Wikipedia:Reference desk/Archives/Science/2014 October 10

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October 10

How does usa.com know precip, average humidity & wind, degree days, and snow for extremely obscure places?

Like every school district (16,000), zip code, and settlement (all 38,000 of them)? Monthly normals, too. Yet it doesn't even know the population of half the named settlements? I also found a value that's 1.5 times the Google consensus number. Where can I go for accurate maps and the best values for averages/normals? The National Climate Data Center doesn't have many stations. How do they make good official maps at all then with that poor coverage? Like the USDA hardiness zone map? Sagittarian Milky Way (talk) 04:38, 10 October 2014 (UTC)

Hello, Sagittarian Milky Way. It appears to me that USA.com is a "data aggregator" site. It formats and presents data from various official websites like the U.S. Census and the National Weather Service. One agency may identify more discrete locations, or different locations, than another. So, just because the weather service thinks that it is important to report weather data from a certain place does not mean that the census bureau reports from the same "place". Weather data is reported from a specific point. Census data is reported for a geographical area, not a specific point. Cullen³²⁸ Let's discuss it 05:12, 10 October 2014 (UTC)

The National Weather Service produces large-scale models and forecasts, and then interpolates to generate "point forecasts" on a 1.6-mile grid: [1]. (The vast majority of these hyper-local point forecasts will be driven by interpolated, estimated values; very few will have weather stations on the ground collecting measurements.) I suspect that most sites offering high-resolution forecasts of U.S. weather are just scraping NWS data. TenOfAllTrades(talk) 15:01, 10 October 2014 (UTC)

USA.com may also get its data from sites that accept everyday people with a home brew weather station in their back yard to report their local weather. Wunderground.com especially has data collected from regular people with these systems. And you can get their weather data specifically. So, just because I live near Burlington, Vermont (Vermont's largest city) does not mean that my weather is the same as the city's. But I can find a local weather station that is within a mile of me which is going to be more accurate for most readings than Burlington's. Dismas|^(talk) 15:20, 10 October 2014 (UTC)

Specifically, schools often have weather stations, but they are not census places. This article specifically mentions how the aforementioned wunderground.com actually helps schools install weather stations [2].

Motion and frame of reference

This is pertaining to my previous question about time dilation issues. How can I make sense of time dilation in these two situations?

Now I want to know, once and for all, if the details in my previous question - the view that whichever object is moving is relative to the frame of reference (like how the view that says the earth is also accelerating toward the particle in the particle's frame of reference) - is valid or not?

75.80.145.53 (talk) 05:34, 10 October 2014 (UTC)

Your link does not work; here is one : GPS time dilation question (I need an expert in physics or special relativity). The twin paradox is well-understood. Inertial frames of reference are not the same as non-inertial frames of reference. —Quondum 13:51, 10 October 2014 (UTC)

(I fixed the original link. -- BenRG (talk) 01:02, 11 October 2014 (UTC))

As I said in that thread (my "simplified geometrical analogy"), there is no symmetry between the worldlines of the objects in this situation. If you have a straight line and a helix spiraling around it, the helix is longer, or denser if you like, in an absolute sense. Likewise, if you've got an inertially moving object and another moving in a circle around it, the latter's clock runs more slowly in an absolute sense. The symmetric case is the case of two inertially moving objects, or in the geometric analogy two infinite straight lines. There is a symmetry (a rotation) that exchanges any two straight lines, so it can't make sense to say that one is longer/denser than the other in any absolute sense. -- BenRG (talk) 01:13, 11 October 2014 (UTC)

There's no relativity of acceleration, either. In the geometrical analogy, unaccelerated/inertial motion is a straight line, and uniformly accelerated motion is a uniformly curved line, i.e., a circle or an arc of one. (The fact that circles curve back on themselves after a finite distance, while wordlines don't, is one place where this analogy breaks down. But in general it's a very close analogy.) So the question is whether from the "perspective of" a circle, the circle is straight and a straight line is circular. The answer is no. They are simply different shapes.

Saying that "everything is relative" in Euclidean geometry or special relativity is merely saying that there are no absolute positions or orientations, only relative positions (distances) and relative orientations (angles, or relative speeds). It doesn't mean that, e.g., circles are fundamentally the same as straight lines. -- BenRG (talk) 02:01, 11 October 2014 (UTC)

Rubbing your hands will make them burst into flames

In this video at around the 6:20 mark, the man says that if the oxygen content in the atmosphere were high enough, you can rub your hands together and they would burst into flames. Is this true, and if so what would the oxygen content of the atmosphere (or environment you're in) need to be in order to achieve that? ScienceApe (talk) 19:48, 10 October 2014 (UTC)

How common is a pair of hands in significantly enriched oxygen anyway? I can't think of a common way of being in mostly oxygen, besides lots of it pouring out of LOX tanks and pooling. (though there's probably an application or job or form of chemistry recreation where it happens. Someone trying to find out the most % oxygen various CO2&O2 mixtures can make before all the species die that enters the greenhouse through an airlock before purging it?). Anyway, if true, there's the possibility it's physiologically possible to make that much speed and pressure but still be extremely uncomfortable to do so. Sagittarian Milky Way (talk) 22:50, 10 October 2014 (UTC)

The Apollo 1 cabin contained pure oxygen at 1.15 bar pressure. While 3 autronauts died in a fire, the cause of the disaster was not due to rubbing hands. Count Iblis (talk) 22:57, 10 October 2014 (UTC)

Slaps forehead. Apollo 1. Maybe this your brain on sleep debt. Really idiotic thing to do, too, fill a spacecraft with overpressure oxygen. Also, I now recall diving suits filled with things like heliox at many bars. Regardless of any flammabity, you can't rub your hands together in them. Sagittarian Milky Way (talk) 01:51, 11 October 2014 (UTC)

Diving suits are rarely filled with heliox, trimix, heliair or any other helium rich gas due to its high thermal conductivity. However, the oxygen partial pressure in an air or nitrox-filled dry suit will always be beyond the atmospheric O.2 bars and will very often be well in excess of Apollo's 1.15 bar. COMEX have not published their safety protocols with respect to the use of hydreliox (an explosive breathing gas which includes a proportion of hydrogen), but it seems unlikely that they include a proscription on shaking hands.2A01:E34:EF5E:4640:E42C:92EB:E3ED:E440 (talk) 06:57, 11 October 2014 (UTC)

So that means that a scuba diving suit is a suit used for diving but not a diving suit, I guess? Wikipedia says they insulate their rubber suit with air or argon and only breath the helium mix. Sagittarian Milky Way (talk) 01:25, 12 October 2014 (UTC)

Your second sentence is correct: diving drysuits (which are rarely made principally from rubber) are typically filled with air, nitrox, or (more rarely) argon. The reason for this is however unrelated to the putative flammability of human flesh at high oxygen partial pressure, even well in excess of 1 bar). A drysuit would not typically be filled with heliox, so your recollection here may be at fault. 2A01:E34:EF5E:4640:5540:B194:D367:F145 (talk) 07:29, 12 October 2014 (UTC)

normally heat on the surface of skin will conduct into the underlying flesh and then be dissipated. You will have to be generating the heat fast enough so that heat is not removed too fast. The speed will be something much faster than humans can move hands I suspect. Graeme Bartlett (talk) 07:17, 11 October 2014 (UTC)

Just a thought about a possible mechanism—you wouldn't necessarily have to heat the surface of the hands to ignition temperature, and you probably can't do it by any reasonable method anyway. (I agree that wet human tissue is a pretty effective heat sink.) What you might be able to do is trigger a static electric discharge. The spark from that could, conceivably, maybe, perhaps, burn off a bit of dead skin, or some hairs, or something. That, in turn, might (possibly, maybe) burn hot enough to start a self-sustaining fire, particularly if it involved your clothing.

Heck, that's a much more plausible mechanism, there. Forget directly igniting a fire on the surface of your hands. Vigorously rubbing your hands together triggers a static discharge in your sleeve, which then goes whoomp in the pure oxygen atmosphere. The very rapid flame propagation under those circumstances makes it look like you started a fire by rubbing your hands together, and you're too busy screaming to correct the misconception. Still, very speculative—I'd need to see the experiment. TenOfAllTrades(talk) 10:58, 11 October 2014 (UTC)

How much are flash points and fire points and flame points and flame temperatures affected by breathable variations in oxygen partial pressure (say 0.07 to 1.6 bars) and total pressure (Armstrong's limit to? I think the pyrology points are lowered by oxygen content. Of course, if there's a relatively small amount of hydrogen or burnable or corrodeable dust, the highly concentrated oxygen will combine with just a spark, extremely quickly, and the air would be enough kindling for your hair and maybe your clothes, which might dry your skin enough to be kindling for your skin, which might be kindling for your fat, which might be kindling for your muscles and organs, all because you rubbed your sleeves in very dusty oxygen. Sagittarian Milky Way (talk) 01:25, 12 October 2014 (UTC)

The related question here is: at what oxygen level will flesh simply catch on fire and burn, as in spontaneous human combustion? Can a malicious spy simply hook an oxygen tank to a smoker's living room and cackle with glee as the mark is consumed by a paranormal phenomenon? Well, I think this has to do with Gibbs free energy, in particular the RT ln Q_r part, where Q_r is the reaction quotient. More oxygen should mean more Gibbs free energy released when it reacts (i.e. more entropy in equalizing oxygen with reactant). We know that normally, meat gives off about 4000 kcal per kg and fat by 9000 kcal per kg, at least when digested by us, which is pretty thorough. We know that heating water by 1 degree takes 1 kcal per kg. So burning meat can raise the temperature of the meat by... 4000-9000 degrees. Hmmmm, even granted a gap of something like 10 kcal at the boiling point, I'm don't quite have an explanation here why people don't make good bonfire material normally... maybe I better pause at this point. Wnt (talk) 14:32, 11 October 2014 (UTC)

I don't know a thing about Gibbs free energy, but doesn't that just mean that if you had a big cocoon of infinitely insulating material that reflected all energy, coated with a 4200°F blackbody containing a centillionth electron volts of thermal energy and filled it with 68°F petrol vapor/oxygen at stochiometric ratio, you'd get (10,800K/(14.7*23.2%+1)+293.15)*9/5-459.7=~4200°F after a spark occurs there, which doesn't sound that impossible, considering that power plant efficiency is limited by the blades melting? Sagittarian Milky Way (talk) 01:25, 12 October 2014 (UTC)

Just hooking a tank of gas to a normal room can't produce more than 1 atmosphere pressure of oxygen, because it'll just leak through the walls and around the doors and windows. The malicious spy would first have to convert the room into a sealed pressure chamber. (The Apollo capsule, being a spacecraft, was a pressure chamber. They had more than 1 atmosphere of pressure in there because they wanted positive pressure on the walls for the test, as there would be in space, and it was pure oxygen because that's what the capsule was designed to be pressurized with, to keep the weight down when in space, where the pressure would be something like 0.3 atmosphere. Perfectly logical—if you don't think about the fire hazard.) --174.88.135.88 (talk) 14:57, 11 October 2014 (UTC)

Unrelated, but how can humans just start breathing a completely different mixture! (pure O2, when our atmosphere is built out of 78% nitrogen). doesn't it come with any biological effects to just remove literally 78% of the air we breathe! don't we use nitrogen for anything? And if not, can't you just replace it with any other inert gas too? How can lungs just go from removing o2 from a mixture that's 78% oxygen, to just breathing pure oxygen? Totally bizarre for me. 212.96.61.236 (talk) 20:29, 13 October 2014 (UTC)

We don't need the N2. It could be anything inert. It's just there to keep embers and sparks of Earth from bursting into flames. I think most of the world would burn in short order if air was that flammable, the burnable parts that is. Climate change caused by burning the world in a short time combined with the difficulty of keeping farms from being destroyed by lighting fires might kill us all. However this is completely self-centered. The inert gas really does have to be nitrogen because if you ask a plant what's wrong with turning the nitrogen into argon they would say that they need it to grow! Sagittarian Milky Way (talk) 22:42, 13 October 2014 (UTC)

What is the smallest Big Bang possible?

As we can see around us, the Big Bang involved an enormous (to us) quantity of matter and now we have trillions of stars and galaxies. But what is the smallest universe that could occur? Could you have a lonely universe with just two solitary stars? --86.174.15.245 (talk) 23:24, 10 October 2014 (UTC)

That is an interesting question, but it would depend not only on the initial mass, but also on the initial expansive velocity. I suspect a universe like that might be a starless cloud of mostly hydrogen or a single black hole. You'd have to specify all the initial conditions, then ask at the math desk for the best experts. Of course, the internet eing what it is, perhaps we do have a site called initialconditions.com μηδείς (talk) 23:59, 10 October 2014 (UTC)

The only possible answer is "we don't know". We don't know how big this universe is--for all we know, it could be infinite. No theory of physics explains how or why the Big Bang occurred. In fact, no theory of physics predicts what the universe was like at the moment of the Big Bang. It is a singularity, which usually indicates a breakdown in our physics. --Bowlhover (talk) 00:16, 11 October 2014 (UTC)

It is not a complete or satisfying answer to just say "it was a singularity." The current accepted theory or standard model of cosmology might give a minimum mass-energy for a universe. If not, why couldn't it have one star and one planet? Or one hydrogen atom? or something less? Edison (talk) 01:10, 11 October 2014 (UTC)

Bowlhover's right. Either we chose arbitrary values, or the ones that are given. If we're going to chose arbitrary values than of course we can chose those that give a two-star or a star-and-planet universe or an ever dissipating cloud of non-metals. I wonder if we have an article that explains the arbitrary? μηδείς (talk) 01:25, 11 October 2014 (UTC)

Edison, you are absolutely right that it is neither complete nor satisfying. That's what scientists are trying to fix. Mingmingla (talk) 01:30, 11 October 2014 (UTC)

I think you and Edison are wrong, Mingmingla, in expecting a definitive prior answer. There are simply things called singularities, past which we cannot see. We cannot see the part of the universe that is further away due to its expansion by about 13 Billion lightyears. We can't see the inside of black holes. We can't see the position and velocity of the smallest particles at the same time. None of this is controversial at all according to current consensus. The idea that we can see what happened before, and hence explain the big bang is simply ludicrous. It's another singularity, anothe event horizon. We can choose random numbers and plug them into a formula to get the results we want, but we can't look past the big bang and pick our own input data--we simply have what we have. μηδείς (talk) 01:52, 11 October 2014 (UTC)

There's a lot of speculation here, but I should point out that singularities just represent the breakdown of an equation, not necessarily of physics itself. In a sense any electron is a singularity, with a hypothetically infinite rest mass due to the intense electric field hypothetically residing near the point particle (and efforts to define a classical electron radius aren't any better). Our article on micro black hole speaks of conjectures about what a remnant singularity would look like, with no clear answers. You can actually buy a pig in a poke, but critiquing a theory without naming what it is is much harder. I hope someone will answer this by referencing actual work on the hypothetical budding off of universes, evolution of universes, etc. (even if I don't really believe it). Wnt (talk) 14:19, 11 October 2014 (UTC)

I should clarify that singularities are types of event horizons in the general sense, not the other way around. If there's any better word for boundary or limit past which we cannot see I am all for it. μηδείς (talk) 15:11, 11 October 2014 (UTC)

Well, maybe they're event horizons, maybe they're firewall (physics), maybe they're fuzzballs ... I don't hear a great degree of certainty. Given the black hole information paradox I find myself ever more skeptical of the "event horizon" concept, because it seems in some sense the information escapes. I would love to read more about whether any other information escapes - in particular, as handy-dandy a sci-fi concept as it is, I wonder whether the notion of using a black hole as a catalyst to convert matter to antimatter will really hold up to examination. Wnt (talk) 17:19, 11 October 2014 (UTC)