Merit Network
Can't find what you're looking for? Search the Mail Archives.
  About Merit   Services   Network   Resources & Support   Network Research   News   Events   Home

Discussion Communities: Merit Network Email List Archives

North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: Semi-on-topic: Light that travels faster than the speed of light?

  • From: David Hagel
  • Date: Mon Aug 22 11:06:31 2005
  • Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=beta;; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=s+0ybjhN4OMm4JJfEcTPGvDhRg3+dlem58HvZZmlgwsRg8pgsDGIUDy+C2iPPrnH1AgOHg/TCoQHABhTBsM8Ns5SCxe0O/Zm/Kb3eKVbVSxJa3SMaUHj4rEn4UiKh4Loy58kyrbwNa2/0e3g+4vt8jlTnSbaYrn4kR9plmYD1/o=

I asked about this article to someone who works on optical properties
of materials. Here's what he says (I don't pretend to understand
everything though):

" This is called superluminal propagation, and many groups have shown
it in different media; this one is in fiber.  However, this does not
violate anything apparently because it is only the leading edge of a
pulse, and information still cannot go faster than c.

 I have been trying to understand what Einstein actually said.
Apparently he said that "information" cannot be transmitted faster
than c.  Now light has a phase velocity which exceeds c all the time. 
The textbooks then say that it is the group velocity that cannot
exceed c.  But I found out while writing my book that even that is
possible near resonances.  Then I saw somewhere that "energy velocity"
cannot exceed c.  Well, I tried deriving that in a general medium and
cannot see why it is fundamentally impossible.  I asked around, and
one of my colleagues says that it is far more subtle than even
Einstein may have is the leading edge of a pulse (or
something like that) that can exceed c, but the whole pulse itself
cannot.  I really don't understand that part, and haven't found any
text describing it.  (Need to find one)."

On 8/22/05, <> wrote:
> No, they were actually over the speed of light for a "portion of the
> signal":
> "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."
> On Sun, 21 Aug 2005, Steve Brown wrote:
> >
> > Okay, guess I should have read the article first, given the title is "Light
> > that travels faster than the speed of light"
> >
> > Steve
> >
> > >
> > > Perhaps they are referring to being able to vary the speed while it is
> > > below the speed of light. That is, slowing it down to 1/10th the speed of
> > > light, and then speeding it up to 1/5th the speed of light.
> > >
> > > Steve Brown
> > >
> >
> James Smallacombe                     PlantageNet, Inc. CEO and Janitor
> =========================================================================

Discussion Communities

About Merit | Services | Network | Resources & Support | Network Research
News | Events | Contact | Site Map | Merit Network Home

Merit Network, Inc.