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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.


2d
comment Space elevator: a Earth rotation brake model
(Though I'm not even sure the dissipation thing is that big of a worry anyway - why wouldn't you just transfer the heat to the cable and let it radiate away slowly?)
2d
comment Space elevator: a Earth rotation brake model
Why would it act as a brake? The only friction mentioned in the article is between the elevator and its cable. The article says this will produce enough heat to worry about getting rid of it, but it won't slow down the Earth any more than a normal elevator in a skyscraper does.
Oct
23
comment At what velocity does space no longer equal a vacuum?
@BenCrowell I'm not sure (it's a while since I read the book in question), but I think this particular thing is based on reality. It's basically just the point that once you're travelling near $c$, the odd H atom or dust particle here and there can no longer be neglected, because of the enormous kinetic energy involved in collisions with them. (I might be wrong though.)
Oct
12
comment Is it possible to start fire using moonlight?
Well, the Moon's surface temperature during the day is about 123 celsius, which isn't hot enough to ignite paper or lighter fluid, so if we had to rely on black-body radiation from the Moon and pure optics then it would be impossible. But since as you say moonlight is reflected rather than re-emitted, it might be in-principle possible. I imagine you'd need a ridiculously large collection area though.
Oct
11
comment Why is $d$ generally not used instead of $r$ in Newton's derivation of force of gravitation?
I would guess it's because the most obvious application of Newton's law is to calculate the force on something orbiting a much heavier object in a roughly circular orbit. (E.g. planets around the Sun, or satellites around planets). In this case $r$ is the radius of the orbit.
Oct
10
comment Describe Ising model dynamics in stochastic differential equation or stochastic process
For the stochastic process approach, you might like to look into "Glauber dynamics". As for whether there's a meaningful way to approximate/summarise the dynamics as coupled differential equations, I don't know. It sounds hard.
Oct
7
comment Are all machines linearly scalable?
An even earlier influential discussion was Discourses and Mathematical Demonstrations Relating to Two New Sciences (Galileo, 1638). As I understand it from second-hand accounts, one of the two sciences was the relation between material strength and scaling, and the other was kinematics.
Sep
28
comment Disequilibrium during infinitesimal steps of a thermodynamic reversible process & cause of maximum work to be achieved during reversible process?
... If there is no friction at all, the oscillations will take place for a very long time - but not forever, because the gas itself has some viscosity, and this will eventually turn the kinetic energy into heat. On the other hand if there's lots of friction the piston won't oscillate at all, but will just slowly move towards its equilibrium point. But in all of these cases the amount of heat generated will be the same. It has to be, because the final position of the piston is the same, so the energy difference between the initial and final states is the same. All that energy must become heat.
Sep
28
comment Disequilibrium during infinitesimal steps of a thermodynamic reversible process & cause of maximum work to be achieved during reversible process?
@user36790 actually it's due to a lack of friction. Imagine the system before you remove the first piece of lead. The pressure force balances the weight of all the lead shot. Now remove one piece - now the pressure is the same, but the weight is less, so the piston will start to move up. But this decreases the volume, and therefore the pressure force. Shortly the weight will be greater than the pressure force, so the piston will slow down and reverse its direction, compressing the gas again. These oscillations will continue until friction damps them, and this friction generates heat. ...
Sep
27
comment Is a chain REALLY only as strong as its weakest link
I've edited my answer - see the last paragraph.
Sep
27
comment Is a chain REALLY only as strong as its weakest link
This isn't really a case of the thicker string being weaker, though, it's just a case of more force being applied to the stronger string than the weaker one.
Sep
27
comment Disequilibrium during infinitesimal steps of a thermodynamic reversible process & cause of maximum work to be achieved during reversible process?
...this means that the total energy change of the system is the same - the question then is how much of that energy went into heat, and how much went into work? In the case of the lead shot, most of it goes into work - when you remove a piece of shot, the piston lifts the rest of it against gravity, which is work. But it also jiggles the piston around a bit and makes some heat. When you remove a grain of sand, the amount of jiggling is much less and so even more of the energy goes into work. By the time you get to infinitesimal grains, there's no jiggling (and no heat generated) at all.
Sep
27
comment Disequilibrium during infinitesimal steps of a thermodynamic reversible process & cause of maximum work to be achieved during reversible process?
@user36790 after you've removed the 1000 pieces of lead shot, you've removed a total weight of $1000mg$. This has allowed the piston to expand, doing work. After you've removed the 100,000 grains of sand, you've removed a force of $100{,}000\times (m/100)\times g = 1000mg$, the same as for the lead shot. So although the total amount of heat generated by friction goes to zero as the size of the grains decreases, the total change in volume and force stay the same. (to be continued...)
Sep
25
comment Why is the sky never green? It can be blue or orange, and green is in between!
There are definitely some green pixels in that image, but I think if you're actually looking at the sky it's very difficult to perceive it as green, rather than a sort of superposition of orange and blue. I'll have to pay attention to it next time I see a sunset like that.
Sep
18
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.
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
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.)