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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
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.
Feb
15
comment Harvesting hydrogen from a star
@Floris e.g. this blog post shows that if you naïvely extrapolate past economic trends you find human energy use will pass the Sun's total output in less than 2000 years. I don't think this figure is particularly plausible, but I do think it's plausible that it could happen eventually. (Not good or bad, just plausible.)
Feb
15
comment Harvesting hydrogen from a star
@Floris the question is coming from the somewhat dystopian perspective that societies' energy requirements can run out of control. Our society is coming close to wrecking our planet because of exponentially increasing energy requirements; the thought experiment is about what would happen if this exponential economic growth continued to the point where we'd end up wrecking the Sun as well. If this happens elsewhere it should be detectable, so I'm hoping this weird dystopian thought experiment can be turned into a testable hypothesis.
Feb
15
asked Harvesting hydrogen from a star
Feb
14
comment What is the interpretatation of individual contributions to the Shannon entropy?
Aah, I'm not sure if it works. My idea was to set up a situation where you can send either signal $A$ or $B$, but where there's a cost to send one of the signals but not the other. Then by trying to maximise (total information transmitted)/(expected cost) you might end up maximising $-p(A)\log p(A)$ to get $p(A)=1/e$ as the optimum. But the exact thing I thought of doesn't work, so I need to think more about it.
Feb
14
comment What is the interpretatation of individual contributions to the Shannon entropy?
Interesting - thanks. I've thought of another case where it comes up as well, which I've been meaning to post as an answer. Let me see if I have time to do that now.