:::It's true that [[proper acceleration]] is absolute. For example, if there are two rockets in deep space that are approaching each other at an accelerating rate due to one of the rockets having its thrusters on, it's possible to perform a local experiment (an experiment involving only short distances and times) to determine whether you're on the rocket with its thrusters on, or on the rocket that's coasting. Indeed, the experiment is trivial; you don't really even need an [[accelerometer]]: If you're pressed up against a surface of the room you're in, then you're in the accelerating rocket, but if you're floating around in your room, then you're in the coasting rocket.
:::It's true that [[proper acceleration]] is absolute. For example, if there are two rockets in deep space that are approaching each other at an accelerating rate due to one of the rockets having its thrusters on, it's possible to perform a local experiment (an experiment involving only short distances and times) to determine whether you're on the rocket with its thrusters on, or on the rocket that's coasting. Indeed, the experiment is trivial; you don't really even need an [[accelerometer]]: If you're pressed up against a surface of the room you're in, then you're in the accelerating rocket, but if you're floating around in your room, then you're in the coasting rocket.
:::However, gravity does not involve a proper acceleration, because gravity in reality is a [[fictitious force#Gravity as a fictitious force|fictitious force]]. Regardless of whether you're in a room attached to the apple, or in a room at the center of the Earth, you're just going to float around in the room, because you aren't undergoing any proper acceleration either way. (If you're in a room attached to the surface of the Earth, then you will be pressed against the floor, but that's because you're undergoing a proper acceleration ''upward'' due to the non-fictitious [[intermolecular force]]s the floor is imparting to the bottoms of your feet, that prevent your [[comoving frame]] from being an [[inertial frame of reference]].) [[User:Red Act|Red Act]] ([[User talk:Red Act|talk]]) 22:11, 24 March 2011 (UTC)
:::However, gravity does not involve a proper acceleration, because gravity in reality is a [[fictitious force#Gravity as a fictitious force|fictitious force]]. Regardless of whether you're in a room attached to the apple, or in a room at the center of the Earth, you're just going to float around in the room, because you aren't undergoing any proper acceleration either way. (If you're in a room attached to the surface of the Earth, then you will be pressed against the floor, but that's because you're undergoing a proper acceleration ''upward'' due to the non-fictitious [[intermolecular force]]s the floor is imparting to the bottoms of your feet, that prevent your [[comoving frame]] from being an [[inertial frame of reference]].) [[User:Red Act|Red Act]] ([[User talk:Red Act|talk]]) 22:11, 24 March 2011 (UTC)
What will be their weight force (w=mg=mg) on each other for settlement analysis? OR they will be weightless [[Special:Contributions/96.52.178.55|96.52.178.55]] ([[User talk:96.52.178.55|talk]]) 05:35, 25 March 2011 (UTC)Eccentric Khattak#1-420
==Sex in Space==
==Sex in Space==
Revision as of 05:35, 25 March 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.
It's popular in Japan; what's wrong with it being sold in US stores? Why do we still have to deal with it the old way when a newer form of hygiene already exists? --70.179.169.115 (talk) 04:07, 21 March 2011 (UTC)[reply]
As soon as I read the article I said "I want one." Maybe you should try importing some and try to sell them. You would soon find either the answer to your question or you would make a profit.--Shantavira|feed me09:04, 21 March 2011 (UTC)[reply]
The cost of importing a washlet is high, reportedly $660 or so[2] bought online. It requires behind the toilet an electric outlet that is properly installed for use near water, with a ground fault interruptor. A Google search for "Washlet" finds many suppliers. Low enthusiasm for washlets in USA is comparable to the low acceptance of a similar bathroom accessory, the bidet. Cuddlyable3 (talk) 09:28, 21 March 2011 (UTC)[reply]
Are showers as common in Japan as in the U.S.? It is not unheard of for someone in the U.S. to duck into the shower after an especially... sticky... experience. Wnt (talk) 09:33, 21 March 2011 (UTC)[reply]
When someone was promoting bidets in Australia some years ago it was discovered that plumbing rules demanded an independent warm water supply because of the possibility of gravity allowing unwanted solids to enter the water supply.[citation needed] Cost then became a big issue. HiLo48 (talk) 11:12, 21 March 2011 (UTC)[reply]
Radiation dose inside a working nuclear reactor?
If you can get inside a working nuclear reactor without disrupting the reaction and stay there for a minute, what dose of radiation would you get? F (talk) 09:48, 21 March 2011 (UTC)[reply]
Based on this chart which breaks down lots of various radiation dosages, standing next to the Chernobyl reactor for one minute during the meltdown would give you about a 5 Sv dose. I'd say that's a good ballpark number for normally-operating reactors, too. That's on the very upper edge of "if you're lucky, you don't die straightaway of radiation poisoning." — Lomn12:38, 21 March 2011 (UTC)[reply]
Even with the author's caveat, I'm not sure that xkcd cartoon is a "reliable source," let alone encyclopedic. Here's Radiation in Perspective from the Department of Energy's Radiation Protection Policy. Each reactor type is different; usually, if you were working with a reactor, you'd have to take a DOE or an OSHA training course. Radiation levels inside the reactor would probably be fatal, maybe or maybe not instantaneously; but if you were actually inside the reactor, you'd have other problems besides radiation to worry about! The temperature isn't comfortable for human life in there, either - and there's not much breathable air - in fact, the nuclear reactor core is not a suitable place for you to go inside, even for a minute. You might equally well ask about environmental safety hazards if you were inside the combustion chamber in an automobile's engine cylinder. Nimur (talk) 14:24, 21 March 2011 (UTC)[reply]
Even inside a tiny research reactor, the radiation would be quickly toxic if you were inside the unshielded core while it was undergoing criticality. The amount of neutrons alone in an operating reactor, much less gammas and other nasty things, is just fantastic. That's the whole point of a reactor. --Mr.98 (talk) 16:23, 21 March 2011 (UTC)[reply]
An alternative interpretation of the question would be if you were inside the containment building of a reactor while it was operating. Early on in the Three Mile Island accident, a spokesman for Metropolitan Edison asserted that he could "walk around inside the containment building, right now, without harm from radiation," implying that the radiation level in the building (and outside the reactor) would not be impossibly high. (He was later shown to be quite wrong: he would have gotten a lethal dose in less than an hour). When a reactor is being refueled, humans work in the containment building and around the reactor, since the valves, switches and pipes do not fix themselves, and a reactor is a very high maintenance device, with constant testing repairs, replacements, and retrofits. While the reactor is operating, I doubt that it is considered safe to wander around in the containment building. Edison (talk) 18:35, 21 March 2011 (UTC)[reply]
Containment building says that you can be in the containment building while it is on full power, but implies you are getting a non-negligible amount of radiation (you can only stay in there a limited amount of time before getting your safe dose). That is about what I would guess. A reactor, even one on full power, is still relatively shielded by the water and the reactor vessel. --Mr.98 (talk) 00:26, 22 March 2011 (UTC)[reply]
Are memories believed to be stored with the same set of neurons throughout the years? Is an individual neuron believed to be able to be a part of multiple completely different memories? 20.137.18.50 (talk) 13:10, 21 March 2011 (UTC)[reply]
It's basically impossible for us to know the real answer right now, but some have hypothesized the existence of specific neurons that store a representation of a complex concept or object (presumably by linking up a whole network of neurons that "remember" different aspects of that concept or object). The classic example is the grandmother neuron which is hypothesized to fire whenever you think of your grandmother, or whenever a stimulus (such as a scent, or the memory of a particular location) evokes a memory of your grandmother. --- Medical geneticist (talk) 15:19, 21 March 2011 (UTC)[reply]
Most neuroscientists believe that memories are stored, not in neurons per se, but rather by altering the strength of the synapses that connect neurons to each other. An individual neuron in the cerebral cortex makes on the order of 10,000 synaptic connections to other neurons, so this gives quite a large potential storage capacity. With synaptic storage, each individual neuron can participate potentially in thousands of memories, or conceivably even millions. Whether a memory is stored in the same set of synapses across the years is a controversial issue -- some neuroscientists think that memories need to be "refreshed" periodically and that this may involve bringing new synapses into play. Our article on synaptic plasticity contains some relevant information, although most of it is pretty technical. Looie496 (talk) 17:50, 21 March 2011 (UTC)[reply]
Expiry date of bottled water
Looking at some bottled water today, I was surprised to notice an expiry date printed on the bottle. Does pure water become unfit for drinking after long periods, assuming the seal of the bottle is not broken? The label on the bottle read 'purified tap water'. 60.48.212.9 (talk) 17:34, 21 March 2011 (UTC)[reply]
A follow-up question: what are those expiration dates based on? Do the manufacturers or maybe the professional organizations have studies that show the leaching rates or demonstrate safety after known periods? Are they just arbitrary? SDY (talk) 17:55, 21 March 2011 (UTC)[reply]
They may have reason to believe that it's of "Acceptable" quality up to that point, but don't study it much beyond that. Still, how long something lasts is so dependent on the conditions under which it is stored that a "look, smell, and taste" test is far better than a date stamped on the package. If your water bottle spent time on the dashboard of your car in the bright summer sun, then it would deteriorate far quicker than in a fridge, probably quicker than the date. There also could sometimes be a sleazy angle to them printing short expiration dates, if they want consumers to toss out their product, while it's still good, and buy more. StuRat (talk) 18:38, 21 March 2011 (UTC)[reply]
As far as I know, in some markets (*cough*EU*cough*) there is a requirement that all material for human consumption has an expiry date. And there also is a requirement that prescribes maximum and minimum expiry times, independent of the product (probably in a directive invented by a different, but similar committee). Put the two together, and... --Stephan Schulz (talk) 19:04, 21 March 2011 (UTC)[reply]
Do you have a citation for that? I ask because we don't have "expiry dates" in the EU, some products have "use by" dates and some have "best before" dates, as noted by Ny156uk above. DuncanHill (talk) 22:55, 21 March 2011 (UTC)[reply]
Here in the UK, I've never seen an "expiry date" on foodstuff, and, of course, fresh unpackaged food has neither a "best before" nor a "use by" date because its condition is usually fairly obvious. In some cases, the "use by" date on packaged goods is mainly for the convenience of the seller to ensure efficient stock rotation. Dbfirs07:52, 22 March 2011 (UTC)[reply]
Annoying. Annoying. Annoying.
Most or all people eventually become annoyed by a sound or short phrase that is repeated ad nauseum. Can anyone point me to any studies or articles about this phenomenon? The closest thing I could find on Wikipedia that was at all related was our semantic satiation stubby article, which isn't really about the same thing. Comet Tuttle (talk) 18:30, 21 March 2011 (UTC)[reply]
There's the phonological loop, which is implicated in earworms. We have a dedicated bit of short-term memory for storing things we've heard recently, and if this were to be repeatedly filled with the same information ... well, I can't see the harm in that at all, actually. Not sure how to make this answer your question, but I feel it must be possible with effort and OR. 81.131.46.134 (talk) 01:59, 22 March 2011 (UTC)[reply]
Temple Grandin says in Animals in Translation (on 49-50) that intermittent noise triggers the "orienting response" in mammals. I'm not sure if that's the same thing you're talking about, but it's something. --Mr.98 (talk) 00:46, 23 March 2011 (UTC)[reply]
vacuum electricity
Nikola Tesla observed that electrons transmitted through a near perfect vacuum in his vacuum tubes appeared as corona several feet through the air surrounding the tube. If there is nothing in the tube between the electrode and the glass, then how do the electrons convey through the vacuum and into the surrounding air.
could this be explained by http://en.wikipedia.org/wiki/Electric_current#Vacuum— Preceding unsigned comment added by Lufc88 (talk • contribs) 19:12, 21 March 2011 (UTC)[reply]
I think that's somewhat of a red herring. The vacuum is an insulator unless electrons are moving through it, yes - but that doesn't answer the issue of why the electrons move through it.
In a vague sense, my impression is that the metal anode fills with extra electrons, typically positioned at the boundary of the conductor, which fill up the conduction band to a level high enough that they can escape it. Once free, the electrons will be pushed away from the electrode and can move in response to any small electric field in the area. But someone with a better understanding of articles like Electronic band structure, Nearly-free electron model, Empty Lattice Approximation, and so on needs to give a better answer. Wnt (talk) 20:59, 21 March 2011 (UTC)[reply]
Abnormal darkness
There are some sources claiming that there were relatively short periods of abnormally intense, unexplained darkness, sometimes even spread over the cities (specifically over Wimbledon, London on April 2, 1904 and over Louisville on March 7, 1911). Is there any explanation for that or it's indeed abnormal?--89.76.224.253 (talk) 21:46, 21 March 2011 (UTC)[reply]
Just watching Dr Jim Al-Khalili's latest BBC programme, in which he explains about the microwave background radiation being the remnant of the Big Bang. I've known about this for some time, but the following question has just popped into my head. Is it possible to calculate at what point this radiation was in visible light, and what would the sky have looked like at that point? Or is it possible to say when the sound waves from the Big Bang would have stopped being audible to human ears? (OK I know humans weren't around then. Humour me, it's a thought experiment!) --TammyMoet (talk) 21:58, 21 March 2011 (UTC)[reply]
The microwave background has a black body spectrum with a temperature of around 2.7 Kelvin. Blackbody radiation is visible to human beings at temperatures from 1000 K to 10000 K, more or less, with the colors shown here (although human beings couldn't exist at those temperatures, so this is all somewhat unrealistic). The ratio between the temperature now and the temperature at an earlier time is given by the redshift factor z. So the radiation would be visible for redshifts from z=1000/2.7 to z=10000/2.7, or z=400 to z=4000, more or less. Ned Wright's Cosmology Calculator will give you the age of the universe for any value of z (enter the value in the box labeled "z", then click "flat"). This gives an age range of 40,000 to 2,000,000 years after the big bang, more or less. But prior to 400,000 years after the big bang the universe was filled with an opaque plasma and there wasn't really a photon background, so it's probably better to say that the photon background was visible from its time of origin (400,000 years after the big bang) until 2,000,000 years after the big bang. It was initially yellow-orange (3000K) and then red (1000K) before fading into the infrared. As for what the sky would look like, take the present-day night sky, remove the stars (since there were no stars), and replace the uniform black with uniform yellow-orange or red. -- BenRG (talk) 02:20, 22 March 2011 (UTC)[reply]
Are you sure there is an upper limit to visible temperatures? While the peak will be out of the visible spectrum, there will still be plenty of visible light emitted too. --Tango (talk) 19:39, 22 March 2011 (UTC)[reply]
Yes, you're right. Oops. (Although at some point it will be bright enough to instantly blind you, making it effectively invisible...) -- BenRG (talk) 08:00, 23 March 2011 (UTC)[reply]
Isn't space a gas?
I was going to smugly reply to the previous question (about the big bang) with "sound waves can't propagate through the vacuum of space, duh". Space isn't a perfect vacuum, though, and it contains a certain amount of hydrogen, so is space actually a very sparse gas, through which sound could travel? 213.122.13.4 (talk) 22:27, 21 March 2011 (UTC)[reply]
The interstellar medium does propagate pressure waves - in essence "sound" - provided the wavelength is large enough. The typical example is the pressure waves associated with the galactic spiral arms, which have a length scale measured in thousands of light years. Of course, this is a "sound" that is so low frequency that no organic ear could ever hear it. Typically to avoid dispersion, one wants the wavelength of the pressure wave to be much larger than the distance that individual particles will travel between collisions. In the interstellar medium, with about ~10 atom / cm^3, one would expect a wave to propagate successfully (rather than dissipate) if the wavelength is greater than ~20 AU. The intergalactic medium (with only 1 atom / m^3) would require the pressure front to be thousands of times larger than that, but it is possible if you had an astrophysical process capable of generating a large enough perturbation. Dragons flight (talk) 00:01, 22 March 2011 (UTC)[reply]
Conserving as much energy as possible by doing as little work as needed to survive is beneficial in situations where food is in short supply 82.43.90.38 (talk) 22:58, 21 March 2011 (UTC)[reply]
Not all work is equal. Humans love certain types of tasks — and you'll find that the jobs people love the most are the ones that satisfy them. For example (per Temple Grandin), we are hard-wired (like most mammals) to love seeking things out. We love the search, love the hunt, love the pursuit, love the flirtation, love the chase. We love the act of finding things more than we like the things found. I think most of us have experienced this in one way or another. That's a definitely genetic predisposition (though not unique to humans at all, which makes sense), but whether we enjoy "working" generally probably is not one. We like certain types of jobs. --Mr.98 (talk) 00:22, 22 March 2011 (UTC)[reply]
I like that theory, but I dispute it. People enjoy creativity (I haven't checked, but I expect the article backs me up on that). Hunting for things is a creative act, provided it's challenging for the hunter. Being a litter-picker involves hunting for litter, but is not a creative act, since old cans and gum and so on don't make much effort to escape. Being a hunter of something which you have mastered the task of hunting for is probably dull. Being an artist is a creative and probably fun job, but only in the most tenuous sense involves searching for anything. 213.122.13.4 (talk) 01:07, 22 March 2011 (UTC)[reply]
Well, that's not what Grandin has found, with humans or with animals. Just saying. "Creativity" is not the kind of category she uses — it doesn't correspond with some sort of basic neural circuit, whereas "seeking" does. --Mr.98 (talk) 12:56, 22 March 2011 (UTC)[reply]
Being an artist is a creative and probably fun job. Being an artist is, for most professional artists, very stressful! Just saying. Pfly (talk) 18:22, 22 March 2011 (UTC)[reply]
For a lot of people, even the most enjoyable activity can be made unpleasant by rigid bureaucratic demands and crappy bosses HiLo48 (talk) 01:12, 22 March 2011 (UTC)[reply]
I think happiness is relative to one's acceptance of the situation, and is related to homeostasis - that is, unhappiness is caused by a notion of things being wrong, and is always in some sense a form of indignation and of aspiration. So people in modern times might be unhappy about work that ancient people would accept as normal, because these days we're dimly aware that there must be a better way. In addition to this, I see you make the assumption that a human unhappy with necessary hard work is a human who refuses to do the essential work, and starves: does that really follow? Evolution has no particular interest in our having a nice time, so long as we breed. 213.122.13.4 (talk) 01:13, 22 March 2011 (UTC)[reply]
There's also the factor of conflicting priorities. People have different ideas about how to do things and different things that make them happy. If you work for a person or a department or a company whose goals and priorities conflict with yours, there's a good chance you won't be very happy. ←Baseball BugsWhat's up, Doc?carrots→ 01:24, 22 March 2011 (UTC)[reply]
Evolution is very slow. We mainly enjoy hunting and gathering, and perhaps farming and herding, because that's what we did for most of human history. The industrial revolution and information economy haven't been around long, and few people have died because they disliked such work, so there is very little evolutionary pressure for us to grow to like it. StuRat (talk) 02:25, 22 March 2011 (UTC)[reply]
I would just add my 2 cents in that I think what most people do for a "job" is not actually what evolutionally would be called work. Sitting at an office at a computer, or fixing some one's plumbing are "detached" from an actual sense of survival. Sure the money you earn gives you those things, but you are earning MONEY not the things you need to survive. Just a personal anecdote which might help illustrate what I mean, whenever I do some gardening at home, admittedly it's not something I particularly "like" doing, I don't "look forward to it", but when I physically OWN and enjoy the efforts of my labour I feel a far greater sense of achievement and pleasure then if I did it for someone else to earn some money, even if I then could use that money to hire someone else to fix my garden. Vespine (talk) 02:48, 22 March 2011 (UTC)[reply]
Joy is not the only motivator. Hunger is a motivator to hunt or gather food. Being cold is a motivator to build a fire or make clothes. Affection for others is a motivator to care for them. Joy is a major motivator in reproduction but most people wouldn't call that work. Also, most humans above a certain age are relatively good at predicting what will serve them in the future, and plan and act accordingly. Human intelligence enables us to make such predictions and actions in situations our basic instincts don't cover. PrimeHunter (talk) 04:38, 22 March 2011 (UTC)[reply]
I think that there should be some adaptation to favor productive labor in general; the problem is that society's notion of labor isn't the same as that. It's not just that people enjoy hunting and fishing - they enjoy gardening, fixing the house, editing a Wikipedia article. What they don't enjoy is when they are coerced by a badly designed economic system to spend their time harming other people or doing something useless - such as telemarketing, for example, which is particularly famous for burning out its workers quickly. They don't enjoy being stood over and threatened. I think it's all too clear that modern American society offers a whole lot of "work" that society would be better off without, and that people are coerced into it solely to prove the dominance of certain high-caste individuals and groups over themselves and others. Spending one's days in abject subjection, strictly as a rite of worship toward the "rich" (i.e. those who claim to themselves control of the Earth's resources or of means of using them) - that is not something people have evolved to accept. In fact, they are adapted to challenge it by violence. Wnt (talk) 04:53, 22 March 2011 (UTC)[reply]
Various things give us some kind of biological high - certainly sex and eating. This is the way that evolution makes a thing enjoyable; it makes us get a buzz out of it. (Perhaps some activities also soothe us.) It can't cause us to enjoy an activity in an intellectual way, it can't make us express sophisticated approval of it. It also has to be an activity which is easily identified on a biological level - it can't take cognition to identify that the thing is happening, or else our genes (which don't describe our plastic brains) have no handle on it. (I mean "dynamically formed" and not "made of plastic".) So, taking weaving as an example:
It would probably be inconvenient if we got high specifically off weaving, and wove things constantly.
I doubt any mechanism could evolve to reliably detect whether we were weaving, anyway, since it's not an instinct.
Detecting productive labour in general is the same problem, multiplied many times (because of all the kinds of work).
And it's rarely a simple matter. After a mature aged career change I am now a high school teacher in a government school. The job is incredibly rewarding, when one realises the advances students have made, often in a lot more ways than just knowing more of their subject matter. But there can also be massive frustrations in the job, in the form of under-resourced schools, incompetent administration, and bureaucratic demands. It's a shame that we can't seem to get one without the other. (And a quick qualifier - the incompetent administration comment is not referring to my current school ;-) ) HiLo48 (talk) 10:40, 22 March 2011 (UTC)[reply]
Not to worry, the incompetent administration probably doesn't know how to use the Internet and never even heard of Wikipedia. StuRat (talk) 14:09, 22 March 2011 (UTC)[reply]
A common complaint about work is that it 'stresses me out'. So a 'love to work' gene may be tantamount to a 'work myself to death gene'. Hardly favorable for genetic propagation. Vranak (talk) 17:06, 22 March 2011 (UTC)[reply]
Well, it's like driving a car. If you drive it wildly, lots of hard acceleration and braking and turning, running over potholes, it's gonna wear down and need a vacation (go to the shop). Same thing with working -- if you are a calm and rational and sensible human being you can accomplish your work without a great deal of stress, one would imagine. However, there are issues like indoor air pollution, so no matter how calm you are at the office, you may be inhaling vast quantities of pollution. See Sick Building Syndrome. Vranak (talk) 17:36, 22 March 2011 (UTC)[reply]
(ec) We have the page Workplace stress. Lots of info and ideas there. The Happiness page might play into the question too. Many people are unhappy, stressed, anxious, etc, whether or not they're at work. Happiness is something we still don't fully understand—at least how and why it happens, and how to stay happy. I'd even suggest most people spend most of their time trying to find happiness, and then trying to stay happy. Seems like almost no one succeeds; the struggle is usually lifelong, no? I've met a few very dedicated (very very dedicated) Buddhists who seem to have a near-constant state of happiness or joy, even when doing work they don't "enjoy". Their happiness seems different from my ordinary understanding of the word (one such "dedicated" and happy person that comes to mind is Bonnie Myotai Treace).
Temple Grandin was mentioned above. I found her book Animals in Translation an excellent description of basic emotions in people as well as animals, how and why they work the way they do, and why emotions can often feel unpleasant or stressful; and, sometimes, all-too-fleetingly, pleasant. An interesting bit I always recall is her notion that while people will generally choose "powerful fear" over "powerful pain", animals (at least "higher" animals like dogs, horses, cows, etc) tend to be more traumatized by powerful fear than powerful pain. Pfly (talk) 18:18, 22 March 2011 (UTC)[reply]
March 22
Earth's tilt and space radiaton.
Greetings!
I have a rather complicated question concerning the tilt of the Earth, the way the atmosphere protects us from radiation, and the effects—for a limited time—of exposure to said radiation.
Right now, our planet's orbit is tilted 23-1/2 degrees to the ecliptic. (This is why the Sun rises 23-1/2 degrees north and south of due east on the solstices.) In the (northern) summer solstice, the Earth approaches perihelion—the closest it will get to the Sun—and approaches aphelion—the farthest away it will get—at the (northern) winter solstice.
In spite of this, however, the southern hemisphere gets just as hot a summer (and just as cold a winter) as the northern hemisphere. This suggests to me that it is not distance per se, but a property of the atmosphere that gives us our tellurian seasons. I'm not an expert at all in the sciences, but I do know that the atmosphere absorbs virtually all Gamma Rays, X-Rays, Ultraviolet Rays, and most Infrared Waves from space. (Only Visible Light, Radio Waves, and some Infrared Waves make it all the way down to the surface). And I also know that around the polar regions, there are "holes"—for lack of a more proper term—where space radiation penetrates far more freely.
Now, suppose that the Earth were tilted on its axis as, or more severely than, Uranus. For simplicity's sake, let's say at an even 90 degrees to the ecliptic. (Also, for all intents and purposes, let's say that all other factors remained unchanged: orbital speed, distance from the Sun, etc.) How would that change the way that space radiation affects us?
Over the course of one Earth day (23 hours and 56 minutes) the Sun would pass through both poles on each of the solstices.
Here are my questions:
As the Sun's radiation penetrated to the surface of the Earth through the "ozone hole" and other "holes" that exist at high lattitudes, what would change about life on Earth?
—Would we see an abundance of natural disasters? (floods, volcanic erruptions, cyclones, earthquakes, etc.)
—Would anatomy and physiology of Earthly lifeforms change? (We know for a fact, the photosynthesis in plants depends on the Sun, and even we humans synthesize Vitamin D from it.)
—Would geology change in any way; to wit, would rocks become lighter or more porous, or some way different. Would the magnetic field change direction or become stronger (or less strong)?
—Would the seasons change in length or demeanor, since the atmosphere would factor differently?
And finally:
—Can such a state be replicated today, under laboratory conditions, in a small, self-contained experiment?
So, assuming that you mean the North Pole would point directly at the Sun during one season, and the South Pole would point directly at it in the opposite season, with things being about how they are now, when halfway between the seasons, here's what I would expect to be different:
1) Far more extreme changes between the seasons. During winter at each pole, temperatures would drop low enough for carbon dioxide to form dry ice, and possibly low enough to produce liquid nitrogen from the air. During summer at the poles, water might boil. This would cause massive storms and currents in the air and water in-between. I doubt if (multi-cellular) animals could survive the extremes at the poles. Bacteria and some other simple life forms might, though. Migrations would become far more extreme, with animals moving to the summer side continuously. Unlike now, this would likely need to include humans. Life might be far more concentrated around the equator than it is now.
2) As for radiation at the poles, yes, there would be more, but this would be a minor concern compared to the temperature extremes.
3) I don't see how this would affect geology or magnetic fields.
4) You would see far more extreme weather (cyclones, hurricanes, tornadoes, etc.), but not earthquakes or volcanoes, because they don't get their energy from the Sun.
Just to note that you've got the perihelion/aphelion–solstice business backwards, Twinpinesmall. At the summer solstice, Earth is approaching its aphelion; and at the winter solstice, its perihelion. See Apsis#The perihelion and aphelion of the Earth. This shows that it's the planet's tilt, far more than its distance from the sun, that determines seasonal variations in temperature (I'm not sure what you mean by your reference to a "property of the atmosphere"). Deor (talk) 02:29, 22 March 2011 (UTC)[reply]
The statement that the northern and southern hemispheres get equally hot summers is false, I believe. Even if they received equal insolation it would be hard to make valid comparisons, though, because (1) a much higher fraction of the southern hemisphere is ocean, and (2) the southern polar region is an ice-covered continent whereas the northern polar region is ocean. The statement that if the tilt were 90 degress the sun would pass over both poles at the solstice is also false -- in fact each pole would experience permanent day for 6 months and permanent night for 6 months. Looie496 (talk) 02:41, 22 March 2011 (UTC)[reply]
tidal energy backup
Would a tidal energy turbine be a good backup energy supply for nuclear power plants? especially in Japan where the plants are mostly on the coasts and they have alot of earthquakes. —Preceding unsigned comment added by 98.221.254.154 (talk) 03:30, 22 March 2011 (UTC)[reply]
No:
1) Being on the coast, they probably would have also been destroyed by the quake and tsunami.
2) The wires used to deliver electricity from them would have also been destroyed.
3) A backup power supply should be something with very little cost when not in use. However, tidal generators are exposed to the sea and weather, and, as such, would require constant maintenance. This could only be justified if they were producing constant energy.
4) The cost of building a tidal energy turbine is quite high, again meaning it only makes sense if it can be run at capacity for many years to pay off the costs.
Now, if you used the turbine to produce energy along with the nuclear power plant, normally, then issues 3 and 4 would go away. Issue 2 could possibly be addressed by putting the wiring underground, although quakes could still be an issue. Issue 1 is the toughest to overcome. StuRat (talk) 04:11, 22 March 2011 (UTC)[reply]
I think this sounds like an excellent backup system. The next time a company wants to build a nuclear power plant, they should build the tidal power system first... then scrap the rest of the plan. Wnt (talk) 04:24, 22 March 2011 (UTC)[reply]
I like to hijack that question: why don't they use stirling engines for backup cooling? As long as there is a need for cooling there is also a heat source to drive the engines. 93.132.164.231 (talk) 19:12, 22 March 2011 (UTC)[reply]
Given that an earthquake can have arbitrarily high strength, nothing can ever be really quake-proof. But unlike a diesel a stirling engine won't mind being under water for some time and could be built very, very robust. 95.112.197.146 (talk) 08:58, 23 March 2011 (UTC)[reply]
I'd argue that there is an upper limit to quakes that can be expected on Earth (say 10.0 on the Richter scale), and a lower limit than this for most locations. However, I'd even settle for a design which would survive the latest Japan quake/tsunami. Is there some reason why a sterling engine can be built more robustly than the nuclear plant's own cooling system/steam engine ? StuRat (talk) 15:13, 23 March 2011 (UTC)[reply]
(ec) I guess that even the type of diesel engine used at Fukushima could have been built more robust than it really was. In addition, stirling engine does not need external air and can survive (and maybe to some extend even operate) being submerged in water. Besides, as far as I heard, the engines were not damaged by the earthquake itself but by the tsunami. 95.112.197.146 (talk) 15:43, 23 March 2011 (UTC)[reply]
A so-called "energy Island" to store electricity, see e.g. here does seem to be a good idea. Apart from the cooling problems, in Japan you now have a shortage of electricity. Also, you can think of applications that need many Terrawatts of power for a limited time (e.g. launching satellites using an electromagnetic rail gun). You can then store the needed energy into such a facility over a long period of time and then release it in a matter of seconds. Count Iblis (talk) 15:35, 23 March 2011 (UTC)[reply]
On first sight I thought the island would work be being filled with water some meters above sea level, but in truth it is emptied below sea level, and energy is gained by letting sea water in, correct? So the tsunami would have filled it, as would have even a medium sized storm. Or do I have some concept wrong? 95.112.197.146 (talk) 16:41, 23 March 2011 (UTC)[reply]
Whether above sea-level or below, that would depend on the volume of water and the elevation difference. Creating a tank, like a water-tower, wouldn't be practical because of the high cost relative to the volume and height. You'd need to have a natural elevation difference already. (I don't know if there are hills around the nuclear plants or not.) StuRat (talk) 17:53, 23 March 2011 (UTC)[reply]
From the pictures on google maps there are no hills near the factories, none worth mentioning. From the pictures shown after the tsunami I have got the impression that a good part of the land is even below sea level. The link given by user Count Iblis talks of an area of 10km x 60km (you can't spare such an area on a densely populated country, inland) and the picture indicates that the dam cannot be much more than perhaps 10m. I'm out of practice doing calculations and if I do there are frequently grotesque mistakes, that is why I asked instead of presenting the numbers I came up. If I'm correct, such a energy island can buffer the output of one reactor of only one hour if it works by storing water above sea level, and the output of 4 hours if it works by pumping water out, 40m deep. 95.112.197.146 (talk) 18:16, 23 March 2011 (UTC)[reply]
If it's 1/10th the size you thought, shouldn't it last 1/10th as long as you thought ? Note that it wouldn't need to provide anywhere near the full output of a reactor, just enough to pump in cooling water. However, this approach still sounds totally impractical here. I'm back to my idea of building the reactor core below sea level so that gravity can provide water, even with no electricity. StuRat (talk) 21:41, 23 March 2011 (UTC)[reply]
No, I actually calculated with 6km, not with 60km. But I found another error in that the height goes in quadratic, not liner. Building the reactor below water level would have other backdraws. But what I'm really wondering about is why they had humans to do the dangerous tasks. Sony has a robot that plays the violin, so I don't understand why there are no robots for this kind of task that could at least be remote controlled from a slightly bigger distance and possibly some shielding. 95.112.197.146 (talk) 22:05, 23 March 2011 (UTC)[reply]
Well, if nobody forces them to do so, they will go with the (immediately) cheapest option, which is not to prepare for a disaster. StuRat (talk) 22:23, 23 March 2011 (UTC)[reply]
As for my idea of using gravity to deliver water, so no electricity is required, the AP1000 reactor does this, although they use an above-ground fresh-water tank rather than ocean water: [3]. This prevents the fuel from being contaminated and rendered useless, but above-ground tanks can crack and quickly empty in earthquakes, so it doesn't seem quite as reliable. Perhaps a combo of the two designs could be made with the fresh-water water tank below ground, with the reactor core below that. StuRat (talk) 22:41, 23 March 2011 (UTC)[reply]
Physicists have obviously been confused all these years. Escape velocity, contrary to what the name might suggest, is not velocity at all, but simply speed, and should be renamed as soon as possible. Well, at least, so a number of contributors (?) to the article would have readers believe. I'm amazed that this article could be allowed to spread these weird notions - WP obviously and desperately needs review panels to vet some of the rubbish perpetrated in its name. Androstachys (talk) 05:14, 22 March 2011 (UTC)[reply]
If a craft travels at an accute angle relative to the tangent of centre of gravity, and its speed is slightly over the escape speed, then it can not escape the gravitational well. However, if the same craft travels radially from the centre of gravity, and at escape speed, then it will escape. Thus, a esccape velocity is a correct term that specifies the direction of the speed. Plasmic Physics (talk) 05:59, 22 March 2011 (UTC
(edit conflict) No, escape velocity is a scalar. It must be measured in the center of mass reference frame, but that alone does not make it a vector, as it has no direction. If the speed of the object exceeds the escape velocity at its location, then it will escape regardless of its direction of travel (provided it doesn't hit anything along the way). Similarly, exceeding the escape velocity implies an orbital eccentricity > 1, and a hyperbolic trajectory. Incidentally, the escape velocity article also stated plainly that it is a scalar before Androstachys started edit warring over it. Dragons flight (talk) 06:58, 22 March 2011 (UTC)[reply]
Escape velocity is a scalar. It is the solution to ½v² = Φ, where Φ is the gravitational potential (relative to infinity). Since the velocity only shows up as v² (that is, v·v), the solution is directionless. Plasmic Physics is incorrect (as is the original poster). -- BenRG (talk) 06:47, 22 March 2011 (UTC)[reply]
NASA launches have to fly through an atmosphere that adds drag and is best avoided. The definition of escape velocity assumes there is no drag or other additional forces. Dragons flight (talk) 07:57, 22 March 2011 (UTC)[reply]
Not to mention that NASA launches are rocket-powered, so escape velocity, with or without accounting for drag, is hardly relevant. The rockets leave the launch pad at a lot less than 11 km/s (which is the escape velocity at Earth's surface). It is relevant for probes like Pioneer after the rocket propulsion and gravitational slingshotting is over with. -- BenRG (talk) 08:21, 22 March 2011 (UTC)[reply]
Correct - the term for this particular type of continuously-powered flight is "gravity burn", indicating that the rocket expends some work against the gravity well that does not contribute to the kinetic energy required to reach escape velocity. One objective of a rocket engineer is often to minimize the amount of "wasted" energy that does not convert to kinetic energy of the rocket payload. On the other hand, if the objective is a lander rocket (such as the Apollo Lunar Module descent stage), the rocket engineer must optimize to minimize kinetic energy of the descent - that is, to land with a low impact-velocity and avoid "crashing." In that case, the spacecraft approaches the target gravity well, gains potential energy from gravity; and the rocket motor must supply enough energy to overcome the kinetic energy gained from losing the "escape velocity", plus additional energy to be "wasted" in gravity burn to control the descent speed through the entire time-integral of the trajectory. Nimur (talk) 16:39, 22 March 2011 (UTC)[reply]
Well, assuming you meant 11 km s-1 not 11 km h-1, then it all depends what you mean by "fly parallel to the earth's surface". If you took away the atmosphere, removed any inconvenient mountains, stopped the Earth from rotating and launched a projectile in a horizontal direction at 11.2 km s-1 then yes, it would escape the Earth's gravity well. However, if you apply continuous thrust to keep its flight path parallel to the Earth's surface (i.e. to keep its height constant) then it is in a powered orbit, and the fact that its speed is equal to escape velocity is irrelevant because it is not on a ballistic trajectory. Gandalf61 (talk) 10:08, 22 March 2011 (UTC)[reply]
Yes you would (I assume you mean s not h). Low earth orbit is about 9 km/s, any faster and you will orbit higher (slowing down in the process). At 11 km/s you won't slow down enough to stay in orbit. Ariel. (talk) 10:18, 22 March 2011 (UTC)[reply]
As it said in the article's intro: Escape velocity is the minimum initial velocity imparted to an object that will enable it to escape a gravitational field without any further boosting. This is a vector as the imparted velocity is directly away from the body's centre of gravity or normal to its surface. Any other angle of launch at the same speed will not escape the gravity well. Anyone here done even a basic course in physics? Androstachys (talk) 11:03, 22 March 2011 (UTC)[reply]
Not so. If an angle of 90 works, and 180 works (the two extremes), then obviously anything in between will work too. The only think left is down toward the ground, but that works too (ignoring crashing into the ground, which has nothing to do with the mathematics of escape velocity). Stop thinking of the earth as a giant sphere, and instead think of it as a tiny dot. No matter which initial direction you go, at some point you will be heading away from the dot. Also, I think you are expecting escape velocity to mean the object is no longer under the influence of the mass - i.e. it will travel in a straight line. That's not necessarily the case, the object might travel in an infinite spiral around the mass, and still have escaped from it because the spiral will never bring it back to the mass - it will circle around it, at greater and greater distance, but forever making circles. Ariel. (talk) 11:09, 22 March 2011 (UTC)[reply]
Minor correction - a ballistic trajectory has to be part of a conic section, so this rules out a spiral path. A ballistic escape trajectory is either a parabola if speed = escape velocity, or a hyperbola if speed > escape velocity. "Straight up" can be regarded as a degenerate parabola or hyperbola that happens to go through the centre of the Earth. Gandalf61 (talk) 11:32, 22 March 2011 (UTC)[reply]
Reply to Androstachys - I am sure that everyone who has replied to you has done at least a basic course in physics, and I expect some have much higher qualifications. I have an A-level in physics and a degree in mathematics. It is you who are clearly out of step on this one. When you are in a hole, it is best to stop digging. Gandalf61 (talk) 11:43, 22 March 2011 (UTC)[reply]
"If you took away the atmosphere, removed any inconvenient mountains, stopped the Earth from rotating and launched a projectile in a horizontal direction at 11.2 km s-1 then yes, it would escape the Earth's gravity well." Well, no. Discounting gravitational effects from the Sun and the planets, it would go into a highly eccentric elliptical orbit around Earth. I would suggest you ask for your money back from whichever institute doled out the A-level in physics. Androstachys (talk) 13:07, 22 March 2011 (UTC)[reply]
Androstachys, you are incorrect and Gandalf is correct. If an A-level wasn't good enough for you, than may be my PhD in Physics will impress you more. A ballistic trajectory at a speed higher than the scape velocity will lead to a hyperbolic trajectory and object will scape if a collision can be avoided. No highly eccentric elliptical orbit will come out of it. So, indeed, Scape velocity is a scalar despite its name. Dauto (talk) 15:26, 22 March 2011 (UTC)[reply]
Please read Gandalf's statement properly: "If you took away the atmosphere, removed any inconvenient mountains, stopped the Earth from rotating and launched a projectile in a horizontal direction at 11.2 km s-1 then yes, it would escape the Earth's gravity well." Now read your own:"A ballistic trajectory at a speed higher than the scape velocity will lead to a hyperbolic trajectory". Small wonder the article is in such a mess. Androstachys (talk) 06:55, 23 March 2011 (UTC)[reply]
Androstachys - it would be fascinating to hear you explain just what exactly you think is inconsistent between my responses and Dauto's. I am saying that a projectile launched horizontally at a speed equal to escape velocity follows a parabolic trajectory; Dauto is saying that a projectile launched at a speed greater than escape velocity follows a hyperbolic trajectory. Both of these are escape trajectories. Gandalf61 (talk) 11:05, 23 March 2011 (UTC)[reply]
Androstachys, I think you have already amply demonstrated that this simple topic goes over your head. As Gandalf said, it would be best if you stopped digging. Gandalf's statement above and mine are both correct. Dauto (talk) 18:51, 23 March 2011 (UTC)[reply]
Everyone seems to be ignoring the effective potential well introduced by conservation of angular momentum. This is deeper the more angular momentum you have, and so your necessary escape speed will increase at greater angles from the radial. —Preceding unsigned comment added by 92.20.215.104 (talk) 12:04, 22 March 2011 (UTC)[reply]
No. A different angular momentum just means a different angle with respect to the radius vector at a given distance. Escape velocity is independent of the direction in Newtonian physics. In General Relativity, it isn't, but the deviations from Newtonian physics are tiny when speaking about planets. In the case of a non-rotating black hole however, even light won't escape if the direction of motion is tangential and the distance from the center (or more correctly: the radial Schwarzschild coordinate) is less than or equal to 3/2 times the Schwarzschild radius. Icek (talk) 12:19, 22 March 2011 (UTC)[reply]
Okay, gloves off, let's do this from first principles. From conservation of energy we know that the speed s and radial distance r for an object in a ballistic trajectory must satisfy
and from conservation of angular momentum we know that
Suppose that at some point in its trajectory, when r = r0, the object's speed is greater than or equal to the escape velocity i.e.
then we know that
The speed of the object is given by
so if we have
If E = 0 there is only one value of r that satisfies this quadratic equation, and if E > 0, there are two roots, but only one of them is positive, and we know r must be positive. So if E ≥ 0 there is only one value of r for which i.e. distance from Earth is a maximum or a minimum. We know the object is not in a circular orbit - it is travelling too fast for that - and it cannot be in an elliptical orbit either, because then there would be two values of r for which (at apogee and perigee). Therefore it is on an escape trajectory. QED. Gandalf61 (talk) 15:30, 22 March 2011 (UTC)[reply]
Another way to see this is to look at the orbit equation.
If , then there exists such that , which from the orbit equation implies that r goes to infinity. The angular momentum affects the eccentricity, and thus the direction of travel at infinity, but as long as there is no value of the angular momentum (expressed in h) such that the eccentricity could be less than 1. Dragons flight (talk) 20:43, 22 March 2011 (UTC)[reply]
Refering to my earlier statement, I was of the impression that a vector description was not limited to linear paths, but also curved paths as in some matrices. Plasmic Physics (talk) 08:12, 23 March 2011 (UTC)[reply]
I think the problem here is that the question itself assumes the speed-is-scalar-velocity-is-vector shibboleth drilled in in high-school physics classes. In high school, one of the hard questions to answer is "how can the thing be accelerating when it never speeds up?" and for this purpose it is very convenient to have two different words and insist on the distinction.
I don't think physicists, though, really pay much attention to it. It's pretty much always obvious whether you are referring to the velocity vector or to its magnitude, and so you don't need to disambiguate in the choice of the word. So we have escape velocity, phase velocity, the velocity of light, all used quite blandly and with no sense that anything is wrong. And why should it be? Velocity is just the Latinate word for "speed"; velox simply means "fast", not "fast in a particular direction". I suspect that using the Latinate word for the vector quantity and the Anglo-Saxon one for the scalar was a quite arbitrary choice at some point, made just for convenience. If it's not convenient for us, there's no reason to follow it. --Trovatore (talk) 08:56, 23 March 2011 (UTC)[reply]
What is the most efficient wind turbine design, in terms of dollars-per-watt?
Or hopefully, watts-per-dollar?
I'm sure the 3-bladed design that we're all familiar with is getting a little old; we already have eggbeater wind turbines and other designs. Now of all the available designs, which would be the most efficient? (Please provide stats and links to more info about that design of turbine.)
"Watts-per-dollar" alone doesn't define the ideal design:
1) Since construction cost is a major factor, this makes "watts-per-dollar" better, the longer it stays in operation. Maintenance cost also figures in.
2) Whether you have high or low wind speeds, and constant versus intermittent winds, would also effect the ideal design.
3) Some consideration also needs to be made for how the electricity is used. If it can be sold to a utility company at a constant rate versus being used immediately at a home, for example, which leaves open the possibility of "wasting" electricity which can't be used. In the second case, you'd want a design that produces a lower, constant rate of electricity over one that varies dramatically. StuRat (talk) 14:03, 22 March 2011 (UTC)[reply]
1. What are some tougher game shows for Watson to tackle? 2. ...
1. What are some tougher game shows for Watson to tackle, and how will they be tougher for the A.I.?
2. What would it take to build an android named "Watson Jr." that'll have enough computing power crammed in its body to actually go to Kindergarten with warm-blooded classmates, get its height readjusted by its scientists every time it advances a grade, pass a high school with high honors, and enroll in a college?
Since a decade and a half is too long for IBM to conduct that experiment, how about one grade level every 2 weeks? What could enable a "Watson Jr." android to become feasible this way? --70.179.169.115 (talk) 07:55, 22 March 2011 (UTC)[reply]
1: Game shows are specifically designed not to be hard - they want the viewers at home to play along. 2: No one knows. Every prediction of the amount of computing necessary has come and gone, so no one will make predictions anymore. Besides the hardware (which everyone assumes will eventually arrive) there is also the software, and no one has a clue about how to do that part. I think most people assume the software will not be written, but rather the machine will learn or evolve on it's own, but both of those require a fitness function, and we don't have that either. Ariel. (talk) 08:12, 22 March 2011 (UTC)[reply]
Watson is a first step toward human A.I. the way climbing a tree is a first step toward reaching the moon (standard analogy). We just don't have the faintest idea how to do human A.I., and Watson doesn't help. IBM doesn't do A.I., anyway; it creates enterprise data management solutions for big corporations with deep pockets. That's what Watson is meant to advertise.
There's a lot of variety in game shows. "Who Wants to be a Millionaire?" would probably be much easier than "Jeopardy" since it's multiple choice. "Wheel of Fortune" is basically mindless and a computer could probably beat any human player, especially if you let it calculate the precise amount of torque to apply to the wheel. "The Newlywed Game" and "Survivor" are too human-centric to be playable. "The Price is Right" might be an interesting target for future research. -- BenRG (talk) 08:53, 22 March 2011 (UTC)[reply]
The Price is Right would be simple for Watson. The data for average prices could easily be loaded into Watson and then it's just a matter of probabilities for most of the games. I wouldn't be surprised if Watson hit every price within ~1%. Dismas|(talk)09:16, 22 March 2011 (UTC)[reply]
Actually, Price would be an interesting challenge for Watson, for a couple of reasons.
Even if accurate to 1%, guessing high (even by a dollar) knocks you out of contention -- so Watson would have to lowball the price. This is algorithmically easy, but it's not something you find in Jeopardy (in case we're talking "Watson-as-is" vs "Watson-with-minor-changes").
Unless Watson is the last player in the round, it would be easy for the human contestants to use the "Watson +$1" strategy. Watson's only actual defense against this would be to guess the price exactly, but that conflicts with problem #1.
That said, assuming Watson got into the final round, it would hold a major advantage with problem #2 removed. — Lomn13:37, 22 March 2011 (UTC)[reply]
Watson is a specialist machine. It is not a generalist. It could probably be tweaked to do similar trivia shows. But it's not like Watson, as is currently programmed, would be able to play Wheel of Fortune. The inputs and outputs would just not make any sense to its program. --Mr.98 (talk) 12:54, 22 March 2011 (UTC)[reply]
Off-topic slightly, I'll bet a piece of software to play Wheel of Fotune would be a lot simpler than Watson. APL (talk) 15:54, 22 March 2011 (UTC)[reply]
Indeed, and not off topic at all! The point is that Watson is a specialist. Even very easy computational tasks are probably well beyond the specific algorithm that plays Jeopardy. It is like the classic (perhaps true? I don't know) anecdote about frogs that only know how to eat flies when they are flying or moving around, and will starve if put into a basin of freshly-killed flies. --Mr.98 (talk) 16:26, 22 March 2011 (UTC)[reply]
2) Attending each grade for only 2 weeks wouldn't work. Watson learns by trial-and-error, like humans. As such, it would need the same number of trials and errors that children need (or perhaps slightly fewer, since it has perfect memory). Therefore, the only way to get it to learn quicker would be to provide input quicker. Since a regular school can't run at hyper-speeds, this accelerated input would need to be provided in another manner. StuRat (talk) 13:52, 22 March 2011 (UTC)[reply]
If you allow it to keep its current database, Watson could probably pass most highschool and college standardized tests now. If you skip the essay questions, anyway.
Erasing its brain and Learning purely from class would be problematic. For us that kind of classroom instruction depends on a huge amount of knowledge we just pick up from observing the world around us. Without background general knowledge even the simplest textbooks would be incomprehensible.
Imagine if you read in a text book "All animals with four legs are quadrupeds.", and then on an exam you were asked "Is a cat a quadruped?" you'd have no problem. You learned this in the book! But you didn't. You only learned part of it from the book. You had outside knowledge that cats have four legs.
IBM gave that kind of general knowledge to Watson by having it read and remember millions of pages of written material. (It wouldn't surprise me if Watson has Wikipedia in his brain somewhere.) Of course, no human could learn that way.
Even solving issues like speech recognition in the classroom, I don't think that Watson is compatible with human methods of learning. It was designed to use massive data-dumps in text format. (Even if the exam had a photograph of a cat it wouldn't help Watson.) APL (talk) 15:54, 22 March 2011 (UTC)[reply]
I always wonder why thinking like a human is still the gold standard for AI. (I know it was for Alan Turing, but a) he was thinking speculatively and b) it was a long time ago. I don't expect a car to get around as well as I do; I expect it to get around much more quickly. I don't expect my computer to sort a file of a million records in the way I would; I expect it to sort the file in minutes. From what's said above, it sounds like Watson solves problems in a very different way from a human. It should be quite good at Countdown, both the anagram games and the arithmetic. Itsmejudith (talk) 16:17, 22 March 2011 (UTC)[reply]
Even your filing algorithm is "like a human," it's just faster (and probably better optimized than most humans, but humans manually could do a insertion sort, too, if they thought to do it). Speed is not the interesting issue; even the most primitive computers and calculators can beat humans at speed. The reason humans are the gold standard is because as far as we can tell, the algorithms are well beyond what we can approximate with machines, even with all of their speed. --Mr.98 (talk) 16:29, 22 March 2011 (UTC)[reply]
Both ways of "thinking" have their uses. One use for a computer that "thinks like humans" is in search engines. The current methods often give results that any human can tell don't match the (intent behind the) search criteria. StuRat (talk) 16:30, 22 March 2011 (UTC)[reply]
But it's not even a way of "thinking". One can marvel at the speed in which computers do things, but their ability to do anything complex is very limited. They usually do just very simple things very fast. I don't consider that "thinking" in any meaningful sense. Just because a computer chip can shuffle cards faster than I can doesn't mean that shuffling cards is a form of "thinking". --Mr.98 (talk) 21:31, 22 March 2011 (UTC)[reply]
That's why I put "thinking" in quotation marks. Would you prefer "processing", to collectively refer to human thinking and machine calculations ? StuRat (talk) 03:20, 23 March 2011 (UTC)[reply]
By the way, when I said the Watson could "probably" pass an exam now, I mean its underlying technology. Some custom software would be needed to create an interface between the Watson engine and the test. (Like whatever software they wrote to handle the "game" aspects of Jeopardy!) APL (talk) 18:46, 22 March 2011 (UTC)[reply]
University Challenge is an interesting suggestion - of course Watson could know all the others, but the buzzer element is very interesting. If I said "Lima is" you could probably shout out "Peru" and be right, or something like but harder in UC. I'm not sure an AI would be able to play the probabilities like that. Grandiose(me, talk, contribs) 19:09, 22 March 2011 (UTC)[reply]
High altitude effects indoors
I was recently watching a basketball game on television, broadcast from Denver, Colorado. The announcers made reference to how the play of the game would be affected by the high altitude of the area. Because the game was being played indoors, would the effect be significantly less than if it were to be played outdoors? Kansan (talk) 13:27, 22 March 2011 (UTC)[reply]
The game being indoors vs outdoors won't change the altitude effects, assuming the basketball arena is unpressurized (I don't know of any that are). Naturally, playing indoors vs outdoors would affect many aspects of basketball, but those effects wouldn't be related to altitude. — Lomn13:32, 22 March 2011 (UTC)[reply]
So all other things being equal, the air inside a building would have the same air pressure of the surrounding area, right? Kansan (talk) 13:34, 22 March 2011 (UTC)[reply]
Yes. There are stadiums with soft covers that are partially supported by increasing the air pressure inside, but I believe that pressure difference is tiny compared with that due to the elevation difference. StuRat (talk) 13:42, 22 March 2011 (UTC)[reply]
Certainly within the tolerance of "has a measurable effect on athletic performance". Any building is going to have slight positive or negative pressure relative to its environment, but that's orders of magnitude smaller than the overall change in air pressure from sea level to Denver. Sea level to Denver is a difference of about 17 kPa, which is also about a 17% change. We note that the differential of a positive pressure enclosure is only about 0.05 kPa, a change of 0.06%. — Lomn13:47, 22 March 2011 (UTC)[reply]
A good way to visualize the relative air pressures is to think about ear popping. You ears probably pop several times as move from sea level to Denver's elevation and back down. How often do they pop when entering or exiting a building ? Not often. So, this shows the pressure differential is far less. (If it was as high, you'd probably burst your eardrums when entering or exiting such a building, as that much pressure change in that little time would be too much for them to handle.) StuRat (talk) 08:08, 25 March 2011 (UTC)[reply]
What is the maximum recommended amount of salt in water for dairy cattle?
What is the maximum recommended amount of salt in water for dairy cattle?
Back ground if your interested: My firm recently drilled a water well for a gentleman who in setting up a rather small dairy farm. The water contains 1520 ppm of sodium, ideally of course there would be none. We are trying to seal the lower parts of the well with a concrete mix, but the question remains. What is the maximum recommended amount of salt in drinking water for dairy cattle? Any help would be greatly appreciated. JohnQposter (talk) 14:00, 22 March 2011 (UTC)[reply]
This site says less than 3000 ppm of "total dissolved solids", which includes sodium, is "Usually satisfactory for most livestock". This site says (specifically about salinity) < 1000 is good, and for 1000-3000 ppm, "Generally no problems; possible temporary diarrhea to animals not accustomed to this water". --Sean15:00, 22 March 2011 (UTC)[reply]
Please note that Wikipedia does not give medical advice, and I assume that means veterinary advice also. This may be an academic response in good faith, but don't trust us when it comes to the cows' (and farmer's) well-being. Wnt (talk) 02:58, 24 March 2011 (UTC)[reply]
Time dilation
I remember reading some time ago an explanation of time dilation in special relativity based on transfer of information and the constancy of the speed of light. So if A is stationery and B travels some distance away they will observe each other's clock to tick slower than their own.
The explanation involved A (using his own clock) sending B one signal each second but due to c being constant for all observers, B receives the signals at more than one second apart (based on B's clock). Does anyone know of this explanation? Thanks. Zain Ebrahim (talk) 15:48, 22 March 2011 (UTC)[reply]
That sounds like the Doppler shift (which exists even in Newtonian physics). At relative rest, signals sent at a constant rate are received at the same rate, but with recessional motion, the received rate is slower:
A/ / B A/ / / B
A / /B A / / /B
A/ / B A/ / /B
A / /B A / / B
A/ / B A/ / B
A / /B A / /B
You can derive all of special relativity from the rule that the ratio of the sent and received rates depends only on the relative speed. Time dilation is not especially easy to derive, though, because it requires synchronized clocks. The twin paradox is easier. -- BenRG (talk) 18:53, 22 March 2011 (UTC)[reply]
Ah yes, but if you assert the signal velocity is still c in the observors rest frame you get time dilation, as explained by the OP, whereas in CM doppler shift, the signal speed would be different in the two frames. —Preceding unsigned comment added by 92.21.86.36 (talk) 15:22, 23 March 2011 (UTC)[reply]
How do axons and dendrites meet up? What is their physical method of motility? Layman's terms would be appreciated, even if simplification makes the answer less than perfect. 20.137.18.50 (talk) 19:16, 22 March 2011 (UTC)[reply]
They meet at specialized junctions called synapses. Dendrites don't extend very far from the cell body, and they grow in intricate tree-like patterns whose rules are not all that well understood. Axons, in contrast, can extend for enormous distances. The tip of a growing axon is a structure called a growth cone, which extends numerous tiny fingers of protoplasm called filopodia, which interact chemically with things that they touch, sticking to some and being repelled by others. These attraction-repulsion processes cause the growth cone to travel through the brain or body, sometimes by very complex routes, extending the axon behind it as it goes. Here is a link to a youtube video that explains the process and shows it in action. Looie496 (talk) 19:51, 22 March 2011 (UTC)[reply]
Real-time glacier data
Hi. Is there any reliable source on the Internet where I can select any monitored glacier from a worldwide database and get real-time or recent data on parameters such as flow rate, temperatures, height changes, precipitation, status of retreat or advance, density, any moulins or glacial lakes and dams, calving events, etc? Thanks. ~AH1(TCU)20:27, 22 March 2011 (UTC)[reply]
What questions are you trying to answer? Most glacier monitoring looks at things like mass balance (e.g. thickness) and edge location, which are variables that change slowly and hence can be recorded infrequently. The number of intensively monitored glaciers is probably very low. Dragons flight (talk) 00:13, 23 March 2011 (UTC)[reply]
Maybe if you bought some seeds directly, but the seeds on a bagel are baked, and thus dead. If you buy a bottle of seeds make sure they are not toasted. Ariel. (talk) 23:22, 22 March 2011 (UTC)[reply]
Or Irradiated. It wouldn't surprise me to find that poppy seeds are routinely irradiated (it's not uncommon for spices), which would kill parasites, but also the seed. Ariel. (talk) 05:24, 23 March 2011 (UTC)[reply]
You can grow the seeds from many other fresh fruit and vegetables. Experiment and see. Searching for growing pips (no ""s) on Google gives a lot of results. 92.15.14.45 (talk) 12:13, 23 March 2011 (UTC)[reply]
I think this is the "definitive source" for a certain type of home enthusiast. The type who often regrets his efforts, that is. Still, any transgression against the cartel's supply side is a blow against Islamic terrorism... Wnt (talk) 04:39, 24 March 2011 (UTC)[reply]
It never occurred to me that the OP might be interested in that aspect. I understand that only opium poppy specie(s) contain enough opium to have any effect. In my country poppies are a common weed and garden flower. The best book for growing seeds from many different types of fresh vegetables and fruit is "The Pip Book", once published by Penguin but now out of print. 92.28.242.170 (talk) 19:59, 25 March 2011 (UTC)[reply]
Irradiation has to take place in a specialized irradiating facility. Sushi and sashimi is prepared using extremely fresh fish. I think it would make it rather prohibitive, unless you're imagining that every Japanese restaurant would have a gamma irradiator or a radiation source on premises. The cost would be huge. --Mr.98 (talk) 01:08, 23 March 2011 (UTC)[reply]
I think that food irradiation equipment is dangerous in untrained hands, they contain Cobalt-60, which is not something you'd want your waiter fiddling with. APL (talk) 01:32, 23 March 2011 (UTC)[reply]
Irradiation could kill the microbes in raw fish, but it wouldn't do anything to stop a variety of chemical reactions that would rapidly reduce it to slime. Any sort of raw meat is full of enzymes that will rapidly break it down if they aren't either denatured by cooking or suppressed by refrigeratiion. Looie496 (talk) 02:56, 23 March 2011 (UTC)[reply]
I was just expanding on the "parasites" statement. That said, while irradiation "wouldn't do anything to stop" spoilage, I also don't know that it would necessarily cause spoilage. Couldn't one irradiate while refrigerating? I agree with APL's comment about cost as the most obvious problem. -- Scray (talk) 03:41, 23 March 2011 (UTC)[reply]
Radiation can change the taste, particularly if the food contains fat, eg fish, so it is reserved for things like herbs with strong flavour and low fat. Graeme Bartlett (talk) 09:29, 23 March 2011 (UTC)[reply]
The purpose of irradiation is to extend the shelf life of foodstuffs. Sashimi is not suposed to have a significant shelf life. Simply chilling the fish works well - don't fix what ain't broke. Roger (talk) 12:41, 23 March 2011 (UTC)[reply]
Although I would agree that one purpose (and the most prevalent current purpose) of irradiation of foodstuffs is to extend shelf life, that was not the OP's question. They asked why irradiation isn't used on sushi and sashimi. They did not say what purpose they had in mind. I would agree with your comment, except that chilling doesn't kill many important parasites, and User:APL previously proposed (in this thread) that it might be used to kill parasites. I don't know whether that's been tried, but the articles I linked (and their reliable sources) do indicate that raw fish (as may be found in sushi & sashimi) are an important contributor to human parasitosis. -- Scray (talk) 16:35, 23 March 2011 (UTC)[reply]
Indeed I seem to recall during one of the US spinach E. coli someone suggesting routine irradiation of spinach (and possibly other foods) would reduce those sort of outbreaks and other occasional food poisonings from such food stuffs, the primary thing stopping it was unwarranted consumer concern. (I'm not saying I agree with their view nor do I see the need to get in to discussions about whether better hygiene and farming practices may have more merit simply pointing out there are plenty of cases when irradiation is used for reasons other then improving shelf life.) Also as our article notes irradiation is used with various fruits for import into places like New Zealand, Hawaii and Australia to try and stop the introduction of pests not currently present in the local environment. Our article also notes various other examples which don't seem to be simply about improving shelf life. Nil Einne (talk) 12:03, 24 March 2011 (UTC)[reply]
Why do you believe that they are not irradiating sushi? Since a couple of weeks, indeed, they are using irradiation on sushi, sashimi and many other foodstuff. 212.169.184.141 (talk) 12:58, 23 March 2011 (UTC)[reply]
In case it's not perfectly clear, 212.169.184.141 is making a joke about the accident at the Fukushima power station. APL (talk) 14:01, 23 March 2011 (UTC)[reply]
I am writing this question in reference to President Obamas Tax Proposal on enviormental improvment projects that gives the American Peaple a Tax break when purchasing an recycling item? Please send me any in formation regaurding this issue? I am also in the means of working in a working on a enviormental project of a large scale which objectives is to confine or section off unwanted flying debris.I aim on marketing my product and can use any information that will help the future coustomer. Thank you God Bless Joseph I.Montoya Alavedga (talk) 01:00, 23 March 2011 (UTC) Jim[reply]
I searched, but I can find no information about such a program or a proposal to make such a program. Can you give more information about it? Where did you hear about it? When? Is it a proposal, or an actual program? Ariel. (talk) 02:06, 23 March 2011 (UTC)[reply]
From what I understand it, inflationary cosmology posits a rapidly-expanding primordial false vacuum which at a certain point is punctuated by the formation and growth of low-potential true vacuum bubble universes, of which our universe is one such bubble. In this view, which genesis corresponds to what people refer to when they refer to "the big bang"-- the original initial-state of the false vacuum multiverse, or the initial formation of each bubble universe? Cevlakohn (talk) 05:40, 23 March 2011 (UTC)[reply]
What you're describing sounds like "old inflation", which is dead as a theory as far as I know, having been replaced by slow-roll inflation—see Inflation (cosmology)#Early inflationary models and the following section. That doesn't really affect your question, though. The answer is that the "big bang" happens at the end of inflation. Technically, though, it refers to a time just before the end of inflation, when there would have been a singularity if the post-inflationary model were correct back to the beginning of time, which it isn't since the inflationary model takes over at some point. So the "big bang" that subsequent times are measured from never actually happened. (See Age of the universe#Explanation.) -- BenRG (talk) 07:56, 23 March 2011 (UTC)[reply]
Probably teaching you to suck eggs, but you might find further information and useful links from the Physiology section of the Thyroid article and from the Thyrotropin-releasing hormone article. At first glance it looks as if the primary known modifier is temperature, but I suppose that in turn may be affected by circadian rhythms. {The poster formerly known as 87.81.230.195} 90.201.110.155 (talk) 11:33, 23 March 2011 (UTC)[reply]
There has not been a great deal of research on this. Recent papers still cite PMID 578614, a study from 1977, which says that there is a rhythmicity: "Thyroxine: Pooled data showed peak values from 8 a.m. to 12 a.m. and lowest levels from 11 p.m. to 3 a.m.". Looie496 (talk) 17:04, 23 March 2011 (UTC)[reply]
I was reading the previous posts about this and none address the possibility of setting off a bomb a a point in the fault that has been identified as having the most potential energy built up (where the most tension exists) to trigger a natural earthquake that might not have happened for another couple of years. Could this be plausible?165.212.189.187 (talk) 14:44, 23 March 2011 (UTC)[reply]
We've discussed this very topic before. Basically:
1) The force required would exceed that of even the most powerful nuclear bombs, unless the fault was ready to go anyway, in which case it would go soon on it's own.
I don't think #1 is quite right. It's true that the comparisons are not the same (though talking about energies released is usually more misleading than clarifying), but it's not clear that large (e.g. megaton range) nuclear weapons could not induce quakes. I think a more accurate answer would say: "we don't know how to do this, we don't have great indications that it would work, but we haven't done much research on this point." Nuclear weapons have effects like small, localized earthquakes; whether one of those could, in the right set of conditions, set off a large earthquake that is "ready to pop," we don't know for sure one way or another.
The relevant article is induced seismicity. As you can see, most academic research focuses on long-term trends, mostly related to changing the structural integrity and the pore pressure in the subterranean strata because of long-term pumping/extraction of ground-water, natural gas, or petroleum. Nimur (talk) 15:24, 23 March 2011 (UTC)[reply]
I think that any further research into controlling earthquakes should be made in the future on other planets where any adverse reactions would be of little consequence since no one is living there. ScienceApe (talk) 19:47, 23 March 2011 (UTC)[reply]
Sounds good to me. Using bombs to set off earthquakes is a topic that's been raised here surprisingly often - I seem to recall some that were before the recent quake in Japan - and I admit I'm mystified by the very idea. No disrespect. You get an earthquake either way, but by using a bomb to trigger it you now also have a nuclear explosion beside Los Angeles (or San Francisco or wherever) to top it off. That doesn't seem like a good trade off to me. And who is going to assume the liability for intentionally causing an earthquake? Every person who so much as chipped a nail during the intentional quake would take part in a class action suit against whoever pulled the trigger. Forget the science; operationally, this is just a terrible idea that nobody in their right mind would assume responsibility for. Matt Deres (talk) 20:47, 23 March 2011 (UTC)[reply]
Taking into account large scale effects (such as non-negligible evolution of the scale factor a(t)) is it right to say that the events which make up my light cone (i.e. those that I can see at a given point in spacetime) are all the points displaced by null 4-vectors (those for which the spacetime interval is zero).
Sorry, I don't know if I am being foolish, but I am having trouble taking into account the evolution of a(t) over the photons time of flight. —Preceding unsigned comment added by 92.21.86.36 (talk) 15:19, 23 March 2011 (UTC)[reply]
Your light-cone is formed by all the null geodesics that pass to your current world point. The tangent vectors to these geodesics are null vectors everywhere. The term "geodesic" takes into account the evolution of a(t) and also space-time curvature due to the matter distribution in the Universe (gravitational lensing). --Wrongfilter (talk) 17:16, 23 March 2011 (UTC)[reply]
Your confusion arises because you're viewing null four-vectors as being displacement vectors. The whole idea of a displacement vector has very little use within general relativity (none that I'm aware of), because unlike in Newtonian mechanics or special relativity, the coordinates used to label events in general relativity don't in general have any physical significance independent of the metric tensor. For example, in general relativity you can't in general get the spatial or temporal distance between two events simply by subtracting the coordinates of the two events. The concept of a vector that does continue to be valuable in general relativity is the tangent vector, such as is used in Wrongfilter's explanation above of a light "cone" in general relativity as consisting of a set of null geodesics. Red Act (talk) 02:55, 24 March 2011 (UTC)[reply]
Only if very close to each other. Cell phones don't have the power or antennae necessary to send messages long distances. StuRat (talk) 16:17, 23 March 2011 (UTC)[reply]
Does very close means some hundred meters? And, is it indeed a minor technical modification, or would it be a huge source of interference among cell-phones?Quest09 (talk) 16:19, 23 March 2011 (UTC)[reply]
Yes, on that order (although what lies in-between has a major impact on range). They would want to use a different frequency for this to avoid interference (specifically, in the US, they would use the FRS and GMRS frequencies). And, of course, walkie-talkies are already designed for this function, and better at it, by using more power (resulting in them going dead much sooner) and having bigger antennae. Ironically, old cell phones were more suitable for this purpose than new ones, since they had the long antennae and big batteries required. StuRat (talk) 16:17, 23 March 2011 (UTC)[reply]
Smart-phones could handle this over very short distances with their Wifi or Bluetooth functionality. Probably only a software change is needed. APL (talk) 18:18, 23 March 2011 (UTC)[reply]
True. The OP is asking about having a cell phone (which uses base stations normally) ALSO being used to directly call other cells phones. StuRat (talk) 23:15, 24 March 2011 (UTC)[reply]
See Carbon filteringIt depends what form the iodine takes. Carbon filters are not good at removing inorganic salts, so radioactive iodine in the form of, say, sodium iodide would not be removed well. On the other hand, most organic iodine compounds (iodomethane, for example) should be removed reasonably well. I'm not sure what chemical form radioactive iodine fallout is likely to take, and I'm having trouble finding any references. Buddy431 (talk) 19:19, 23 March 2011 (UTC)[reply]
You could precipitate the iodine by adding an excess of silver nitrate. Filtering this solution and then treating with something like sodium carbonate or sodium sulfate would then precipitate the silver, excessive ingestion of which can lead to argyria.--Atemperman (talk) 20:12, 23 March 2011 (UTC)[reply]
Before playing around with poisonous chemicals you should consider the short half live of I-131. The simplest and safest way to deal with it is to wait until it has decayed naturally. Provided that you have access to "older" water. 95.112.197.146 (talk) 21:22, 23 March 2011 (UTC)[reply]
Amino acids and fatty acids in durian
The main site, a few minutes of Googling, and nutritiondata.com are unhelpful in providing details on the fatty-acid and amino-acid profiles of durian. Anyone have a clue? --Atemperman (talk) 20:15, 23 March 2011 (UTC)[reply]
Shape of the Universe
Hi, I'm sure my question is answered somewhere in Wikipedia, but my brain has glazed over somewhat, and I'm hoping someone can spell out the answer in simple terms. As far as I understand it, the standard model of the Universe says that at the time of the Big Bang all of space was concentrated into a tiny region, which then began to expand. I visualise this as being like surface of an expanding balloon, except in 3D space rather than 2D space (probably I got this from some science show on TV). Yet at Shape of the Universe it says "Within the Friedmann-Lemaître-Robertson-Walker (FLRW) model, the presently most popular shape of the Universe found to fit observational data according to cosmologists is the infinite flat model". Is this consistent with the earlier picture I drew? How can something closed and finite, like the 3D analogue of the surface of a sphere, ever become infinite and flat throuh expansion, without some sort of "rupture" event? If the Big Bang is accepted, then how can the Universe now be any shape other than "closed", like it was originally? 86.181.202.145 (talk) 23:20, 23 March 2011 (UTC)[reply]
Sorry, I'm not sure if this a rhetorical way of saying that according to the usual model it wasn't initially closed, or that you don't know but want to raise it as a suggestion? 81.159.104.17 (talk) 03:49, 24 March 2011 (UTC)[reply]
A possible problem is that the "balloon" model is misleading. The balloon expands in 3 dimensions. All of space is represented as 2 dimensions on the surface of the balloon. Everything inside and outside the balloon is not part of space. Only the surface of the balloon is space. Then, you think that space is 3 dimensions, so it is an expanding balloon. Well, the space on the balloon is only 2 dimensions. If you want 3 dimensional space, you need a four dimensional balloon - which is very hard to imagine. So, you have to drop the idea that space is three dimensions if you want to imagine the balloon, which is a spherical model. What if, instead of a sphere, the big bang blew out a ring shape that expanded to a tube? Then, the 2D space would be on the surface of an expanding tube. What if the big bang blew a ring that wasn't hollow in the middle? It is a disk that gets wider and wider, but remains flat? Then, the 2D space would be on an every-increasing flat space. You can imagine cones, cubes, or any other kind of strange shape you like. I like the idea of two conical shapes expanding out of a singularity in opposite directions. I know the data doesn't support it, but I like imagining that shape for space. -- kainaw™02:23, 24 March 2011 (UTC)[reply]
I understand the dimensionality issues. I think the only purpose of introducing the balloon is because it's otherwise difficult for ordinary mortals to imagine any type or curved or closed space. 81.159.104.17 (talk) 03:49, 24 March 2011 (UTC)[reply]
I think I'll trot out this image that I made a few months ago (that I've so far used only on the reference desk). This is not an accurate depiction of our universe, but it is an accurate depiction of a FLRW universe with different values for the adjustable parameters of the FLRW model. What's nice about these particular parameter values is that the spacetime you get is the spacetime of special relativity. This diagram is plotted in special relativistic x and t coordinates, with the future at the top and the past at the bottom, and light travels along 45° diagonal lines. (To get the full four-dimensional version of the diagram, rotate it in the third dimension around a vertical axis through the center to get a cone shape, then rotate that through the fourth dimension to get a hypercone.)
It may look like this toy universe is finite and expanding at the speed of light, but to a cosmologist, it's infinite. Cosmological time is measured by clocks that are moving with the Hubble flow. Because of time dilation, the Hubble-flow clocks near the sides of this diagram tick slower. All clocks show the same elapsed time at the surface of last scattering (the upper boundary of the bright region marked "opaque plasma"). This surface, which is shaped like a hyperbola (or a hyperboloid when you rotate the image into four dimensions), represents the universe at a particular time (the last scattering time), and as you can probably see, it's infinite in size and contains an infinite number of galaxies (spaced more or less evenly). It's also negatively curved, even though the spacetime is flat. And it's expanding, but not at the speed of light or any other particular speed; rather, the distance between galaxies is increasing at a rate that's proportional to the distance between them.
So this is what it means for the universe to be "smaller in the past" and yet infinite at all times, and this is how you can get an infinite universe without any faster-than-light expansion. The details are slightly different in the real world, but the idea is the same. -- BenRG (talk) 06:56, 24 March 2011 (UTC)[reply]
This is very interesting and cool. But, having seen it the last time you posted it, what I'm still unable to quite figure out is, does it (or at least, can it) have infinitely many distinct baryons in a spacelike 3-d slice? And if not, are there models that do, that are consistent with observations? I had thought there were, but in your picture it looks like an infinite spacelike slice does not have uniform density; it falls off as you move away from the center line of the drawing, and the total number of baryon world lines could be finite (though perhaps it wouldn't have to be). --Trovatore (talk) 19:09, 24 March 2011 (UTC)[reply]
Along lines of constant cosmological time, the density is uniform with respect to the spacetime interval (but not with respect to Euclidean distance on the diagram, which is why it looks like it's falling off). So, yes, there are infinitely many baryons. If you take a horizontal slice through the diagram (constant special-relativistic t coordinate), you still get a picture of the whole universe, since all of the worldlines have to cross every slice, but it's not uniformly dense; it's actually the Klein model of the hyperbolic space. -- BenRG (talk) 00:03, 25 March 2011 (UTC)[reply]
Here's a silly animation I just made to illustrate the uniform density (linked because inline animations are annoying). This shows the entire diagram above being successively Lorentz boosted with the bottom vertex (the "big bang") held fixed. If you look at the lines representing the Hubble flow, they don't appear to move. Actually, they are moving "one galaxy to the left" on every animation frame (as you can see by looking at the here-and-now dot). You can keep boosting like this forever in either direction, bringing new galaxies to the center, without the density ever changing. -- BenRG (talk) 03:43, 25 March 2011 (UTC)[reply]
March 24
Falling of the Newton's Apple
As we all know the reason of the falling of the Newton's apple on earth is that it's acceleration towards earth is greater than the acceleration of earth towards apple.
Therefore would Newton's apple fall OR accelerate towards earth if it's size (both mass and volume wise) increased exactly to size of the earth?
An increase an extra mass might shift them to new orbit But would they have weight pressure on each other as both equal and opposite accelerations cancel each other?74.198.150.220 (talk) 00:13, 24 March 2011 (UTC)Eccentric Khattak#1-420[reply]
The acceleration of the apple is due entirely to the mass of the Earth. It is unrelated to the mass of the apple insofar as all objects at the Earth's surface accelerate at 9.8 m.s-2, regardless of their mass. Similarly, the acceleration of the Earth towards the apple is due entirely to the mass of the apple and is unrelated to the mass of the Earth.
If two planets of equal mass are close enough to influence each other to a measurable degree, both would have the same acceleration, but in opposite directions. There is no science behind the idea of equal and opposite accelerations cancelling each other. If two objects are gravitationally attractive and have equal accelerations in opposite directions, they collide! Dolphin(t)00:47, 24 March 2011 (UTC)[reply]
I think the problem here is the common misconception of action and reaction forces "cancelling" each other out. That isn't the case. When an object gravitationally pulls on another object, the reaction force is that second object pulling back on the first object. The end result is the exact same - the two objects accelerate toward each other and collide. 99.236.18.156 (talk) 01:25, 24 March 2011 (UTC)[reply]
Also, it's only your perception that the apple is the one object "falling", because you're sitting on the ground and the apple looks so small compared to the earth. As far as you perceive, "you and the earth" could be very light and falling towards a massive apple composed of white-dwarf matter. It's all about your frame of reference regarding relative motion of the apple. DMacks (talk) 09:09, 24 March 2011 (UTC)[reply]
I thought that acceleration was absolute? In other words, it really is the case that the apple is accelerating much more than the Earth, not just one's perception... 109.153.232.142 (talk) 18:43, 24 March 2011 (UTC)[reply]
It's true that proper acceleration is absolute. For example, if there are two rockets in deep space that are approaching each other at an accelerating rate due to one of the rockets having its thrusters on, it's possible to perform a local experiment (an experiment involving only short distances and times) to determine whether you're on the rocket with its thrusters on, or on the rocket that's coasting. Indeed, the experiment is trivial; you don't really even need an accelerometer: If you're pressed up against a surface of the room you're in, then you're in the accelerating rocket, but if you're floating around in your room, then you're in the coasting rocket.
However, gravity does not involve a proper acceleration, because gravity in reality is a fictitious force. Regardless of whether you're in a room attached to the apple, or in a room at the center of the Earth, you're just going to float around in the room, because you aren't undergoing any proper acceleration either way. (If you're in a room attached to the surface of the Earth, then you will be pressed against the floor, but that's because you're undergoing a proper acceleration upward due to the non-fictitious intermolecular forces the floor is imparting to the bottoms of your feet, that prevent your comoving frame from being an inertial frame of reference.) Red Act (talk) 22:11, 24 March 2011 (UTC)[reply]
What's striking about that page, and the "Physiological issues" section in particular, is how monumentally bad it is. I don't see one claim regarding the physiology of sex in that section that is supported by a reliable source. There are a few statements about rodent development in microgravity that have some support, but that's not the subject represented by the title. -- Scray (talk) 04:22, 24 March 2011 (UTC)[reply]
I saw a science program on TV that considered this. One thing they suggested was a sort of hammock, but with a top on it too, so the parties involved wouldn't float away from each other. Then there's the hygiene issue, with bodily fluids floating around. StuRat (talk) 05:04, 24 March 2011 (UTC)[reply]
I cheated flagrantly on this one and clicked-through the original image to find out it was taken in Malaysia. Searching Google Images I decided it looked like a Malaysian Bay Owl. Searching that term, I got back to the original image which says that it is "Taken in Bird Park Penang, Malaysia. Oriental Bay Owl (Phodilus badius). Thanks bubo_strix for ID." ... which is a wrap --- provided bubo_strix is the right person to copy off of at exam time ;) Wnt (talk) 03:37, 24 March 2011 (UTC)[reply]
: Cheated?? No you didn't, you thought it through and used a successful strategy to achieve the goal and attributed the image. No one was hurt, humiliated or robbed. Contrary to some people's opinion this is not a competition arena. Well done! Richard Avery (talk) 08:11, 24 March 2011 (UTC)[reply]
Well, I cheated in the sense that I didn't learn anything about the taxonomy of owls, and if I see another photo like this that doesn't offer more information on click-through, I'll be clueless.
Hi. In this page, there is a simple "derivation" of time dilation with 2 identical clocks - one in a rocket and one in lab (with both being observed from the lab). My question is: wouldn't length contraction cause the lab to observe the length of the clock (L) to be different in the moving rocket than the clock in the lab? That derivation assumes that the length (according to the lab) doesn't change. Is that true? 163.202.48.108 (talk) 10:19, 24 March 2011 (UTC)[reply]
If I'm interpreting the diagrams correctly, the 'clocks' in each frame (lab and rocket) are both oriented perpendicular to the direction of the rocket's travel. The Lorentz contraction only occurs in the direction of travel, so the clock doesn't get narrower. TenOfAllTrades(talk) 13:17, 24 March 2011 (UTC)[reply]
Few months ago, I received an ore from my uncle, who is geologist. He claims that the ore he gave me is sperrylite (platinum arsenide). The ore looks somewhat golden-gray in colour, while many samples on the internet is silvery white. This make me curious.
Thus I conduct some experiment, the other possible ore that look like this is pyrite, but it is much more golden. When I put in in hydrochloric acid, it produce few tiny bubbles and change the hydrochloric acid to slightly yellowish in colour. If it was pyrite, I expect it to bubbles more.
So I decided to show the ore's photo here and hopes wikipedians will help me identify it better.
And ends my curiousity. The picture of the ore and its streak can be viewed here,in my blog:
Wikimedia Commons has media related to Sperrylite.
I do not have equipment to find its specific gravity,but with porcelain streak plate (which I use bottom of my porcelain crucible) it did produce black streak,the picture of it can be viewed at my blog.So,does this confirm the material I have is sperrylite? —Preceding unsigned comment added by 175.140.146.69 (talk) 13:24, 24 March 2011 (UTC)[reply]
As Chris.urs-0 says it would be good to check the hardness, if it is Sperrylite you would expect it to be able to leave a scratch on a penknife blade. Mikenorton (talk) 13:48, 24 March 2011 (UTC)[reply]
Also did your uncle say where it came from? If someone gives me a lump of something to identify (half the time it's a lump of slag), that's the first question that I ask. Mikenorton (talk) 14:06, 24 March 2011 (UTC)[reply]
Sperrylite has a specific gravity of 10.6 - roughly the same as lead - so dense that even without proper equipment it should be possible to make a rough estimate that rules it in or out. Just measure the ore like a block, in three dimensions, and compare the volume that gives you to its weight. If this crude estimate comes in around 7 or higher, then it's not galena, and you know it must be something good.
Suppose an earthquake is about to happen that would release X joules of energy. We trigger the earthquake prematurely by detonating nuclear devices with total energy Y, with Y much less than X. Is there any way, even in theory, for the resulting earthquake to release much less than X joules of energy? Or will the released energy be closer to X-Y? --140.180.18.11 (talk) 17:21, 24 March 2011 (UTC)[reply]
Some seismologists have suggested that the common occurrence of foreshocks before many large earthquakes (about 70 % for M>7 events) suggests that they are part of a preparation process in which a series of smaller earthquakes (which would be similar to the nuke in your question) form a sort of cascade continuing until the mainshock is triggered. However many foreshocks seem instead to be just indicators of the enhanced stress levels that eventually trigger the mainshock, this is supported by an observed relationship between the rate of foreshocks and the rate of aftershocks. In this case the foreshocks (or any other source of energy) do nothing to trigger the mainshock. Mikenorton (talk) 17:44, 24 March 2011 (UTC)[reply]
In my lifetime, seismologists seem to have become less certain about the possibility of precise earthquake prediction. How would you know where to do your nuclear detonations? HiLo48 (talk) 17:50, 24 March 2011 (UTC)[reply]
The nearest peak is Evans Peak, almost completely obscuring Alouette Mountain - check it out on google earth (which is what I did), the shape is distinctive. Mikenorton (talk) 20:28, 24 March 2011 (UTC)[reply]
Body heat sun's heat
Is it true that the human body produces more heat than an equivalent volume of the sun's matter. As Dr. Al Khalili states. Sounds improbable. Phalcor. — Preceding unsigned comment added by Phalcor (talk • contribs) 20:23, 24 March 2011 (UTC)[reply]
I think that would depend on what part of the sun. At the core, I don't think so: 150 g/cm3 at 13.6 million kelvin. At the corona, however, it may reach similar temperatures, but it so thin that the same volume will actually contain less overall heat than the human body. --T H F S W (T·C·E)20:29, 24 March 2011 (UTC)[reply]
Yes it's true. The sun is very dilute - but enormous. Take a look: power per mass for sun = 1.934×10^(-4) W/kg power per mass for human = 1.6 W/kg. (A human outputs an average of 100 Watts per day[7]). A human can put out 8,000 times more power than the sun - and that's a resting average. At peak power a human can do about 9 times as much, so 75,000 times as much as the sun. But the sun is absolutely stupendous in total mass, so even as dilute as it is it puts out a huge amount of power. Also, be aware that all the power in the sun is generated in the core, so calculating just in the coregets 0.0088 W/kg (at most), which is still tiny compared to a human. Ariel. (talk) 20:36, 24 March 2011 (UTC)[reply]
As above, depending on what you mean, it's plausible. The sun's output is about 4*1026 J/s, whereas a human's output is around 100 J/s (assuming about 2500 kcal fully converted to heat -- it's probably wrong, but I don't think it's orders of magnitude wrong). The sun is about 1027 m3 in volume, a human about 0.1 m3 (all numbers from Google searches). Dividing those pairs of numbers, the sun radiates 0.4 J/sm3 while a human radiates 1000 J/sm3. So humans are stupendously more heat-producing per unit volume! Well, if you compare a human (where all of the volume is producing heat) with the sun (where only a small portion -- the core -- of the sun is actually producing heat). I've little doubt that the numbers would swing if restricted to the portions of the sun where fusion actually occurs. — Lomn20:39, 24 March 2011 (UTC)[reply]
I just added numbers from only the core to my reply above. And they are so small I wonder if we can ever make fusion power work! The sun's core has a density 100 times that of water, and yet produces power so slowly, how can we hope to beat it? Ariel. (talk) 20:52, 24 March 2011 (UTC)[reply]
The reaction that happens in the sun is different from the reaction that happens inside a fusion power plant. The sun fuses Hydrogen. A power plant fuses deuterium and tritium. Dauto (talk) 22:53, 24 March 2011 (UTC)[reply]
One minor thing: you're listing power per mass rather than power per volume -- adjusting that, the human body only has a 2:1 edge. Not quite the swing I was expecting, but back into the realm of cautionary notes about back-of-the-envelope calculations. — Lomn21:17, 24 March 2011 (UTC)[reply]
Just one last crazy thought on this subject. If we could find a way to artificially duplicate the heat production efficiency of the human body in a machine, perhaps we would have an efficient power plant. Comment not seriously expected. Phalcor (talk) 21:29, 24 March 2011 (UTC)[reply]
As far as I know nuclear reactors do not have iodine or even iodide in them. So how has the Japanese nuclear disaster resulted in radioactive iodine in tap water? How did it get there, where did it come from? Thanks 92.24.188.210 (talk) 20:50, 24 March 2011 (UTC)[reply]
BTW, Iodine-131 has a half life of only 8 days, so the damage will be limited. The other main product is Cesium-137, which lasts a lot longer, but unlike iodine has no biological role, so is not stored by the body. Ariel. (talk) 20:57, 24 March 2011 (UTC)[reply]
If it has a short half-life, that means it gives off all it's radiation in a short period, making it even more dangerous if it's in your thyroid during that period. Also, if it causes DNA changes, those could then take years to progress into cancer. StuRat (talk) 23:09, 24 March 2011 (UTC)[reply]
Our article on 137Cs says that it does mimic potassium...it's not stored (highly incorporated into biochemical/biophysical structures) but it sure does pass through lots of pathways before clearing (which takes several months). DMacks (talk) 21:26, 24 March 2011 (UTC)[reply]
The main difference is that the radiation from cesium is spread out in the body, rather than concentrated in the thyroid, so it's far far less harmful. (The body can handle low levels of radiation, but the concentrated radiation from iodine in the thyroid causes more harm than would be expected by the low dose.) Ariel. (talk) 22:27, 24 March 2011 (UTC)[reply]
Yah, although probably not for the water in Tokyo. It's yield in reactors is low (about 1/3 of I-131), it's half life is so long that it's not very radioactive - it's almost 1 billion times less radioactive than I-131, and when it does decay the decay energy is low and is less harmful (about 1/10 of I-131). Overall while I-129 is carcinogenic, I-131 has not been found to be[8]. (With a biological half life of 11 days to a few month, the I-131 is cleared out of the body before it can do much harm.) Ariel. (talk) 01:17, 25 March 2011 (UTC)[reply]
Thanks. What happens to the fission products when the reactor it working normally? Where do they go? Do they eventually end up in landfill, for example? 92.24.188.210 (talk) 21:16, 24 March 2011 (UTC)[reply]
Comet Tuttle is correct; the US doesn't do any civilian reprocessing of spent fuel. It was considered at one point but killed in the 1970s because of the security implications. (Inventory control is a very serious problem with reprocessing. In a large plant like the Rokkasho Reprocessing Plant in Japan, the amount of "material unaccounted for" is, no matter what you do, going to be on the order of several Nagasaki-sized bombs per year. That means you essentially cannot detect theft or diversion through inventory control alone, which is rather unsettling. This isn't a matter of building better instruments — there is some inevitable loss in the process that you cannot account for, even at best times, and that adds uncertainty in your ability to track it. It may only be 1-2% of lost material, but when that material is plutonium, "a dab'll do ya".) We don't even do waste disposal at the moment. Things are stuck in a really horrible political/legal/technical situation and there has been little progress so far. There is currently a Blue Ribbon Commission that is supposed to be figuring this out. Good luck to them. --Mr.98 (talk) 00:54, 25 March 2011 (UTC)[reply]
In the US, they stay in a swimming pool there at the reactor, for at least 5 to 20 years (see spent fuel pool), then they may stay in the pool forever, or may be pulled out and put into dry cask storage. The Yucca Mountain plan was formed because there was no US national policy to deal with spent nuclear fuel. As the Yucca Mountain article states, the US still has no functioning policy; it's sort of cut off or suspended at the moment, and court challenges are ongoing. Comet Tuttle (talk) 22:14, 24 March 2011 (UTC)[reply]
Highly radioactive fission products have short half lives, and decay relatively quickly into more stable things. So your immediate waste is very hot, but after a year or five in the spent fuel pool, they cool off pretty considerably. The problem is that the "more stable" things are still radioactive — and because they are more stable, they stay that way for thousands of years. But the stuff that ends up in the waste site (in countries that actually have waste sites) is not as "hot" as the stuff that comes right out of the reactor, or is stored in the spent fuel pool. --Mr.98 (talk) 00:54, 25 March 2011 (UTC)[reply]
coriolis effect in deep space?
the coriolis effect on water down the plug hole due to the rotation of the earth seems easy to grasp, but when I look at Hubble deep space photos of spiraling/spinning galaxies, all of those I've seen seem,(from the telescopes view point) to be spinning in the same direction. Given the apparent random nature of the universe it seems that coincidence is unlikely. Could the universe, as a whole, be spinning, having the same effect on the galaxies? And if so, could that cause the red shift effect attributed to universal expansion. Phalcor (talk) 22:56, 24 March 2011 (UTC)[reply]
Water down the hole does not spin because of Coriolis.
It would be interesting to see numbers on how many galaxies observed are aligned with the Milky Way (or some other axis) vs. opposite to it. Wnt (talk) 00:02, 25 March 2011 (UTC)[reply]
I have encountered the following interesting light wave problem:
Two waves of light in air, of wavelength 612.6 nm, are initially in phase. They then travel through plastic layers as shown in figure below, with L1 = 4.07µm, L2 = 3.60µm, n1 = 1.41, and n2 = 1.56. In wavelengths, what is their phase difference after they have both emerged from the layers? Do not enter units with your answer.
The solution is almost correct but you are missing the fact that the two waves do not emerge from the plastic layers at the same position because the layers have different thickness. BTW, you are not deceiving anybody. We know that's homework. Dauto (talk) 03:46, 25 March 2011 (UTC)[reply]
