Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

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.

April 21

Big Bang-- free lunch?

What actually cuased the big bang to occur, and how did it know where to ocurr in the supposed previous nothingness. Also, whereabouts was this nothingness that the big bang exploded into? Are we all enjoying the ultimate 'free lunch'?--178.108.238.49 (talk) 00:24, 21 April 2016 (UTC)[reply]

Ah. If I could answer those questions, I would be the next Einstein.--Aspro (talk) 00:29, 21 April 2016 (UTC)[reply]

The Planck epoch is the limit of prediction. At least for now. Sagittarian Milky Way (talk) 00:38, 21 April 2016 (UTC)[reply]

Big_Bang#Speculations lists some theories, including brane cosmology. StuRat (talk) 01:44, 21 April 2016 (UTC)[reply]

A big issue I have with the Big Bang is that more and more stuff happens the further back you look. It gets ever hotter, ever denser the closer you go to the moment. So if you look at something like the logarithm of time, maybe that makes more sense as "true time" that things happen in than the non-logarithmic form we use, even though the normal form of course is proportional to specific physical processes. And if you look at time in smaller increments, then the velocity of anything less than lightspeed is less (same way as if you double a velocity, it never goes over lightspeed). And distances are greater, since that means light travels more increments of time to go between two given points. And particle lifespans are greater, and so forth. For much of the life of the universe it might even have had roughly the same size by that criterion. What you lose is the invariance of atom size - obviously, near the Big Bang they would be immense, the size of the universe even, but kept shrinking. So I continue to wonder, if you look at the universe in this sense, can you see it as something with an infinite history, and potentially a warm future (though one with really teeny atoms with generally very short half-lives!)? In any case, it illustrates the notion that you may simply not have a continuum of time going before the Big Bang at all. Wnt (talk) 01:53, 21 April 2016 (UTC)[reply]

I would not rule out the possibility that time itself was created at (near?) (just before?) the beginning of the big bang, and that the concept of "before the big bang" has no meaning. I also would not rule out the possibility that the answer to the ultimate fate of the universe question involves time itself ending. When dealing with the unknown, it is risky to rule out anything without a sound reason for doing so.

Well, using log time sort of changes how you view the later eras also. Maybe in the cold dead corpse of the cosmos, as commonly portrayed, it takes a billion years for the same amount of stuff to happen as happens in a nanosecond today. And the universe is larger by about the same proportion. But if you use a correspondingly larger unit of time, then the universe seems about the same size with the same amount of stuff happening. It's just that it's a universe where atoms have gotten really tiny and their transitions absurdly high in energy, whereas maybe a thermal neutrino seems about the right size and stability for interesting chemistry to occur (I don't know this!) Wnt (talk) 22:39, 21 April 2016 (UTC)[reply]

"In the beginning, God created the heaven and the earth." That sounds like Bible mythology, but it's also as much as we know, or think we know, about the start of the Big Bang. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:02, 22 April 2016 (UTC)[reply]

Exactly. What I want to know is: where was He sitting when he did the creation?--178.108.238.49 (talk) 16:49, 22 April 2016 (UTC)[reply]

Do we know how much speed can have voyage in large scale structure?

(I can not surely be back)49.135.2.215 (talk) 01:52, 21 April 2016 (UTC)Like sushi[reply]

It's difficult to understand this question, but I think you may be asking what the speed of galaxies and such is in the universe. Is this what you meant ? StuRat (talk) 01:55, 21 April 2016 (UTC)[reply]

I don't understand the question, but the maximum speed is 299 792 458 metres per second.--Shantavira|^{feed me} 07:41, 21 April 2016 (UTC)[reply]

See plane and train speeds. As the Atmosphere of Earth is essential in higher sppeds the gases of the atmosphere behave more and more like You know from walking trough water. Higher speed is a question of costs for safety and energy. By saving energy the wrong way, people begin to save the brain usage, ending up in failed staates or any primitive dictatorship. Successful digging for oil caused wealth and education became a minimum standard. Before plastic was invented, workers found out a lead battery built in a glas container works better when sunlight is applied trough it's glas container. It took 140 years until a solar cell was built. Missing in the Wikipedia, in 1985 the German ICE 1 reached 406 kmph (= 252 mph) [1] (On board the test drive Heinz Riesenhuber). In the German railway system the tunnels of the rails in pairs were not separated per direction, causing a speed limit to 250 kmph (= 155 mph). The high air pressure of oncomming trains inside tunnels is able to derail the trains. The first TGV world speed record was 9 years before, all superseded by Shinkansen. Another invention to save destrubing sideeffects and unneccessary material waste on high speed trains was made by Talgo. The American speed limit on highways is set to an optimal number of vehilces per time. Higher speeds increase the safety disdance causing less vehicles per time, slower seeds are jamming a pulk of vehicles. In 1999 Japan brought the fuel efficent car on the road. With increasing costs of energy, supersonic speed passenger planes were not longer used. Another incident to this decission was an unqualified maintainance arround Air France Flight 4590. --Hans Haase (有问题吗) 17:48, 23 April 2016 (UTC)[reply]

"relativity" would, behave relative to another, but absolute to oneself.

inbetween light cone and gravity cone...

where gravity doesn't work... 49.135.2.215 (talk) 01:31, 26 April 2016 (UTC)Like sushi[reply]

Pathfinder question(s)

Two related questions: (1) At what distance is the angular size of a common wrought nail-head (or a common house-fly) equal to 1 minute of arc? (2) What is the group size of a Kentucky rifle at 100 yards? (Question(s) inspired by Fenimore Cooper's novel The Pathfinder, or more precisely by Mark Twain's criticism thereof.) 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 07:25, 21 April 2016 (UTC)[reply]

I rashly calculate the answer to question 1 as (roughly) 0.6 metres, based the formula in Minute and second of arc, group size = tan(⁠m60⁠) × distance, and presuming the fly is 10mm in length per Housefly, (Actually, google did the heavy lifting. --Tagishsimon (talk) 09:30, 21 April 2016 (UTC)[reply]

Wrong. About 20 meters. More for a housefly or very large nail that's over 6 millimeters. Sagittarian Milky Way (talk) 20:41, 21 April 2016 (UTC)[reply]

So, how far away can a person see a common wrought nail-head (or housefly), allowing for hyperacuity? 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 10:02, 21 April 2016 (UTC)[reply]

I don't know how big a common nail head is but if we say 8 millimeters then possibly under 100 yards (~18 seconds of arc). Sagittarian Milky Way (talk) 20:51, 21 April 2016 (UTC)[reply]

In answer to your Kentucky rifle question, this source says "about the size of a half-dollar". Alansplodge (talk) 10:09, 21 April 2016 (UTC)[reply]

Thanks, Alansplodge and Sagittarian! So, another instance of Twain's criticism being misplaced -- Hawkeye actually could see the nail at that distance, and while he could not hit it repeatedly as described in the book, he could cluster the shots in a nickel-sized area centered on it -- so Cooper exaggerated, but not by a whole lot (definitely well within the limits of legitimate hyperbole). 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 22:40, 21 April 2016 (UTC)[reply]

Does gravity slow down time sundial clocks?

I read that a clock on the top story of a skyscraper will tell time a little faster than a clock on the ground floor, because gravity slows down time, as Einstein’s General Theory of Relativity predicted. My first question is how can you tell that one clock is going faster than the other, as all local clocks will be affected by gravity?

My main question has to do with sundials. I am wondering if gravity would affect one sundial differently to another, that is, one sundial on the top floor, and one on the ground floor. Wouldn’t they both tell the same time, unlike the mechanical clocks next to them? Myles325a (talk) 07:40, 21 April 2016 (UTC)[reply]

The sundial at ground level will be fractionally behind the one at height - because the light from the sun will have taken very slightly longer to reach it. The difference, of course, will be way to small to be observed on something as inherently inaccurate as a sundial. 81.132.106.10 (talk) 09:57, 21 April 2016 (UTC)[reply]

It seems likely that any miniscule difference in the light would be overwhelmed by any small difference in positioning of the two sundials. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:00, 22 April 2016 (UTC)[reply]

Good question! This is in general an example of the difference between the local time and the time as determined from some external reference. No matter how massive the planet and how close you are to it, the sundial of course still goes around once a day. But ... the time dilation from being in heavy gravity is still real. So the day itself must appear shorter from the perspective of the person near the planet! In much the same way, the days of other planets, the years of other planets, the periods of pulsars etc. all have to seem shorter. The key to trying to understand this is redshift/blueshift - as we perceive the light from deep in a gravity well, it is like a recording with all the playback sped up. And the reason for that is because, even though in a Newtonian sense we seem to stay the same distance from the sun, in relativity gravity is acceleration and we really are constantly being accelerated toward all the external sources of light! So we are constantly getting ahead of our default rest position of where we would be relative to the light if we were falling. (It is about at this point where my intuition has yet to be led...) Wnt (talk) 11:54, 21 April 2016 (UTC)[reply]

To tell if two clocks are running at the same rate, you will have to do a time transfer. You could send the time by pulses or data using an electromagnetic means, eg on an optic fibre or a radio wave. You could use network time protocol. Then at the other clock you could compare and see if the signal is getting behind or ahead. Another way is to first synchronise the two clocks at one place and then move one of them to the other spot, such as the top of the tower, and then later bring the clocks together. Graeme Bartlett (talk) 05:56, 22 April 2016 (UTC)[reply]

Another complication to the once a day rotation of the sun, is that a massive spinning object actually twists space along with it by frame dragging. For the Earth it takes hundreds of millions of years to bend the space a whole turn, but for spinning pulsars, this may be rotating space several times per second. Graeme Bartlett (talk) 05:56, 22 April 2016 (UTC)[reply]

Canadian geese that travel in pairs

I often see Canadian geese travel in pairs or fly in V formation (if they are in a group), but mostly travel in pairs. I read on Wikipedia that geese form monogamous couples for life or until one partner dies. Do these geese use any cues to determine their sex? As far as I can tell, they all look the same to me. Do they usually come in pairs with one male and one female, or is it possible to have a pair with two males or two females? If a same-sex pairing does occur, do they engage in same-sex sexual activity together? 140.254.229.116 (talk) 13:20, 21 April 2016 (UTC)[reply]

First, they are more properly Canada Geese. Any old snow goose might be Canadian (due to where it was born), but "Canada goose" is the name for what you're talking about, Branta canadensis if you want to use the scientific name. They have lots of ways to tell what sex the other is, including courtship behavior, sound, and yes, even visual cues. They may all look the same to you, but individual birds have subtly different markings. Here [2] is a study that shows young canada geese can recognize siblings when they are only a few days old. Here [3] is a study that shows that canada geese can distinguish individuals by vocal call. As for homosexual pairings: that's not uncommon in Canada geese. See List_of_birds_displaying_homosexual_behavior, with a reference for B. canadensis. Here [4] is a whole study of male-male homosexual pairings in a different goose. I couldn't find one specifically on Canada geese, but most waterfowl will exhibit some same-sex pairing, especially in captivity or when sex ratios are skewed. If you're interested in diversity of pairing and mating in the animal world, I suggest the book Evolution's Rainbow [5] written by Joan Roughgarden, one of the current leaders in the study of evolution of social behavior, courtship and sex. SemanticMantis (talk) 14:44, 21 April 2016 (UTC)[reply]

For understanding why you can't tell Canada goose apart, but they easily can, see Out-group homogeneity for the general concept. In simplest terms, the more unlike you a group of beings are, the less likely you are to be able to know what cues are necessary to tell one individual from another. This is not a problem for members of said group. --Jayron 32 18:11, 21 April 2016 (UTC)[reply]

As for travelling in pairs or in larger groups, they travel in pairs over short distances (often walking), while they form up into flocks for longer flights, during migration. StuRat (talk) 14:58, 21 April 2016 (UTC)[reply]

"They all look the same" is an anthropocentric statement. We are all trapped within our own sensory experiences, but these may not be the same as other organisms. Have a look (no pun intended) at the Bird vision article. Most birds are tetrachromic - they have a cone cell type additional to our own. This does not mean they simply see a few more colours, their whole visual perception is completely different to ours. This is especially true for birds that are visually UV-sensitive (afraid I don't know about this for Canada Geese]]. Their visual perception of the world is likely to be entirely different from our human experience. So, it is extremely unlikely they see the same homogeneity we humans do. DrChrissy ^(talk) 21:40, 22 April 2016 (UTC)[reply]

However, genders of some animals do look far more alike than others. There are dramatically different sizes, like a queen bee versus a drone, and there are very different coloration patterns, like a mallard drake versus female (hen ?). Some look so much alike that they can fool each other, like some male cuttlefish which pretend to be females so they can approach other females without having to battle larger males. StuRat (talk) 17:19, 23 April 2016 (UTC)[reply]

Yes, and male cuttlefish can display as a female on one side of their body while displaying aggression to other males on the other side of their body. Two-faced (but very clever) buggers, I say! DrChrissy ^(talk) 17:33, 23 April 2016 (UTC)[reply]

Seismology patterns today

Well Ive been reading about increased seismic activity the last couple of years and, while no scientist by training, how does this stack up? Is there a source somewhere to indicate the average number/intensity/depth of tectonic movements?

also most earthquakes happen, obviously, beside plate boundaries, but why is there this outlier in OK? Is it increased fracking that I heard about? Also Hawaii is slap bang (or thereabouts) in the middle of the most volatile plate, how does it, then, get that activity (volcanoes yes but earthquake)?

Finally, is their a real time source for volcanic activity like the above for earthquakes.Lihaas (talk) 15:46, 21 April 2016 (UTC)[reply]

Sorry, this is very important, so please excuse the bold type: Yes, fracking and associated fluid injection can cause earthquakes, and is the causal agent for the recent sharp increase in earthquakes in OK. See this clear headline [6] saying "Injection wells blamed in Oklahoma earthquakes". See also this [7] 2013 review article published in Science, this [8] article looking at how to cope, and this [9] general assessment of fracking impacts, including pollution, global warming, earthquakes, etc. There's no dispute - fracking is bad for almost everything, except exploiting previously inaccessible petrochemical resources. SemanticMantis (talk) 16:35, 21 April 2016 (UTC)[reply]

I would say that fracking induces ~~triggers~~ earthquakes, as opposed to causing them. They are still caused by plate movements, it's just that fracking might trigger them earlier than they would have happened without it. Note that while only small earthquakes have been triggered so far, larger quakes are possible, too. StuRat (talk) 16:46, 21 April 2016 (UTC)[reply]

I am no seismologist, so I will defer to the fine folks at Science on this one. They say "Sharp increase in central Oklahoma seismicity since 2008 induced by massive wastewater injection" [10] -emphasis mine. Our friends at wiktionary say "induce" means "To cause, bring about, lead to" [11]. So you can say what you want, but I'll go with the experts here. Put another way: If your nemesis pushes you off a tall building and you plummet to your demise, feel free to blame gravity as your cause of death. Me, I'd say it was the one who pushed you. See also Proximate_and_ultimate_causation. SemanticMantis (talk) 17:05, 21 April 2016 (UTC)[reply]

Example: A poured pile of sand will end up stable until it's getting soaked with water.--TMCk (talk) 17:16, 21 April 2016 (UTC)[reply]

Comment regarding terminology: induced seismicity is a thing, and triggered seismicity is a different thing; if you read the scientific literature, these are not the same. When reputable scientists write about this topic, they use the word "induced" to refer to seismic activity caused by human activity. (Well, sometimes even scientists munge the terminology, too; for example, I used to hang around at the Center for Induced and Triggered Seismicity - and they have something to say about what's behind the earthquakes in Oklahoma!). Here is a website published by USGS: Induced Earthquakes, which will help introduce the topic. Nimur (talk) 17:51, 21 April 2016 (UTC)[reply]

OK, I changed the word in my post, but my point remains the same. StuRat (talk) 18:44, 21 April 2016 (UTC)[reply]

A doctor can induce pregnancy without having planted the seed himself, though I wonder if an angry husband has ever misunderstood this point. :) Wnt (talk) 22:43, 21 April 2016 (UTC)[reply]

"Doctor, you say I'm pregnant, but can you make sure ?" "Of course I can, but that might make your husband jealous." StuRat (talk) 14:27, 24 April 2016 (UTC) [reply]

To directly answer the question about a "real-time source" of information on volcano activity:

One resource is the Alaska Volcano Observatory, operated by the University of Alaska, Fairbanks, in conjunction with the US Geological Survey. It principally monitors Alaskan volcanos; but they have a fascinating "mission control"-style room with a lot of experts and researchers who tend to pay attention to any activity worldwide.

Another great resource is the Hawaiʻi Volcano Observatory, which principally monitors the active volcanos in the main island of Hawaii. Both of these facilities have great websites and link to several other facilities of the US Geological Survey, among many other worldwide agencies.

If you should ever find yourself in Fairbanks, the AVO is sometimes available for tours. The Geophysical Institute coordinates activities and has special sessions geared towards physics researchers and for the generally-interested public.

The Hawaii Volcano Observatory has a public museum inside the Hawaiʻi Volcanoes National Park. Depending on your visit, the volcano activity may be observed remotely from that station - they have telemetry, video links, and loads of scientific data, much of which is also available at no cost via the internet at the park service's website and the Geological Survey's website; if weather and geological conditions are safe and legal, you can even get down to the lava flows.

As I live in an active seismic zone, and frequently find myself traveling unpleasantly-close to active volcanos, I keep the Earthquake Hazards Program website in browser's bookmarks so that I can check it daily. When there is notable volcanic activity, it is frequently accompanied by other seismic activity, and the earthquake page usually makes a note of it.

Nimur (talk) 17:45, 21 April 2016 (UTC)[reply]

Thanks yall.

Was also wondering about the first question, is there a general sudden trend in activity?Lihaas (talk) 18:07, 21 April 2016 (UTC)[reply]

Not globally - like other random events, earthquakes tend to come in clusters, giving the impression of greater activity at certain times. If we're talking about induced seismicity, then if somebody starts to carry out deep wastewater injection on a large scale, you can expect small (and potentially moderate) earthquakes to follow. This effect has been known about for many years, ever since the Denver earthquakes[12]. Mikenorton (talk) 18:17, 21 April 2016 (UTC)[reply]

Classical momentum problem

Hello, I'm a first year physics student with no formal education on relativity, so forgive me if a fallacy in this problem involves using classical physics to solve it. This was just a thought that came to me when learning about modern physics (i.e., momentum and energy of light). Consider a beam of light being shone in the positive x-direction towards a mirror far away in space, isolated from any other body. The light beam has a momentum ${\vec {p}}={\tfrac {h}{\lambda }}{\hat {i}}$ , and the mirror is at rest. Say that the light beam (which I can consider a photon) has an elastic collision with the mirror, and rebounds with momentum ${\vec {p}}=-{\tfrac {h}{\lambda }}{\hat {i}}$ . The change in momentum for the photon is thus $\Delta {\vec {p}}=-2{\tfrac {h}{\lambda }}{\hat {i}}$ , and since the system is isolated, we would expect the mirror to end up with a momentum of $-\Delta {\vec {p}}$ . Yet, since the collision is elastic, then the change in (kinetic) energy is conserved, and since the energy of a photon is $E_{\gamma }=hf=\|{\vec {p}}\|c$ , we have $K_{M}+E_{\gamma }=E'_{\gamma }+K'_{M}$ . However, the kinetic energy of the photon did not change (frequency should still be the same, and it is still moving at the speed of light), implying $K_{M}=0$ , which means that despite gaining momentum, the mirror is still at rest! This seems to violate the conservation of momentum to me; the mirror did not gain speed, and it couldn't have gained mass... What's wrong here? Thanks for the help! 70.54.113.74 (talk) 19:15, 21 April 2016 (UTC)[reply]

The assertion that the photon's frequency is is unchanged is only correct if the mirror stays perfectly at rest. However, in reality it starts to move a little bit because of the collision, and therefore the frequency (and thus energy) of the photon changes due to the Doppler effect. - Lindert (talk) 19:29, 21 April 2016 (UTC)[reply]

(edit conflict) You are doing pretty well, but you messed up one of your assumptions. In a classical elastic collision (not involving light) you assume that energy and momentum are conserved and then solve for the two final velocities. In your case, you should assume that energy and momentum are conserved, and then solve for the final velocity of the mirror and the final frequency of the reflected photon. The rebounding photon only has the same energy is the mirror is infinitely heavy. For a normal mirror it transfers some of its energy to the mirror and hence the reflected photon is (slightly) less energetic than the incident one. Dragons flight (talk) 19:38, 21 April 2016 (UTC)[reply]

This is called Compton effect. The only difference is that the "particle" here is the mirror. Ruslik_Zero 20:10, 21 April 2016 (UTC)[reply]

If a person who got an orchiectomy has an extra testicle (with an epididymis), then can this person's vas deferens recanalize and restore fertility?

As in, recanalize (grow back) and attach itself to this person's extra testicle and epididymis.

Also, Yes, this is certainly a completely serious question; after all, there certainly *are* people who have *more than* two testicles:

Polyorchidism. Futurist110 (talk) 20:20, 21 April 2016 (UTC)[reply]

Our article on vasectomy cites this source that says that 1/2000 of the time the vas deferans can reconnect. I did not access the full text to see whether this is by the ends finding each other or by some other means. It is at least conceivable but astronomically unlikely that an extra testicle that never had a vas deferans nonetheless forms some kind of fistula with the severed end of a vas deferans after orchiectomy. On the other hand, it is also at least conceivable that the surgeon cannot count to two! The problem with this line of questioning is that you're getting into areas where things are so unlikely and involve such unlikely circumstances there's almost no chance of finding empirical data about what happens, and in biology there's no data that is not empirical. It is entirely possible that the same genetics that causes polyorchidism has an effect on the rate of vasectomy failure, for example, but nobody knows, because only a few people with polyorchidism ever had vasectomies and none of their doctors got together to do a study. Wnt (talk) 22:54, 21 April 2016 (UTC)[reply]

I mostly agree with Wnt here. In fact, the likelihood that the surgeon would simply screw up and not disconnect the other testicle was something I was thinking of to your earlier question before anyone replied. (In particular, I was thinking you could do either an ultrasound or MRI, but the technician who does the scan could make a mistake so this doesn't given a guarantee. And in fact, the bigger advantage to having the scan would likely be in detecting such screwups. Admitedly I didn't think until now that if it was from a twin, there is question whether you should really be considered the father anyway.)

Notably while I gave several scenarios which I said would be very unlikely, I didn't mention other scenarios which came to mind but weren't particularly related to your question. E.g. perhaps there is someway a testical from a parasitic twin could produce functioning sperm that would somehow end up fertisiling an ovum which will survive until birth. However there's probably also theoretically some way functioning sperm from a removed testical could accidential end up fertilising an ovum. Or for that matter, if a person has ever released any sperm (which if they're past puberty they surely have), that these sperm have somehow end up fertilising an ovum. These are possibly less likely than your latest question but I'm not sure.

The point is there are no guarantees and once you start to look at very unlikely possibilities, you should consider there are surely many that you have missed. It makes far more sense to accept a resonable risk level. (P.S. I'm mostly assuming accidental cases here. For non accidental cases you could come up with many possibilities of how you can be a father even years after you're dead. Particularly if we include the likelihood we could one day produce sperm from any somatic cells. Actually I thought there was a case where it was claimed that conception only happened years after sex, but I can't seem to find this so most likely either I'm remembering wrong or the evidence this really happened was slim. So I'll leave years after out of my non accidental examples.)

Nil Einne (talk) 16:15, 22 April 2016 (UTC)[reply]

What's with the red displays in front of buses now appearing in NYC?

I see from The Real Hustle that the UK has similar buses. I find the letters displayed hard to read. Not sure whether my slight red-green color blindness is a factor. But surely there's a more pleasant color out there? 69.22.242.15 (talk) 22:19, 21 April 2016 (UTC)[reply]

Do you mean this?

Those are orange. Sagittarian Milky Way (talk) 23:15, 21 April 2016 (UTC)[reply]

Specifically, by "display" do you mean the destination sign (reading "M15 SOUTH FERRY")? As SMW says, it's orange. If you're red-green color-blind then you might not see that.

In my experience single-color LED signs of this type (not only on buses but in other places) are most often orange, although when they were a new thing, red was common. I just did some Google searches to try to find out why orange is so commonly preferred, but couldn't find anything. I think it's safe to say that most people find it more legible than red, and maybe it's just cheaper than another color such as white or green. --69.159.61.172 (talk) 04:37, 22 April 2016 (UTC)[reply]

Among hobbyists, red and green and yellow are typically the "cheap" LEDs while blue and white are typically considerably more expensive, for the equivalent "type" at least. I think yellow is simply the most visible and least "unpleasant' out of the cheap ones, I think green and red are unnecessarily saturated and more contrasted than yellow. Vespine (talk) 04:52, 22 April 2016 (UTC)[reply]

For whatever reason the subway train equivalent is red (

). At least there's only one symbol to hurt your eyes instead of many and there's no I, O, or 0 train to confuse with the 1 or each other. The signs on the side that say what train this is are big and yellow (

). The signs on the inside that say what train this is are also an easy color. Those signs also show the time (too infrequently) and current/next station both in red (

). This serves the purpose of making the easiest to read things the ones you've had many chances to see already and the hardest to get ones vital information. Sagittarian Milky Way (talk) 19:40, 22 April 2016 (UTC)[reply]

Thank you. 69.22.242.15 (talk) 20:10, 22 April 2016 (UTC)[reply]

Red/Green colorblindness means that you can't distinguish red from green - not that any of those colors are indistinguishable from a black background. SteveBaker (talk) 05:09, 22 April 2016 (UTC)[reply]

There's different types and degrees of red/green color blindness. See the article Color blindness: "Protans have difficulties distinguishing between ... red and green colors. ... Pure reds cannot be seen, instead appearing black ... protanomalous individuals are less sensitive to red light than normal. ... They also suffer from a darkening of the red end of the spectrum. This causes reds to reduce in intensity to the point where they can be mistaken for black." While deuteranomaly is more common than protanomaly, they're both considered red/green colorblindness, and protanomaly is still fairly common within the subset of people with red/green color blindness. -- 160.129.138.186 (talk) 22:33, 22 April 2016 (UTC)[reply]

Two Nostril questions

My Q is in two parts: a) Why do the human nostrils point downwards instead of forwards like lots of other anim,als?. b)I can breath freely using either nostril at the moment but some people say that nostril usage alternates from one to the other with one always blocked. Is that true if not/so, why/not?--178.108.238.49 (talk) 23:35, 21 April 2016 (UTC)[reply]

For question two, see nasal cycle which I found by going to nostril. Dismas|^(talk) 23:40, 21 April 2016 (UTC)[reply]

Thanks for that tidbit! Was a question from...someone...here a few weeks ago. DMacks (talk) 14:32, 22 April 2016 (UTC)[reply]

For question one: we stood up. - Nunh-huh 23:57, 21 April 2016 (UTC)[reply]

Regarding the down-facing nostrils, it is an evolutionary feature common to not just humans but all apes and Old World monkeys, see Catarrhini (as opposed to Platyrrhini, the New World monkeys). As such, this trait pre-dates bipedalism by millions of years. --Dr Dima (talk) 00:54, 22 April 2016 (UTC)[reply]

As to why this trait evolved we may never know, although people are always tempted to come up with "just-so stories" to explain the origin of various traits. One such just-so story is that humans have larger noses to warm up cold air or to filter out dust; yet proboscis monkeys have noses that would put any human to shame. --Dr Dima (talk) 01:04, 22 April 2016 (UTC)[reply]

Downward-pointing nostrils certainly making swimming less hazardous. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:51, 22 April 2016 (UTC)[reply]

Aquatic ape hypothesis talks about some human features that may be explained by humans spending a good bit of time in the water. Not a terribly well supported hypothesis, but interesting. Currently our article only mentions our noses briefly, and without reference. SemanticMantis (talk) 13:09, 22 April 2016 (UTC)[reply]

Note that gene pools of humans that evolved in colder climates have smaller nostrils, in general. This correlation implies that the cooling provided by breathing in and out air rapidly in not needed in colder climates, and may even be harmful. Downward pointing nostrils would similarly slow the rate at which air is inhaled, especially when moving forward quickly, as in running. This doesn't explain downward pointed nostrils in hot regions, though. Perhaps sand and dust avoidance plays a role there. StuRat (talk) 17:56, 22 April 2016 (UTC)[reply]

Will everything be the same as today some day in the future?

If time is infinite (not sure if it is), will the universe, some time in the future, be exactly as it is today? That is, many googolplex years from now. --Llaanngg (talk) 23:44, 21 April 2016 (UTC)[reply]

The universe is thought to be one of three universes. Closed, open or flat. A closed universe involves gravity being to high, and the universe closing in on itself to a singularity. An open universe involves gravity being too high, where the universe will keep on expanding forever making things really far apart (If memory serves me right observations which have led to the idea of dark matter make this less likely). A flat universe is one where in the future it would (correct me if I am wrong) stop expanding somewhere in the future and not contract. In any case, the only possible universe where the universe could be exactly like today is in a closed universe, which would invariably be different. So to give you a short answer, no. JoshMuirWikipedia (talk) 02:18, 22 April 2016 (UTC)[reply]

None of us will be around, so it's not possible for "everything" to "be the same". ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:49, 22 April 2016 (UTC)[reply]

Well, philosophically speaking there really isn't any very good reason why none of us will be around, apart from probability, but as time approaches infinity, even very low probabilities approach certainty. There isn't any very good reason why there couldn't be another universe where everything is exactly the same, except my hair is blond instead of brown. It might not be "THIS" universe, but "some" universe.Vespine (talk) 04:00, 22 April 2016 (UTC)[reply]

None of us will be around even a hundred years from now, never mind googolplexes of years from now. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:12, 22 April 2016 (UTC)[reply]

I sure hope you wont be around posting your useless bullshit here for evermore. --178.108.238.49 (talk) 20:17, 24 April 2016 (UTC)[reply]

Entropy says "No". The entropy of the universe increases over time - so it can never return to a previous state everywhere. However, if the universe is spatially infinite (which is possible) - then small regions might turn up with precisely the same configuration of matter and energy as occurred trillions of lightyears away and billions of years ago might occur. Infinity is a large number! There are only just so many ways that the matter and energy withing (say) a cubic parsec can be arranged - and while that's an ungodly large number - it's not even close to infinity. So there must be repetitions of many (indeed infinite) numbers of cubic parsecs of space. So that one of them should happen to be identical to the cubic parsec we happen to be occupying right this instant seems pretty much inevitable.

So I believe that if the universe is spatially infinite - then the same situation will repeat itself for some small-ish regions of the universe - but it's impossible for the entire universe to repeat, no matter how long it lasts. SteveBaker (talk) 05:03, 22 April 2016 (UTC)[reply]

To be clear -- barring some kind of physical reason e.g. cyclic time, the universe should not return to the same state. Even in infinite time, only an infinitesimal fraction of the infinite variations can be sampled. Whether a local region the size of a person or a room returns is harder to say. On one hand, you can say that there are only so many ways the atoms in a room can be positioned, and so each one will be achieved an infinite number of times on average. But ... who says the current state is average? Maybe the current state is infinitely unlikely, and we only see it because that's what we're looking at. (Like, if you pick a random real number from 0 to 1, it is infinitely unlikely it will be precisely .5, but if .5 happened to be your pick -which is as likely as anything else after all- you can go on from there) If you suppose that minor differences in the positions of atoms don't matter, you can say that some positions would have to be infinitely more likely than others for that to happen, but... we don't actually know that's not the case. Wnt (talk) 10:28, 22 April 2016 (UTC)[reply]

The only way to get out of the "There are infinite numbers of copies of you!" argument is to claim that the probability of the precise arrangement of atoms that is "you" is literally infinitely improbably - so then you have an infinity-divided-by-infinity answer for the number of copies of "you" that there are in an infinite universe. Clearly you can make that number come out to be anything you want...it can be anywhere from zero to infinity. What are the odds that it comes out to be precisely 1.000? It requires REALLY special reasoning for there to be only one copy of you in an infinite universe.

Then, of course, we don't need to have an exact copy of you as you are right now. There can be a copy of you that's identical except that the fingernail on the left pinky finger is 0.1mm longer - but everything else out to several parsecs is otherwise identical. There are VERY many variations on "you" that would be recognizably "you" and you have to argue that all of them are as improbable as the exact copy. This requires extremely special pleading!

Of course it doesn't matter that there are infinite copies of you because the odds are insanely low of any of those copies being inside the (infinitely) small bubble that is the "observable" universe - and if none of them are, then it's only a matter of philosophical concern. And, of course, the universe may very well be finite - which solves the whole problem. SteveBaker (talk) 20:50, 22 April 2016 (UTC)[reply]

To be clear, what I have in mind is that it might be infinitely improbable that any kind of life exists at all, or even interesting matter of the kind we see throughout the observable universe. (The latter case is sort of a "finite universe", in that it might be supposed that some 'local' phenomenon makes our particular part of the universe more interesting). The odds of us existing might be exactly zero - like picking .5 as your random number. But ... if you have as a starting postulate that that's what you picked, then you have one, and it's unique. Wnt (talk) 12:45, 23 April 2016 (UTC)[reply]

See Arrow of time and Entropy (arrow of time) for the current state of understanding of how time works. If you really want to get deep on the mathematics, Minkowski space and Geodesics in general relativity deals with time as a dimension with special properties, specifically that one can only travel along the time-like dimension in a single direction. --Jayron 32 13:17, 22 April 2016 (UTC)[reply]

there very possibly is a near identical copy of you around the place, see [13] As to the future - well I suppose it depends what happens to our universe or whether even if it lasts an infinite time there is a time after it. Dmcq (talk) 13:30, 22 April 2016 (UTC)[reply]

Eternal return is probably our most relevant article. Evan ^{(talk|contribs)} 14:03, 22 April 2016 (UTC)[reply]

But the universe can't last forever in it's present state because of entropy. Things will inevitably turn into a uniformly warm sea of fundamental particles - there is no "infinity" in time...only (perhaps) in space. SteveBaker (talk) 20:50, 22 April 2016 (UTC)[reply]

Things have never been more like they are today than they are now?--178.108.238.49 (talk) 20:13, 24 April 2016 (UTC)[reply]

April 22

Special relativity. Simultaneity 3

Question

Remark

According figures 31-38, 31-39 on pages 492-493 "Physics for the Inquiring Mind" (by Eric M. Rogers), before Lorentz contraction where must be situated clocks in ε' coach for correct observation of desynchronization? Like that : https://archive.org/download/feynmanlectures_631/160422072400.PNG ?

If yes, then we have next table:

ε' frame				ε frame
time coordinate	clock reading & x-coordinate			time coordinate	clock reading & x-coordinate
$t'=0$	$\theta _{(t'=0),self}^{[}=0$ $_{(x'=-L'/2=-{\tfrac {L/2}{\sqrt {...}}})}$	$\theta _{(t'=0),self}=0$ $_{(x'=0)}$	$\theta _{(t'=0),self}^{]}=0$ $_{(x'=L'/2)}$	$t=0$	$\theta _{(t=0)}^{[}=?$ $_{(x=-L/2)}$	$\theta _{(t=0)}=0$ $_{(x=0)}$	$\theta _{(t=0)}^{]}=?$ $_{(x=L/2)}$
$t'={\tfrac {L'/2}{c}}$	$\theta _{(t'=L'/2c),self}^{[}={\tfrac {L'/2}{c}}$ $_{(x'=-L'/2)}$	$\theta _{(t'=L'/2c),self}={\tfrac {L'/2}{c}}$ $_{(x'=0)}$	$\theta _{(t'=L'/2c),self}^{]}={\tfrac {L'/2}{c}}$ $_{(x'=L'/2)}$	$t=\tau _{1}={\tfrac {L/2}{c+u}}$	$\theta _{(t=\tau _{1})}^{[}=\theta _{(t=0)}^{[}+\theta _{(t=\tau _{1})}$ $_{(x=-L/2+u\tau _{1})}$	$\theta _{(t=\tau _{1})}=\tau _{1}{\sqrt {...}}$ $_{(x=u\tau _{1})}$	$\theta _{(t=\tau _{1})}^{]}=\theta _{(t=0)}^{]}+\theta _{(t=\tau _{1})}$ $_{(x=L/2+u\tau _{1})}$
				$t=\tau _{2}={\tfrac {L/2}{c-u}}$	$\theta _{(t=\tau _{2})}^{[}=\theta _{(t=0)}^{[}+\theta _{(t=\tau _{2})}$ $_{(x=-L/2+u\tau _{2})}$	$\theta _{(t=\tau _{2})}=\tau _{2}{\sqrt {...}}$ $_{(x=u\tau _{2})}$	$\theta _{(t=\tau _{2})}^{]}=\theta _{(t=0)}^{]}+\theta _{(t=\tau _{2})}$ $_{(x=L/2+u\tau _{2})}$
...
...				$t={\tfrac {L/2}{u}}$	$\theta _{(t={\tfrac {L/2}{u}})}^{[}=\theta _{(t=0)}^{[}+\theta _{(t={\tfrac {L/2}{u}})}$ $_{(x=0)}$	$\theta _{(t={\tfrac {L/2}{u}})}={\tfrac {L/2}{u}}{\sqrt {...}}$ $_{(x=L/2)}$
$t'=A$	$\theta _{(t'=A),self}^{[}=A$ $_{(x'=-L'/2)}$	$\theta _{(t'=A),self}=A$ $_{(x'=0)}$	$\theta _{(t'=A),self}^{]}=A$ $_{(x'=L'/2)}$	$t=B$	$\theta _{(t=B)}^{[}=\theta _{(t=0)}^{[}+\theta _{(t=B)}$ $_{(x=-L/2+uB)}$	$\theta _{(t=B)}=B{\sqrt {...}}$ $_{(x=uB)}$	$\theta _{(t=B)}^{]}=\theta _{(t=0)}^{]}+\theta _{(t=B)}$ $_{(x=L/2+uB)}$
Note 1. ${\sqrt {...}}$ means ${\sqrt {1-u^{2}/c^{2}}}$ . Note 2. $L'={\tfrac {L}{\sqrt {...}}}$ . Note 3. $\theta$ means readings of clocks of ε' coach. "[" means left clock according picture (hind), "]" means right end clock (front). $\theta _{self}$ means readings of clocks of ε' coach seen from ε' coach (frame). We neglect time needed light to reach eye (there are no observers).

Is table correct?

How to calculate $\theta _{(t=0)}^{[}$ and $\theta _{(t=0)}^{]}$ analytically?

https://archive.org/download/PhysicsForTheEnquiringMind/Rogers-PhysicsForTheEnquiringMind.djvu , page 492

Wikipedia:Reference_desk/Archives/Science/2016 March 18#Light path analysis and consequences

Wikipedia:Reference_desk/Archives/Science/2016 March 20#Null result of Michelson.E2.80.93Morley experiment extrapolation

Wikipedia:Reference desk/Archives/Science/2016 March 28#Special relativity. Derivation of formula

Wikipedia:Reference desk/Archives/Science/2016 March 29#Special relativity. Simultaneity

Wikipedia:Reference desk/Archives/Science/2016 April 4#Special relativity. Simultaneity 2

Wikipedia:Reference desk/Archives/Science/2016 April 10#Special relativity. Simultaneity 2.

37.53.235.112 (talk) 05:33, 22 April 2016 (UTC)[reply]

I think the image [14] does show the thought-experiment you're interested in. But it's not more correct than any other thought-experiment. You could observe the desynchronization (or rather different synchronizations) with the clocks in other locations.

I think the table is okay, but I only spot-checked it. It's similar to the last table and you filled that one out correctly.

One way to calculate

\theta _{(t=0)}^{[}

is to first write down

x'(\theta ^{[})=-L'/2

t'(\theta ^{[})=\theta ^{[}

and then use the Lorentz transform to get

t(\theta ^{[})

, and then set

t=0

and solve for

\theta ^{[}

. -- BenRG (talk) 06:50, 22 April 2016 (UTC)[reply]

Thanks. Using your suggestion I derive

$\theta _{(t=0)}^{[}={\tfrac {L'u}{2c^{2}}}$ ;

$\theta _{(t=0)}^{]}=-{\tfrac {L'u}{2c^{2}}}$ .

It works for $\theta _{(t=\tau _{1})}^{[}=\theta _{(t=\tau _{2})}^{]}$ , which was derived independently from statement that all reference frames are applied to single world.

But when left clock from ε' arrives to point x=0 , it must show same reading as clock from ε, which is also situaded in x=0. So we must have:

$\theta _{(t={\tfrac {L/2}{u}})}^{[}={\tfrac {L/2}{u}}$ .

Let's check:

$\theta _{(t={\tfrac {L/2}{u}})}^{[}=\theta _{(t=0)}^{[}+\theta _{(t={\tfrac {L/2}{u}})}=$

$={\tfrac {L'u}{2c^{2}}}+{\tfrac {L/2}{u}}{\sqrt {...}}={\tfrac {Lu}{2c^{2}{\sqrt {...}}}}+{\tfrac {L{\sqrt {...}}}{2u}}={\tfrac {Lu}{2c^{2}{\sqrt {...}}}}\cdot {\tfrac {u}{u}}+{\tfrac {L{\sqrt {...}}}{2u}}\cdot {\tfrac {c^{2}{\sqrt {...}}}{c^{2}{\sqrt {...}}}}$

$={\tfrac {Lu^{2}+Lc^{2}(1-u^{2}/c^{2})}{2uc^{2}{\sqrt {...}}}}={\tfrac {Lu^{2}+L(c^{2}-u^{2})}{2uc^{2}{\sqrt {...}}}}={\tfrac {Lc^{2}}{2uc^{2}{\sqrt {...}}}}={\tfrac {L}{2u{\sqrt {...}}}}\neq {\tfrac {L/2}{u}}$ .

Why? 37.53.235.112 (talk) 12:02, 22 April 2016 (UTC)[reply]

I think you calculated both clock readings correctly, and they are indeed different. Here's a "Euclidean spacetime diagram" of the situation (later times on top):

   |    E    |
   |   /|   /|
   |  / |  / |  /
   | /  | /  | /
   |C   |/   |/
   A    O    B
  /|   /|   D|
 / |  / |  / |
   | /  | /  |

The unprimed clocks at A, O, B show 0, and the primed clocks at C, O, D show 0. If the clocks at E had the same reading, that would mean CE=OE, which clearly isn't the case. In Euclidean geometry,

CE/OE=\cos \theta

where

\theta

is the angle between the lines. In relativistic/Minkowskian geometry,

CE/OE=\cosh \alpha =1/{\sqrt {\cdots }}

where

\alpha

is the rapidity. -- BenRG (talk) 19:27, 22 April 2016 (UTC)[reply]

I don't understand such diagrams. Are lines t-axes or trajectories (world lines)? What do you mean about 'unprimed' and 'primed'. Why point C is above horizontal? I imagine this diagrame next way : https://archive.org/download/feynmanlectures_631/160423120000.PNG . So point C (where hind (left) moving clock shows 0) is below x-axis.

37.53.235.112 (talk) 10:16, 23 April 2016 (UTC)[reply]

Well, some calculations show that

\theta _{(t=\tau ) \atop (x=0)}^{[}=\tau

only when

u\to 0

. But it's very strange, as all moving clocks from ε' coach we believed were synchronized manually with middle clock of ε coach. So in few moments after synchronization of middle clocks none of clocks are synchronized.

37.53.235.112 (talk) 11:58, 23 April 2016 (UTC)[reply]

The lines are world lines. "Unprimed" means the ε coordinate system (or the clocks at rest wrt ε) and "primed" means ε'. "Prime" refers to prime (symbol). This is standard terminology.

My "Euclidean spacetime diagram" is not at all standard. The reason C is above A is that it's the Euclidean version of the problem, where the "moving" set of clocks is just rotated. I thought it would be easier to see in the Euclidean diagram that there's no symmetry that would make the clocks agree at E. OCE is a right triangle, not an isosceles triangle. -- BenRG (talk) 07:51, 24 April 2016 (UTC)[reply]

Flu shot...

I am having a hard time finding a reliable source for this one.. "How many people die from the flu shot every year?" Such a simple inquiry... unfortunately the prevalence of anti-vaxers on the internet is equivalent to the quantity of porn on the internet... I'm just curious as to how many actually DIE from it.. (If they died from the flu shot there is no way they would survive an influenza infection!) 199.19.248.20 (talk) 05:50, 22 April 2016 (UTC)[reply]

Death would most likely be from a severe allergic reaction I'd think, so they might have survived the flu itself. I'll see if I can find some numbers for you. EvergreenFir (talk) Please {{re}} 05:54, 22 April 2016 (UTC)[reply]

Closest thing I can easily find is VAERS. It's a reporting database of adverse events associated with vaccines. It does not indicate that death occurred because of the vaccine however. It allows you to specify the types of events, type of vaccine, date range, etc. EvergreenFir (talk) Please {{re}} 06:07, 22 April 2016 (UTC)[reply]

Assuming there have been people whose death has been attributed to the flu vaccination, the answer to the OP's question is that the number who die per year is a random variable. If the number who die every year is a random variable then there is no answer to the question "How many die every year". It might make some sense to ask "How many died in 2015" but asking how many die every year makes no sense. Dolphin (t) 11:39, 22 April 2016 (UTC)[reply]

Wouldn't an average be able to be given though? "An average of X number of people have died per year from Y over time span Z". Dismas|^(talk) 13:02, 22 April 2016 (UTC)[reply]

[15] is a study of the deaths reported to VAERS over a period of about 15 years. It doesn't only include deaths reported after having an influenza vaccine but does seem to provide some related statistics. They didn't detect any concerning pattern suggested that very very few, if any, of the deaths were caused by the vaccine but that obviously isn't a number. I didn't look in to the actual paper so I'm not sure if they attempted to estimate number of deaths actually due to the vaccine or anything of that sort. And they could obviously only look at deaths where there was an available report.

Note as the EvergreenFir said, although on average you should reduce your chances of dying even if you're a healthy and fit young adult by receiving the vaccine, if anyone does die due to the vaccine it's possible they will not have died if they didn't receive it. (Whether because of different circumstances at the time they received the vaccine, the cause of death which as mentioned would probably be an allergic reaction is something which may not have resulted even if they were infected with influenza or simply because they wouldn't have been infected anyway.)

Nil Einne (talk) 13:29, 22 April 2016 (UTC)[reply]

Your paper says that in 2009-2010 there were 107 deaths that occurred shortly after receiving an influenza vaccine (among 15 million doses delivered). This was apparently an unusually high number. Dragons flight (talk) 13:51, 22 April 2016 (UTC)[reply]

I also found [16] which says "The CDC is aware of four deaths linked to influenza vaccination from 1990 to 2005". Unfortunately I haven't been able find any sign of this statistic elsewhere so don't know where it came from. The author still appears active on Quora so you could ask them. While I know usage of the flu vaccine has increase, it seems unlikely this is simply the number of reports to VAERS unless the criteria for reporting has change very significantly.

BTW according to [17] (far from a RS but it links to an RS which unfortunately isn't working for me) there were 3 deaths compensated due to the flu vaccine in the period covered under the so called Vaccine court system in the US. According to our article, for favourable adjudication the claimant "must show a causal connection; if medical records show a child has one of several listed adverse effects soon after vaccination, the assumption is that it was caused by the vaccine". This ia a data point, even if considering the nature of such court proceedings and the laws governing them, it's difficult to say for sure how many deaths were really caused by the vaccine; and it's likewise difficult to know how many deaths cause by the vaccine either never went to the court or didn't receive favourable adjudication. Also it only applies to children I believe.

Nil Einne (talk) 14:29, 22 April 2016 (UTC)[reply]

Well, that's the rub, isn't it? Post hoc ergo propter hoc means that simply showing that a child died after receiving a flu shot doesn't mean they died because they received the flu shot. There is a convoluted set of questions that this comes down to:

People who died after they received a flu shot
People who died after they received a flu shot for whom it was reported, reported, or claimed that happened (that is, someone needs to make a record of the temporal relationship between the flu shot and the death, and not miss it or ignore it)
People who received compensation after dying after getting a flu shot (either voluntarily, or court ordered).

Not that none of this is a record of people for whom it is known that the flu shot caused the death. For that to be shown to be true, we need more than a temporal relationship (that is, death coming after flu shot). We also need a mechanism; that is the means by which the flu shot caused the death, such that we could show that if they had not received the flu shot, they would not have died. That data is often quite lacking, because largely that group 2 listed above is a MUCH smaller subset of group 1, and even THAT group may not have had a causal relationship. --Jayron 32 15:41, 22 April 2016 (UTC)[reply]

This is why they ask you if you're allergic to chicken eggs, as the strains are often grown in petri dishes containing egg derivatives. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:30, 22 April 2016 (UTC)[reply]

Usually not in petri dishes, but in actual hen's eggs [18] neat, isn't it? SemanticMantis (talk) 14:29, 22 April 2016 (UTC)[reply]

Ha, I must have heard wrong. So the yolk's on me! ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:31, 22 April 2016 (UTC)[reply]

That joke leaves me petrified. StuRat (talk) 16:20, 25 April 2016 (UTC) [reply]

Can thinking about sex reduce pain?

Can pain or discomfort be reduced simply by thinking about erotica? I don’t know how somebody could find this topic on Wikipedia—if it’s already here. --Romanophile (talk) 12:44, 22 April 2016 (UTC)[reply]

Thinking about erotica is essentially to increase dopamine levels in the blood. Dopamine plays an important role in pain regulation. So yes, it's possible.196.213.35.146 (talk) 12:52, 22 April 2016 (UTC)[reply]

Original Research: the answer to any question involving humans and sex is "Yes, probably, for some people." I approached the OP's question from the pain side. Our article on Pain management has a reasonably well-sourced section on psychological approaches - nothing specific to sex. "Got Pain? Think Sex" from WedMD is journalistic, but cites university research. "Does using fantasy to outwit pain and fear sound far-fetched? It's not, claims a study presented at the annual meeting of the American Pain Society in October 1999. A research team from Johns Hopkins and other universities found that people who fantasized about a highly pleasurable sexual scenario experienced the least pain." And here's a New Scientist article on sexual arousal and brain changes, including pain perception. These offer a start, at least. Carbon Caryatid (talk) 14:08, 22 April 2016 (UTC)[reply]

What if you're a masochist? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:32, 22 April 2016 (UTC)[reply]

Thinking about sex won't reduce pain if one suffer's from a penis injury. StuRat (talk) 23:51, 22 April 2016 (UTC) [reply]

I often thought that some sort of diversionary stimulation would be good whilst being drilled and probed in the dentist's chair. But with the cost of basic treatment these days, I doubt if I could afford the additional cost of that luxury. :( --178.108.238.49 (talk) 21:57, 24 April 2016 (UTC)[reply]

First device to produce non-static electricity

Historically, what was the actual first device to generate non-static electricity (direct current)? As I understand it, Francis Hauksbee's generator from c. 1705 still generated only static electricity known to the ancients. Was it Faraday's dynamo or there were previous rough, but working devices? Thanks. 93.174.25.12 (talk) 19:47, 22 April 2016 (UTC)[reply]

Was not it a chemical battery? Ruslik_Zero 20:37, 22 April 2016 (UTC)[reply]

Indeed, before the experiments of Luigi Galvani and Alessandro Volta, the electricity was either produced by friction between a suitable pair of materials, or (far less controllably) made briefly available by the use of a lightning rod. Lightning rod pre-dates voltaic pile by several decades; however, lower atmospheric electricity is also static in its origin. On a closely related subject, storage of (static) electricity in what we now call a capacitor also pre-dates voltaic pile by a few decades, see e.g. Leyden jar. --Dr Dima (talk) 21:02, 22 April 2016 (UTC)[reply]

And please see the Georg Wilhelm Richmann article for a good reason to use a Voltaic pile rather than a lightning rod o_O ... --Dr Dima (talk) 21:11, 22 April 2016 (UTC) [reply]

(EC) A static electric generator basically produced very high voltage electricity(kilovolts) at very low current (microamperes typically).The Leyden Jar or capacitor, invented 1745, could accumulate the electricity produced by a static electric generator. Once the Leyden jar was charged, it could be discharged through a conductor in a diminishing surge of high current until it was discharged. In the right circuit the discharge might oscillate for a bit back and forth. In the 1770's Joseph Priestly used a set of Leyden Jars as a source of high current to make pieces of wire glow and melt ,a graphic demonstration that it was a high current of electricity.Edison (talk) 22:02, 22 April 2016 (UTC)[reply]

PS: Lest you should think that there is a gap in Wikipedia's comprehensiveness, the link is Leyden jar. Alansplodge (talk) 09:10, 23 April 2016 (UTC)[reply]

The artifacts known as the Bahgdad batteries have been considered to be a very early form of galvanic cell, but this is no longer the academic consensus. (The poster formerly known as 87.81.230.195} 90.199.208.67 (talk) 21:57, 23 April 2016 (UTC)[reply]

Contractile vacuole in Paramecium.

1. Why is the contractile vacuole in Paramecium star shaped as depicted in this image:

2. Do Paramecium have eyes? How do they know what they are doing? --Augustous (talk) 22:00, 22 April 2016 (UTC)[reply]

Paramecium doesn't have eyes - it's a single-cell organism so it cannot have organs, only organelles - but it does have a photoreceptor and it does exhibit phototaxis. --Dr Dima (talk) 22:49, 22 April 2016 (UTC)[reply]

The first one is an interesting question - certainly I had not looked up anything about contractile vacuoles in ages, and our own article certainly is not leaving me with a settled feeling. Apparently the structure is quite a nuisance to try to isolate. In part this is because it is a dynamic structure, not a physical one - the CV is surrounded by acidocalcisomes, and it does not have a continuous channel to the outside, at least in certain random organisms, not paramecia, I was just reading about. See [19] for a CV, surrounded by acidocalcisomes, caught in the act of kissing one of them. The paper also describes the structure as a "transport hub" for membrane proteins to the surrounding acidocalcisomes.

Looking at the Paramecium article itself, they have a hint of starriness but certainly don't look like in the illustration. My guess from what I just read over is that the distribution of acidocalcisomes around the CV, and periodic connections made with them, might give it a very roughly center-and-petals type arrangement when viewed overall over time. But I don't really know this at this point.

On the second one, dinoflagellates famously have eyes - even with lenses! - but I don't think any such thing has been observed for paramecia. Wnt (talk) 22:51, 22 April 2016 (UTC)[reply]

Each Contractile vacuole has a high surface area to volume ratio for efficiency when it periodically gathers water from the cell and then expels water by contraction. Paramecia are occupied 24/7 with maintaining their osmotic balance with their environment, swimming using their cilia in search of edible microorganisms like bacteria, algae, and yeasts, and occasionally backing up when they feel a collision with an obstacle. Paramecia have so little concern with Circadian rhythm, identifying prey without tasting it or optical rangefinding that to grow a multicellular photorecepter such as an eye never occurs to them. See Eye#Relationship to life requirements. AllBestFaith (talk) 22:59, 22 April 2016 (UTC)[reply]

This video and some others by the same author are really pretty nice - at exactly 0:45 the paramecium rolls and if you hit the space bar you can see the CV surrounded by six other little structures, which I assume are the acidocalcisomes? It's not really a regular star but it looks pretty damn cute anyway, much better than most of the shots I was looking at. Wnt (talk) 23:11, 22 April 2016 (UTC)[reply]

Great video Wnt! Regarding the Erythropsidinium or ocelloid-bearing dinoflagellates in general - yes, their ocelloid (and surrounding structure) is currently hypothesized to work like an eye for all practical purposes, and certainly bears similarity to an eye; but it is not an eye. By the strict definition eyes are organs - multicellular structures - which ocelloids are not. The boundary may be rather tenuous, though, because plastids, classified as organelles, very likely evolved from endosymbionts. --Dr Dima (talk) 23:33, 22 April 2016 (UTC)[reply]

That is not uncommon as a definition, but it doesn't seem very useful to me. Eyes can be immense, as in humans, or be made up of just a few cells as in ocelli/stemmata, various lancelet visual organs, etc. If the term can encompass that level of diversity of size and function, I don't see a use for an arbitrary boundary at the one-cell level. To me the concept of an "image-forming eye", i.e. something with a lens, seems a more fundamental distinction. Similarly, it would seem more useful to me simply to admit that paramecia have mouths and anuses, rather than resorting to awkward circumlocutions. Wnt (talk) 10:44, 23 April 2016 (UTC)[reply]

I seem to remember during my biology degree that contractile vacuoles were always depicted as stars. Perhaps it is a convention historically adopted by biology illustrators. DrChrissy ^(talk) 00:01, 23 April 2016 (UTC)[reply]

OK, I just found a video that knocks the socks off the last one I posted: [20] In this one you can really see the "star" type arrangement, and in particular, the filling of the surrounding chambers that then fuse into the CV. Wnt (talk) 02:38, 23 April 2016 (UTC)[reply]

It's not the amps that kills you, it's the power

So from my understanding, there's a misconception that electrocution is caused by amps rather than volts. But instead the truth is that the power of the current is actually what kills you, not merely the amps. Let's take a taser that has a voltage of 50,000 and a current of .0021. So this should produce a power of 105 watts. If we were to reverse this and have a taser with a voltage of .0021 volts and a current of 50,000 amps this should still be "relatively" less than lethal right? If so, how would this affect a person if he was shot by reversed taser like this? Would he still feel pain? ScienceApe (talk) 23:02, 22 April 2016 (UTC)[reply]

I think you need to review Ohm's Law. Voltage and current are not independent variables. --Trovatore (talk) 23:06, 22 April 2016 (UTC)[reply]

As Trovatore mentions above, you need to understand Ohm's law. Even though it's the current that can be lethal, you can't get a current of 50000 amps through your body with a voltage of only 0.0021V, simply because the current directly depends on the Voltage applied AND the resistance of your body. The resistance of skin has a 'range' of resistance of about 50Kohm to 10Mohm, depending on many factors like stress, how wet the skin is, how much pressure is applied on the contact points, etc... Even though a car battery can deliver 100s of Amps, it can't kill you because applied to your body, 12V will only produced a few micro-amps through dry skin. Also, if a taser can generate 50000V, but is limited to 0.0021 Amps, then as the current flows through a body, the voltage decreases (down to about 4000V). We can estimate that with a body resistance of 2Mohm for instance, the power going through it would be only about 8.8W (not 105W). Dhrm77 (talk) 01:03, 23 April 2016 (UTC)[reply]

Normally, people say: "It's not the volts that kill you, it's the amps" --Llaanngg (talk) 23:37, 22 April 2016 (UTC)[reply]

I've heard "it's the volts that jolts; it's the mills that kills", as in "milliampere". But when you're talking about electrocution there are other things to take into account. Organisms aren't ideal spherical masses of uniform density. The path the current takes through the body is one important factor. Even a fairly small current can kill you if it travels through your heart and induces cardiac arrest. Conversely a very large current can just injure you if it travels through your extremities. This is why some people survive lightning strikes and others don't. --71.110.8.102 (talk) 00:14, 23 April 2016 (UTC)[reply]

Another point: Electricity can hurt you in more than one way. You can have your heart rhythm disrupted, which is the case that people are often concerned about because it takes a relatively small current. (And I've read, but I don't know where, that it even has a random element, depending on when in the heart's cycle the shock comes.) But you can also simply be burned to death, and that is a matter of power. --69.159.61.172 (talk) 02:58, 23 April 2016 (UTC)[reply]

I think what a lot of people don't understand when they talk about the effects of "voltage" versus "current" is twofold. First of all, for direct current anyway, the two things are proportional to one another. You can't change one without changing the other in lockstep.

So what does the voltage-v-current question even mean? Well, the thing is, very rarely do you have either a pure voltage source or a pure current source, something that will deliver the same voltage or the same current regardless of the resistance.

Instead, you have electricity sources with internal resistance. If you put an infinite resistance across its poles, you get the nominal voltage, but the current is zero. If you short-circuit it (give it zero resistance), you get the maximum current it can deliver, but now the whole voltage drop is internal; there is no potential difference between the poles at all.

Here's an extreme example: In ordinary circumstances, the electric potential of the air at the height of your head is maybe a couple hundred volts different from ground, depending on your height. (It could be millions of volts in an electrical storm, before you actually get a lightning bolt.)

Now, if you put a voltage source with 200V DC to your bare scalp, and your feet are in wet dirt, maybe it won't kill you (but I take no responsibility if it does), but in any case I'm pretty sure you're gonna feel it.

So what gives? Why aren't you getting shocked all the time?

Well, the thing is, air has a high resistance (much higher than your skin). So a few inches from your head, you've got charged air at a potential of 200V relative to ground. But right at your head, as soon as a tiny trickle current starts to flow, it uses up all the charge carriers from the air touching your head, and more cannot easily flow in to replace them. So there's still a circuit with a 200V potential difference that has your body as part of it, but almost none of that potential difference is actually across your body. The tiny current that does flow through your body corresponds to the tiny potential difference between the skin of your head and the skin of your feet; the rest of the potential difference is explained by that tiny current trying to make its way through the unyielding air.

Does that help? --Trovatore (talk) 03:44, 23 April 2016 (UTC)[reply]

Hang on, if I hold one probe of a multimeter at head height and one at the ground, it reads less than 0.01 mV . Not 200V, so what are you talking about? Greglocock (talk) 08:01, 23 April 2016 (UTC)[reply]

The impedance of your multimeter is far too low to make that measurement; in effect you are shorting out the voltage. If you had more suitable test equipment, you would measure somewhere in the genertal neighborhood of 100 Volts per meter. See our article on Atmospheric electricity and our Wikiversity page on the Natural electric field of the Earth. --Guy Macon (talk) 08:18, 23 April 2016 (UTC)[reply]

More than pure statics, you need to look at dielectric breakdown. Tasers work on a principle similar to how lightning and arcing work. See Van de Graaff generator for an example. Voltage can build up to very large amounts and then collapse when a conduction channel is formed in the dielectric. Once formed, the low resistance channel conducts. A taser starts at a high voltage, senses the channel and shuts down both the voltage and current. It cannot sustain the same voltage after dielectric breakdown reduces the impedance. The pointy tips of lightning rods increase the Volts/meter field difference to be maximimum near the tip so dielectric breakdown happens at the lightning rod before surfaces that aren't as pointy. That breakdown starts the chain reaction and ultimate discharge. --DHeyward (talk) 09:05, 23 April 2016 (UTC)[reply]

The article on electric shock goes through some of the basics. The power causes electrical burns, using the body as an ordinary heating element. (However, fibrillation is more dangerous, which is a different phenomenon) As others say, voltage and amperage are not independent variables -- if we denote the resistance of the body as R, the voltage logically as V, the current or amperage not so logically as I, then V = IR and the power is V² R or I²/R. But R is also not dependent of voltage - as explained at the article, the skin degrades and the resistance gets less and less with higher voltage. So there is some function R(V) you could write. Because resistance goes down with high voltage, there should still be a one-to-one relationship between voltage and amperage. So given a value for the voltage or the current, and the position of the electrodes on the body implying some resistance, you should be able to work through the math and figure out how much heat is being liberated. The catch is that voltage is a quantity known in advance - you can put a HIGH VOLTAGE sign on a piece of equipment. The amperage is an empirical measurement of exactly what the resistance really is, which makes it more accurate at predicting how badly a person will be hurt .... if you happen to have a multimeter rigged to him at the moment of his injury. However, that is not particularly uncommon, since there are fuses in many pieces of equipment one might unwisely poke into. Since the fuse is very low resistance at one end of the circuit, it measures power and amperage interchangeably based on its internal resistance. Since the article says that 30 milliamps of alternating current or 500 milliamps of direct current to the heart frequently cause death by fibrillation, it should be enlightening to compare the rating of the fuse to the rating of the heart!

Bottom line - it's true that "it's the amperage the kills" in the sense that the voltage is the same whether you are wearing rubber gloves and rubber shoes or have a death-house electrode smeared with conductive jelly strapped to your shaved head. But ordinarily it is not practical to measure the amperage, and if you knew all the circumstances it would simply be a function of voltage. Wnt (talk) 10:31, 23 April 2016 (UTC)[reply]

And resistance Shirley.!--178.108.238.49 (talk) 20:28, 24 April 2016 (UTC)[reply]

The problem with Wnt's formulation is that it doesn't emphasize that voltage, in any sense that matters for the purposes under discussion, is a difference between two points in the circuit, and it's terribly important which two points you pick.

In the case with the rubber gloves and shoes, the voltage drop between the poles of the voltage source may be the same, but the voltage drop across your heart is much less. Let's consider the DC case for simplicity; electrocution for capital punishment actually generally uses AC, but that's a distraction here.

In the rubber-glove case, there's a big voltage drop across the gloves and the shoes, and a much smaller drop across your actual body. Then there's also a drop across your dry skin before the electricity gets into the more conductive wet interior; some of that drop would be removed by the conductive gel in the electrocution case.

So if you look at the part of the circuit where your heart actually is, it makes no difference whether you consider voltage or current. The two things are directly proportional.

But it's hard to measure that, whereas it's somewhat easier to measure the voltage difference between the poles of the source. That's presumably the reason people say that it's the current that kills. It's easier to know what current is flowing through the circuit, than it is to know how much of the voltage drop is taken up by resistive elements along the way (like the gloves and shoes). --Trovatore (talk) 21:42, 24 April 2016 (UTC)[reply]

April 23

Meaning of Berl. Ber.

In citations in scientific papers, I've seen German sources cited as [Author name] Ber. Ber. [year]. What does Berl. Ber. mean? Something or other Berlin?? 121.215.1.130 (talk) 03:54, 23 April 2016 (UTC)[reply]

I believe it's an abbreviation of berliner sitzungsberichte, meaning 'Berlin meeting reports,' and it refers specifically to the Proceedings of the Royal Prussian Academy of Sciences in Berlin. Sandbh (talk) 05:58, 23 April 2016 (UTC)[reply]

How can I get a copy of a paper that does not appear to be available anywhere online?

I am looking for LeMessurier and Hills. (1965) Decompression Sickness. A thermodynamic approach arising from a study on Torres Strait diving techniques. Hvalradets Skrifter, Nr. 48, 54–84. I cannot find it on the internet and none of my academic contacts have been able to get it through their university libraries. I live outside of Cape Town in South Africa and have no access to major libraries. I need the paper both to verify existing article content and to write an article on the content of the article, which is a major landmark in its field. • • • Peter (Southwood) ^(talk): 06:45, 23 April 2016 (UTC)[reply]

The best place to go to on Wikipedia is WP:REX. If that is not successful, many libraries (even smaller ones) offer interlibrary loans for a small fee. --Stephan Schulz (talk) 08:01, 23 April 2016 (UTC)[reply]

You could try emailing the Academy itself. Their email address is at the bottom of this page.[21]--Aspro (talk) 11:51, 23 April 2016 (UTC)[reply]

Thanks, I have e-mailed them, • • • Peter (Southwood) ^(talk): 17:14, 23 April 2016 (UTC)[reply]

Let us know how you get on. This journal is now defunct (the tide against whale hunting I suppose) but as these two guy did much of their reseach in Australia, their libraries show this Journal on their catalogs.--Aspro (talk) 01:25, 24 April 2016 (UTC)[reply]

Salts

I need a few answers when it comes to chemistry. After finishing a unit on acids, bases, and salts, I got a good score but I honestly don't understand a thing. So my questions are, how do precipitation and titration work? (like really work, not: they work because ... science), what defines a salt?, and what is the difference between an acid and a base? (not just pH-wise, chemically). Thanks. Jdbepono (talk) 06:49, 23 April 2016 (UTC)[reply]

The term salt is used broadly in chemistry to refer to any ionic compound where the cation is not the hydrogen ion and the anion is not the oxide or hydroxide ion. A more narrow definition is that a salt is the ionic compound that results from the reaction of an acid with a base, but that is practically restricted to Arrhenius theory (wherein acids were substances that produce hydrogen ions in solution and that bases were substances that produce hydroxide ions in solution). A simple salt like magnesium chloride (MgCl₂) satisfies both definitions in that it is ionic with cation Mg²⁺ and anion Cl⁻ and the salt can be produced from an Arrhenius acid-base reaction:

2 HCl + Mg(OH)₂ → MgCl₂ + 2 H₂O

However, if I describe Zeise's salt with formula K[PtCl₃(C₂H₄)]·H₂O as a salt, you will struggle to produce it in an Arrhenius acid-base reaction. The base would be potassium hydroxide (KOH) but the required acid would have the anion [PtCl₃(C₂H₄)]⁻ and thus be H[PtCl₃(C₂H₄)], which is unlikely to exist (especially in water).

The definitions of acid and base change depending on the level of theory used, from Arrhenius to Lowry-Brønsted to Lewis theory. Under Arrhenius theory, HCl is an acid because the gas ionises to produce the hydrogen ion in aqueous solution

HCl (g) → H⁺(aq) + Cl⁻(aq)

and NaOH is a base because it dissociates to produce the hydroxide ion in solution.

NaOH (s) → Na⁺(aq) + OH⁻(aq)

The reaction of HCl with NaOH can be written as

HCl (aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

and can reduced (like all acid-base reactions under Arrhenius terms) to:

H⁺(aq) + OH⁻(aq) → H₂O(l)

Under L-B theory, acidity relies on the ability to donate protons (H⁺) and so HCl(g) is acidic as it donates protons to its solvent in water:

HCl (g) + H₂O(l) → H₃O⁺(aq) + Cl⁻(aq)

The resulting hydronium ions react with the hydroxide ions from the NaOH in another L-B acid-base reaction:

H₃O⁺(aq) + OH⁻(aq) → 2 H₂O(l)

Lowry theory is not really a great way to look at aqueous reactions of simple acids and bases like these.

Turing to an acid–base titration with the acid in the burette and the base in the conical flask. A small amount of indicator is added and the acid-form of the indicator (colour A) will react with the base in the flask producing the base form (colour B). As the acid is slowly added from the burette, the reaction occurring is mostly between the acid and the base. However some acid + base form of the indicator occurs, leading to colour changes as small amounts of the acid form of the indicator are formed. Since the amount of base present is still large (compared to the amount of indicator), this reaction is quickly reversed. The idea of a titration is to find the equivalence point, when the acid added from the burette is exactly the amount needed to react with all of the base in the conical flask. If the indicator chosen is appropriate then the next drop after the equivalence point will react to change the base form of the indicator to the acid form and produce a permanent colour change. We measure the end point (the colour change) and assume that it is a good to very good approximation to the equivalence point we sought. If our technique is good and the indicator is appropriate (which means the pH range within which it changes colour corresponds to the pH at the equivalence point) then the assumption is valid and we get useful results. If we choose poorly, the end point may not be near to the equivalence point. The equivalence point cannot be directly measured using colourimetric titration. EdChem (talk) 08:06, 23 April 2016 (UTC)[reply]

The numeric scale called pH that specifies the acidity or basicity (alkalinity) of solutions may give more general understanding than individual reactions. pH is a physical electric measure of the activity of the hydrogen ion: solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Titration is the quantitative measurement of the amounts of an acid and a base that together yield a neutral solution i.e. their "salt plus water" product, that is detected by eye with the aid of a pH indicator substance. A well known example of a pH indicator is Litmus which consists of organic dyestuffs, typically dried on paper strips, and displays the colors Red = strong acidic or Blue = string basic. The point of change between these colors i.e. purple indicates that the titration product is close to neutral (pH = 7 approx.). The linked article mentions other indicators, their colors and pH ranges; what they have in common is that they are chemical detectors for hydronium ions (H₃O⁺) or hydrogen ions (H⁺) in the Arrhenius model. AllBestFaith (talk) 09:48, 23 April 2016 (UTC)[reply]

That first answer kind of makes my eyes glaze over, so I think I'll try to give you another bite at the apple. I don't promise this will be any better. :)

To start with, precipitation is a matter of solubility. If a given set of compounds stays uniformly distributed in solution, they stay dissolved. But sometimes you get a positive and a negative ion that get together and create an attractive place for more positive and negative ions to stick. Or you have a chemical in solution but you add another solvent, and now it sticks to itself better than it sticks to the combined solvent. So at some point there is nucleation and the compound manages to get a small organized particle set up that keeps pulling more and more out of solution. Eventually, a saturated solution (mother liquor) remains, and the rest is usually some sort of crystal (though if the process is rushed the substance can come out as an oil or something with a less well defined structure).

titration is something completely different. You're just slowly adding solution A to solution B, stirring carefully, until something happens. Usually that something is a color change in an indicator dye as the pH changes. The pH changes depend on the buffers present in solution, but if you have just strong acid versus strong base you have a sharp equivalence point even if your pH indicator works over a large range, because the pH changes so fast in the middle.

A salt can be defined as an acid + a base, or as something without H+ or OH- (as described above). The definition can get technical, as described well above; I'd say the main effect of all that qualification is that people expect "salts" to be sort of neutral-ish, but you can come up with some weird cases where they are quite corrosive.

The fundamental difference between acids and bases is that some are electron haves and some are electron have-nots. The classic acid is a proton, a lone hydrogen nucleus with no electrons, H+. It tends to wander around looking for anybody with electrons to hang off of, including water molecules so it is usually hydronium. By contrast, a base is something like ammonia, which has a lone pair because nitrogen starts with 5/8 electrons in a quantum shell. The shells are determined by the geometry of how waves of electrons can circulate around an atom in orbitals (this is quantum mechanics), and they mean that nuclei with some numbers of protons will tend to want more electrons around them than protons, and other numbers of protons will tend to want less. Some things like hydrogen can kind of go either way to get to a preferred quantum shell, losing or gaining an electron (the H- is called hydride and much rarer to see though). Anyway, these funny rules create all kinds of compounds that are looking to gain or lose electrons, hence the Lewis acid definition. But in aqueous solution most of them get cashed in for H+ or OH- in the end, which is why simpler definitions in terms of H+ and OH- are useful in many situations. Wnt (talk) 21:00, 24 April 2016 (UTC)[reply]

As the resident chemistry teacher, let me take a go at this:
A salt is a crystalline ionic solid, which is also not an Arrhenius acid or an Arrhenius base. That's probably the best, most inclusive definition I can give.

Precipitation is the process whereby you mix two solutions and a solid (powdery) product forms. If you have two clear solutions, and mix them, and it goes all cloudy, that's precipitation. It's usually a type of double replacement reaction, and it happens when one of the products of that reaction is relatively insoluble, compared to the reactants. The easiest heuristic is known as the solubility rules, but eventually you'll learn to deal in equilibrium expressions like the solubility product to predict this.

Titration means careful mixing of two solutions for the purpose of quantitative measurements; that is how much of solution A needs to be mixed into solution B to produce some sort of visible chemical change (color change, pH change, precipitation, etc.)

What defines the difference between an acid and a base depends on which theory you're working with (theory = model). That is,
Arrhenius acid base theory explains that an acid produces hydronium ions in water, while a base produces hydroxide ions in water.

Bronsted-Lowry theory removes water from the explanation, and attempts to make acids & bases defined in relation to one another. Picture a simple chemical reaction where a hydrogen ion (H+) is exchanged between two substances. The one that gave the hydrogen ion is an acid; the one that got the hydrogen ion is a base.

Lewis acid-base theory is sometimes also brought into the discussion, and it explains acids and bases in terms of bond formation: in the formation of new chemical bond (where a bond has 2 electrons) you often get a situation where one substance has a "lone pair" of electrons (more negative), while another substance has an open orbital (more positive) in which to receive those electrons. In this case, the species giving up the extra electrons is a base, and the one getting the extra electrons is the acid. Lewis theory is often considered too broad by many chemists, so when one talks about "Lewis acids" or "Lewis bases", one is considering substances that don't often meet the strict definition of an acid or a base. Many who don't like these terms (often organic chemists) have come to using the terms electrophile and nucleophile to avoid the confusion between this theory, and the other two.

Hope that helps a bit. --Jayron 32 21:16, 24 April 2016 (UTC)[reply]

I resolved two redlinks in your post. DMacks (talk) 02:19, 25 April 2016 (UTC)[reply]

Leyden jar

Was the Leyden jar ever used in warfare to zap enemies? 2601:646:8E01:515D:D52:C360:441C:37B8 (talk) 10:47, 23 April 2016 (UTC)[reply]

I've not found any examples of such .It was used to zap friends, such as a group of soldiers to amuse their rulers or a group of monks who somehow got volunteered to all take a shock. It was at least powerful enough to kill birds. It could have been used as a gimmicky novelty defense of a structure, as when they grab the doorknob, not knowing it is connected to a Leyden Jar with the other terminal connected to earth, they get knocked on their ass as if Tasered.The challenge was keeping the hot lead insulated so the charge did not drain off. In experiments in the 1740's they used insulated wires (supported by insulators) to carry the charge a mile or more See the book The History and Present State of Electricity, 1775 edition, by Joseph Priestly at [22]. It would have been effective for torture, but once batteries were developed an induction coil would have made a more effective torture device, and they already knew all about lots of other simple to use torture devices. Edison (talk) 12:39, 23 April 2016 (UTC)[reply]

Back in the day, they were regularly used to zap schoolboys for the nefarious amusement of physics teachers. Alansplodge (talk) 16:49, 23 April 2016 (UTC)[reply]

In the next World War, you might find one useful as a simple electroscope-ionization chamber fallout meter with which fallout radiation can be measured accurately.[23]. The ionizing radiation depletes the charge in the jar, giving you a good estimate of hour many hours, days or months it will take you to die from radioactive fall out.--Aspro (talk) 01:39, 24 April 2016 (UTC)[reply]

Maybe. --Jayron 32 21:05, 24 April 2016 (UTC)[reply]

Who was it?

Who was the person who invented scissors ? 210.56.124.57 (talk) 16:05, 23 April 2016 (UTC)[reply]

See Scissors#History. --Dr Dima (talk) 16:45, 23 April 2016 (UTC)[reply]

Overload question

In Arthur Hailey's novel Overload, there is a scene where a lineman gets zapped with 500 kV (!) from a high-voltage power line, gets badly burned (including getting his dick vaporized), but survives -- is this even remotely plausible? 2601:646:8E01:515D:D52:C360:441C:37B8 (talk) 11:23, 23 April 2016 (UTC)[reply]

I've posted the above on the user's behalf due to an edit filter false positive. Jackmcbarn (talk) 18:19, 23 April 2016 (UTC)[reply]

I've disambiguated the OP's link to the novel, and fixed the spelling of the author's name to avoid the redlink. Loraof (talk) 18:38, 23 April 2016 (UTC)[reply]

According to our Electric shock article, the record is held by one Harry F McGrew of Utah, who survived 340 kV. However, although our article states that this is from Guinness World Records, it doesn't appear on their site, and no reference to the book is given. Appropriate tags have been added to the article. To answer the OP's question, 500 kV is (just about) plausible, but rather more than the actual maximum that (apparently) has been survived. Tevildo (talk) 19:08, 23 April 2016 (UTC)[reply]

Thanks to Wnt, we have a more definite reference for one Brian Latasa, who survived 230 kV in 1967. Further away from 500 kV, of course - it might be possible to survive it, as it's possible to survive falling 30,000 feet out of an aeroplane, but it's extremely unlikely. Tevildo (talk) 21:24, 23 April 2016 (UTC)[reply]

Well, it's a reference, but it's a reference to a Guinness comic strip. There's no motivation for them not to overstate the case. For example, he might not have been grounded, and been shocked solely from the capacitance of his body and perhaps some other object as the alternating current went back and forth. (I think people working on high tension lines can touch them safely if not grounded, but I don't know if that holds for extreme voltages. In any case, you need merely postulate a lump of metal as large as needed to make the capacitance cause a small burn!) The other one, well, I commented on the talk page that it was "fixed" from an initial "Mgcrew" by someone who apparently didn't have access to the source. At this point, I think I'm going to take it out because it is at least nominally an unsourced statement about a WP:BLP, and in any case, looks like dumpster scrapings on a plate. Wnt (talk) 21:30, 23 April 2016 (UTC)[reply]

Tevildo came up with a better reference for that case, which I've added ... the poor kid was reportedly burned over 40% of his body and completely paralyzed "except for the eyelids". Wnt (talk) 00:45, 24 April 2016 (UTC)[reply]

Do ostriches ever fledge?

I've just looked through multiple definitions of fledging/fledge. They almost all relate to flying or developing feathers enabling them to fly. Does this mean that flightless birds never fledge? Some (very few from my survey) definitions focus on the bird's ability to leave a nest. What about birds that do not make a nest - does this mean they don't fledge? (At this point, I am trying to think of a flightless bird that does not build a nest! - got one, the emperor penguin.) DrChrissy ^(talk) 19:04, 23 April 2016 (UTC)[reply]

Think the equivalent of 'fledge' for a penguin would be when the parents no longer look after the chick – left the bio-nest so to speak. Of course it can't fly or swim but is just stuck there on the ice looking cute and fluffy. It then becomes a fledgling when it molts away it downy feathers. --Aspro (talk) 02:16, 24 April 2016 (UTC)[reply]

According to a story by (iirc) Larry Niven, an ostrich is a roc that never matures. —Tamfang (talk) 06:58, 25 April 2016 (UTC)[reply]

This is like "Is a hamburger a sandwich?" right? Maybe yes, maybe no; if it matters just clarify. Anyway, fledgling-as-first-flight is basically the same time as leaving the nest for many birds, but not for e.g. ducks and geese. So the murkiness of the term comes up even for flying birds- if I say a wood duck fledged- do I mean it left the nest, flew, or did something else? The general gist of fledging is maturation, less dependence on parental care, etc. Flightless, non-nest-building birds generally all go through that process, and it might make sense to call it fledging. If you want to be guided by usage rather than definitions, here [24] [25] are a few peer-reviewed journal articles that discuss penguins fledging, meaning leaving the nest. SemanticMantis (talk) 14:09, 25 April 2016 (UTC)[reply]

There are several shades of meaning of "fledge".[26] One is to acquire feathers. Another is to be fit to fly. Another is to be ready to leave the nest. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:46, 25 April 2016 (UTC)[reply]

That definition is not suitable for flightless birds though. Look a chicken (and this probable goes for penguins as well considering the temperature) they emerge out of the egg with downy feathers and not naked like other birds. A chicken chick can and does start pecking away and anything edible (an ostrich chick possible the same but I've never met one). They also follow mum around (or you if you incubated them yourself) A penguin chick has to be protected from the elements under one of the parents (bio-nest)and fed regurgitated food. Eventually they fledge and leave mum and dad to huddle with other baby penguins. Finely they become fledgling when the develop proper waterproof feathers. The evolution is the same, save that they already have feathers when hatching and the time taken to become fledglings is longer. Whether these chicks can be properly said to 'fledge' though I am uncertain but they do become fledgling. Lifecycle of the Emperor Penguin. By now DrChrissyhas probably emailed Dr. Lorenz and received a definitive answer back so can put us out of our misery, incase someone else posts a similar question here in the future. --Aspro (talk) 20:18, 25 April 2016 (UTC)[reply]

I think you are trying to draw a difference between precocious and altrichial chicks. I'm not sure why you have included domestic chicken as flightless birds. They (egg laying chickens) can fly, although this is limited. My reason for raising question this is that our own Fledge article does not contain any sources and I wanted to get some feedback from others. I'll edit the article tomorrow. I think the summary to this one is - "depends which book you read"! DrChrissy ^(talk) 22:46, 25 April 2016 (UTC)[reply]

Stellar classification

If the entitled article is for population I stars, than what is for population II & III? -- Apostle (talk) 19:33, 23 April 2016 (UTC)[reply]

Population III stars are a theoretical concept - so far none have actually been identified. Population II stars are very rare - only a handful have been observed. That simply means that there are not enough of them to classify them. 81.132.106.10 (talk) 19:44, 23 April 2016 (UTC)[reply]

I thought subdwarfs (VI) were metal deficient hydrogen-burning stars. Like G2VI for a Sun-colored subdwarf. Metal deficient enough to be Population II? Sagittarian Milky Way (talk) 19:53, 23 April 2016 (UTC)[reply]

Any ideas/assumption/presumtion/hypothesis say for, if there was a population IV, V, VI stars and so on? Whether the temperature/K would be hotter than the current ones or not, at any stage/phase? -- Apostle (talk) 05:26, 24 April 2016 (UTC)[reply]

Astronomy is just starting to become capable of getting real evidence about what is out there (or in here). Just realize the contrast between all these wild theories about "dark matter" and the fact that we have no clue yet, nomatter its supposed to be everywhere around us. --Kharon (talk) 05:47, 24 April 2016 (UTC)[reply]

Please note that stellar population and spectral type (as discussed in the stellar classification article) are separate concepts. 91.155.193.199 (talk) 10:53, 24 April 2016 (UTC)[reply]

Yes I know, I'm concerned about the temperature of the populations because of primodial atom. - I understand everything roughly, but this thing is a confusion... -- Apostle (talk) 18:40, 24 April 2016 (UTC)[reply]

April 24

SETI not successful at finding extraterrestrial intelligence

If there are so many possible earth-like planets in the Milky Way Galaxy, which makes the chances of finding alien life very high, why hasn't SETI been able to detect extraterrestrial civilizations? — Preceding unsigned comment added by 24.207.71.235 (talk) 04:56, 24 April 2016 (UTC)[reply]

Because you need some synchronization to recieve information over radio signaling and SETI is only listening for 26 years now which is a joke in relation to the assumed age of our universe. Ask again when we have listened for 500 Million years without finding anything :D --Kharon (talk) 05:36, 24 April 2016 (UTC)[reply]

P.S.: Ok, ok, 500 million may be to conservative aproach scientifically speaking and i get you can not be that pacient.. so how about asking again after listening just 500 years which roughly relates to the assumed age of the universe like 1 Minute in a 60 years Lifespan. --Kharon (talk) 06:04, 24 April 2016 (UTC)[reply]

Fermi paradox and rare Earth hypothesis are relevant. A large number of possibly earth-like planets doesn't make it likely that we'll detect intelligent life. We don't how how likely it is that a possibly earth-like planet has intelligent life on it (at the time we look). -- BenRG (talk) 06:05, 24 April 2016 (UTC)[reply]

If the OP can give numbers to use in the Drake equation that estimates the number of communicative extraterrestrial civilizations in the Milky Way, the question will be better posed than asking in qualitative terms of "so many" and "very high chances". AllBestFaith (talk) 08:46, 24 April 2016 (UTC)[reply]

There's also the sensitivity of our radio telescope. There may be an intelligent civilisation with radio transmitters 1 kiloparsecs away from us (not very far astronomically speaking), but our telescopes may not be sensitive enough to detect them. Suppose a human-like society exists just 3 parsecs away (we don't really expect them closer than that) and that society has FM radio stations like we have. We would have to point our most sensitive radio telescopes at their planet, staring for years before we'd be able to detect their radio station as a small bump in the radio spectrum above background noise. We have other things to do for our radio telescopes. And FM radio may be a short-lived technology. Already we are moving to broad-band digitally encoded radio, which is far harder to discriminate from random background noise.

There's more hope if the aliens use powerful transmissions, beamed in a narrow beam directly towards Earth. This could give a decent range at a bitrate somewhat higher than 1 bit per century. Maybe a bit per second would be possible over 100 parsecs, I didn't calculate what transmitter the aliens would need. But even then, both the transmitter and the receiver would have beams of an arcsecond width and those would have to be pointed right at one another at the right time. The odds aren't very good for that to happen. PiusImpavidus (talk) 11:16, 24 April 2016 (UTC)[reply]

If there are aliens in a distant galaxy, the length of their day is not likely to be the same as ours. Even if it was, the aliens are not likely to have divided it up into the same 24hr/60min/60sec divisions that we use. So, whereas we use the second as our basis for the data rate in our transmissions, who knows what basis they would use for theirs? Wouldn't a different basis make transmissions mutually incomprehensible? Maybe all the noise we hear is actually the aliens communicating amongst themselves. Akld guy (talk) 12:53, 24 April 2016 (UTC)[reply]

@Akid guy If you are suggesting that terrestrial data communications are all locked to a 1 Hz timebase, that is incorrect. Common digital modulation methods convey data at many different rates derived from independent clock sources and receivers are designed to synchronise themselves to incoming signals. AllBestFaith (talk) 14:49, 24 April 2016 (UTC)[reply]

Even if they were locked to a multiple of 1Hz - it wouldn't matter because of doppler shift. I'm quite sure that SETI aren't looking only on exact numbers of hertz - that would be a ridiculous thing to do. SteveBaker (talk) 19:28, 24 April 2016 (UTC)[reply]

I didn't say anything about a 1 Hz signal. We base our bit rate timings on 1 second, but if an alien culture based their "second" on some small division of the length of their day, the length of their "bit" might be a very small fraction of the length of ours. So small in fact, that it sounds like noise. Maybe we don't yet have the technology to extract anything meaningful from such short bit rates, let alone decode any encryption that they might use. Akld guy (talk) 20:12, 24 April 2016 (UTC)[reply]

That would be a matter of more advanced technology, not of the day length. If our day were a hundred times as long, but our technology were the same, we wouldn't make our data transfers a hundred times slower. —Tamfang (talk) 07:39, 25 April 2016 (UTC)[reply]

@Akid guy 1 Hz or Hertz means a frequency or rate of once per second which is exactly what you are harping on about, like the ticking of a clock. Mechanical clocks are hopelessly inadequate to measure the durations of bits in modern digital communications that now are routinely sized in milliseconds, microseconds, nanoseconds and picoseconds. High bit rate implies short bit duration and there is no such thing as a human standard bit. Of course some competence is required to draw connections (if any) between the Sexagesimal time divisions of Babylonian astronomy and the theory in SETI that any communication signal is distinguishable from thermal noise by its Autocorrelation. In this way an inquisitive alien who picks up a GPS satellite transmission and first wonders why earthlings seem to transmit "noise" to themselves, on closer inspection deduces that GPS satellites transmit periodic PRBS for time measurements. AllBestFaith (talk) 12:56, 25 April 2016 (UTC)[reply]

@AllBestFaith: I'm not impressed with the way you stated that I'm "harping on". I responded to questions. I'm also well aware of what a Hertz is, thank you very much. See my profile. I began building radio equipment in the 1960s and have written software in both Basic and Assembler and have interfaced it via a serial port, developing my own KISS code. Your condescension, by referring to a mechanical clock, is totally out of place. Read what I said (unfortunately I spoke of bit rate when I should have said bit length). Our bit length is based on our second. If an alien culture has a different day length, their bit length is almost certainly going to be different from ours, and it may be so much shorter that we perceive valid data as simply "noise". Akld guy (talk) 16:35, 25 April 2016 (UTC)[reply]

I recommend http://www.seti.org/faq - I'll quote one of their FAQ points: "If an extraterrestrial civilization has a SETI project similar to our own, could they detect signals from Earth? In general, no. Most earthly transmissions are too weak to be found by equipment similar to ours at the distance of even the nearest star. But there are some important exceptions. High-powered radars and the Arecibo broadcast of 1974 (which lasted for only three minutes) could be detected at distances of tens to hundreds of light-years with a setup similar to our best SETI experiments."

...and that's an important point. The aliens would have to be beaming a very high powered (by our standards) signal - and aiming it right at us - and timing that precisely so that it arrives when we're listening - and they'd have to be within "tens to hundreds of light-years" of us. If you look out to 100 light years, there are maybe a dozen potentially inhabitable planets.

SETI also say "...while there are hundreds of billions of stars in our galaxy, only a few thousand have been scrutinized with high sensitivity and for those, only over a small fraction of the available frequency range."

So it's really no surprise at all that we're not finding anything.

SteveBaker (talk) 19:28, 24 April 2016 (UTC)[reply]

About 1980, i think, Science had an article about what Earth would look like in radio waves as seen at various nearby stars. (I've seen the claim elsewhere that Earth puts out as much radio as a small star; though we may be dimmer now, with conversions to narrowcast.) Observers could infer the length of our day from periodicities, the size of Earth and its orbit from Doppler shifts, and some hints of the geographic distribution of cities (brightest on the limb, because most of the energy goes out horizontally). —Tamfang (talk) 07:39, 25 April 2016 (UTC)[reply]

One possibility is that life intelligent enough to develop radio communications tends to be "intelligent" enough that it also develops ways to snuff itself. So the window for something like SETI could be quite brief in the context of the age of the universe. Shock Brigade Harvester Boris (talk) 00:08, 26 April 2016 (UTC)[reply]

April 25

Could it be that a person can stop his pulse or is it fake?

This video (around the minute 6:30) shows how a person stops his pulse for 15 seconds. I just would like to ensure if it's possible (true) or not fake). 93.126.95.68 (talk) 00:29, 25 April 2016 (UTC)[reply]

Supposedly Superman can. But how would a mere mortal stop his heartbeat and live to tell about it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:02, 25 April 2016 (UTC)[reply]

This and this may be relevant. The simple method is to simply hold a rubber ball in the right spot under the arm to cut off the blood flow to the wrists (how most people measure the pulse). Doesn't affect heartrate at all. The harder method involves training the muscles throughout the body to slow blood flow (though this does not actually stop the heart). Does affect heartrate, and could be combined with the rubber ball trick to make one appear totally freaking dead (as long as they're checking the pulse from the wrist). If they had attached monitors somewhere besides his finger tips (I'm not counting a credulous hand as a monitor), they'd've spotted it. Ian.thomson (talk) 11:24, 25 April 2016 (UTC)[reply]

Great answer! thank you 93.126.95.68 (talk) 18:01, 25 April 2016 (UTC)[reply]

I would be skeptical because cardiac muscle is spontaneously pulsatile. External nerves govern the rate, but have they evolved to make it stop? Nothing's impossible in biology but some things seem pretty darn unlikely, demanding good evidence. Wnt (talk) 20:38, 25 April 2016 (UTC)[reply]

Trying to identify a berry

My fiancee and I live in the Seattle area, and we came across some orange relatives of the blackberry that grow very low, a type of ground cover. She called them salmonberries, but we've now discovered that that name refers to Rubus parviflorus, an obviously related but clearly different species. The last time I saw them was at Saint Edward State Park growing at the base of the walls around the old seminary building. She indicated that there are also patches of them near SeaTac. It's possible that these are Rubus spectabilis, but the description on that page indicates a taller shrub with substantial height. The orange berry image on that page, however, appears accurate, though the red is clearly the wrong berry. Is it possible that these are just smaller versions of the same plant, or is this a different species? 73.19.23.200 (talk) 11:57, 25 April 2016 (UTC)[reply]

Maybe some kind of Euonymus? --Jayron 32 12:55, 25 April 2016 (UTC)[reply]

It would appear that both parviflorus and spectabilis are sometimes called salmonberry (which is why biologists prefer the Latin binomials rather than the common names). Don't put too much weight on the described size of the plants: any shrub can end up being stunted if the conditions are not right. Planted up close to a wall may mean little soil, or in a coastal area the effects of salt winds might reduce plant growth. If flower, fruit and leaf match that counts for more than the general shape and size of the whole plant. 81.132.106.10 (talk) 13:47, 25 April 2016 (UTC)[reply]

Just for the fun of it, check out dewberry - another Rubus species complex. . SemanticMantis (talk) 14:11, 25 April 2016 (UTC)[reply]

Also, in general, the way to ID a berry is not through the berry or the bush shape, it's by the flower. SemanticMantis (talk) 14:14, 25 April 2016 (UTC)[reply]

Unfortunately, if they are seeing the fruit, it is probably the wrong season to spot the flowers. 81.132.106.10 (talk) 16:02, 25 April 2016 (UTC)[reply]

Phenology varies quite a bit. Also it's not that odd to see flowers and berries on the same plant at the same time [27]. Also this general advice may be useful for next season, or to ID other berries :) SemanticMantis (talk) 16:40, 25 April 2016 (UTC)[reply]

Eye damage due to eye exams

An eye exam seems to involve them shining bright lights into a fully dilated eye. Couldn't they use a dim light, paired with a highly light-sensitive digital camera, instead ? StuRat (talk) 20:59, 25 April 2016 (UTC)[reply]

What eye damage? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:13, 25 April 2016 (UTC)[reply]

Well, the most "classic" exam you see in movies and TV all the time when a doctor shines a pen light into someone's eye is a Pupillary light reflex test, which is not an eye exam but a neurological test. Apart from that, while a bright light can be uncomfortable and leave you with spots in your vision that can last a while, it doesn't actually damage the eye, it's actually the heat and radiation from something like the sun, welding arc, or a powerful enough laser that cause damage to the retina, just a "bright light" is typically not enough. disclaimer: Don't use this as an excuse to stare into extremely bright lights, it's still not a GOOD idea even if it doesn't cause permanent damage. Vespine (talk) 00:03, 26 April 2016 (UTC)[reply]

Indeed. See Photokeratitis for our relevant article. It's the ultraviolet that does the damage, which shouldn't be an issue with an opthalmoscope. Tevildo (talk) 00:05, 26 April 2016 (UTC)[reply]

Painting the Moon

Wikipedia has a harebrained scheme to send a draft of the encylopedia to the Moon. [28] I want to see the idea improved on with this invention, which claims to keep 360 TB stable for 13.8 billion years. With that kind of stability, you can leave a message for some future species that is trying to figure out what Earth was like, even if the planet has been entirely resurfaced like Venus after some man-made climate mishap.

The catch is, how do they find the disk? It should gradually sink into the regolith. (of course, it could get hit by a meteor directly, but I'm assuming luck or multiple scattered disks laid over time)

On to the question: is it possible to take some freaky, rare element, I dunno, ~~lutetium or something~~ maybe one of the tracers described in File:Rareearthoxides.jpg, and spray a small amount of it on the Moon, and taint the small area where it lands so thoroughly that it can be detected from an orbital survey, and have micrometeorites hitting anywhere in the small area constantly stirring it up, so that the mark never fades? What stands out the most, and can the logic here hold or is it doomed to be diluted into invisibility? Wnt (talk) 21:02, 25 April 2016 (UTC)[reply]

Rather than make it visually obvious, how about placing a strong, permanent magnet there ? Probably not detectable from space, but some future aliens might notice the disturbance of the magnetic field when exploring the surface near the area. StuRat (talk) 21:33, 25 April 2016 (UTC)[reply]

In Tycho, of course. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:11, 25 April 2016 (UTC)[reply]

Why ? StuRat (talk) 22:30, 25 April 2016 (UTC)[reply]

To turn the tables on a key plot element of 2001: A Space Odyssey. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:35, 25 April 2016 (UTC)[reply]

To be clear, I was hoping that a small quantity of rare earth, even a mere kilogram might suffice to create a notable spectroscopic anomaly on the order of ten meters wide that can withstand the gradual tilling of the regolith by micrometeorites over millions of years. (a large impact would vaporize the disc, so there's no sense worrying about it). Whereas a buried permanent magnet would definitely involve an impractical amount of mass to be noticed. Wnt (talk) 00:21, 26 April 2016 (UTC)[reply]