6,004 reputation
1641
bio website jfitzsimons.org
location Singapore, Singapore
age 32
visits member for 3 years, 5 months
seen Dec 6 '13 at 16:11

I have just moved to the Center for Quantum Technologies in Singapore, after spending the last 3 years as a Merton College JRF in Theoretical Physics and a Senior Research Fellow in Oxford University Department of Materials. My research focuses largely on theoretical aspects of quantum information processing. In particular I am interested in spin networks, measurement based computation, cryptography and computational complexity.


Jan
23
comment Can gravitational potential energy be released in a fire?
@Sklivvz: Yes, it does. However, it is in a subtle way: The gas produced falls into equilibrium, so this heat is not caused by the combustion reaction, but at a later stage.
Jan
23
comment The origin of the value of speed of light
It doesn't have to be 1, you can pick any non-zero value.
Jan
23
comment The origin of the value of speed of light
+1 for pointing out the only sane choice of units (none!).
Jan
23
comment The origin of the value of speed of light
@Johannes: That is not the point at all. The way units are defined in terms of setting specific values to physical constants doesn't mean those constants can't change. The consequence is simply that a better measurement of the speed of light means that my apartment is a different size in those units. This clearly does not mean c or $\mu_0$ or $\epsilon_0$ are fixed, simply that their measurement in SI units is. This is a quirk of the choice of units, not something fundamental.
Jan
23
comment The origin of the value of speed of light
@Johannes: that's not true. Their value in SI units is defined, but that is because they are used to define the units. It's not the same thing at all.
Jan
23
comment The origin of the value of speed of light
@Johannes: All three are measurable quantities, so you are free to define any one in terms of the other two.
Jan
23
comment Double slit experiment near event horizon
@Columbia: you clearly aren't violating it, as the linearity of quantum mechanics is preserved. The theorem is a simple consequence of linearity.
Jan
23
comment Why does a ballerina speed up when she pulls in her arms?
@Sklivvz: you referred to how hard she pulled in her arms. That is clearly a reference to force. If you remove or correct that paragraph, I'll remove my downvote.
Jan
23
comment Can gravitational potential energy be released in a fire?
@Sklivvz: of course you don't see an effect if you model the whole atmosphere without gravity (which is what you are doing here), but that model does not reflect reality.
Jan
23
answered The origin of the value of speed of light
Jan
22
comment Can gravitational potential energy be released in a fire?
@Georg: I'm afraid I'm one of those too, but I'd like to think I'm still ok on thermo and statistical mechanics.
Jan
22
comment Can gravitational potential energy be released in a fire?
(By here I mean in the answers to this question, not this specific answer)
Jan
22
comment Why does a ballerina speed up when she pulls in her arms?
@Carl: Exactly, it's the work done that counts, not the profile of force used.
Jan
22
comment Can gravitational potential energy be released in a fire?
@Georg: The GR stuff is nonsense. It is obviously not necessary to include GR effects to solve this problem. There is simply a huge amount of noise to signal here.
Jan
22
comment Can gravitational potential energy be released in a fire?
@Sklivvz: You do have them at a lower height, that's the whole point. The charred remains may stay at the top, but anything that has literally gone up in smoke will reach equilibrium with the atmosphere, which will alter its average elevation.
Jan
22
comment Why does a ballerina speed up when she pulls in her arms?
@Sklivvz: She needs to apply a constant force to keep the arms in the new position, yes, but this doesn't mean that pulling in harder will make her spin faster, her arms reach a new position and to keep them there there is only one value of F she can apply. The harder she pulls in initially the faster her arms reach that new position, but in the end the force has to be the same.
Jan
22
comment Can gravitational potential energy be released in a fire?
@Sklivvz: No, its not. It's due to the fact that the Gibbs states for a gas in a gravitational potential are different to those for a gas free from gravity.
Jan
22
comment Why does a ballerina speed up when she pulls in her arms?
@Sklivvz: This isn't a personal attack, it simply that the line "This is due to the fact that the spin velocity is a function of how hard you pull your arms in." is false, and I was pointing that out. It's an unfortunate coincidence that I have problems with your other question in parallel. I've been trying to raise the quality of the answers by flagging errors.
Jan
22
comment Can gravitational potential energy be released in a fire?
To explain further, imagine there was no atmosphere at all, and you add gas either at sea level or at a much higher altitude. The gas has to settle into a pressure gradient in both cases, but in the latter this involves molecules falling on average, where as in the latter some will need to rise.
Jan
22
comment Can gravitational potential energy be released in a fire?
@Sklivvz: No, it doesn't. The molecules literally fall (on average).