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Light faster than light?

  1. Aug 27, 2007 #1
    I just read an article that was released 2 years ago about something that some of you may have heard about and maybe even posted threads about at some point but I have to throw this out there because I really want to learn more about it.

    Researchers from EPFL claim to have made light travel faster than normal using fiber optics.

    Here's a quote:

    "They were also able to create extreme conditions in which the light signal travelled faster than 300 million meters a second. And even though this seems to violate all sorts of cherished physical assumptions, Einstein needn't move over – relativity isn't called into question, because only a portion of the signal is affected."

    When I read the above all I could say was "What the...? Assumptions? A portion at c+ is OK?"

    I expect many to have a similar reaction to mine but someone out there just might be able to explain it. Please do.

    In the meantime here's the article:
    http://www.eurekalert.org/pub_releases/2005-08/epfd-ltt081905.php

    I'm going to hunt for more info on this.
     
    Last edited: Aug 27, 2007
  2. jcsd
  3. Aug 27, 2007 #2
    Here's a couple of quotes from an article about a different experiment and this one is amazing:

    "In the most striking of the new experiments a pulse of light that enters a transparent chamber filled with specially prepared cesium gas is pushed to speeds of 300 times the normal speed of light. That is so fast that, under these peculiar circumstances, the main part of the pulse exits the far side of the chamber even before it enters at the near side."

    "Someone who looked only at the beginning and end of the experiment would see only a pulse of light that somehow jumped forward in time by moving faster than c."

    And here's the article:

    http://partners.nytimes.com/library/national/science/053000sci-physics-light.html

    I sincerely hope by starting this thread that I'm not just rehashing a bunch of old stuff that everyone else here has already beat to death. If that's the case I apologize. It's just that I had never heard of these experiments and I'm also new to this forum.
     
  4. Aug 28, 2007 #3
    Yep, it's rehash.

    Lets say trains (light) travel at a constant speed c, and I have a train (light pulse) which initially contains lots of passengers (photons) seated in the middle carriages and only a few passengers seated in the front or back carriages.

    Each time my train passes through a station, the following happens: The first time the station master happens to notice a passenger in a moving carriage, he tosses a few extra people in through that door ("gain"), but then the station master's arms get tired, and from then on he grumpily orders that every subsequent passenger he sees must immediately disembark ("attenuation").

    After passing through many stations, this means there will be lots of passengers in the front carriages, and very few back in the rest of the train. If the train was very long (and many stations are very close together), you would find that *most* of the passengers disembarking at the final station actually do so earlier in time than when *most* of the passengers boarding at the first station board. To put a spin on this, you might say this rail system transports seated passengers faster than the speed of train carriages.
     
    Last edited: Aug 28, 2007
  5. Aug 28, 2007 #4
    Thanks for the explanation.
     
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