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484204
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location New York City
age 41
visits member for 3 years, 7 months
seen 2 days ago

I do not participate on this site any longer, except to respond to comments regarding my own text, if that text is unavailable in another form. I do not accept the political moderation atmosphere here, it is not compatible with open science. Unfortunately, this seems to be a recurring pattern on such sites--- they grow with promises of open participation, and then shut down in a phase transition of censorious moderatorship. Hopefully physicsoverflow.org will be the first exception to this rule, as the policies there were crafted specifically to avoid this phenomenon.


Nov
3
comment Is Stephen Wolfram's NKS, an attempt to explain the universe with cellular automata, in conflict with Bell's Theorem?
@agemO: It does not give any results either. The local protein mutations which change fitness can be counted on one hand--- moth color and sickle-cell anemia, that's about it. Those are exceptions, not the rule, but they are put as the rule in the books. The picture is simply wrong, because it is a non-computing picture, and it is also deliberately wrong, because it fits with an atheistic idea that natural computations don't exist. This type of no-computation-in-nature atheism is falsifiable and falsified. You had the impression because it is dogma, it's what everyone says, wrongly.
Nov
3
comment Is Stephen Wolfram's NKS, an attempt to explain the universe with cellular automata, in conflict with Bell's Theorem?
@agemO: It only superficially seems to work to the naive intuition, it doesn't really work, and this is what many critics of modern synthesis evolution have been pointing out for decades. It gets impossible to mutate-evolve past a certain complexity without co-evolving the mutation mechanism along with the system. The reason is that the distance between roughly equal fitness maxima generically grows with complexity, so that the steps you make must be larger. The current model is simply not correct. But the correct mechanism to fix this is also obvious today--- RNA editing of DNA.
Nov
2
comment Is Stephen Wolfram's NKS, an attempt to explain the universe with cellular automata, in conflict with Bell's Theorem?
@agemO: The ridiculous part is that the mutation mechanism is brainless and non-computing. There is no evidence for this. It is true that SNP type mutations in proteins are random, but they are also generally pointless, they make clock-like neutral evolution. The interesting aspects of evolution is the effect on non-coding DNA, and these changes are extremely complicated, and certainly regulated by RNA networks making a sophisticated computation. These mutations bear no relation to the models in population genetics, they look more like intelligent design, with RNA being the designer, not God.
Nov
2
comment Einstein's postulates $\leftrightarrow$ Minkowski space for a Layman
@Arafat: I invented this proof to teach relativity, it's not difficult at all though. The proof is interesting because it applies Euclidean techniques in a case where we have zero intuition, so that all the implicit assumptions hidden in traditional Euclid style proofs are revealed. The middle parallelogram square has side length c, so it's area is $c^2$. The implicit assumption is that area in space-time is invariant under the transformation to a moving frame, an equivalent implicit assumption appears in Euclidean proofs of the pythagorean theorem.
Oct
30
awarded  homework-and-exercises
Oct
30
awarded  terminology
Oct
29
comment What if we could give photons some mass?
@IncnisMrsi: I was complaining that he claims that photon propagation in a medium, where the speed of light is reduced, is an example of making light massive. The definition of "massive" is quadratic dispersion with a gap, not linear dispersion with an altered propagation speed.
Oct
29
comment What if we could give photons some mass?
@IncnisMrsi: yes, that's the one difference--- material superconductivity picks out a rest frame, while relativistic condensates don't. But other than being relativistically invariant, they are just the same as nonrelativistic condensates.
Oct
25
comment Reading the Feynman lectures in 2012
@ArtBrown: A long time, a long time, but classic underappreciate work. Thanks for the info, it might have been Mead, I honestly don't remember, I found it in a bookstore and flipped through it, didn't like it that much, but noticed it was based on what Feynman intended.
Oct
19
comment Are gravitomagnetic monopoles hypothesized?
@BenCrowell: Weak energy is never violated in the classical limit, and strong energy is only violated by scalar VEVs.
Oct
11
comment What is a non linear $\sigma$ model?
@New_new_newbie: Sure, all is well in the sense that you have an approximate theory. It will have infinitely many parameters though that you need to fix, these ultimately should come from QCD, but if you fix them phenomenologically order by order, you get by.
Oct
11
comment What is a non linear $\sigma$ model?
@New_new_newbie: Renormalizability is not important today, but 1960 is well before QCD, and Gell-Mann and Levy didn't yet know about quarks.
Oct
11
comment What is a non linear $\sigma$ model?
@New_new_newbie: I don't know a reference, I worked it out for myself by considering what would happen if you simulated the nonlinear sigma model on a lattice. The natural way to do this is to use "x,y,z,w" coordinates with the lattice constraint that the sum of the squares is constant, and then doing a block-renormalization step, averaging the four fields, you just get back the usual scalar field model with O(3) symmetry, because the block renormalization doesn't preserve the hard constraint. It's the same argument as for the Ising model turning into $\phi^4$, and this is shown in Polyakov.
Oct
9
comment Why singularity in a black hole, and not just “very dense”?
@pabouk: Regarding 'settled state', the end point for the black hole is always a Kerr-Neumann static solution, the major issue is what happens to the interior matter in the case that it misses the singularity, i.e. when you have a charged/rotating collapse. My feeling on this is that it is partially ejected, and the black hole is only produced to the extent that mass-energy is destroyed at the singularity, and this is only massless stuff, for highly charged or highly rotating black holes. I suspect the full answer requires string theory, the classical theory has nonsense extra universes.
Oct
9
comment Why singularity in a black hole, and not just “very dense”?
@pabouk: Not clear. The singularity is timelike if the black hole is spinning or charged, and in this case, we don't have exact collapse solutions. It should be possible to figure out the behavior of exact charged collapsing dust, but it hasn't been done. The singularity theorem has been misinterpreted to mean that there is a spacelike singularity which swallows all matter, and this is only true for spherically symmetric collapse, it fails when the singularity is timelike. My own opinion about what happens in this case is that there is a partial explosion, but this is not what others think.
Sep
30
awarded  Explainer
Sep
24
awarded  Autobiographer
Sep
22
awarded  Nice Answer
Sep
17
comment Is the universe a quantum computer - is light speed barrier a computational constraint
@celtschk: here universe==the observable universe. The number of bits is assumed by the number of Planck areas on the cosmological horizon. The U atom with electrons has 350 particles, which, with even a coarse quantum description swamps the size you can simulate with a classical computer that size. But of course, for ground states, or low excited states there are better methods like DFT.
Sep
16
awarded  Nice Answer