nothing, and would be unqualified to offer criticism), but may I ask: do you have any reason to believe that the phenomena of diagravity and paragravity ought to exist, or any evidence that they might exist? They are not part of the standard theories of gravity. Dbfirs 10:11, 22 January 2011 (UTC)[reply]
gravity did not form the universe
I wrote some were : 'it is not correct that we say any thing about all over the world when
we have many shortages in calculating and formulation of the data and observations '. what is my meaning ? I want to show that basic subjects of astrophysics shows that gravity is not only.....a. mohammad zade ( i will write the continue)--78.38.28.3 (talk) 08:07, 22 January 2011 (UTC)
--78.38.28.3 (talk) 08:04, 22 January 2011 (UTC)[reply]
How are we supposed to know what you mean? You wrote it... --Tango (talk) 13:52, 22 January 2011 (UTC)[reply]
Different brand of growth hormone
What is the difference between the different brands? Is there a reason why usually old people with a deficiency use a specific brand, bodybuilders or HIV victims (Serostim I believe) use another brand and short children use a different brand? I thought they were all the same product. —Preceding unsigned comment added by 76.169.33.234 (talk) 10:05, 22 January 2011 (UTC)[reply]
We have articles on growth hormone and growth hormone treatment. You did not specifically give us the names of the brands that you associate with various users, but I suspect that the answer to your question is that there are versions of the hormone that are approved by the FDA (in the USA at least) specifically for "medical" uses, while others may be manufactured and used outside of the established medical system (or simply approved for use in a different country and thus not generally available in all parts of the world). Another possibility is that manufacturers may use slightly different methods for producing the synthetic hormone and/or different delivery methods. --- Medical geneticist (talk) 14:40, 22 January 2011 (UTC)[reply]
How to identify used-up batteries with a multimeter?
I have eight identical AA 1.5v alkaline batteries. Four of them I've just removed from a radio after they have been used up. Unfortunately I've mixed these up with four other batteries, two or three of which have been used to varying extents.
How can I best identify the batteries which have the most energy left in them? I would like to identify the most energetic four batteries to put in my digital radio. Altghough I have a multimeter, I've never used it and I only have a superficial understanding of the dials and markings etc. Thanks 92.29.126.0 (talk) 11:38, 22 January 2011 (UTC)[reply]
what you want to do is set the multimeter to measure DC voltage, usually it is the V with straight lines, not wavy lines. Then just put the probes on the battery terminals. It doesn't really matter which way, they'll give you the same reading, just ignore whether it is +ive or -ive. Then just pick the ones with the highest numbers... From memory, a "full" battery will give a reading of about 1.8v a flat one will be about 1.3 or less. Vespine (talk) 13:07, 22 January 2011 (UTC)[reply]
It is hard to help you with out knowing what kind of multimeter it is. The best option is if the multimeter has some battery testing range that tests the battery under load. In other case you can measure the no load voltage, this should give you some indication but is not reliable when comparing batteries of different manufactures or different models, all batteries need to have roughly the same temperature. You need to find a setting for measuring voltage up to at least 2 V, connect the testing cables correctly to the multimeter for that setting and connect the testing cables to the ends of the battery with the correct polarity. The higher the voltage the better battery, you should get something like 1.4 V to 1.6 V. Small differences in voltage can indicate large differences in remaining energy, 1.55 V can be fully charged while 1.50 V can be almost empty, it depends on the exact type of battery. An more reliable indication could be the short circuit current but measuring that could degrade the battery.--Gr8xoz (talk) 13:07, 22 January 2011 (UTC)[reply]
Ideally one should use a load in the form of a resistor but if you have never used a MM before, this should be good enough. Check that Black probe is plugged into MM socket COM. Red probe into VωmA socket. Turn the center control to point to 20 in the V direct voltage section (usually left-hand side top). There should be a straight line to the right of the V symbol with dots underneath it. If it's a V with a wavy line next to it, it is the wrong sector. Touch the red probe on the battery + and black probe on other end. If it reads about 1.5 or more, then there is life in the battery. If it is 1.3 or below it is probably very nearly dead. I would throw below this, as your getting to the point where it will start leaking,--Aspro (talk) 13:19, 22 January 2011 (UTC)[reply]
Turn the centre control (from position in photo) two more places anti-clockwise to position 20. That means it will indicate up to 20 volts DC. Bottom right-hand socket (COM) for plugging in black probe. Red Probe plug in next socket up (VωmA). Then: Follow instructions as per my first reply. Touch the red probe on the battery + and black probe on other end. If it reads about 1.5 or more, then there is life in the battery. If it is 1.3 or below it is probably very nearly dead. I would throw below this, as your getting to the point where it will start leaking, Afterwards return control to straight up (OFF). Adopting this habit will extend the internal battery life. I guessed that 19 times out of twenty, if anyone has a MM and doesn't know how to use it, then the chances are, it will have the ubiquitous layout of inexpensive MM's, which are common through out the world – as was, in this case.--Aspro (talk) 14:52, 22 January 2011 (UTC)[reply]
Volume of sound at cold temperatures
When the outside temperature drops below -40 °C/°F the sound of the local Learjet 25 seems much louder. I live about 2.5 kilometres (1.6 mi) north of the Cambridge Bay Airport and at current temperatures it sounds as if the plane is flying right over the house and may even cause dishes to rattle slightly (I should have checked on the pressure at departure to see if that was affecting the rattle). This does not seem to happen when the temperature is higher but still below 0 °C (32 °F). I did do some searching on the Internet and came across this but wasn't sure if it was correct. The bit about the density I mean. I know the Speed of sound decreases as the temperature decreases. So is the sound louder or just higher pitched and seems louder at cold temperatures? CambridgeBayWeather (talk) 12:12, 22 January 2011 (UTC)[reply]
It is a very common phenomena caused by temperature inversion, which is also responsible for sometimes making things visible even thought they are over the horizon. See:Jets in the Living Room? Blame Inversions--Aspro (talk) 12:41, 22 January 2011 (UTC)[reply]
I would assume that it is things under the horizon that becomes visible, things over the horizon can normally be seen with out an inversion.--Gr8xoz (talk) 12:47, 22 January 2011 (UTC)[reply]
Very quick answer. Thanks. In case you were interested this is how the street in front of my house looks around this time of year. CambridgeBayWeather (talk) 13:23, 22 January 2011 (UTC)[reply]
'Tis never too late to move and follow the Sun south! :-)--Aspro (talk) 13:29, 22 January 2011 (UTC)[reply]
Using this Rule .. Can we conclude that Energy Have mass or weight ??
It's proved that Energy = mass multiply the speed of light square
does this mean that energy contain mass ? — Preceding unsigned comment added by Meshmesh micho (talk • contribs) 13:55, 22 January 2011 (UTC)[reply]
See Mass–energy equivalence, which answers this very clearly in the opening paragraphs: "The equation E = mc2 indicates that energy always exhibits mass in whatever form the energy takes". --Mr.98 (talk) 14:25, 22 January 2011 (UTC)[reply]
Sigh. We can argue endlessly about this. What the equation really says is that a particle of mass m has energy E = mc2 when it is at rest. The reverse statement can be made for composite systems where internal motions give the system an effective mass (when the system as a whole is at rest) but it is useless and misleading for particles without internal structure because it seems to imply that mass and energy are the same thing, which they are not. Mass is an intrinsic propery of a particle, energy describes the state of a particle. --Wrongfilter (talk) 15:06, 22 January 2011 (UTC)[reply]
My intent is not to argue endlessly about this (or anything) — just to point the OP in the direction of the article which they should really read first before coming back here for further discussion (endless or otherwise). This question is pretty directly discussed in the article. --Mr.98 (talk) 15:43, 22 January 2011 (UTC)[reply]
(EC) But rest energy is that same property? So mass is the same as energy surely? Just that it can have different origins. The statment is surely most explicit in natural units, where c=1 with no dimensions. So the relation becomes E=m. —Preceding unsigned comment added by 129.67.37.227 (talk) 17:21, 22 January 2011 (UTC)[reply]
As has been pointed out on this desk numerous times this week, the use of the term "mass" to refer to rest-mass, or effective gravitational mass, varies between physicists. If you want to debate whether "mass" and "energy" are the same, you're waging a language-battle better suited to the language desk. A more useful question is, "does an increase in energy affect the gravitational force?" The answer is an easy "yes." Let's not devolve into semantic quibbling. We should steer interested people to investigate the physical realities and phenomena, without fighting about the various different names that other scientists use for the exact same phenomena. Nimur (talk) 19:37, 22 January 2011 (UTC)[reply]
Nonsense. That equation really means that (relativistic) mass and energy are the same thing. It also means that (rest) mass and rest energy are the same thing. rest mass is an intrinsic property of the particle while the (relativistic) mass describes the state of the particle. You could ask "Isn't that redundant?". Yes it is redundant. That's why, by convention, the word mass is used to describe rest mass (and/or rest energy) while the word energy is used to describe relativistic mass (and/or energy). Dauto (talk) 17:18, 22 January 2011 (UTC)[reply]
Precisely, thus photons feel gravity. —Preceding unsigned comment added by 129.67.37.227 (talk) 17:23, 22 January 2011 (UTC)[reply]
No, photons take the path they do near massive objects because photons travel in straight lines, and spacetime in the vicinity of a massive object is curved. Viewing photons as "feeling" (i.e., being acted upon by) a gravitational "force" is a Newtonian picture of gravity, which works quite poorly when dealing with light. If you try to use E=mc2 and Newtonian gravity to calculate how much deflection of light there should be as it passes near a massive object, you wind up with an answer that's only half of the actual deflection. See Tests of general relativity#Deflection of light by the Sun. Red Act (talk) 21:11, 22 January 2011 (UTC)[reply]
This formula prove that energy and mass is equal. Essentially all mass is a form of energy. Plus, all "mass" have a potientially energy if it is fully converted to energy. A food for thought. --Tyw7 (☎ Contact me! • Contributions) Changing the world one edit at a time! 18:00, 22 January 2011 (UTC)[reply]
Not only can energy have mass, most of the mass you deal with day-to-day is energy. The mass of protons and neutrons are much greater (by about eighty times) than the summed masses of the constituent quarks. It's the energy associated with bringing the quarks together that accounts for the rest. Most of the mass of protons and neutrons (and by extension of most things) is due to energy, rather than (rest) mass of fundamental particles. -- 174.21.229.4 (talk) 18:50, 22 January 2011 (UTC)[reply]
I am trying to re-find the name of the man who effectively discovered the link between food consumption and its use to provide the human body with the energy we need to exist as human beings. This man may have operated in the Middle Ages because I remember seeing a photograph of an oil painting of him sitting on a primitive weighing machine in a darkened, candle-lit, almost windowless room, wearing long robes. But as this might have been seen as heretical in this era, perhaps he was active in the early days of The Enlightenment.
Basically what this man did was to weigh himself at frequent intervals, to weigh everything he ate and drank and, in the interests of science (!), he weighed everything he excreted. Not sure how he factored in sweating though.
After many observations he consistently found that the sum of his beginning weight plus the weight of food consumed over a period, less the weight of all excretions during that period, did not equal his actual weight at the end of the period. His weight was always less than this figure. And the difference, of course, was the fact that the body had been consuming some of this food to provide all the energy our bodies need to function.
I would be curious to learn more about this man, but searches across the web and within Wikipedia reveal nothing. And yet the photo I saw, along with the above brief description of his work, was in a book about the greatest discoveries in medical history, alongside such luminaries as Jenner on inoculation, Simpson on anaesthesia and Fleming on penicillin.
Can anyone throw light on this? —Preceding unsigned comment added by 86.139.150.81 (talk) 15:05, 22 January 2011 (UTC)[reply]
If that's not it, it is likely Jan Baptist van Helmont, see Jan_Baptist_van_Helmont#Observations_about_digestion. He also made similar studies about trees (though arrived at the wrong conclusion). He's a very important early scientist; though his predecessor Roger Bacon and his followers Robert Boyle and Antoine Lavoisier get a lot better pub, van Helmont was a prescient scientist in his dilligence and adherance to the scientific method. --Jayron32 16:52, 22 January 2011 (UTC)[reply]
That sounds a lot like Van Helmont's work, yes, although I don't know of him doing quantitative work on human digestion. Physchim62(talk) 17:36, 22 January 2011 (UTC)[reply]
I remember seeing the painting or reading about this. The robes could have been from long ago or from the Middle East. He might have been the same possibly Turkish person who, during a plague, thought that dipping things under water would be a protection. 92.24.182.196 (talk) 20:30, 22 January 2011 (UTC)[reply]
Head-splitting volume of fire and other alarms
I can almost understand why alarms are loud in public places or large building, and why they continue their mind-numbing racket for long after surely even the dead have been advised, but why do the ones manufactured for homes also do this? The noise is so great that it is painful and it so fills my head that I cannot think while it is screaming. In a house with two people, within 2 feet of one another, this seems not just overkill (so to speak) but actively unhelpful as it blocks any ability for a reasoned response. Is there such a thing as a remote silencer that allows you to shut off the racket while you work out the safest path out of the house? (We have done the route mapping in advance, but there are many possibilities depending on where a fire starts and which access points are blocked to a wheelchair.) I don't mind the volume at first, to ensure we are awake and paying attention, but why is it necessary after that? (Our insuror says that any tampering with the alarm itself may lead to the cancellation of our insurance.) Bielle (talk) 16:49, 22 January 2011 (UTC)[reply]
That is indeed true, if you tamper with your firealarm, CO detector, etc, the insurance can be canceled. They are loud for one purpose: To make sure you know the danger, and so you can get out of the house/building. I don't know of any remotes that will silence them, Sorry. Tofutwitch11(TALK) 16:51, 22 January 2011 (UTC)[reply]
They are loud as they may have to be heard through closed multiple intervening doors by people who may be heavy sleepers, intoxicated, drugged or a combination of all three. The are designed to galvanise the person out of sleep with a "fight or flight" response so they can instantly start escaping. Exxolon (talk) 17:21, 22 January 2011 (UTC)[reply]
Yes. The annoyance factor comes from the fact that the alarms almost certainly only get activated once with good reason (when your house is about to burn down) and any number of seemingly malicious false alarms that seem to prefer going off at 3 in the morning (my CO detector did that three or four times in a month and never before or since). While it's undeniably a pain the... ears, the volume overkill is almost certainly responsible for saving my house and all my possessions and perhaps even saving the lives of my family. We heard the shriek through the walls of our freehold condo and were able to react to a fire in our neighbour's kitchen. That, of course, is only small consolation when your eardrums gets pushed so far into your skull that they nearly meet in the middle, but there you go... Matt Deres (talk) 17:37, 22 January 2011 (UTC)[reply]
Actually, my alarms have been activated many times, never for a good reason (usually because my toaster was acting up). I think that's part of the difficulty — you're going to have far more false positives than you will emergency situations, and by definition the alarm can't distinguish between the two. --Mr.98 (talk) 22:47, 22 January 2011 (UTC)[reply]
The way I would put it is that you would set your telephone or your doorbell to a volume at which you're pretty certain to hear it but at which you can ignore it if you feel like it. You set your alarm to a volume at which you can't ignore it even if you want to! Physchim62(talk) 17:47, 22 January 2011 (UTC)[reply]
In-laws should come with similar settings, and be set to the lower one... Physchim62(talk) 17:49, 22 January 2011 (UTC)[reply]
In theory it should be possible to opt for more expensive insurance and quieter alarms, with a slightly greater risk of death and less annoyance. Consumer choice, and all that. In practice, I don't suppose such products are on the market. Googling "quieter fire alarm" didn't turn up anything promising. Probably it's illegal to choose not to be annoyed. 213.122.5.253 (talk) 17:53, 22 January 2011 (UTC)[reply]
This looks like what you want - if you're not in canada, then it isn't much use, but it might lead you to others wherever you do live - I was searching for "fire alarm silencer remote". I can assure you from my OR that the volume is indeed a good thing as Exxolon has pointed out - it can take a while to wake you if you are suitably (or unsuitably) inebriated but they do work eventually! SmartSE (talk) 19:25, 22 January 2011 (UTC)[reply]
Some fire alarms have a hush button on them, I think it's more common on the mains powered ones. Mine peeps after it is hushed until the smoke goes away. If it gets a lot thicker, then it starts again - I've never tried to hush it a second time. CS Miller (talk) 20:24, 22 January 2011 (UTC)[reply]
Even at such a volume, smoke alarms have been found less than adequate at waking children leading to special products like: "square wave" [21] and the screaming parent's voice model[22]Rmhermen (talk) 21:41, 22 January 2011 (UTC)[reply]
I will just add that one of the flaws that the review committee on the Three Mile Island accident found was that the alarms were too loud, too shrill, and could not be turned off in the middle of the disaster, which made it more difficult to actually deal with the accident as it was having. My point is just that the engineering logic that goes into making an alarm is not necessarily the same logic that actually tells you about how the alarm will work in the real world. --Mr.98 (talk) 22:47, 22 January 2011 (UTC)[reply]
Weight
In the book it shows that weight can be calculated by the formula w=m1m2/d^2. How in the world do you drive this formula? As long as I know, the formula to find out the weight is the same as the force of the grivational attraction between two objects (formula Gm1m2/d^2). How can you calculate the weight (first formula) without the gravitational constant G? --Tyw7 (☎ Contact me! • Contributions) Changing the world one edit at a time! 17:58, 22 January 2011 (UTC)[reply]
you do need to know the gravitational constant to calculate the weight. You can obtain the gravitational constant from cavendish experiment83.134.145.153 (talk) 18:00, 22 January 2011 (UTC)[reply]
How did the text book derive the first equation? --Tyw7 (☎ Contact me! • Contributions) Changing the world one edit at a time! 18:05, 22 January 2011 (UTC)[reply]
That's clearly a typo. Dauto (talk) 18:29, 22 January 2011 (UTC)[reply]
It somewhat depends on the context. The first formula is valid if everything is in a natural units system where the gravitational constant has been set to one. Technically speaking, the first equation is valid for all unit systems, it's just that you need the factor G to convert the somewhat useless (mass)^2/(distance)^2 units to more conventional (force) units. -- 174.21.229.4 (talk) 18:37, 22 January 2011 (UTC)[reply]
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