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Electrical Pulses Break Light Speed Record 68

Posted by chrisd
from the canadians-show-us-the-way-again dept.
J'raxis writes "PhysicsWeb writes that 'Pulses that travel faster than light have been sent over a significant distance for the first time. Alain Haché and Louis Poirier of the University of Moncton in Canada transmitted the pulses through a 120-metre cable made from a coaxial 'photonic crystal.' Haché and Poirier emphasize that their experiment does not break any laws of physics. Although the group velocity exceeds the speed of light - an effect permitted by relativity -- each component of the pulse travels slower than light.'"
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Electrical Pulses Break Light Speed Record

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  • Re:Well.... (Score:4, Interesting)

    by PhuCknuT (1703) on Friday January 25, 2002 @02:42AM (#2899509) Homepage
    I forgot to mention how this IS important. What this type of research will lead to is reduced latency. Instead of information traveling down a cable at 2/3 of the speed of light, they can use methods like this to send data at much closer to the speed of light. Not more data, but slightly lower ping times.
  • by richie2000 (159732) <rickard.olsson@gmail.com> on Friday January 25, 2002 @10:22AM (#2900377) Homepage Journal
    The other article linked to from the one in the submission says:

    Next they send a 3.7-microsecond long laser pulse into the caesium cell, which is 6 centimetres long, and show that, at the correct wavelength, it emerges from the cell 62 nanoseconds sooner than would be expected if it had travelled at the speed of light. 62 nanoseconds might not sound like much, but since it should only take 0.2 nanoseconds for the pulse to pass through the cell, this means that the pulse has been travelling at 310 times the speed of light. Moreover, unlike previous superluminal experiments, the input and output pulse shapes are essentially the same.

    Correct me when I'm wrong, but doesn't this mean that the pulse went out of the cell 61.8 ns before it went in? When I try to picture this phenomena my brain just overloads and dumps the core.

  • by renehollan (138013) <rhollan AT clearwire DOT net> on Friday January 25, 2002 @10:44AM (#2900471) Homepage Journal
    is a problem akin to Shannon's Theorem: you know, the maximum data rate of a channel is related to the bandwidth and noise floor?

    In this case, the effect occurs close to the intentional absorbtion band, where signals get reflected because of impedance mismatch. So, the signal gets strongly attenuated. Gets there faster, but is much weaker, yes?

    The effect of the thermal noise of the receiver in the band of interest thus gets more significant. More relative noise, less bits per pulse (think AM).

    So, what would be a 1 km cable capable of carrying 100 mb/s (for example -- I'm pulling these numbers outa my...) now looks like a 100 m cable capable of carrying 1 Mb/s... great for wire latency, lousy for bandwidth.

    Now, we all know that for typical packet sizes, wire latency is insignificant to data serialization latency: the time it takes for the last bit in a packet to leave the transmitter, compared to the first bit. So, you've cut wire latency by 90% and increased data latency by much more.

    What am I missing here? Or, is there, as I suspect, NSTASFL

  • Brain Teaser (Score:3, Interesting)

    by Mignon (34109) <satan@programmer.net> on Sunday January 27, 2002 @05:03PM (#2910610)
    As a youngun', I was told by an adult friend that if you closed a pair of scisors fast enough, the point where the two blades crossed would move faster than the speed of light. It was presented as a sort of paradox about how something could go faster than light. (Note to Marilyn Vos Savant [wiskit.com]: it's 'cause the thing moving faster than light has no mass, not 'cause Einstein was wrong.)

    Actually, I may be the dope - I never verified if this was true. Anyone know?

Thus mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true. -- Bertrand Russell

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