Ron Maimon

44,852 reputation

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	age	39
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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.

	44,852 reputation	bio	website		visits	member for	1 year, 9 months
245121 badges		location	New York City		seen	May 18 at 6:25

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Dec 4	awarded	Caucus
Dec 4	comment	(Co)homology of the universe @ChrisGerig: Ok, but I see now why you said what you said, and I agree with you regarding the content. I wasn't right in laying all the repulsion to Pauli, there's a part that's nuclear repulsion once the electron shells overlap, and this is a tradeoff. You could have made the argument explicit, though, rather than relying on authority.
Dec 4	comment	(Co)homology of the universe I think I gave your argument too little credit--- I see now where you are coming from--- the near surface forces are a mix of exclusion and nuclear repulsion, and the exclusion is only for keeping the bulk phase stable, while the repulsion can dominate the touching force, for example if the spins on the surface electrons are anti-aligned. But in this case, you tend to shear off the electrons from one solid in chemical bonds to the other. Maybe I should update the answer to that "what makes matter hard" question (although it is important to say that it's exclusion that sets matter's scale).
Dec 4	comment	(Co)homology of the universe @ChrisGerig: The electromagnetic part is net attractive even when you are close, so long as you don't have overlap. I see your point now--- consider the opposite e-spins hydrogen, which becomes a molecule, and then the electrostatic repulsion of the nuclei keeps it from collapsing, even though there is no electron exclusion, and it can be a d-2 atom with bosonic nuclei. The electrostatic repulsion is important in cases where you have molecular bonding, to understand why the nuclei don't come closer then they do. But it's still the issue of fermionicity at core, bosonic electrons will clump up.
Dec 4	comment	Fermi surface nesting and CDW/SDW/SC orders It is interesting though whether the best overlay of FS always gives the CDW vector. One has to check independently of Johannes and Mazin, because they claim things that are wrong. I was worried that you can't calculate the electronic energy reduction for incommensurate case, but this is not so, since you can still use a classical phonon background to give the perturbative electronic energy shift, and this is lowering electron energy when the Q-vector links FS to FS. So the overlaying rule of thumb should be nearly perfect, and I don't believe the claims that it isn't so. Any real examples?
Dec 4	comment	Fermi surface nesting and CDW/SDW/SC orders @wsc: Yes, this is now clear, thanks, I couldn't make heads or tails of a nonperiodic diagram for a BZ, now I see you're supposed to fold it in. The main issue is that the Q-vector in Brouet is linking the inner diamond to the outer diamond so that the corners lie on top of each other--- this matches two segments of the inner diamond to two partial segments of the outer diamond, so that a substantial chunk of the FS is overlayed, nearly 50%. The supposedly better nesting in the Johannes and Mazin paper only overlays one line of the inner diamond with the outer diamond, and is in fact worse.
Dec 4	comment	(Co)homology of the universe Also, F_EM is purely attractive at distances greater than touching, it's Van-Der-Waals force.
Dec 4	comment	(Co)homology of the universe There is no excess complications--- string theory allows for nontrivial topology, and you have to argue why it's not disallowed by causality, since wormholes are disallowed. a periodic identification is not disallowed (if it is spacelike), a topology like a Calabi Yau is not disallowed, and an orbifold is not disallowed, even though they are complicated topologically. This is also where homology links to actual physics, since the Euler characteristic is the generation number. I don't know how to make it less wordy, because these are wordy concepts, not math-y concepts.
Dec 4	comment	(Co)homology of the universe @ChrisGerig: A "patch" is a region inside a cosmological horizon--- it's a standard cosmology term. The "FRW phase" is when the universe is expanding, i.e. not inflation and not 100 billion years from now when it's dominated by cosmological constant again. The normal expansion allows new stuff to come in from the boundary as new stuff gets visible, and one has to consider if this new stuff can be a handle. It can be an orbifold, or a black hole, why not a handle? The reason is that wormholes are incompatible with causality (this is the boosting argument, also found elsewhere here).
Dec 3	comment	(Co)homology of the universe @ChrisGerig: When you say "we are unsure of the topology", you are referring to two things: 1. there is some question of whether the observable universe has identifications inside the cosmological horizon, but it probably doesn't, since we would see it in WMAP 2. we don't know the topology of the unobservable universe and we never will. I am adressing point 1 by assuming the experimental data is conclusive (which it nearly is), and point 2 by rejecting the idea that the universe extends past the cosmological horizon.
Dec 3	comment	(Co)homology of the universe @ChrisGerig: There are no symbols, but there is math. If you consider the universe a 3-disk bounded by the cosmological horizon, then topologically it's a manifold with boundary, and it is deformation retractable to a point (ignoring other boundaries, like black holes on the interior), so it's homology is trivial. This is a (simple) theorem: a space which deformation retracts to a point has trivial homology. The case when you have black holes in the interior introduces nonretractable 2-cycles, it's the 3-disk with punctures topologically, and the dimension of H2 is the number of BHs.
Dec 3	comment	Why is cold fusion considered bogus? Yes--- a beam of electrons would work if it at 100KeV-1MeV, but preferably a commercial LINAC at 20 MeV, this should be excellent to stimulate the cold fusion. The Auger process is what I am exploiting, except I am noting that you get Auger deuterons also in a deuterated metal, not just Auger electrons, and that Auger deuterons are delocalized and fuse, and the fusion seeds more Auger deuterons through it's K-shell holes. This is the main point. I am glad you are grappling with it, but I encourage you to keep reading and keep criticising, as you will see there is no problem with my idea.
Dec 3	comment	On Parallel Transport @AnamitraPalit: The Christoffel symbols are differential they give you the rate of change of the vector, you need to mulitply by the (infinitesimal) displacement to get the actual change. Your example is bogus, it's a misunderstanding, try drawing it out on an actual sphere, you will see that moving the vector on the little segment of lattitude near the north pole does next to nothing. It only gives a tiny differential change.
Dec 3	answered	Nuclear fusion: what causes this “resonance” peak?
Dec 3	comment	On Parallel Transport @AnamitraPalit: The change in orientation is infinitesimal in dx, and when you traverse a loop, the change in angle is the area of the loop times the curvature. So when you go along the meridian, basically nothing happens. Only as much change in angle as the teeny triangle has area.
Dec 3	comment	Fermi surface nesting and CDW/SDW/SC orders @wsc: I can't see the match (sorry, probably stupid) the Brouet paper is what I saw (and a textbook that reproduced the picture), and the nesting vector is supposedly linking the small diamond in the ARPES data with the big diamond to the right. It's an incommensurate transition, so I have no intuition for what the fermi surface, and I have not gotten the hang of these ARPES or numerical plots. In the simulation paper, the CeTe3 surface had a different nesting vector that overlayed what looked like a completely different part of the Fermi surface. I was mystified by the lack of matching.
Dec 3	comment	Can bosons that are composed of several fermions occupy the same state? @Friedrich: Not exactly--- the wavefunction is only exactly the same for two bosons if they are non-interacting. If they have a repulsion at ultra-short distances, the wavefunction is entangled so that it is very close to the product of the wavefunction with itself at most points, but the entanglement zeros out the diagonal (so they aren't ever at the same point). This is a property of higher dimensional multi-particle wavefunctions. The best definition for the condensate wavefunction by giving the effective field for the boson a VEV, and this only produces a product state for a free field.
Dec 3	revised	Fermi surface nesting and CDW/SDW/SC orders explain why a true statement is still false in spirit
Dec 3	awarded	fluid-dynamics
Dec 3	comment	(Co)homology of the universe @ChrisGerig: That's very strange--- I understand this stuff completely, and usually people have no trouble following what I write (at least, I think they don't, from comments). What is un-understandable about it? Can you quote, so I can make it clearer? I don't find it written in a hard to understand way when I reread it. What confused you here?