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Sep
13
comment Theoretical Physics - How to?
@ptomato: I don't think it is at all reasonable to assert that theorist "who think they can be a good theoretical physicist with a background in pure mathematics, are not well-rounded enough to be good physicists." In fact, it seems trivial to find counter examples.
Sep
13
comment Theoretical Physics - How to?
@ptomato: Of course I don't think that's all they do, but experimental physics is fundamentally different from theoretical physics. They are distinct subjects, and while there are some people who are good at both, they are few and far between. You are asserting that experimentalists need to know differential geometry, but the fact is that most don't know any, and with good reason. It is simply not relevant to whatever they are working on. Similarly, theoretical physicists often come from purely mathematical backgrounds, and are unfamiliar with many experimental techniques.
Sep
13
comment Theoretical Physics - How to?
@ptomato: If they trying to seal a vacuum chamber? Sure. It's simply not relevant to that specific task. Very few experimentalists will have ever studied differential geometry, or example, but it is absolutely fundamental to much of theoretical physics.
Sep
13
awarded  Necromancer
Sep
13
comment What can the D-Wave quantum computer do?
@Jus12: Yes, I know. I just thought I should point out that the statement needed is slightly stronger.
Sep
13
revised What can the D-Wave quantum computer do?
added 169 characters in body
Sep
13
comment Size of a quantum computer to effectively calculate macroscopic reality from quantum mechanics
This answer is incorrect and tries to violate the Holevo bound. From an $n$-qubit system, you can at best extract $n$ bits.
Sep
13
comment What can the D-Wave quantum computer do?
@Jus12: Solving an NP-complete problem would mean that it could solve any problem in NP (drop the -complete), and as factoring is in NP, you are correct that it could solve it. However, you will notice that nowhere in my answer do I say it could sole NP-complete problems in polynomial time, and DWave has backed away from making such claims. Thus, even if it works as advertised, there is no reason to believe it would be could at factoring. There is a generic polynomial speed-up from quantum mechanics, and that is what they are counting on, even for exponential time algorithms.
Sep
13
comment What can the D-Wave quantum computer do?
@Lagerbaer: Factoring is not known to be NP-complete, but this can't be proven without first proving that P$\neq$NP.
Sep
12
answered What can the D-Wave quantum computer do?
Sep
12
comment Theoretical Physics - How to?
I disagree with the emphasis you are putting on having an experimental background. In many of the top universities theoretical and experimental physics are different departments, and there is a reason for this. Theoretical physicists need a very different set of skills than experimental physicists. Their ability to do path integrals, for example, tends to be of much greater importance than their ability to align optical elements. Both fields require a huge amount of background knowledge, and it is very rare to be successful at both (I can think of examples, but they are few and far between).
May
13
awarded  Nice Answer
Mar
16
comment Home experiments to derive the speed of light?
@Nic: yes, you are right of course.
Feb
19
comment Why can't the outcome of a QM measurement be calculated a-priori?
@Sklivvz: There has been plenty of work on this basis issue and there are fairly good reasons why you don't see superposed states. Decoherence, for example, means that the states become non-local so asking why we do not observe them as a superposition is a simple case of the fact that we are making a local observation on a non-local state and so cannot observe all coherences.
Feb
19
comment Why can't the outcome of a QM measurement be calculated a-priori?
@Sklivvz: I don't understand. Are you dismissing the Everett interpetation out of hand? It is certainly the most widely believed interpretation among quantum physicists, followed closely by the "shut up and calculate" school. Penrose has some weird and very non-standard views about quantum measurements, so his book may not be the best primer on the subject.
Feb
18
comment Why can't the outcome of a QM measurement be calculated a-priori?
@Sklivvz: That's totally incorrect. In the Everett interpretation there is no instantanous measurement event, it can all be treated as unitary evolution.
Feb
18
comment Why can't the outcome of a QM measurement be calculated a-priori?
@Sklivvz: Only in the Copenhagen interpretation is there any discontinuity. In the Everett interpretation there is no such issue. However there is no experimental way to distinguish the two.
Feb
18
awarded  Nice Answer
Jan
25
comment Does decoherence need non-determinism?
@WIMP: I know you didn't ask whether it leads to signalling. I am saying that it is impossible (even for the kinda sorta collapse you talk about) because it allows it implies signalling. That is a reason to discard it as a theory immediately.
Jan
23
comment Can gravitational potential energy be released in a fire?
@Noldorin: Yes, but there is an ambiguity in the question. As Peter mentioned, if there is no (or little) gas emitted then the situation is different.