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 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, [EMAIL PROTECTED] <[EMAIL PROTECTED]> 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 > [EMAIL PROTECTED] > http://3.am > ========================================================================= > >