6,212 reputation
1943
bio website jfitzsimons.org
location Singapore, Singapore
age 32
visits member for 4 years
seen Nov 17 at 5:14

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 Does decoherence need non-determinism?
@WIMP: Can you please revise the question to make it clear exactly what you are asking? It's currently not clear either from the question or subsequent comments.
Jan
23
comment Does decoherence need non-determinism?
You need to rephrase your question if both myself and Matt have misunderstood your intention. Are you now asking if you can deterministically collapse to a particular eigenstate? The answer to that is no, because it violates linearity.
Jan
23
comment Does decoherence need non-determinism?
@WIMP: The first line of my answer reads: "if by deterministic you mean possessing a local hidden variable interpretation". Certainly global hidden variables can be made to work, but then they always can.
Jan
23
comment Can gravitational potential energy be released in a fire?
@Sklivvz: If the entire mass of the fuel did remain at the top, then you would be correct. However, this is not presumably not the case. When you burn something, in most cases you are converting a significant proportion of the mass to gas.
Jan
23
comment Why does a ballerina speed up when she pulls in her arms?
@Sklivvz: I have no objections to the new form, and have removed my downvote.
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.