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  1. PeterDonis

    B Black hole horizon and Hawking evaporation

    Hawking is not saying what you think he is saying. He is not saying the models that are actually used in black hole physics, for example to study quasars, or to model the black hole at the center of our galaxy, or to model black hole mergers in order to analyze data from LIGO, are speculative or...
  2. PeterDonis

    I Binomial distribution of "worlds" in MWI

    This is indeed a common criticism of the MWI.
  3. PeterDonis

    I Is the electric field of an atom a superposition or mean of electron positions?

    More precisely, the Coulomb potential of the nucleus is not quantized; it is just a function ##V(r)## in the Hamiltonian. But that Coulomb potential is not "the electric field of the atom" or "the electric field of the electron in an orbital". All of this is interesting history, but it's...
  4. PeterDonis

    I Can Newtonian gravity be thought of as a theory of curved time?

    There are several different statements being discussed in this thread, which it is important to keep conceptually distinct: (1) We can define a connection and a curvature tensor on spacetime, considered as a 4-D manifold, for Newtonian gravity. This is what is meant by "Newtonian spacetime is...
  5. PeterDonis

    I Is this why a pilot wave theory cannot be accepted?

    Since the OP is based on a misunderstanding, this thread is closed.
  6. PeterDonis

    I Can Newtonian gravity be thought of as a theory of curved time?

    I don't have the book, so I don't know what exactly he claims, but the field equation itself does not imply that there must be a spacetime metric in Newtonian gravity. It only implies that there must be a space metric, since the space geometry is the one that has the nabla operator as a...
  7. PeterDonis

    A BOT Fools Humans on Reddit

    I meant the eight articles it generated in response to the specific instructions and introduction provided for the Guardian article.
  8. PeterDonis

    I Can Newtonian gravity be thought of as a theory of curved time?

    No. The best you can do, which is what Newton-Cartan theory does, is define a spacetime that has two metrics, a three-dimensional space metric and a one-dimensional "time metric" (the term "metric" is kind of a misnomer in that case, basically for the reason @haushofer gives), which are distinct...
  9. PeterDonis

    I Binomial distribution of "worlds" in MWI

    This depends on which interpretation of QM you adopt. No, we don't. As I've already said, "probability 1" is meaningless in this context. If you continue to make this assertion, this thread will be closed. The MWI is completely deterministic, as I've already said. From the MWI point of view...
  10. PeterDonis

    B Black hole horizon and Hawking evaporation

    The answer to whether black holes actually evaporate in our actual universe (and even whether the objects we call "black holes" are actually black holes in the sense of having true event horizons) is not yet clear, yes. But, as I said in the article, if it turns out that our current ideas about...
  11. PeterDonis

    I Is this why a pilot wave theory cannot be accepted?

    You shouldn't. The only "standard" that PF recognizes for QM is the minimal framework described in this Insights article: https://www.physicsforums.com/insights/the-7-basic-rules-of-quantum-mechanics/ There is no "standard" QM interpretation that PF recognizes beyond that.
  12. PeterDonis

    B Black hole horizon and Hawking evaporation

    Yes, that's my understanding. I'm not entirely sure what that means. It might be that that portion is also technically an outgoing Vaidya region, just with a different mass function. I think part of the problem might be that the model in that figure is leaving out the collapse part--the...
  13. PeterDonis

    I Is this why a pilot wave theory cannot be accepted?

    Where are you getting this "consensus" from? Where are you getting this "standard interpretation of QM" from? Personal theories and personal speculations are off limits here.
  14. PeterDonis

    A BOT Fools Humans on Reddit

    I don't think that's quite a fair description. First, GPT-3 was given instructions, and was also given an introduction, as described at the end of the article. Second, GPT-3 produced eight different outputs, and the Guardian picked "the best parts" of each and combined them into a single...
  15. PeterDonis

    B Black hole horizon and Hawking evaporation

    I know. But that doesn't mean you can't put a portion of the outgoing Vaidya spacetime, one that doesn't include the white hole region, into a model that includes portions of other spacetimes as well. The model I described, and which is shown in Figure 2 of the paper I referenced, does that: it...
  16. PeterDonis

    B Black hole horizon and Hawking evaporation

    Because you're only using a portion of the full spacetime described by the outgoing Vaidya metric. The portion being used does not include the white hole region of the outgoing Vaidya metric. It's no different from the fact that the Oppenheimer-Snyder model you refer to does not have a white...
  17. PeterDonis

    I Is the electric field of an atom a superposition or mean of electron positions?

    Because it doesn't work; you make wrong predictions.
  18. PeterDonis

    B Black hole horizon and Hawking evaporation

    There are models of evaporating black holes that do have one; the simplest is the one Hawking originally used. But it's still an open question whether those models actually describe things in our real universe.
  19. PeterDonis

    B Black hole horizon and Hawking evaporation

    I think a spacetime that includes a region similar to the Oppenheimer-Snyder collapse, joined to its future with an outgoing Vaidya region, in turn joined to its future with a Minkowski region inside the last "shell" of outgoing radiation, would work. The fact that the outgoing Vaidya region in...
  20. PeterDonis

    B Black hole horizon and Hawking evaporation

    See this Insights article: https://www.physicsforums.com/insights/black-holes-really-exist/ It discusses the scenario you describe and why there is no actual contradiction. No, we don't. The horizon is in the future light cone of a distant observer. In a spacetime with a black hole that...
  21. PeterDonis

    I Is the electric field of an atom a superposition or mean of electron positions?

    Which, of course, means that you are not using classical EM to describe the atom itself.
  22. PeterDonis

    I Is the electric field of an atom a superposition or mean of electron positions?

    You use that approximation for the interaction of the atom with external fields. That is not what the OP is asking about. The OP is asking about the "electric field" due to the atom itself (more precisely, of an electron in some orbital of the atom). You cannot describe that with classical EM...
  23. PeterDonis

    B Difference between an Einstein frame and a String frame?

    From equations (2) and (3) in that paper, it looks like the "Einstein frame" is the usual FRW coordinates used in standard cosmology, and the "string frame" is a conformal transformation of those coordinates that rescales time and distance in a way that varies with the value of the dilaton field...
  24. PeterDonis

    B Difference between an Einstein frame and a String frame?

    Can you give any specific references?
  25. PeterDonis

    I Binomial distribution of "worlds" in MWI

    Yes. This seems to be a common statement in the context of the MWI, but I don't think it's correct. This meaning of the term "probability" is not applicable in the context of the MWI, because the MWI is completely deterministic. In that completely deterministic context, the only thing that...
  26. PeterDonis

    I Binomial distribution of "worlds" in MWI

    While this is true, I don't think it applies to the scenario described in the OP; that scenario appears to me to be about repeated measurements on identically prepared single particles, not single measurements of systems containing multiple particles.
  27. PeterDonis

    Git and Github: best practices for merging branches in my repo

    Even with this rule (which I agree is a good one), "one feature" can still be enough of a change to warrant being captured in more than one commit. This is probably more likely to be true on a large and complex project, not a small one with only a few developers, but I think it's worth keeping...
  28. PeterDonis

    Git and Github: best practices for merging branches in my repo

    Yes, that seems like a good general set of policies. In some cases, you might be. Sometimes there is valuable information in those individual commits. See below. Yes: the change might be incomprehensible to future viewers (including future you) because you squashed it all into one commit...
  29. PeterDonis

    I Conservation of energy in Everett's MWI

    @name123 I am closing this thread since your question has been answered and we are just going in circles at this point.
  30. PeterDonis

    I Conservation of energy in Everett's MWI

    It's the squared modulus of the coefficient in the wave function. I've already explained this. I've already explained this too. I'm not going to repeat myself. It seems to me like you need to learn more about the basic math of QM. Look up "expectation value" for a start.
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