Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum Sending Photons Backward In Time

Physicist Costas Soukoulis and his research group at the U.S. Department of Energy?s Ames Laboratory on the Iowa State University campus are having the time of their lives making light travel backwards at negative speeds that appear faster than the speed of light. That, folks, is a mind-boggling 186,000 miles per second ? the speed at which electromagnetic waves can move in a vacuum. And making light seem to move faster than that and in reverse is what Soukoulis, who is also an ISU Distinguished Professor of Liberal Arts and Sciences, said is ?like rewriting electromagnetism.? He predicted, ?Snell?s law on the refraction of light is going to be different; a number of other laws will be different.?

For the full story:
http://www.sciencedaily.com/releases/2006/07/060721152533.htm

No wonder you believe the BCS theory!!

Great:

Very interesting and curious.
jjw

JB ... the fact that I post something means I find it interesting.

You are reading into my post things that "seem" to be there.

You'd be well advised to stop doing it.

I find the "faster than the speed of light" idea very interesting, but didn't really understand the article. It travels in the opposite direction...sounds to me like a mirror. And, from the diagram it just looks like a 180 degree phase change. Guess that's why I'm not a physicist

Touche!

Since this involves the study of metamaterials, could this be termed "Metaphysics"?

Hi DrBarr,

Anything that is supposed to be superluminal or faster than light is tricky. Whenever anybody starts talking about such things hold onto your wallet.

The problem with faster than light (FTL) is mostly with causality. Here's how it goes.

Suppose that we have event one, say the transmission of an FTL signal, with coordinates (x1, t1). Also let the second event be the reception of the signal at coordinates (x2, t2).

For convenience and with no lose of generality suppose that x2 > x1 and t2 > t1. Set

delta_x = x2 - x1
delta_t = t2 - t1

Suppose that the signal has a velocity U > c. (c is the speed of light.)

Now suppose that there is a passing observer with speed v (less than that of light) so that

c^2 / U < v < c.

Now use the Lorentz transforms to determine what the passer by sees.

First set a = 1/ sqrt[1 - v^2/c^2]

then for the new coordinates we have

delta_x' = a [delta_x - v delta_t]
delta_t' = a [delta_t - v delta_x / c^2]

Just look at the second equation. Factor out the delta_t to get

delta_t' = a delta_t [1 - v U / c^2].

Now, because of above the inequality, where v was chosen we have

v U / c^2 > 1

therefore delta_t' is negative. In other word the passer by sees things in reverse. So the effect precedes the cause.

If you are not used to special relativity this may be a bit hard to take in. It is worth going through the calculation because of the importance of what it says.

Dr. R.

A bit of sanity check here ....

The phrase "faster than the speed of light" must be based upon the medium in which the light is travelling. A lens performs refraction precisely because the speed of light is altered. We have also seen light slowed down to a pace where I could outwalk it with ease.

Reading lay articles to comprehend these topics often leads to misunderstandings due to the fact that the author and editor don't truly understand what they are writing.

Right you are DA Morgan.

The speed of light does depend on the media. (It is the vacuum speed of light divided by index of refraction assuming a simple media.)

In the cited article there are some remarks about beating the speed of light. An old yellow dog jouranlism trick, a screamer, that gets the attention. The point I am trying to make here is that there are serious problems with causality involved with any putative FTL phenomena.

Anyone who know's about refraction, dispersion etc. will automatically make the mental adjustment in response to such nonsense. However, many do not know what the real problem with FTL actually is. The arguement I gave above requires only simple algebra and the Lorentz (see google) transformation and show the causality problem in an easy way.

Dr. R.