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Light and negative-speed

  1. Jan 18, 2008 #1
    Alright. I think, perhaps, I might have a handle on this. Maybe. I read this article a few months ago, but if someone could explain it a little better I'd appreciate both your effort and candor.

    The article itself- http://www.rochester.edu/news/show.php?id=2544

    My question is, how accurate is this? Is it possible FTL as it purports, a circumvention of relative limitations, or merely another victim of sensationalist reporting?

    Insofar as it's [the pulse] not being able to carry information, what exactly does 'information' mean in this context? The information describing this pulse as 'light' for instance, or that of a signal transmission, or...
    Last edited: Jan 18, 2008
  2. jcsd
  3. Jan 19, 2008 #2


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    It is sensationalist reporting. All they do is sending light through a nonlinear medium, which changes the shape of the light pulse, so that the peak of the pulse appears to travel backwards. As the peak is not associated with the speed of light or transport of information, there is no sensation here at all.

    As a more easily understandable toy model imagine a train full of people. The train starts and people are distributed evenly all over the train. Now all the people start going to the back of the train with different speeds. You will notice, that the position of the "peak" of the number of people changes. Depending on the speed of the train, this position might even move backwards. Nevertheless this has absolutely no influence on the speed of the train.
  4. Jan 21, 2008 #3
    Sorry, been a while since I’ve gotten the chance to come back here. Wasn’t expecting to find the thread moved, but perhaps it does fit a bit better beneath the classical umbrella.

    cthugha said:
    Yeah… At first glance I figured it was something about the erbium laced fiber. However, after some thought it registered that he was discussing something a little different, hence my asking about the possibly sensationalistic language of the original article.

    To point some out [emphasis mine]:

    So, I considered that one, figuring that the reporter had left out some important information, namely that it was only the leading edge that was exiting the other end of the fiber before the 'peak' of the pulse had even entered. But that didn't make sense. Boyd, and the reporter, were clearly suggesting something else.

    Reconstruct, Boyd says, in a direct quote [given, of course, that the reporter hasn’t taken any liberties] I started to wonder about what was really going on.

    Ok. With nothing in the article stating otherwise, I thought perhaps, perhaps the erbium laced fiber is encased in another medium, an atmosphere, so to speak, that also inhibits the speed of the 'twin' pulse outside of the fiber. Maybe the interior of the fiber isn’t quite as stifling as that without.

    It would explain the discrepancy in speed, but...

    Choosing to avoid the awkwardly posed ‘funhouse mirror’ explanation near the end of the article, I’ll instead bring into relief the descriptions of the four-stage graphic that illustrates the process.

    I understand that the speed of the laser through the fiber doesn’t equal c, and this is what I mean by asking if it was sensationalist reporting- but is it, as you say, merely a fluid squash-and-stretch of one pulse?


    Hypothetically speaking, and giving the reporter’s journalistic integrity a big benefit of the doubt here-

    What if somehow the interior of the fiber [no matter the ‘actual’ speed of the pulse through it] is akin to a superfluid, where all ‘quanta’ throughout the ‘fluid’ are acting in unison- a ‘one for all, and all for one’ kind of thing.

    Could it, or a phenomen like it, account for the reported propagation of the ‘same’ pulse at the exiting end of the fiber as well as the ripple-like reverberation of the split-pulse backward into the initial?

    Could this as well, account its exiting speed relative to the speed of its twin reference travelling outside the fiber?

    Last edited: Jan 21, 2008
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