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bio website nathanielvirgo.com
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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.


1d
comment Thermodynamics: heat transfer
No time to write a detailed answer, but in short you're 100% correct, energy flows in both directions, always. The second law applies to the net transfer of hot-to-cold minus cold-to-hot, averaged over time.
2d
answered Is speed an intensive property?
Sep
16
awarded  Necromancer
Sep
16
answered MIcrocanonical and Canonical - The thermodynamic limit
Sep
14
awarded  Nice Question
Sep
12
answered How to do linear stability analysis on this system of ODEs?
Sep
12
comment Entropy / Structure Relations
Order is tricky to define, and I'd suggest you're better off not trying to. Entropy is often said to measure disorder, but I find it better to think of it as measuring, well, entropy. We tend to find it correlates inversely with our intuitive notions of order, but this isn't always true. (For example, is an emulsion more ordered than phase-separated oil and water? My intuition says no, but entropy-as-disorder says yes.) For me the greater insight is attained by understanding entropy for what it is, rather than trying to map it to concepts like order. But that's just my opinion.
Sep
10
awarded  Nice Question
Sep
10
comment Monte carlo simulation for continuous spin model (e.g. XY or Heisenberg model)
Why do you need to discretise it? My intuition says that it's no different from most other continuous physical phenomena, where a floating point representation is plenty good enough.
Sep
8
comment Difference between heat capacity and entropy?
@AndréNeves I'm pretty sure he means the entropy change is material independent - any material heated by an amount $\delta Q$ at temperature $T$ will change its entropy by $\delta Q/T$. The total entropy is material independent, however, precisely because the heat capacity is material dependent.
Sep
6
comment Quantum Entanglement - What's the big deal?
I use detectors aligned at 0 and 90 degrees, depending on the question I'm asked, and you use detectors aligned at 45 and 135 degrees. If you work through it, you should find that gives the expected score I quoted.
Sep
4
comment Is there a minimum energy content of information, other than 0 Joules?
Landauer's principle doesn't apply to storing or transmitting bits. In fact it says that in principle neither of these things take any energy. Landauer's principle says the only thing that takes energy is erasing bits, which isn't needed for transmitting them. (The points about the noise floor are quite reasonable though.)
Sep
2
comment $\mathrm{CO_2}$ rate of deposition
That's basically what the paper says that John Rennie linked to - they propose a liquid nitrogen cooling system, which requires energy input, but it's much more efficient than doing it in a warmer climate where you have to cool the air a lot more.
Sep
2
comment $\mathrm{CO_2}$ rate of deposition
The main figure in the Nat Geo article is correct though - they did measure a temperature of $-93^\circ\mathrm{C}$ by remote sensing. But that's just a momentary thing - the average temperature is much higher, so any CO2 formed will sublime again later, especially during the summer. If the temperatures regularly get that low, I suppose it might be possible to store the resulting dry ice in insulated containers, preventing it from turning back to gas. But my intuition says this probably can't be done on a large scale.
Sep
2
comment $\mathrm{CO_2}$ rate of deposition
Hmm, there's something a bit fishy there - the article says "Antarctic regions are always cold, averaging a nippy -127°F (-83°C) and fluctuating only a few degrees up and down", but in fact $-127^\circ\mathrm{F}$ is $-88^\circ\mathrm{C}$, not -83. Sadly, I suspect this figure is just a mistake on the part of the author.
Sep
2
comment $\mathrm{CO_2}$ rate of deposition
Can you give a source for the figure of $-83^\circ\mathrm{C}$ as a mean temperature? From some informal googling, it looks like there are recorded temperatures well below that, but I'm not finding anything that low quoted as an average. The lowest I can see is the daily mean temperature at Vostok Station in August, which is $-68.0^\circ\mathrm{C}$. If there were areas with annual averages lower than $-78.5^\circ\mathrm{C}$, one would probably expect to find deposits of solid $\mathrm{CO_2}$ there already.
Aug
31
comment Why is it so hard to mix spaghetti with meatballs?
@Jim if the question was "what can I add to the sauce to make these items mix" then it would be a cooking question, but it isn't, it's "why don't they mix?". It's an excellent example of an everyday physics question, and what's more, from a physics point of view the answer isn't at all trivial or obvious as far as I can see.
Aug
31
comment Why is it so hard to mix spaghetti with meatballs?
Or another way to tell: before cooking the spaghetti, break it up into small pieces, maybe about an inch long (2cm). If granular convection is the reason this should make no difference - the meatballs will still separate. But this should greatly reduce the entropic effect, so if my hypothesis is right then doing this will make the meatballs and spaghetti mix more easily.
Aug
31
comment Why is it so hard to mix spaghetti with meatballs?
The other possibility is: mix spaghetti and meatballs in a shallow pile on a big plate. If the meatballs always sit on top of the spaghetti, this suggests granular convection is the reason, but if they end up next to the spaghetti it suggests a different explanation, which might be the entropy-driven phase separation I described, or it might be something else.
Aug
31
comment Why is it so hard to mix spaghetti with meatballs?
@fffred they're two different hypotheses, and to me it seems likely that both are at play. It's hard to think of an experimental way to test between the two --- other than the rather expensive method of cooking pasta on the international space station. If the meatballs separate even in zero-g then we know it's not due to granular convection.