The Scharnhorst effect - Can light travel faster than light? (5'56")

Calculations carried out by Klaus Scharnhorst at the Humboldt University in East Berlin suggest that light particles may be able to travel faster than the accepted speed of light. This extraordinary prediction is made by drawing on the traditional theory of Quantum Electro-Dynamics. Philip Campbell, Editor of `Physics World', explains how Scharnhorst reached his conclusion to David Thomas.

THOMAS: Take two conducting plates; put them in a vacuum; then move them closer together. Now what have you got? Well according to a new theory, you've built yourself a `faster than light' machine. This extraordinary prediction results from work carried out at the Humboldt University in East Berlin, and it's already being referred to in some circles as the Scharnhorst Effect, after the physicist who's made the calculations. Before you get too excited, the only thing that could be travelling faster than light would be light particles, or photons themselves. But the new work adds some fascinating complications to the theory of Quantum Electro-Dynamics, or QED. It all revolves around so-called virtual particles which QED says must be `flickering' in and out of existence and reacting with photons as they travel through a vacuum. When this interaction takes place, the photons briefly form electrons and positrons. If you could somehow stop the virtual particles existing, the theory goes, the photons would have to do less work and would speed up, effectively travelling faster than what we now accept as the speed of light. Scharnhorst has now calculated that this is theoretically possible, and as Philip Campbell of `Physics World' explained to me, that's where the two plates come in.

CAMPBELL: If you look at a vacuum between two closely spaced parallel sheets of conductor, it's a very well-known phenomenon that the properties of that vacuum as described by these flickering particles is changed. Now that has certainly been known for a long time. And the very first effectively predicted in this sense was that you would get a compressive force between two such plates. Now the reason for this is that you are effectively removing energy from the vacuum between the two plates compared to the energy of the vacuum outside those two plates. Between the two plates you can get only certain types of particle/photon interactions taking place which are actually restricted by the distance there is between those two plates, you can actually show that there is a relationship between that distance and that indeed the force between the two plates actually pulls them together to an extent that increases as they get closer.

THOMAS: This is the Casimir effect, isn't it?

CAMPBELL: That is the Casimir effect. And in fact it's quite interesting to know that it was first predicted because Casimir was asked to look into what sort of forces can exist between particles, because the known forces at the time that he was asked this back in the 40s, could not account for the stability of paint. Phillips had a division that was looking at the stability of paints, and the way in which you inhibited coagulation and the separation of the stuff of which paint is made could not be explained by conventional theories. And it turned out that indeed you did need this extra force between particles to account for that.

THOMAS: Now Scharnhorst's work though is theoretical isn't it, and what he's suggesting is that you can take the Casimir effect and such like one step further to explain away how photons could be effectively speeded up?

CAMPBELL: Yes. It has to be said that people had wondered about this effect previously, but this is the first hard-headed attempt to really go through all the different aspects of the quantum electro-dynamics that you require to see how a photon behaves in this unique type of vacuum space if you like. And it turns out that if you incorporate the extra little effects that take place, just to give you an example of the complexity you have to go to, as these two particles, the electron and the positron are formed in this vanishingly small amount of time, they themselves can exchange photons. And if you take all those into account, and this is exactly what Scharnhorst does, you find that if you have two plates that are only a micron apart, that is a millionth of a metre apart, you find that the velocity of light of a photon travelling from one plate to another, is increased by one part in ten to the 36, that is an incredibly small number and one that is in fact beyond all conceivable experimental tests at the present time.

THOMAS: But even theoretically speaking, why is it that if you have the plates that close together, why should it be then that a photon could be slightly faster than we would normally accept in a vacuum?

CAMPBELL: It is precisely because of the Casimir effect, as I stated before, involves the suppression of certain of these fluctuations, that is some of the photon and particle pair interactions that I was describing before get suppressed. Now that is the phenomenon that actually changes the energy level if you like within the vacuum, that is the phenomenon that produces the compressive pressure that I mentioned before, that's the Casimir effect. What it also does of course is suppress some of these photon interactions, where a photon actually has to turn itself into these particles and then get regenerated. That is, to use a phrase that you used earlier on, it actually has to do less work to make its way through the vacuum between these plates than it has to outside these two plates, according to this theory. And that means that it can travel faster.

THOMAS: Now does this mean that we're saying is we should revise what we think of as the speed of light and that the speed of light through a vacuum is slightly different from the maximum speed of a photon, or does it really mean that we're throwing all the theories that have been handed down from the people like Einstein into the air and we're going to upset a lot of physicists as a result?

CAMPBELL: I wish I knew the answer to that one. The point is that you can imagine circumstances where a photon can reach another photon outside the vacuum between these two plates faster than a photon travelling an equivalent distance without any interaction with this plate vacuum at all. And that certainly does seem to break the fundamental rule that you cannot convey information faster than the speed of light in a conventional vacuum. I have talked to a number of physicists about this particular point, and they are reduced at the current time to saying either that they're sure that there must be some other effect that this person hasn't taken into account that would actually remove the effect that he's talking about, or, and this is an incredibly nebulous expression, that somehow the universe will conspire to ensure that you couldn't possibly observe the effect of conveying a signal faster than the speed of light in the conventional vacuum. What that simply means is that people who have tried to do the work that Scharnhorst has done have verified it as far as it has gone. I know that a couple of people have been through his calculations and can find no flaw with them. The question is now to look to see whether there are indeed other factors that they have not taken into account which will ensure that the basic principle of Einstein is indeed conserved.

THOMAS: In the meantime, the universe is innocent until proven guilty, as normal in these sort of experiments I guess?

CAMPBELL: That's right. And you have to remember that there are no possible ways that these authors can envisage at the moment that you can possibly exploit the Scharnhorst effect, as people are already calling it.

THOMAS: Philip Campbell on some unsettling implications for quantum theory.