Wikipedia:Reference desk/Archives/Science/2016 April 21

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

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)

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

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

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

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)

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)

"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)

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)

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

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)

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)

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)

"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

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)

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(m/60) × 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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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. --Jayron32 18:11, 21 April 2016 (UTC)

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)

"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)

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)

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)

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)

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)

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)

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)

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)

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)

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

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)

"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)

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)

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)

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)

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)

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)

(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)

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

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)

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)

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)

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)

Do you mean this? Those are orange. Sagittarian Milky Way (talk) 23:15, 21 April 2016 (UTC)

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)

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)

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)

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

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)

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)

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)

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

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

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

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)

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)

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

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

• 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. --Jayron32 13:17, 22 April 2016 (UTC)

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)

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

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)

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