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Apr
25
comment If randomness doesn't exist, how come the universe isn't a perfect sphere with predictable distribution of matter?
Also, I'm not sure what the phrase "pure randomness" means. What makes a particular distribution purely random by your definition?
Apr
25
revised If randomness doesn't exist, how come the universe isn't a perfect sphere with predictable distribution of matter?
added 88 characters in body
Apr
25
comment If randomness doesn't exist, how come the universe isn't a perfect sphere with predictable distribution of matter?
Nowhere that I can find did the OP say he wanted a jargon-free answer. Even if he did, a certain level of jargon is useful to know, and most of it was clearly explained. I've added an explanation for the particular phrase in question.
Apr
24
comment Angular Momentum Addition Theorem - Sanity Check
Yes. If you pick $j_1$ to be the larger of the two then it's unnecessary.
Apr
24
answered Angular Momentum Addition Theorem - Sanity Check
Apr
24
answered If randomness doesn't exist, how come the universe isn't a perfect sphere with predictable distribution of matter?
Apr
24
comment In the known universe, would an atom not present in our periodic table exist?
Neutron stars are bound states, but for me the question of whether or not they are nuclei is more subtle than that. Neutron stars are composed of quark matter, and so I can't consider them nuclei which are bound states of nucleons in my definition. Of course some of the physics is the same, but a neutron star has at least as much in common with a star as with a nucleus.
Apr
24
comment In the known universe, would an atom not present in our periodic table exist?
@lurscher: Neutron stars are bound by entirely different physics, namely gravity, from the strong interaction in nuclei. As such, I don't really like thinking of them as large atomic nuclei. As for whether or not the island of stability is hypothetical, I more meant that the idea that some particular nuclei will have extremely long half-lives, on the order of decades or longer, which would be necessary for applications.There are definitely confirmations that there is an island of stability, but exactly how stable the most stable nuclei are is still open as far as I know.
Apr
24
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Apr
24
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Apr
24
revised In the known universe, would an atom not present in our periodic table exist?
added 3 characters in body
Apr
24
comment In the known universe, would an atom not present in our periodic table exist?
I don't really understand why you claim there is no other possibility (unless you are an astronomer, because then of course they are metals by your definition). Perhaps you are claiming that these high-Z elements certainly would not have the properties of any known nonmetals, which I agree with, but it isn't at all obvious to me that they should be similar to known metals either. I decided to change dubious to unobvious, because that's more what my sentiment is, but I definitely don't think it's obvious.
Apr
24
comment In the known universe, would an atom not present in our periodic table exist?
I don't think that's as obvious as you are claiming. As far as I know, most high atomic number elements that have been synthesized have been in small quantities, so that we can't really study their bulk properties. Cn is known to be a metal, but other elements with Z>108 are not known. One can try to use theory to predict that these elements should have the properties of metals, but in the particular regime nuclear chemistry becomes increasingly important to consider and results from condensed matter theory are questionable without experimental demonstration.
Apr
24
answered In the known universe, would an atom not present in our periodic table exist?
Oct
11
answered experimental bounds on spacetime torsion
Sep
21
comment What do theoretical physicists need from computer scientists?
I should add a caveat that I agree with Peter's original comment entirely, as I read it. I thought he was commenting the idea that "more powerful computers will always be available" is irresponsible. If I seem to support such a position, in fact I do not. That some of my colleges thought this way is part of why I moved out of computation into more mathematical areas. It makes algorithm analysis seem pointless, which it isn't. However, I also think that procedure and algorithm-based programming has its limits. Machine learning and data-driven theory are the next step when stuff hits a wall.
Sep
21
comment What do theoretical physicists need from computer scientists?
What I'd really like to see is if someone could come up with a list of commonly used algorithms in physics that aren't well known outside physics. That would be a post in the algorithm analysis area that I'd support. But I think such general things as "Improve your algorithms" or "Give us $O(n^2)$ matrix multiplication" aren't terribly good examples for this question. The former is somewhat irresponsible without having read the algorithm itself. How do you know that improving the algorithm will solve the problem better than machine learning? The latter is discussed in the previous comment.
Sep
21
comment What do theoretical physicists need from computer scientists?
Alright, I now understand what you're talking about, and I can see that you may be right. However, if that's what he meant with that comment, I think it's off topic on this site and this question. The question is about what theoretical physicists want particularly, not what everyone who does computation wants in general. I'd be ecstatic for $O(n^2)$ matrix multiplication, but I don't think that's a reasonable thing to ask. It'd be like asking mathematicians to answer the Hodge conjecture. It's already well-publicized and people are working on it, but it's not an easy problem.
Sep
21
comment What do theoretical physicists need from computer scientists?
I'm afraid I don't understand what point you're trying to make, then. I agree that algorithms can be improved, but barring a rather drastic and unlikely advance it wouldn't seem that programmatic computation alone will solve the issues posed. Are you disagreeing with me here? Or are you disagreeing when I say that using machine learning techniques may help alleviate the issue? I'm finding myself agreeing with what you say, so I'm not sure what I said that you're disagreeing with. I suspect it may be a misunderstanding. Could you give a quote to which statement I made that you don't agree with?
Sep
21
comment What do theoretical physicists need from computer scientists?
I'm well aware of the problem of optimizing matrix multiplication, but I'm not convinced this is something that is specifically or especially wanted by physicists. Virtually everyone in the world who does any computations wants to multiply matricies faster. Of course if someone can find a faster algorithm for matrix multiplication, singular value decomposition, fourier transform, etc. then it would greatly benefit physicists, but that's fairly obvious. Also, at the time I posted this answer, Aaron was asking for specific examples; hence, I tried to stay fairly concrete with the problem.