Please turn on javascript in your browser to play chess.
Posers and Puzzles

Posers and Puzzles

  1. Standard member wolfgang59
    Infidel
    08 Jan '10 16:36
    Does anyone know anything about John Singleton who thru 2006-2009 claims to have made radio waves travel faster than light?
    (He does this by 'abusing' them!!!???)

    Googling just gives me loads of articles which seem to be cut&paste from same source(s)

    Is it some kind of April Fool that got out of hand??
  2. Standard member Palynka
    Upward Spiral
    08 Jan '10 16:42
    Seems legit...

    http://www.magnet.fsu.edu/search/personnel/getprofile.aspx?fname=John&lname=Singleton

    Singleton, J.; Ardavan, A.; Ardavan, H.; Fopma, J.; Halliday, D. and Hayes, W., Experimental demonstration of emission from a superluminal polarization current- a new class of solid-state source for MHz-THz and beyond, IRMMW2004/THz2004, Karlsruhe, October (2004); Published in IEEE Conference digest 04EX857, 04EX857, 591-2 (2004)
  3. Standard member PBE6
    Bananarama
    08 Jan '10 16:53 / 1 edit
    Interesting! I found this article on Wikipedia, and apparently even thought under certain circumstances the "group velocity" of a wave can exceed the speed of light, this does not mean that any information travels superluminally:

    http://en.wikipedia.org/wiki/Dispersion_(optics)#Group_and_phase_velocity

    The article quotes the following Nature article, which I haven't read:

    Stenner, M. D., Gauthier, D. J., and Neifeld, M. A. (2003). "The speed of information in a 'fast-light' optical medium". Nature 425: 695.

    I'd reserve judgement until reading the actual article to see what kind of stipulations apply in these cases, but on the surface at least it appears legit.
  4. Standard member wolfgang59
    Infidel
    08 Jan '10 17:19
    Originally posted by PBE6
    Interesting! I found this article on Wikipedia, and apparently even thought under certain circumstances the "group velocity" of a wave can exceed the speed of light, this does not mean that any information travels superluminally:

    http://en.wikipedia.org/wiki/Dispersion_(optics)#Group_and_phase_velocity

    The article quotes the following Nature article, whi ...[text shortened]... kind of stipulations apply in these cases, but on the surface at least it appears legit.
    Thats way beyond me!
    I'll wait for a layman's explaination.

    Thanks.
  5. Standard member Palynka
    Upward Spiral
    08 Jan '10 17:39
    Originally posted by PBE6
    Interesting! I found this article on Wikipedia, and apparently even thought under certain circumstances the "group velocity" of a wave can exceed the speed of light, this does not mean that any information travels superluminally:

    http://en.wikipedia.org/wiki/Dispersion_(optics)#Group_and_phase_velocity

    The article quotes the following Nature article, whi ...[text shortened]... kind of stipulations apply in these cases, but on the surface at least it appears legit.
    But then it's only the group velocity which is faster than light, not the signal velocity.
  6. Subscriber AThousandYoung
    Proud Boys Beware
    08 Jan '10 17:43
    Originally posted by Palynka
    But then it's only the group velocity which is faster than light, not the signal velocity.
    Right. I remember something about this, but it sounds like you know more. Can you offer the layman's version?
  7. Standard member Palynka
    Upward Spiral
    08 Jan '10 18:28 / 4 edits
    Originally posted by AThousandYoung
    Right. I remember something about this, but it sounds like you know more. Can you offer the layman's version?
    What I know is from my own field and data filters, so I don't know if it is exact in this case. Anyway, since this is non-technical it might not matter...

    In a wave, the peaks will seem to "increase" and "decrease" as the wave moves. Like the wiki illustration here:
    http://upload.wikimedia.org/wikipedia/commons/b/bd/Wave_group.gif

    You can then see that the wave seems to move faster than its shape, because the highest peak eventually starts "decreasing" and the next peak becomes the largest one. So eventually you'll reach the same shape as before, but with the previous peak being the highest one! The speed of that shape is the group velocity.

    Signal velocity is the speed at which a wave carries information. Imagine a disturbance in the wave, that disturbance would move at a certain speed which is the signal velocity. The easiest way to think about it is how fast it gets from point A to B from the moment when you originally send it from A (sometimes also called the front velocity, but it's the same AFAIK).
  8. Standard member wolfgang59
    Infidel
    08 Jan '10 19:01
    Originally posted by Palynka
    What I know is from my own field and data filters, so I don't know if it is exact in this case. Anyway, since this is non-technical it might not matter...

    In a wave, the peaks will seem to "increase" and "decrease" as the wave moves. Like the wiki illustration here:
    http://upload.wikimedia.org/wikipedia/commons/b/bd/Wave_group.gif

    You can then see tha ...[text shortened]... lly send it from A (sometimes also called the front velocity, but it's the same AFAIK).
    Thanks for the link. cant get my head around it at the moment though!
  9. Standard member Palynka
    Upward Spiral
    08 Jan '10 19:07
    Originally posted by wolfgang59
    Thanks for the link. cant get my head around it at the moment though!
    No problem. But what link are you talking about?
  10. Subscriber AThousandYoung
    Proud Boys Beware
    08 Jan '10 22:38
    Originally posted by Palynka
    No problem. But what link are you talking about?
    http://upload.wikimedia.org/wikipedia/commons/b/bd/Wave_group.gif
  11. Subscriber AThousandYoung
    Proud Boys Beware
    08 Jan '10 22:41 / 1 edit
    Originally posted by wolfgang59
    Thanks for the link. cant get my head around it at the moment though!
    Imagine a long conga line of people. Every beat in the music, someone raises their hand in sequence; first the first guy, then the second on the second beat, then the third on the third beat...
    Every four beats everyone also takes a step forward.

    The "raised hand" will move faster than the individual people will.

    Or better, think of a football game when people do "the wave". "The wave" moves around the stadium very quickly but each person stays in their own spot.
  12. Standard member Palynka
    Upward Spiral
    08 Jan '10 22:52 / 1 edit
    Originally posted by AThousandYoung
    http://upload.wikimedia.org/wikipedia/commons/b/bd/Wave_group.gif
  13. 08 Jan '10 23:13 / 1 edit
    Originally posted by AThousandYoung
    Or better, think of a football game when people do "the wave". "The wave" moves around the stadium very quickly but each person stays in their own spot.
    I went to a football match with my girlfriend once. And a wave started at the other end. The wave approached and I made my part of the wave. I was excited because this was my first crowd wave ever, so I turn to my girlfriend to tell her my impression. But she wasn't there, I couldn't see her. She had propagated with the wave.
    Later she came back with two hot dogs in her hand and gave me one of them. I asked her how it felt to be carried away by the wave, but she just said that it was nothing. She didn't really understand what I meant.
    Fantastic, isn't it!?
  14. Standard member wolfgang59
    Infidel
    09 Jan '10 12:46
    Originally posted by AThousandYoung
    Imagine a long conga line of people. Every beat in the music, someone raises their hand in sequence; first the first guy, then the second on the second beat, then the third on the third beat...
    Every four beats everyone also takes a step forward.

    The "raised hand" will move faster than the individual people will.

    Or better, think of a football ...[text shortened]... "The wave" moves around the stadium very quickly but each person stays in their own spot.
    But isnt that the speed of the wave? (ie c for radio waves)
  15. 09 Jan '10 13:00
    Originally posted by wolfgang59
    But isnt that the speed of the wave? (ie c for radio waves)
    Yes, it's a bad example.

    It's quite simple. "Things" can travel faster than light, but "influences" cannot.