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    • CommentAuthorbr
    • CommentTimeJan 20th 2015 edited
     
    I've recently been intrigued by a series of experiments showing apparently FTL signals.

    These are:

    End-to-end electric dipoles:
    1a, http://www.cumberlandastronomicalsociety.org/memberspotlight/speedofcoulombforce.pdf
    1b, http://www.cumberlandastronomicalsociety.org/memberspotlight/Allens_Paper_part_2.pdf

    Charge and 'magnetostatic' forces
    2a, http://www.gsjournal.net/old/physics/erdmann.pdf
    2b, http://www.gsjournal.net/old/physics/erdmann2.pdf

    Magnetic near-field
    3a, http://scitation.aip.org/content/aip/journal/jap/101/2/10.1063/1.2409771 (subscription for full text)
    3b, http://iopscience.iop.org/0295-5075/93/6/64004/fulltext/epl_93_6_64004.html (should be readable)

    Electron beam coulomb field
    4, http://arxiv.org/pdf/1211.2913.pdf

    and a 'theory' paper mentioning QFT
    5, http://arxiv.org/pdf/0706.1661.pdf

    There were also a few about quantum tunnelling, but I prefer to stay away from that for a moment.

    So what are the chances that these results are correct? If they are mistaken, where do they go wrong?

    Maybe Al could set up a quick test :) they only require fairly basic equipment. I had a quick go myself, but was confounded by reflections and cable pickup, so while the equipment is simple, it can be hard to keep the experiment clean.
    •  
      CommentAuthorAngus
    • CommentTimeJan 20th 2015 edited
     
    As near as I can figure on a quick scan the first four references are too vague to be useful. I'm not willing to part with $30 to read the fifth.

    The Italian paper is interesting. As they say, the results seem to show that the field is a rigid structure that travels along with the electron. This is only a problem if you imagine virtual photons having to go out and construct it all the time. I'm not sure I do have to imagine that. Virtual photons are nebulous enough that maybe it makes sense that they do things differently.

    As usual I don't understand the theory paper.

    ETA I've seen some stuff on FTL tunnelling. As I understand it there is a kind of dispersion that can make it seem like some part of the spectrum of a pulse is arriving too fast but the contents of the pulse still takes the same amount of time to arrive.
    • CommentAuthorbr
    • CommentTimeJan 20th 2015
     
    Is this link any better?

    http://iopscience.iop.org/0295-5075/93/6/64004/fulltext/epl_93_6_64004.html

    Or if you whispered an email address I could forward on whichever.
    • CommentAuthorbr
    • CommentTimeJan 20th 2015
     
    Posted By: AngusAs near as I can figure on a quick scan the first four references are too vague to be useful.
    What would you like to see? I have been in contact with the authors, who may be happy to clear things up, although as you can tell they don't come from academic backgrounds.
    •  
      CommentAuthorAngus
    • CommentTimeJan 20th 2015
     
    It seems to be a different paper, but I can read it anyway.
    •  
      CommentAuthorAngus
    • CommentTimeJan 20th 2015
     
    Posted By: br
    Posted By: AngusAs near as I can figure on a quick scan the first four references are too vague to be useful.
    What would you like to see? I have been in contact with the authors, who may be happy to clear things up, although as you can tell they don't come from academic backgrounds.


    For starters, a drawing of their experimental setup.
    • CommentAuthorbr
    • CommentTimeJan 20th 2015 edited
     
    Posted By: AngusIt seems to be a different paper, but I can read it anyway.
    same basic experiment, I'll include it in the top post.

    p.s. A figure from the subscription paper (#3a) is included as Fig 2 of the 'theory paper (#5), showing that v=c does not fit the data, but v>10c does.
    • CommentAuthorbr
    • CommentTimeJan 20th 2015 edited
     
    Posted By: AngusFor starters, a drawing of their experimental setup.
    I know what you mean :)
  1.  
    Just cut to the chase: have any of the phenomena been used or observed to transfer _information_ at superluminal speed?


    And I'm afraid that "clean" experimentation is incompatible with my local spacetime continuum.

    Or clean anything, really.
  2.  
  3.  
    None of which hold water according to current understanding. Unless negative mass-energy exists, that is.
    •  
      CommentAuthorAngus
    • CommentTimeJan 20th 2015
     
  4.  
    I see no determination there that signalling cannot exceed c.
  5.  
    Excuse me. There are several papers available on group velocity exceeding light speed with actual data!
    •  
      CommentAuthorAngus
    • CommentTimeJan 20th 2015 edited
     
    It is known that you can (appear to) see group velocities faster than light in tunnelling or evanescent wave experiments. The argument is about what it all means. I understand that there is pretty good evidence that it still doesn't imply you can send signals faster than light, even by tunnelling. It all has to do with how the spectral components that make up a pulse get spread out in the process of tunnelling.

    I think.

    ETA: to put it another way - in these experiments the shape of a pulse is not preserved because the propagation is dispersive. The problem then becomes how you determine when a pulse has left somewhere and when it has arrived somewhere else. It will have no sharp leading edge, and whatever leading edge it has will change by the time it arrives at the detector.
  6.  
    Group velocity != signal velocity, necessarily. Group velocity > c has indeed been demonstrated. Yet to be demonstrated is signal velocity > c.
  7.  
    I did not say anything about signal velocity. It is very likely impossible to transfer information FTL....in our 3-space at least.
  8.  
    Posted By: Andrew PalfreymanI see no determination there that signalling cannot exceed c.
    Posted By: magic momentExcuse me. There are several papers available on group velocity exceeding light speed with actual data!
    Posted By: Andrew PalfreymanGroup velocity != signal velocity, necessarily. Group velocity > c has indeed been demonstrated. Yet to be demonstrated is signal velocity > c.
    Posted By: magic momentI did not say anything about signal velocity. It is very likely impossible to transfer information FTL....in our 3-space at least.
    Excuse me too.
    •  
      CommentAuthorAngus
    • CommentTimeJan 20th 2015
     
    Children!...please...!
    • CommentAuthorAsterix
    • CommentTimeJan 20th 2015
     
    Isn't all of this discussed in that--oh, what's its name--uh, Wikipedia?