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Scientist makes radio waves travel faster than light

  1. Oct 27, 2008 #1
  2. jcsd
  3. Oct 27, 2008 #2
    can't find the paper they presented, do you have a link?

    I recently saw an article about a group in europe who entangled two photons, sent them in opposite directions for 9kM and mesured the interference patterns. The long and short of it is that the photons were still communicating with each other, at a speed around 10x that of c.
     
  4. Oct 27, 2008 #3
    In the article, the scientist involved explains by talking about waving a laser beam around and saying that the beam cutting across the face of the moon is travelling at greater than c. This is a well-known fact and has been well known for many years. If you send a radio wave or a beam of light down a waveguide, the angular velocity in the guide will be greater than c. However, the linear velocity of the wave between the entrance point and exit point is less than c. Picture yourself standing on a seawall, with a water wave approaching you at an angle of 45 degrees to the wall. As you stand facing the wave, there are two velocities involved. The first is the velocity of the wavefront directly towards you; the second is the velocity of the wave/wall intersection approaching you along the wall. They will both reach you at exactly the same time, but the distance along the wall is greater than the direct distance from you to the wave at sea. So the angular velocity (or phase velocity) along the wall is greater than the wave velocity. Replace that analogy with a light wave in a waveguide and you can see how the velocity along the wall of the guide is greater than c. But this in no way invalidates the ultimate velocity of c! It is a matter of perspective only. However, up until now I don’t believe anyone has found a way to utilize this effect. It is not at all clear to me that this is a new breakthrough and if the effect can actually be utilized for anything. Since it is coming from a scientist working at Los Alamos, it cannot be disregarded out of hand.
     
  5. Oct 27, 2008 #4
    Isn't this whole thing sort of ridiculous? The spot of light on the moon *doesn't* travel, any 'appearance' of it travelling would in reality be new photons that you sent up, hitting the moon at another location. So what's there really to discuss?
     
  6. Oct 27, 2008 #5
    schroder & Raap

    You seem to be focusing on an unrelated throwaway example from the article.
    The article is not about waving laser beams about; nor about a resultant spot moving faster than light.

    It is about:
    "This Los Alamos National Laboratory gadget, called a polarization synchrotron, combines radio waves and a rapidly spinning magnetic field, which forces radio waves to travel faster than the speed of light."

    I do not know whether it is correct or not but please get to the proper substance of an article before debunking it.
     
  7. Oct 27, 2008 #6
     
  8. Oct 27, 2008 #7
    I suggest, if your curiosity is enough to motivate you, you look up "group velocity". Hecht has a fair treatment in his "Optics" book. Essentially, waves may resonate in such a way that a waveform is created that travels faster than any of it's constituent waves.
     
  9. Oct 28, 2008 #8
    Your comment has me wondering if you actually bothered to read what I wrote before rushing to reply. The scientist involved used the laser pointing at the moon in his explanation of the principle; I used the water wave and the seawall. Neither of these explanations refers directly to the specific device or technology under development. They are just simplified explanations of the general principle involved. Nowhere in my post am I attempting to “debunk” anything.
     
  10. Oct 28, 2008 #9
     
  11. Oct 28, 2008 #10
    Hi schroder. I read the article. I read your post. I've reread your posts and the article.

    I know I won't convince you but you are wrong to think that laser example was being used to explain the principle at all.
    They are talking about speeding up the light itself; not its effect.
    Try to read the article more carefully.
     
  12. Oct 28, 2008 #11

    uart

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    Science Advisor

    That article is not talking in enough detail to really say anything definitive about how it works.

    My personal guess is that the device utilizes some rotating field with a phase velocity greater than c (which as schroder has pointed out is nothing new or special) which is probably the "polarizer" part of the "polarization synchrotron". I also wouldn’t mind betting that this is the only part of it that relates to being faster than c.

    Looking at the proposed applications of what they have achieved it appears that it most likely relates to some kind of new technique in narrow beam forming and that the actual radiation it produces does not travel faster than c (that's my best bet anyway).

    If this is the case then the most likely explanation for the overwhelming emphasis of the "faster than light" aspect in the article is that it overly impressed some science journalist who didn't know any better (or if he did know better he just focused on this aspect to "beat up" the story).
     
  13. Oct 28, 2008 #12

    Cthugha

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    Science Advisor

    The linked report relates to this paper on arxiv: http://arxiv.org/PS_cache/arxiv/pdf/0710/0710.3364v2.pdf, which in turn relates to this paper:

    http://scitation.aip.org/getabs/ser...00096000008004614000001&idtype=cvips&gifs=yes
    (which might not be free to read. In a nutshell, they have a look at the emission of a polarization current distribution, which moves superluminal.)

    A quote from the second paper:
    "The coordinated motion of aggregates of
    subluminally-moving charged particles can give rise to macroscopic
    polarization currents whose distribution patterns
    move superluminally."

    So the emission itself is not superluminal and this coordinated motion stuff sounds pretty similar to the phase velocity concept. That does not really sound spectacular.
     
  14. Oct 28, 2008 #13
    I agree with that assessment. I found another paper by John Singleton (the same scientist mentioned in the article) concerning this research. Here is a brief abstract:

    Moving sources of electromagnetic radiation whose speeds exceed the speed of light in
    vacuo have already been generated in the laboratory [1–4]. These sources arise from sep-
    aration of charges: their superluminally moving distribution patterns are created by the
    coordinated motion of aggregates of subluminally moving particles. A polarization current
    density is, however, on the same footing as the current density of free charges in the Amp´ere-Maxwell equation, so that the propagating distribution patterns of such polarization currents radiate, as would any other moving sources of the electromagnetic field.


    It is clear that he is talking about a superluminal rotating source (the polarization synchrotron) but the wave that is emitted is not superluminal. The advantage is the rapid phase combining in the source’s rotating field which results in the emission of an extremely narrow and powerful beam. While there is no doubt such highly focused beams would be very useful for satellite and deep space communications, I don’t think we will be seeing it incorporated in cell phones any time soon, judging from the size of the apparatus in the photo! But it is very interesting work. Anyone interested in his full paper can find it here:

    http://www1.physics.ox.ac.uk/~ardavan/papers/0709.1283.pdf
     
  15. Oct 28, 2008 #14
  16. Oct 29, 2008 #15
    Looks a LOT like “Space Invaders”.

    Here is the description provided by MOJAVE Project:

    REU student Quinn Looker and Prof. M. Lister have developed an Adobe flash applet that illustrates the concept of superluminal motion in relativistic jets. The user can set the viewing angle, intrinsic speed (Lorentz factor), and distance to the jet, and then watch how a luminous relativistic object effectively chases its own light signals to give the illusion of superluminal transverse motion. These jets are powered by the accretion of material onto billion-solar-mass black holes located in the nuclei of active galaxies. Their rapid brightness variations and apparent superluminal motions indicate that they contain highly energetic plasma moving nearly directly at us at speeds approaching that of light.

    The apparent superluminal motion depends mainly on the viewing angle. This is exactly the same phase velocity effect already discussed.
     
  17. Oct 29, 2008 #16
    Thanks Schroder.

    Can I get more of your help?
    Who does the animation "give the illusion of superliminal transverse motion" too?
    Is it the viewer of this animation or is it the radio telescopes?
     
  18. Jan 21, 2011 #17
    Ok, none of you quite have it right. Here's what they did. The first experiment they did was to build 50 or so switches in a line. The switches control a voltage source that polarizes a piece of alumina. If you switch one on and then switch it off while you're turning on the next you make a sort of polarization wave. There is no speed limit to this...it is all a function of your timing. The faster you can work the switches the faster the polarization current. This current is also the dP/dt term in maxwells 4th equation and is a possible source of radiation, but since it is massless and, for less obvious reasons but you'll just have to believe me or work it out for yourselves, has spatial extent it can move at any arbitrary speed. Singleton says imagine a line of a lot of slow moving drummers. If they get their timing right they can sound like a machine gun despite the fact that each of them goes slowly.

    Now for the pulsar it is a bit more complicated. A pulsar has a magnetic field because it is a spin polarized neutron star. If there happens to be polarizable stuff around the neutron star then there would be dP/dt terms that would be very large and would make radiation (as always this radiation goes c...it has to) whose intensity falls off slower that 1/r^2 for reasons similar to the reason that sound intensity falls off slower for a sonic boom. Singleton built one of these switch devices in a circle and measured the radiation as a function of distance and angle and lots of stuff. He is the first person to measure radiation from a superluminal polarization current as far as I know. Also these guys have done mathematical work that strongly supports this as the mecanism for pulsar emission. In fact, pulsar signals are not smooth "blips" like you would expect from a rotating light source. There is a structure to them that these guys can reproduce with their machine. They are right. This is probably the most misunderstood source of distant radiation there is...remember the intensity falls off slower than other sources.

    The title of this thread is wrong. The radiation measured here goes c. The polarization current is the thing that goes faster than c, and it is not restricted to the speed of light because it is massless and because it has spatial extent.
     
    Last edited by a moderator: Jan 23, 2011
  19. Jan 21, 2011 #18
    The article has been so dumbed down and the description so abbreviated it's hard to know exactly what is being described.

    A phenomenon was discovered nearly a hundred years ago that had physicists thinking for a while that radio waves were traveling faster than light. That was when they first realized that radio waves were being refracted, not reflected, by the ionosphere. In order for the wave to be bent downward, the part in the ionosphere must be traveling faster than the part below the oinosphere and the part below it is already traveling at the speed of light. As was mentioned above, it was only group velocity that was traveling faster than c.
     
  20. Jan 21, 2011 #19
    Yeah, I think I'm actually more confused now than when I first read from the OP.
     
  21. Jan 23, 2011 #20
    Seriously, the original article is stupid. Radio waves are not moving faster than the speed of light. The source of the radio waves is moving faster than the speed of light, but it is allowed to since it is not a real object...just like the laser dot on the moon. The faster than light polarization current has interesting consequences and may one day be used to describe the mechanism of pulsar emission.

    I mean c'mon...newspaper reporters don't understand physics. They should have just let Singleton write the article.
     
    Last edited by a moderator: Jan 23, 2011
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