SMeznaric

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bio	website	physics.ox.ac.uk/qubit/…
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	521 reputation	bio	website	physics.ox.ac.uk/qubit/…	visits	member for	9 months
12 badges		location	Oxford, United Kingdom		seen	23 hours ago

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1d	comment	What is the general statistical definition of temperature? Yes, but what if for example you have exact information about all the particles in your system (ie full momentum-position information), then temperature will cease to be useful. If you are lucky enough for the particles to be in the ground state then you can set it to zero, otherwise not sure how you can continue this representation.
1d	comment	What is the general statistical definition of temperature? Thanks, updated.
May 17	comment	How do we simulate Nuclear explosion? It's not necessarily a bad question, just needs to be clarified a bit. Are you trying to simulate the look of the explosion, the force resulting from the explosion, hydrodynamics of the surrounding atmosphere (and how far away are we talking?)? If you can clarify further I am sure somebody might be able to help you.
Jan 14	comment	Does conformal gravity explain the Bullet cluster lensing effects? @zhermes Another question in this regard is whether it could be that the natural mass-energy distribution in the universe might not somehow lead to the same results anyway. Of course for consistency it must be the exact same distribution required to arrive at the rotation curves for galaxies, otherwise you have falsified the theory and you need to discard it. Is it inherently obvious why this scenario could not lead to the same results? (Sorry had to put it into two comments due to the space limit).
Jan 14	comment	Does conformal gravity explain the Bullet cluster lensing effects? @zhermes Yeah, that sounds very convincing. I can see how those locations would be natural if you just assume nice spherical halos. Consider the following question as a result of my lack of understanding of the dark matter models: Is there a standard dark matter halo distribution that applies to every galaxy or do you need to find it in each individual case based on the rotation curves and/or lensing data?
Jan 14	comment	If quantum computation is reversible, what is the point of Grover's search algorithm? You can invert it in principle but it could be very hard. That's the problem. Grover's algorithm makes it "easy".
Jan 14	comment	Does conformal gravity explain the Bullet cluster lensing effects? @zhermes But does it really require that much of a conspiracy? The question here is really whether there is some fundamental reason why the preferred locations are special and we expect those exact locations to be preferred. You can equally consider the dark matter distribution to have conspired to produce those points, just as you can consider the universe to have conspired. On the other hand, perhaps we can consider it simply as a coincidence of either the dark matter distribution or the universe. Or did you have another reason in mind why this could be a conspiracy?
Jan 11	comment	Does conformal gravity explain the Bullet cluster lensing effects? @ChrisWhite That is true. I can see how this can rule out MOND theories, where you change the potential in a classical (Newtonian) way. I think conformal gravity is a bit different in this regard, as here you modify action to be the square of the conformal tensor from the Ricci scalar, which changes space-time around a matter distribution in a way potentially dependent on matter outside the distribution of interest. It's not obvious to me that this could not effectively change the lensing effects to reproduce the apparent shift in the Newtonian potential. Can you explain more on this?
Jan 11	comment	Does conformal gravity explain the Bullet cluster lensing effects? So does that mean it is ruled out? From what I have heard, one of the reasons why conformal gravity seems to reproduce the dark matter rotation curve profiles is that the iron sphere theorem does not apply and that matter outside can contribute to the potential. Given that, is it obvious how this misalignment means conformal gravity is ruled out?
Oct 26	comment	Is there a quantum state for a large system No, if I understand John correctly he is saying that a burger will in principle follow quantum behaviour regardless of the number of degrees of freedom but that in practice this cannot be observed because of the fast interaction with the environment (and this behaviour is still quantum actually, it just happens also to coincide with the classical physics).
Oct 26	comment	Faster than light due to reference position This thinking is exactly where special theory of relativity comes from. Concluding that light would travel at twice the speed of light is Newton, concluding that light would travel at the speed of light in all reference frames is Einstein.
Oct 25	comment	Why we use $L_2$ Space In QM? This question reduces to "Why Born rule?". As of this moment we don't have a fully satisfactory answer.
Oct 24	comment	Many-worlds: Where does the energy come from? @Killercam This is actually one of the main arguments made in favour many worlds. The question for those not supporting it is usually "Why should observers not themselves be quantum?". The formulae I wrote are just the usual quantum decoherence, about which you can read more on wikipedia: en.wikipedia.org/wiki/Quantum_decoherence
Oct 24	comment	Many-worlds: Where does the energy come from? No, what I am saying is that you start with an initial state $\|\psi>\otimes\|0>$, where $\|0>$ is the observer remembering not having measured anything. Now you measure the state and what happens is the joint state is transformed to $\sum_k M_k \|\psi> \otimes \|k>$, where $M_k$ are measurement operators and $\|k>$ is observer remembering outcome $k$. In general this is an entangled state. The Schmidt number of this state is your number of branches. Notice that for a different observer who does not know anything of this measurement there is still just one universe.
Oct 24	comment	Many-worlds: Where does the energy come from? The problem is that you consider branches as worlds, where in fact they are not worlds. This is a misunderstanding. What actually happens is that you must consider your own brain to be a quantum object. When measurement occurs it becomes entangled with the measured wavefunctions. So what you call different words are merely different states of your brain with distinct memories of the measurement outcome. If you have a problem with energy conservation here then you must also have a problem with conservation in quantum mechanics in general.
Oct 23	comment	Is the statistical interpretation of Quantum Mechanics dead? Yeah, Bell inequalities basically reduce to the marginal problem, where given a number of marginal probability distributions you cannot construct a joint distribution. If you could Bell inequalities would be satisfied. We had a discussion about this on mathoverflow (mathoverflow.net/questions/107007/…) and I am also currently writing a doctoral thesis which will contain a discussion of this. If you are interested I can send it to you by email. I have not found any other reference where this is proven directly.
Oct 22	comment	Energy can't be created or destoryed? Good question. There is still a lot we don't understand about the early universe and your question essentially reduces to how did the universe with its energy content pop into existence. Whether it popped into existence in the first place is still a matter of debate (since one can say Einsteinian time started with the universe and therefore one cannot talk about before the universe). Until we figure it out, not knowing is the exciting part about physics as lots of people try to figure this out.
Oct 22	comment	Is the statistical interpretation of Quantum Mechanics dead? Arnold is right. The problems with locality begin only when you try to take the statistical interpretation further and insist that all outcomes of all observables must have a joint probability distribution. Say if for a pair of particles you require that $p(x_1, x_2, p_1, p_2)$ exists, where $x_i$, $p_i$ are position and momentum, then you can show that Bell inequality is always satisfied when observables correspond to momentum and position. If you extend this requirement to all observables, you find Bell inequality is always satisfied. This is how far precisely you can go with statistics.
Oct 19	comment	Does the nonlocality of the preferred basis mean QM is nonlocal? If you start with input into only one port of the first beamsplitter then the second beamsplitter should reconstruct that state and the photons come out at one of the output ports of the second beamsplitter. This is probably what he means by the preferred basis. But the "basis" is really only generated through the virtue of inputting photons into only a single port of the first beamsplitter. If that did not happen you would need a measurement somewhere to generate the basis.
Oct 19	comment	Why does bad smell follow people (assuming they are not the source)? Interesting. In combination with what anna said above in a comment to my question, it explains what I have observed circumstantially.