Wikipedia:Reference desk/Archives/Science/2018 August 7

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August 7

How long does it take for the Heisenberg uncertainty principle to scramble the weather?

Knowing every law of physics and particle in the observable universe to the quantum level and having a real-time Planck length and Planck time-scale physics model wouldn't let you predict Earth's weather beyond x weeks in advance right? What is x?

2. At what point does the 2018 level of knowledge of the current state of the atmosphere become the weakest link? There should be a level of weather computer power where no amount of extra computing power could help much without better weather satellites or something right? It might be orders of magnitude better than current weather computers but more computing power can't keep making predictions better forever at the current (or any finite) level of input detail. Sagittarian Milky Way (talk) 03:31, 7 August 2018 (UTC)

There is no need to invoke quantum mechanics here; weather is way waaaaaayyyy beyond the limit where classical mechanics applies. The problem is that weather is a chaotic system. x is the Lyapunov time. Without knowing everything about the initial conditions of the system, you can only predict its future state out so far. In practice there are other limitations as well, like our lack of complete understanding of the Navier–Stokes equations. There's a Millennium Prize in it for you if you can fix that! --47.146.63.87 (talk) 04:20, 7 August 2018 (UTC)

So how far could God predict the weather if he turned off his omniscience for the dice rolling? 3 weeks? 4? More? Sagittarian Milky Way (talk) 05:18, 7 August 2018 (UTC)

You should start here and then read the references cited in that paper. Someguy1221 (talk) 05:37, 7 August 2018 (UTC)

How do you know the weather is not exactly the way God plans it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:37, 7 August 2018 (UTC)

No one can know but this seems to be a fire-and-forget God. Maybe there's an afterlife though. We'll find out one day. Sagittarian Milky Way (talk) 05:47, 7 August 2018 (UTC)

Well, that's the religion of causality. As I understand it, the creed is roughly that there were some kind of small random variations a very long time ago, which may or may not have been planned by somebody, and these "caused" our current situation, which is therefore only planned in a "watchmaker God" model if there is a deterministic physics. I would think it would make sense that the boundary conditions would be set at present or future points of spacetime, but the whole notion of the past "resulting" from mathematical consistency with future events seems to conflict with the dogma. Wnt (talk) 12:32, 7 August 2018 (UTC)

• The Heisenberg Uncertainty Principle only applies in situations where the DeBroglie wavelength is on scale with the size of the object in question. For anything larger than a molecule, like say "the entire planet Earth", the DeBroglie wavelength is so insanely small that both the uncertainty in position and momentum can be close enough to zero as to make no difference. The general equation is Δx•mΔv ≥ hbar/2. The deal is, because the mass of any macroscopic object is so large, you can set both Δx (uncertainty in position) and Δv (uncertainty in velocity) to be about 15 decimal places to the right of the zero, and STILL get it to be greater than hbar/2, which is a TINY number. The only time uncertainty comes into it is when the mass is on the same scale as hbar, which only happens at the molecular scale and below. So no, the Heisenberg Uncertainly Principle doesn't even come into play on processes whose scale is as large as the weather. Good old chaos theory are sufficient to screw up long-term predictions. --Jayron32 13:44, 7 August 2018 (UTC)

As you predict further and further in advance you need to know the state of the atmosphere at time 0 to greater greater accuracy for it to work. Wouldn't you eventually need to know where every molecule is and its momentum, and then need to know where every molecule is and its momentum to more detail than is possible? Sagittarian Milky Way (talk) 16:40, 7 August 2018 (UTC)

You can't know that because the behavior of gases is an emergent behavior which does not depend on the individual motion of the molecules, but rather on the statistical behavior of the entirety of the system. Concepts like temperature, pressure, entropy, fluid behavior, etc. don't come out of the individual behavior of the individual molecules, but rather on the bulk behavior of the system. You can't understand weather by looking at the individual molecules even if quantum mechanics wasn't a thing. This sort of statistical thermodynamics was developed by people like Ludwig Boltzmann decades before Max Planck even thought of fixing the ultraviolet catastrophe with his quantum kludge. If you want a really good overview over the difference between individual molecular behavior (time independent) and the time-dependant statistical behavior of bulk systems, google the Feynman lecture of Entropy. It's in 2 parts, and explains it pretty well. --Jayron32 16:50, 7 August 2018 (UTC)

Back of the envelope estimate. Let's take the largest Lyapunov exponent to correspond to a doubling of the uncertainty of the state of the weather per 3 days. Then we assume that this exponential increase in error holds for the smallest perturbations, so not just for the uncertainties in specifying the initial thermodynamic state of the and flow velocities, but also the way the thermal noise in specifying the exact state and the fluctuations in the forcing would affect the evolution. So, on top of the exact deterministic flow equation there is a stochastic component due to Brownian motion of the molecules. The average effect of this Brownian motion is already accounted for by the viscosity and the thermal conductivity. But on top of this average there is a fluctuation, and part of that fluctuation will be due to quantum effects.

To answer the question we can reason as follows. The quantum uncertainty in the position of molecules is of the order of the thermal deBroglie wavelength, which is given by ${\frac {h}{\sqrt {2\pi mkT}}}$. This fundamental uncertainty present in the position of all the molecules of the system will then double every 3 days. Relative to a classical picture where the system is described as a deterministic N-body problem where we take all effects including Brownian motion into account exactly, the system will thus drift away in a random way. If we take 100 km random displacement of all moleculues to be a totally new configuraion of the system, then this should take about 152 days. Count Iblis (talk) 00:19, 8 August 2018 (UTC)

Shortest person

Who is the shortest person in the world without some kind of genetic abnormality?

Living or dead? People were generally much shorter in the past. ~Anachronist (talk) 06:15, 7 August 2018 (UTC)

0.1 mm is about the smallest for a human. Most are this size immediately after conception. Graeme Bartlett (talk) 10:02, 7 August 2018 (UTC)

Even less impressively, we all once weighed about 0.004 of a milligram. InedibleHulk (talk) 11:32, 7 August 2018 (UTC)

Ah, mass. A 609 picogram sphere of styrofoam is a lot more not microscopic than it sounds, 10kg of iridium is a lot smaller than it sounds. Sagittarian Milky Way (talk) 17:38, 7 August 2018 (UTC)

According to polystyrene, "expanded polystyrene" (in corporatese) has density 0.016 g/cm^3; iridium is at 22.56. That's a ratio of 1410, which means that the size of spheres of the two differ by a linear factor of 11.2. Compress a styrofoam sphere by a factor of 11.2 in all directions, and it's dense as iridium/osmium! Density really has a lot less range to work with than a lot of other physical properties. Wnt (talk) 21:10, 7 August 2018 (UTC)

How do you compress styrofoam that much? With explosives? It's still made of a compound with a density of about 1 g/cm^3. It'd be neat to see what happens if you compress it to the highest pressure diamond vices can make though (slowly enough that it doesn't melt or something) Sagittarian Milky Way (talk) 22:06, 7 August 2018 (UTC)

You may also be interested in List of the verified shortest people and Preterm birth#Notable cases where 20cm is given for a live born person. Graeme Bartlett (talk) 10:05, 7 August 2018 (UTC)

Presumably the OP (193.64.221.25) meant the shortest adult person. Obviously, everyone starts out as a single-celled entity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:28, 7 August 2018 (UTC)

Not an answerable question, given that there is no-one without some kind of genetic abnormality ... or, thinking it of the other way, people are just different rather than abnormal. Klbrain (talk) 22:57, 7 August 2018 (UTC)

The op says "without some kind of genetic abnormality", which is another vague statement but presumably means someone affected by dwarfism. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:49, 8 August 2018 (UTC)

I read the list of shortest people here, and almost all of them listed some named disorder or abnormality.

Being somewhat pedantic, note that dwarfism (or "short stature") is a descriptive term, not a diagnostic term. Our article says "short stature is clinically defined as a height within the lowest 2.3% of those in the general population", which roughly corresponds to an adult height of less than 147 centimetres (4 ft 10 in). Short stature can have a wide variety of causes, some of which are not genetic (although most are). Gandalf61 (talk) 11:52, 9 August 2018 (UTC)

Mars and Moon

When I observed the recent lunar eclipse in Poland, Mars was below and to the right from the Moon, but on this photo from Australia it's above and to the left. Why was that? Inverted photo? Thanks. --212.180.235.46 (talk) 19:42, 7 August 2018 (UTC)

A person standing in Australia is oriented differently (relative to the stars) than a person standing in Poland, because the Earth is a sphere. CodeTalker (talk) 20:30, 7 August 2018 (UTC)

The picture is inverted because the camera was inverted, the camera was inverted because the photographer was inverted and the photographer was inverted because that's what happens when you're down under. PiusImpavidus (talk) 07:55, 8 August 2018 (UTC)

No, no, no. We Aussies are the right way up. It's you northerners who are upside down. HiLo48 (talk) 08:27, 8 August 2018 (UTC)

On your typical Aussie map, which edge is northward? ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:42, 8 August 2018 (UTC)

Whichever edge the mapmaker randomly decided to make it. --Jayron32 17:45, 8 August 2018 (UTC)

I was supposing there was a standard approach inside Australia. How often do you see American mapmakers print a map with Texas at the top? ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:09, 8 August 2018 (UTC)

When observing the moon, we tend to be facing the equator, which is north of Australia and south of the USA. To make it look in the northern hemisphere the way it does in the southern hemisphere, look at the moon when facing the north pole. (Also, have something to lean on so you won't fall over backwards.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:42, 8 August 2018 (UTC)

This is also why in Australia the horns of the moon point the other way, as this diagram illustrates:

                     CRESCENT MOON (EVENING VISIBILITY)

Northern hemisphere                                     Southern hemisphere

E      S      W                                         W      N      E
            ) ☼                                         ☼ (

So the mnemonic of adding a line to visualise the first letter of the French word premier, "first [quarter]", or dernier, "last [quarter]", does not hold. 95.150.52.197 (talk) 13:47, 8 August 2018 (UTC)

Although the other french mnemonic of visualising the first letter of croissant (growing) or décroissant (shrinking) does work (when in applying this in France, people need to add 'but the moon is lieing') 89.225.227.82 (talk) 07:35, 9 August 2018 (UTC)

"This is also why in Australia the horns of the moon point the other way". They point the same way east or west in both emispheres, but you are rotated 180 degrees so you see east and west swapped in the first place. Or you can say that down under the sun turns the other way round? 194.174.76.21 (talk) 12:35, 9 August 2018 (UTC) Marco Pgliero Berlin

Northerners might be interested to know that the standard constellations are up the other way in the southern hemisphere. This means Orion doesn't look like a hunter. I learnt to recognise the saucepan, where the stars of Orion's belt are the base, and his sword is the handle.

Presumably Orion is not circumpolar. With a constellation like the Great Bear (Ursa Major) which never sets we see it from all angles. 95.149.37.51 (talk) 10:53, 10 August 2018 (UTC)

bisexuals, heterosexuals, and tall women

I read a forum post a while back saying that heterosexuals differ from bisexuals in their attraction to women because heterosexuals greatly undervalue tall women. I feel like that has to be spot on, but is there evidence? Wnt (talk) 21:14, 7 August 2018 (UTC)

Completely anecdotal and bad sample, but as only a 1 on the Kinsey scale and 6'2"/190 cm, this scene comes to my mind whenever I see tall and/or strong women. However, I've noticed that's an eccentricity on my part.

I'm having total source amnesia, but I would assume based on prior reading of long since closed articles that relevant sources would discuss:

• long-term evolutionary explanations for why men favor small women focused on neoteny or... ancient likelihood of physically seizing a mate... (ugh)
• sociological or psychological explanations focused on gender roles, security in manhood, etc
• explanations combining evolution and sociology, such as how the average population height tends to shrink during and after especially terrible plagues/famines/wars because smaller people require fewer calories to function (counterbalanced with need for larger men even during these times)

But I get the feeling that the matter really hasn't been completely settled (although some of the sources would probably present their views as something that should just be taken for granted) and that it's probably a combination of factors.

I'm not as certain there will be sources regarding the specific issue that straight men tend to favor short women while bisexual men are more open to taller partners. Ian.thomson (talk) 21:46, 7 August 2018 (UTC)

I think we should start by acknowledging that its difficult even to empirically validate both premises put forward here (that men tend to favour shorter women on the average and that for bisexual men the average preferred height is a little taller). Given the variances in behaviour between both cultures and individuals--as well as difficulties in formulating psychological research procedures which validate such a difficult-to-access mental processes as attraction--its difficult to know the degree to which these phenomena even exist, let alone to come up with concrete explanations for why it occurs that will be widely affirmed by the research community of cognitive scientists working in this area.

That said, I think your shortlist of broad categories of likely factors is not bad. However, there is a much more specific and well understood factor which would certainly be playing a role here, as it is one of the strongest known influences on mate selection and attraction--and one of the best researched for that matter. All mammals, humans most assuredly included, tend to favour mates which look similar to those upon whom they imprinted when young. For example, if you dye a family of mice, recently birthed young included, all pink, then the offspring will later show a preferential attraction to other pink mice, but the parents will continue to prefer more conventionally coloured partners. The same effect can be seen in the fact that humans tend to choose partners who look like their siblings (and thus themselves); if you compare small details of body and facial morphology, you will find that most husbands and wives have features (length of the bridge of the nose, contour of the ear lobe, depth of the brow, ect.) which are substantially closer to eachother than they are to the average for any immediate local population that they belong to. It is by no means the only factor by which people choose their partners (and there's reason to believe the effect has itself been influenced by increases in ethnic integration in modern societies as well as media exposure to paradigms of physical beauty that youthful individuals would not otherwise be exposed to in their immediate environment), and so not absolutely determinative of what any given individual's partner will look like, but as a general factor operating over large groups of people, it is empirically undeniable.

To the extent that this propensity maps to height as well, this goes a long way to explaining why the average man would, at a minimum, typically prefer a woman who is shorter than him, because the women in a family are almost always shorter than the men; indeed, baring developmental abnormality, it is virtually certain that male offspring in a family will be taller than their full-blooded female siblings. Of course, smaller than a given male individual does not necessarily equate to smaller than average, but it is a starting point for looking at population trends. Now, all that would make for a difficult analysis of the question of why bisexual men deviate from this norm with regard to their female partners (if that is indeed the case); one can speculate that there is some bleed-through of the traits which they find attractive in their partners, male and female. It might also be (and has been) argued that our preferred model for decoding sexual attraction is backward and upside-down and that rather than trying view individual features as components that conform to archetypes (including maleness and femaleness) we ought instead to be looking at the indvidual features as the drivers of attraction, on to to which the composite archetypes are later stamped. If that's the case, it would make perfect sense that an individual attracted to both men and women might have a span of heights that they find attractive and to which either male or female partners may conform. But that's as far as I can go into the matter based on the current state of research without striking off into a degree of speculation which would be inappropriate for the reference desk. Snow ^{let's rap} 03:44, 8 August 2018 (UTC)

It could be related to sexual dimorphism and general attraction for the opposite sex for reproductive reasons: among other traits that display sexual identity, women on average tend to be shorter than men, although their are exceptions. —PaleoNeonate – 04:38, 8 August 2018 (UTC)

Adding: if this is correct, for the same reasons many women would be attracted to tall males. —PaleoNeonate – 04:40, 8 August 2018 (UTC)

Anne Meara was taller than her husband Jerry Stiller. Lauren Bacall was taller than Humphrey Bogart. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:44, 8 August 2018 (UTC)

What's the approximate height of the world's tallest building that can fit on 20x100 feet of land?

• 25x100 feet?
• 45x100 feet?
• 60x100 feet?

Are there any taller towers that start above the ground floor? That is, they have a tower of stuff that can stand small floors (like condos) sticking out of wider floors that might have stuff that hates small floors even more (like parking, supermarkets, offices, casinos). (in some areas zoning even has to encourage wide base/thin tower or everyone would just block the sun with a lot more floors that fill their land)

What about in 1983? Reading about a zoning law passed in 1983 has made me curious about this. Sagittarian Milky Way (talk) 21:26, 7 August 2018 (UTC)

Trying to answer your last question, I think you are asking if there are any buildings which are narrower at the base than higher up; University Hall (University of Illinois at Chicago) is, and it's one of the tallest buildings in Chicago outside of the loop. The building also has an open ground floor; just pylons/stairways/elevators that you can enter from the courtyard. --Jayron32 16:17, 8 August 2018 (UTC)

I have found 150 North Riverside in Chicago. It's footprint is much longer than 100 feet but only several dozen feet thick and it has the challenging shape seen here so a 100x45 rectangular prism of the same strength/production values/usable to total space ratio can probably be built to at least 75 floors and 750 feet. In 1983 when concrete was less strong? I don't know. Sagittarian Milky Way (talk) 20:04, 9 August 2018 (UTC)

• The answer to the question "What's the approximate height of the world's tallest building that can fit on 20x100 feet of land" is 71,572 km (44.472 mi). See Space elevator (which can be in the form of a building). --Guy Macon (talk) 00:02, 10 August 2018 (UTC)

Have macroscopic materials with enough tensile strength been invented yet? Sagittarian Milky Way (talk) 00:17, 10 August 2018 (UTC)

We need high specific strength, which can be accomplished with high tensile strength or with light weight. And no, we haven't invented the material yet, but diamond nanothreads look promising.

References

--Guy Macon (talk) 17:16, 10 August 2018 (UTC)

RfC Announce: Should the EmDrive be labeled as Pseudoscience?

Talk:RF resonant cavity thruster#RfC: Should the EmDrive be labeled as Pseudoscience? --Guy Macon (talk) 22:56, 7 August 2018 (UTC)