[83680] in North American Network Operators' Group
Re: Semi-on-topic: Light that travels faster than the speed of light?
daemon@ATHENA.MIT.EDU (David Hagel)
Mon Aug 22 11:05:33 2005
Date: Mon, 22 Aug 2005 11:05:08 -0400
From: David Hagel <david.hagel@gmail.com>
To: "up@3.am" <up@3.am>
Cc: Steve Brown <nanog@stellablue.org>, nanog@merit.edu
In-Reply-To: <Pine.BSF.4.44.0508221009360.62430-100000@richard2.pil.net>
Errors-To: owner-nanog@merit.edu
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.=20
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 realized..it 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, up@3.am <up@3.am> wrote:
>=20
>=20
> No, they were actually over the speed of light for a "portion of the
> signal":
>=20
> "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, becaus=
e
> only a portion of the signal is affected."
>=20
> On Sun, 21 Aug 2005, Steve Brown wrote:
>=20
> >
> > Okay, guess I should have read the article first, given the title is "L=
ight
> > that travels faster than the speed of light"
> >
> > Steve
> >
> > >
> > > Perhaps they are referring to being able to vary the speed while it i=
s
> > > below the speed of light. That is, slowing it down to 1/10th the spee=
d of
> > > light, and then speeding it up to 1/5th the speed of light.
> > >
> > > Steve Brown
> > >
> >
>=20
> James Smallacombe PlantageNet, Inc. CEO and Janitor
> up@3.am http://3.am
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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>=20
>
