Nathaniel

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I'm a post-doctoral researcher with a wide range of interests. My career is in complex systems science (or maybe cybernetics) and the origins of life, but I also have research interests in

the foundations of statistical mechanics and its relationship to information theory
Earth systems science
non-equilibrium thermodynamics in general

I'm also generally interested in the foundations of quantum mechanics and in black holes, though I wouldn't say I'm an expert on those things.

It's probably worth noting that despite the fact that my research is in physics-related areas, all my degrees are in other subjects. If I occasionally seem to start talking in an alien language, this is probably why.

	6,259 reputation	bio	website	nathanielvirgo.com	visits	member for	1 year, 7 months
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Jul 7	comment	Why are the physical sciences described perfectly by mathematics? @Argus yes, but maths is just communication taken to an extreme of precision. But I was also being a bit flippant - the purpose of mathematics as a tool for communication does not automatically explain our success in using it to describe the world. This is a deep mystery with no easy answer, in my opinion.
Jul 7	comment	Phase space volume and relativity @PeterMorgan having looked at it a bit more closely, I'm not sure if Qmechanic's link does answer my question - or at least, if it does, it does it in the context of QFT (which I have no background in), whereas for the moment I'm primarily interested in systems composed of classical particles. I hope my recent edits to the question will make it easier for an answerer to address it on a level that I can understand.
Jul 7	comment	Why are the physical sciences described perfectly by mathematics? What else would you use to describe them?
Jul 7	revised	Phase space volume and relativity added 1587 characters in body; added 8 characters in body; deleted 19 characters in body
Jul 7	comment	Phase space volume and relativity @PeterMorgan there's a bit too much GR jargon in Qmechanic's link for me to easily digest it. Given time I'm sure I can extract what I need from it by myself, but if you're able to do it for me perhaps you could post it as an answer? (By the way: I know that the system's state is not Lorentz invariant; I suppose I'm hoping that with the correct generalisation of phase space volume this will turn out not to matter.)
Jul 7	comment	Phase space volume and relativity @JerrySchirmer I've edited the question to make it clear that I know special relativity can't change or invalidate Liouville's theorem in itself. Hopefully this will make it clearer that what I'm asking ("how does the phase space volume change under a Lorentz boost?") is a different question.
Jul 7	revised	Phase space volume and relativity added 350 characters in body
Jul 7	asked	Phase space volume and relativity
Jul 4	comment	Why is the temperature outside the airplane lower than the ground temperature? @RonMaimon I'm not sure of that figure - I just know that the atmosphere as a whole is more or less a black body at IR wavelengths. Some colleagues of mine will probably know though - I'll ask them later in the week.
Jul 4	comment	Can the lightning be captured and used as power source? Another consideration that could be added is that the available power from lightning isn't really all that much. The power source for lightning is only a tiny fraction of the wind energy that powers the storm - so it would make more sense to extract the power from the wind in the first place, or from the sunlight that ultimately powers the wind.
Jul 4	comment	Why is the temperature outside the airplane lower than the ground temperature? See, for example, asd-www.larc.nasa.gov/ceres/brochure/rad_bal.gif for figures on how much IR is absorbed and remitted versus transmitted.
Jul 4	comment	Why is the temperature outside the airplane lower than the ground temperature? There's a slight mistake in this answer: although the atmosphere is transparent to visible light, it's really, really good at absorbing and emitting in the infra-red range, to the point that it behaves as an almost perfect black body. The top is cold because it's good at emitting, not because it's bad at absorbing. If you don't believe me, use the Stefan-Boltzmann law to calculate the Earth's temperature assuming it's a black body, and you'll get the temperature of the stratosphere. The reason the surface is warmer is the greenhouse effect.
Jul 3	comment	Why does Joule-Thomson expansion of a gas do no (external) work? Yes, that's it :)
Jul 2	comment	Why does Joule-Thomson expansion of a gas do no (external) work? @BerndJendrissek it doesn't; it doesn't need to. The $pV$ term just tells you how much energy the gas loses due to doing the pushing, or gains from being pushed. Whether the thing being pushed is a turbine or just more gas makes no difference - it's equal to $pV$ in either case. In this case the thing being pushed is indeed just more gas.
Jul 2	comment	Why does Joule-Thomson expansion of a gas do no (external) work? @BerndJendrissek I should be a bit clearer - the work associated with the pressure change is done by some parts of the gas on other parts (i.e. it's the $pV$ terms in my answer), so it's not counted as work done on an external system. In the Joule-Thompson experiment there is no heat exchanged with an external system (because it's insulated), and there's no work done on an external system, because there's nothing that's being moved against a force, other than the gas itself. This is why the difference in the $pV$ terms can't do anything other than change $U$.
Jul 2	answered	Does turbulence violate Galilean relativity?
Jul 2	comment	Why does Joule-Thomson expansion of a gas do no (external) work? If the gas were ideal, it would still need to do work in order to force the gas packet out; it's just that (I think) this would be equal to the work done by the gas packet as it leaves the valve. Deviations from the ideal gas law don't make the $pV$ terms go to zero, they just introduce a difference between $p_1V_1$ and $p_2V_2$. Does that make it clearer?
Jul 2	answered	Why does Joule-Thomson expansion of a gas do no (external) work?
Jul 2	comment	Why does Joule-Thomson expansion of a gas do no (external) work? No, wait - a gas expanding into a vacuum should stay the same temperature, not cool down. I guess I don't fully understand the Joule-Thompson effect after all. I'll look into it and get back to you.
Jul 2	comment	Why does Joule-Thomson expansion of a gas do no (external) work? I'm not sure if the above answers your question - if you feel it does then say so and I'll post it as an answer.