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> Self-taught. Why does that matter? It doesn't. All that matters is that the science is correct (see Ron Maimon for instance; self-taught but far more knowle

> Self-taught. Why does that matter? It doesn't. All that matters is that the science is correct (see Ron Maimon for instance; self-taught but far more knowledgable than most physicists). However, I get in far too many discussions involving QM online (mostly Reddit) where I learn that I wasted my time arguing with a 14 year old that watched "Through the wormhole" or something. > P.S. It turns out you were right about this You sound surprised. My graduate research is in quantum chemistry (and related areas), so I should have at least a few concepts correct. As someone with more of a QC background, perhaps my definition of what theoretical physicists consider "entangled" is inaccurate, so I am reading up on the matter. But I'm finding their specification of "entangled" to be an unintuitive and unobvious choice of wording.

lisper 12y ago
> I wasted my time arguing with a 14 year old Well, I'm about to turn 50 so you don't have to worry about that. :-) FWIW, I wrote this: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf > You sound surprised. No, I'm not. (How does one "sound surprised" in an on-line conversation?) > perhaps my definition of what theoretical physicists consider "entangled" is inaccurate An entangled state is one that can't be factored. See e.g. http://www.theory.caltech.edu/people/preskill/ph229/notes/book.ps http://www.theory.caltech.edu/people/preskill/ph229/notes/bo... section 2.4.1. (I am a bit nonplussed by how someone who does graduate research in quantum chemistry can not know this. It's a pretty basic concept.)
- Xcelerate 12y ago
  You really shouldn't be nonplussed about it (which, I'm not sure if you intended it this way, but calling it a "basic" concept seems a little passive aggressive. I could equally say that someone self-taught in QM should know the "basic" fact that product states would unitarily evolve out of that configuration). It just depends on what area you focus on and what your background is. Scott Aaronson says on his blog that he has explained Bell's Theorem to QFT professors that had never heard of it. Just wasn't relevant to their work. Does that make them bad physicists for not knowing such a well-known part of QM? Heck, it's better than a professor I had that did DFT work who thought the single-particle wavefunction was the most fundamental aspect of quantum mechanics. Nevermind the fact that DFT is trashed for its lack of ability to account for electron correlation. (And I do mean trashed. I was at the Gordon Research Conference in quantum chemistry this past summer where Peter Gill gave a lecture titled "the obituary of DFT". And if anyone has a right to rag on it, it's certainly him.)
  - lisper 12y ago
    > I could equally say that someone self-taught in QM should know the "basic" fact that product states would unitarily evolve out of that configuration. Well, that would depend on how far my studies have gotten me, no? My general assumption is that anyone who actually does QM for a living knows at least as much as I do, and almost certainly a great deal more. (Case in point: I presume that QFT is quantum field theory, but what is DFT?) I prefer to view this as humility rather than passive aggression. In any case, I don't think either one of us should be losing any sleep over it :-) But can we agree that there are states that can be factored, and states that can't, and that this is a useful distinction to make? And that this distinction is physical, i.e. that it produces observable effects? (And not just observable, but interesting and useful?)
    - Xcelerate 12y ago
      > But can we agree that there are states that can be factored, and states that can't, and that this is a useful distinction to make? And that this distinction is physical, i.e. that it produces observable effects? (And not just observable, but interesting and useful?) Oh certainly. I've never disagreed on this haha.
      - lisper 12y ago
        If you say so. "All components of a quantum system are always entangled" sounds like a contrary claim to me, but I don't want to quibble over it. It does make an interesting puzzle, though, how it can be physically possible to prepare a state that is both unentangled and pure. I don't actually know the answer to that off the top of my head.
      - deleted 12y ago
        [deleted]

lisper 12y ago

> I wasted my time arguing with a 14 year old Well, I'm about to turn 50 so you don't have to worry about that. :-) FWIW, I wrote this: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf > You sound surprised. No, I'm not. (How does one "sound surprised" in an on-line conversation?) > perhaps my definition of what theoretical physicists consider "entangled" is inaccurate An entangled state is one that can't be factored. See e.g. http://www.theory.caltech.edu/people/preskill/ph229/notes/book.ps http://www.theory.caltech.edu/people/preskill/ph229/notes/bo... section 2.4.1. (I am a bit nonplussed by how someone who does graduate research in quantum chemistry can not know this. It's a pretty basic concept.)

Xcelerate 12y ago
You really shouldn't be nonplussed about it (which, I'm not sure if you intended it this way, but calling it a "basic" concept seems a little passive aggressive. I could equally say that someone self-taught in QM should know the "basic" fact that product states would unitarily evolve out of that configuration). It just depends on what area you focus on and what your background is. Scott Aaronson says on his blog that he has explained Bell's Theorem to QFT professors that had never heard of it. Just wasn't relevant to their work. Does that make them bad physicists for not knowing such a well-known part of QM? Heck, it's better than a professor I had that did DFT work who thought the single-particle wavefunction was the most fundamental aspect of quantum mechanics. Nevermind the fact that DFT is trashed for its lack of ability to account for electron correlation. (And I do mean trashed. I was at the Gordon Research Conference in quantum chemistry this past summer where Peter Gill gave a lecture titled "the obituary of DFT". And if anyone has a right to rag on it, it's certainly him.)
- lisper 12y ago
  > I could equally say that someone self-taught in QM should know the "basic" fact that product states would unitarily evolve out of that configuration. Well, that would depend on how far my studies have gotten me, no? My general assumption is that anyone who actually does QM for a living knows at least as much as I do, and almost certainly a great deal more. (Case in point: I presume that QFT is quantum field theory, but what is DFT?) I prefer to view this as humility rather than passive aggression. In any case, I don't think either one of us should be losing any sleep over it :-) But can we agree that there are states that can be factored, and states that can't, and that this is a useful distinction to make? And that this distinction is physical, i.e. that it produces observable effects? (And not just observable, but interesting and useful?)
  - Xcelerate 12y ago
    > But can we agree that there are states that can be factored, and states that can't, and that this is a useful distinction to make? And that this distinction is physical, i.e. that it produces observable effects? (And not just observable, but interesting and useful?) Oh certainly. I've never disagreed on this haha.
    - lisper 12y ago
      If you say so. "All components of a quantum system are always entangled" sounds like a contrary claim to me, but I don't want to quibble over it. It does make an interesting puzzle, though, how it can be physically possible to prepare a state that is both unentangled and pure. I don't actually know the answer to that off the top of my head.
    - deleted 12y ago
      [deleted]