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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.


Jul
28
comment What does it mean to say “Gravity is the weakest of the forces”?
It may or may not also have been Feynman who said words to the effect that the question "why is gravity so weak?" can be rephrased as "why is the mass of the proton so small?".
Jul
23
comment Sea surfer position displacement
@Renan oh, there's no need to delete your answer, it's not wrong! It's just that buoyancy is only one of the forces that contribute to balancing the gravity force, especially if you're on a smaller board. The other is hydrodynamic lift, which is similar to the aerodynamic lift provided by a wing. I imagine the fluid dynamics of this are somewhat complicated, but I've never looked into them in detail. (I'm only a surf beginner myself, but I've tried standing on a longboard while not moving and it does sink. This must be even more so for shortboards.)
Jul
22
comment Sea surfer position displacement
Buoyancy isn't all that important for surfing. Unless it's a foam board (a very big, very buoyant design that's easy for beginners) a surfboard will sink if you try to stand on it in still water. Surfing works because of lift generated by moving along the water surface.
Jul
19
comment What conditions do a bunch of atoms need to satisfy to have a temperature?
@ticster maybe, but it's very dependent on me finding time - I'd say don't hold your breath!
Jul
19
comment What conditions do a bunch of atoms need to satisfy to have a temperature?
Great question! I could write a great answer if I had time, but it would be an awful lot of work. The short short version is that a system really needs to be in equilibrium to have a temperature, and the two beams travelling in opposite directions are not in equilibrium, since you could certainly extract work from such a system. But that's an over-simplification, because there are lots of systems that have temperatures without being in equilibrium. (E.g.: a human being.) Disentangling that in a formal way is possible, but as I said, a lot of work.
Jul
18
comment Not-so-hot black shirt
Not a proper answer, but when looking at an image of myself taken with an IR camera I was surprised to find that my black fleece top appeared white. So that kind of synthetic material might be an example, although I wouldn't want to wear it on a hot day!
Jul
18
comment Do objects gain and lose heat at the same rate?
@alemi that's very dependent on the situation, e.g. the geometry of the object and its surroundings. Sometimes it does make a big difference. In engineering situations where people really care about heat flow rates, people go to a lot of effort to calculate the convective heat flux. Usually you can only do it by numerically simulating the air flow, and software packages to do this are a profitable business. I've used them in the past. In this case I would expect the sign of the temperature difference to have a measurable effect.
Jul
18
comment Do objects gain and lose heat at the same rate?
This is a good answer, but it would also be worth mentioning convection. A warm object in a cold fridge will heat up the air surrounding it, which will rise up to the top and draw in more cold air from the sides. This increases the rate of cooling. However, a cold object in a warm room will cool the air surrounding it. Cold air sinks rather than rising, so it will mostly just hang around the object and stay cold. So the rate constant will actually be different in the two cases as well.
Jul
18
comment Can you explain Fermat's Principle to me?
Please say which text book you are referring to. Always, always, always give your source when quoting, on this site or anywhere else.
Jul
11
comment Should a radiation-filled Universe be scale invariant?
I'm not 100% sure of my reasoning here, but if the universe is filled with radiation then doesn't that radiation have to have a particular temperature? If so then the Planck formula gives it a characteristic wavelength, which breaks the scale symmetry. I don't know but I would assume the Friedmann equation is based on radiation at equilibrium at some temperature (which is constant over space but not time for an expanding universe).
Jul
11
comment Why do almost all nuclear reactions release energy?
I don't understand how an endothermic process can consist of exothermic steps. Obviously there can be some exothermic steps, but they have to be outweighed by other ones that are endothermic, because energy is a state function. Right? (I don't know anything about nuclear processes, but thermodynamically what you said sounds odd, unless I didn't understand it correctly.)
Jul
9
comment Is there an upper limit to a rocket's size/payload?
@Jason I've added the missing explanation to my answer.
Jul
9
comment Is there an upper limit to a rocket's size/payload?
@KyleKanos I've fixed the answer so that it explains the issue with gravitational acceleration properly, and also explains why Asad's answer to the linked question is wrong (and yours is right).
Jul
7
comment Why is there water coming out of a car’s tail pipe?
@TimS I meant by volume, which is proportional to mole number for gases.
Jul
6
comment Is there an upper limit to a rocket's size/payload?
@KyleKanos thanks, you're right that I should have included the gravitational acceleration in the equation. But unless I misunderstood it on my quick reading, I don't really agree with Asad's answer. He assumes the burn rate remains constant as the rocket size changes, which seems a weird assumption to me. If you let it scale proportionally to the mass you still end up with $m_f$ times a constant, as in my answer.
Jul
6
comment How is the logarithmic correction to the entropy of a non extremal black hole derived?
I wonder what this looks like in non-Planck units. There must be a bunch of constants inside that $\ln$ to make its argument dimensionless, and knowing what they are might give some insight into your question. (I know this is old, but just saying.)
Jun
27
comment Why does sand stick to my shoes?
I don't know for sure but I always assumed it's because salt crystallises out as the water evaporates. The test would be to use pure silica sand wetted with pure water, and see if it sticks to clean shoes.
Jun
17
comment Why isn't the best case classical solution to the CHSH game 100%?
This is getting silly. How can a question about the CHSH game be off topic on a physics site? The idea that questions have to be "about physics" has always been a bit flaky (i.e. blatantly subjective), but if you're going to draw the line here it's just ridiculous.
Jun
16
comment Reconciling “The Big Crunch” with the 2nd Law of Thermodynamics
Huw Price discussed this subject in depth in his 1996 book Time's Arrow and Archimedes' Point (prce.hu/w/TAAP.html). Price argues that entropy must indeed decrease in a big crunch, because it is the time reverse of a big bang, in which entropy increases. Note, however, that due to more recent observations the expansion of the universe is now thought to be accelerating (the cause of which is unknown but is referred to as "dark energy"), so it is no longer thought that a big crunch will occur. (This does not resolve the question, however!)
Jun
13
comment At an instant, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges?
@SpacetimeEngineer entropy doesn't have anything to do with it. I illustrated my answer with a two-body system in order to male that clear. There are no entropic effects in a two-body system, and hence the time reverse looks much like the forward version. Of course I can't construct an orbital system out of like charges, but that only supports my argument.