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    • CommentAuthorAsterix
    • CommentTimeOct 13th 2021
     
    But never modulated a single photon...
  1.  
    Once again, the main question is ignored in favour of nitpicking.
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      CommentAuthorjohnq
    • CommentTimeOct 13th 2021
     
    amplitude, frequency, phase or polarization?
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      CommentAuthorAngus
    • CommentTimeOct 14th 2021
     
    All of the above, not always intentionally.
  2.  
    At root the issue is whether information has mass-energy and how this is explicitly expressed in a black hole's mass.
    kT/c2 Kg per qubit might be one guess.
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      CommentAuthorAngus
    • CommentTimeOct 14th 2021
     
    Materialist!
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      CommentAuthorAngus
    • CommentTimeNov 10th 2021
     
  3.  
    The simplest systems can be confusing.
    https://www.youtube.com/watch?v=gezZklOsGbg

    Feynman elaborated, showing e.g. that a charge placed next to a magnet appears to result in a continuously circulating Poynting vector, which does not seem to admit of any rational physical explanation. In what sense is energy circulating? And if it is, can we coerce any real work out of it?

    We need Al (since Nikola Tesla is no longer with us) to start experimenting with massive magnets charged up to massive voltages!!
  4.  
    Leaving the fascinating issue of the Poynting vector aside for now, good ole engineer Dave spells it out.
    https://www.youtube.com/watch?v=VQsoG45Y_00
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      CommentAuthorAngus
    • CommentTimeNov 29th 2021
     
    Posted By: Andrew PalfreymanThe simplest systems can be confusing.
    https://www.youtube.com/watch?v=gezZklOsGbg

    Feynman elaborated, showing e.g. that a charge placed next to a magnet appears to result in a continuously circulating Poynting vector, which does not seem to admit of any rational physical explanation. In what sense is energy circulating? And if it is, can we coerce any real work out of it?

    We need Al (since Nikola Tesla is no longer with us) to start experimenting with massive magnets charged up to massive voltages!!


    The Wikipedia article explains this apparently circulating energy quite satisfactorily, for me anyway.
  5.  
    https://en.wikipedia.org/wiki/Poynting_vector#Static_fields
    is pretty good. But it still leaves me with an uneasy feeling (as it did Feynman).
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      CommentAuthorAngus
    • CommentTimeNov 30th 2021
     
    I understand it by remembering that the condition "static" is a fiction. No real-universe field can be without a temporal boundary of some sort. But if you imagine it is truly a static configuration, then there is no way you can ever tell that the energy is circulating in there.
  6.  
    Yabut that seems like a paradox. In order for there to be a flux of any sort, there needs to be a potential gradient. Now two points about that: EM fields are conservative, and the topology of the Poynting vector is a ring. See the inherent contradiction?

    cf. Escher.

    ETA Oh hang on - superconducting ring currents work just fine...
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      CommentAuthorAngus
    • CommentTimeNov 30th 2021
     
    Just so. And they don't even have to have been going forever.
    BTW propagation of an electromagnetic wave does not imply it is falling down a gradient in a scalar field. Or any wave for that matter. It is carrying energy from one place to another, but I don't think that implies there is less energy in the place where it is going than in the place it left.
  7.  
    Also, a superconducting ring current does not fall down a potential gradient. And zero resistance means there are no potential gradients. Rather, the electrons remain at a constant velocity, with no need of external force to maintain that state.

    Energy flux aka "divergence" is slightly weird.
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      CommentAuthorAngus
    • CommentTimeDec 11th 2021
     
    This explanation of Noether's theorem is neat and simple
  8.  
    I've come across several vids by that bloke and they've all been quite good. Here for example is something I was never taught (or was, but forgot) and which I found particularly insightful in regards to the classical underpinnings of QM.
    https://www.youtube.com/watch?v=Nd4b0_vJZUk
  9.  
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      CommentAuthorAngus
    • CommentTimeDec 19th 2021
     
    Jaron Lanier !
    It's probably a virtual idea.
  10.  
    One wonders what the objective function is supposed to be.