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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.


Feb
24
comment Simplest example of spontaneous breaking of time reversal symmetry
Thanks for the answer. I do realise that the Ising model can already be seen as a spontaneous breaking of time symmetry for this reason, but I'm looking for a non-equilibrium transition in a system with an explicit time dependence.
Feb
24
comment Simplest example of spontaneous breaking of time reversal symmetry
That's interesting - it clearly is an example of spontaneous time symmetry breaking, but it doesn't have the feel of a phase transition. I'll think more about this example - thank you.
Feb
24
asked Simplest example of spontaneous breaking of time reversal symmetry
Feb
23
comment Is there a thermodynamic limit on how efficiently you can solve a Rubik's cube?
@CJDennis I'm not sure what you mean by "the original solution." Do you mean a case where one input cube can be solved by transferring information about its initial state onto a dummy cube? This can indeed only work if the machine is designed on the assumption that the dummy cube has a particular initial state. Otherwise there will be at least two different inputs that go to the same output (where "input" includes the state of the cube to be solved and that of the dummy cube), so it can't be implemented without an information-erasing step that would generate heat.
Feb
22
comment What physics concepts support the observation of the book and paper falling together?
I think the comments and close votes are misunderstanding the question. I interpret it as saying that if you place a sheet of paper on a book, it falls with it rather than being separated and slowed by air resistance.
Feb
22
comment Is there a thermodynamic limit on how efficiently you can solve a Rubik's cube?
@CJDennis that's the point - the information is not in the result from the XOR, it's in the correlations between the result and the inputs. If you keep all but one of the inputs, you still have the information, but if you erase more than one of the inputs, you don't. Thus, you can't use XOR to store information about the initial state of more than one input cube in a single 'dummy' cube, because solving the input cubes erases the inputs to the XOR.
Feb
17
answered Heat transfer through radiation and its relation with temperature
Feb
17
comment Why is spacetime not Riemannian?
From a mathematician's point of view, surely the relevant question should be "out of all the possible mathematical structures spacetime could have, why should it be Riemannian in particular?" Could you say why you feel a positive definite metric would be more reasonable/desirable/intuitive to you?
Feb
16
comment Is there a thermodynamic limit on how efficiently you can solve a Rubik's cube?
@CJDennis XOR is only a reversible operation if you also store one of its inputs. Given only the final state of the dummy cube you can't reconstruct the initial state of more than one input cube, so information has been lost.
Feb
16
comment Harvesting hydrogen from a star
@RobJeffries I have to admit I haven't. (Would like to do the calculation, don't have time right now.) I imagine it's implausibly huge, but then it doesn't have to be just one. As with the star-eating scenario, each BRJ can in principle produce the matter as well as the energy to make more, so they can multiply exponentially. I guess that's a thing that could happen - since there's more interstellar H than there is in stars, there would be little to stop such a process if anyone ever has the means and motive to start it.
Feb
16
comment Harvesting hydrogen from a star
I forgot to mention that in the scenario I'm considering, the reason for using the Sun instead of Jupiter is that Jupiter has been used up already, or soon will be. Of course the amount of energy available from fusing the mass of Jupiter is immense, but under exponential growth it won't necessarily last all that long. Although H nuclei are hard to fuse, my feeling is that a civilisation this advanced would have the technology to do so, e.g. via the CNO cycle. But if it's much harder than I'm imagining I'm willing to be corrected.
Feb
16
comment Harvesting hydrogen from a star
@annav I thought about gathering interstellar hydrogen, for example using a Bussard ramjet, but my thought was that this might be slower and less economical than harvesting from the huge gravitationally-bound lump of hydrogen nearby. Whether this is so will depend partly on whether there is a practical way to get hydrogen from the star at all, which is part of my motivation for the question.
Feb
16
revised Harvesting hydrogen from a star
Cosmologists are the people most likely to able to answer it.
Feb
15
comment Harvesting hydrogen from a star
Thanks, some useful information here. I guess the main signature would be the waste heat in that case. Since this would be of a similar or greater magnitude to the star's total output, it would probably be quite easily detectable I suppose.
Feb
15
revised Harvesting hydrogen from a star
added 195 characters in body
Feb
15
comment Harvesting hydrogen from a star
@Floris the civilisation would mostly not be on the planet.
Feb
15
awarded  Enlightened
Feb
15
awarded  Nice Answer
Feb
15
revised Harvesting hydrogen from a star
edited tags
Feb
15
comment Harvesting hydrogen from a star
@annav yes, absolutely. That's why I don't think humanity will be doing this in 2000 years. But things are different for a highly advanced space-based society that can perform fast, controlled fusion in reactors. The only resource they need is hydrogen, since they can create both energy and other elements from it, and thus support whatever population they desire. So there's basically no limits to their growth until the hydrogen starts to run out.