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  1. atyy

    I Attractors in general relativity

    In classical Hamiltonian mechanics, because of Liouville's theorem about the volume of phase space being preserved by time evolution, there are no attractors. Naively, I think of the Raychaudhuri equation in GR as showing a shrinking volume. However, I guess Raychaudhri's equation does not...
  2. atyy

    I PBR and relativity

    In relativity, the wave function in different frames is not unitarily related, because the wave function collapses at different times. For example, in a Bell experiment, in a frame in which Alice and Bob measure simultaneously, there is no collapse. But in a frame in which Alice measures...
  3. atyy

    Physics major wins US Open

    I don't play golf. but this caught my eye. https://www.bbc.com/sport/golf/54229887 US Open 2020: Bryson DeChambeau storms to first major title at Winged Foot, New York "DeChambeau's unique methods have divided opinion since he turned professional in 2016. Fans find them innovative, critics call...
  4. atyy

    International students may need to leave US if their universities transition to online-only learning

    https://edition.cnn.com/2020/07/06/politics/international-college-students-ice-online-learning/index.html International students may need to leave US if their universities transition to online-only learning
  5. atyy

    B Free Online Public Lecture - Seeing the Unseeable: Capturing an Image of a Black Hole

    Seeing the Unseeable: Capturing an Image of a Black Hole A Free Science Lecture Led by Dr. Sheperd Doeleman, the Event Horizon Telescope (EHT) project made history by capturing an image of the event horizon of a black hole, where gravity is so strong that even light cannot escape. You are...
  6. atyy

    I Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

    Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime Sean Carroll https://www.amazon.com/dp/1524743011/?tag=pfamazon01-20 Review of the book by Matt Leifer Does the many-worlds interpretation hold the key to spacetime? https://physicstoday.scitation.org/doi/10.1063/PT.3.4366
  7. atyy

    I Lattice standard model (Wang & Wen)

    There is a proposal for a generalized lattice standard model by Juven Wang and Xiao-Gang Wen. Could this be correct? I've put this under BTSM because it also mentions grand unified models. https://arxiv.org/abs/1809.11171 A Non-Perturbative Definition of the Standard Models Juven Wang...
  8. atyy

    A Lattice QED

    [Moderator's note: This thread was spun off from a previous thread since it was getting into technical issues beyond the scope of the previous thread. The quote at the top of this post is from the previous thread.] But even before going into the technical details, here is a heuristic that may...
  9. atyy

    Geometry Elementary Geometry

    Could I get recommemdations for textbooks that start by defining cosine and sine using power series and then recover their geometric properties? John Roe's "Elementary Geometry" does that, but it's not in my current university's library.
  10. atyy

    Gravitational waves pioneer Ronald Drever dies

    http://www.bbc.com/news/science-environment-39212305
  11. atyy

    I Wilsonian viewpoint and wave function reality

    In the Wilsonian viewpoint, quantum electrodynamics is an effective theory, where the low energy predictions are obtained by coarse graining eg. some form of lattice QED where the lattice is taken very finely. In the Copenhagen interpretation, we are agnostic as to whether the wave function is...
  12. atyy

    Can decoherence be formulated in the Heisenberg picture?

    In another thread, stevendaryl and I were trying to understand whether MWI can be formulated in the Heisenberg picture. Since neither of us really understands MWI, I tried to retreat to safer ground by asking: Can decoherence be formulated in the Heisenberg picture?
  13. atyy

    Why does wavelength affect diffraction?

    This question came up in the biology section https://www.physicsforums.com/threads/explain-different-types-of-light-microscopy.833990/. Q1: The longer the wavelength of a wave, the more easily it bend around an obstacle. I do understand the mathematics, but is there any intuition for it? Q2A...
  14. atyy

    Status of lattice standard model

    What is the "consensus" status of the existence of a lattice standard model? These two sets of notes don't seem to be in agreement. Wiese's 2009 notes http://www.itp.uni-hannover.de/saalburg/Lectures/wiese.pdf say "Thanks to a recent breakthrough in lattice gauge theory, the standard model is...
  15. atyy

    Measurement problem in classical probability

    This question is inspired by ephen wilb's https://www.physicsforums.com/threads/quantum-theory-of-others.816818/#post-5130620. In Bohmian Mechanics, everything is exactly as in classical probability theory. How, from the point of view of BM, does the measurement problem arise? Since the...
  16. atyy

    Implications of Bell's theorem (Laloe paper)

    [this thread was forked from another thread, as it is an interesting topic in its own right] Yes, a variant of Bell's theorem says that quantum mechanics is truly random as long as we cannot signal faster than light. http://arxiv.org/abs/quant-ph/0508016 http://arxiv.org/abs/0911.2504
  17. atyy

    Graphene light bulb

    http://www.bbc.com/news/technology-32101473 The BBC reports that a graphene light bulb will go on sale. What are its advantages over current technologies?
  18. atyy

    Impossibilty of hidden variables (Bohm, 1951)

    Bohm writes in his 1951 book "Quantum Theory" (p623): "We conclude then that no theory of mechanically determined hidden variables can lead to all the results of quantum theory". He bases his argument on the uncertainty principle. Presumably the argument is not correct, since Bohm himself...
  19. atyy

    Collapse and Peres' Coarse Graining

    Collapse is the sudden change in wave function after a measurement. Unless otherwise stated, I will assume that neither the wave function nor collapse are necessarily physical, and are just calculational tools that are part of the experimental success of quantum mechancs. Collapse is in almost...
  20. atyy

    Rough paths and QFT

    Because of the Feynman path integral, QFT can be made into a statistical field theory. In rigourous relativistic field theories, this is formalized by the Osterwalder-Schrader conditions. At any rate, there are well established links between quantum field theory and statistical physics. A...
  21. atyy

    Local hidden variables for double slit

    The double slit experiment is not known to violate any Bell inequality, and thus may have a local hidden variables description. Does Bohm-Dirac theory provide a local hidden variables description for the double slit? Are there other local hidden variables descriptions for the double slit? (If...
  22. atyy

    Art Hobson's "No Particles"

    This thread continues the discussion at https://www.physicsforums.com/showthread.php?t=767018
  23. atyy

    Are PVMs more fundamental than POVMs from the view of decoherence?

    In quantum mechanics, POVMs can be considered more fundamental than PVMs because PVMs can be considered a special sort of POVM. However, because of the Naimark extension, one can formally consider POVMs to always be derived from PVMs. Accordingly, one could argue that choosing PVMs or POVMs to...
  24. atyy

    Naimark extension for continuous variables

    For discrete variables, a POVM on a system can be thought of as a projective measurement on the system coupled to an apparatus. This is called the Naimark extension. Is this also true for continuous variables? http://arxiv.org/abs/1110.6815 (Theorem 4, p10)
  25. atyy

    Eventum Mechanics and CSL

    Eventum Mechanics is summarized at https://www.maths.nottingham.ac.uk/personal/vpb/research/cau_idy.html . As required by the rules of this sub-forum, the work has been published in peer-reviewed journals. http://arxiv.org/abs/quant-ph/0512188 Belavkin, Nondemolition Principle of Quantum...
  26. atyy

    Many-worlds, Schroedinger, Heisenberg pictures

    I've usually heard the many-worlds interpretation described in the Schroedinger picture, in which the wave function evolves unitarily. Does a Heisenberg picture exist for many-worlds, or is the Schroedinger picture more fundamental in that interpretation?
  27. atyy

    Sequential measurements of conjugate observables

    There is an argument that accurate sequential measurement of conjugate observables A and B on the same state is possible if the state is an eigenstate of one of the observables. When the state is an eigenstate of A, an accurate measurement of A will not disturb the state, so B can then be...
  28. atyy

    Primordial B-modes?

    Cosmic inflation: 'Spectacular' discovery hailed http://www.bbc.com/news/science-environment-26605974 BICEP2 2014 Release Papers and Data Products http://bicepkeck.org/index.html#papers Commentary by Liam McAllister on Motl's blog...
  29. atyy

    Joint distribution of position and momentum

    In quantum mechanics, there doesn't seem to be a joint distribution of position and momentum. But in Bohmian mechanics there is. But Bohmian mechanics is quantum mechanics, so what is the error in my reasoning?
  30. atyy

    Does quantum mechanics need a conscious observer?

    Textbooks like Landau and Lifshitz avoid the observer having to be conscious, by saying a measurement is the interaction of a quantum system with classical apparatus to produce a classical result. However, there is an analogy that is often drawn that wave function collapse is like statistical...
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