# Travelling faster than the speed of light?

1. Feb 9, 2010

### Aero_Marty

Hey everyone,

Im new to this forum, was not sure whether or not to post this question here...

I heard about an experiment where a beam of light was aparently teleported a short distance, I am unsure as to how this is possible, but my question is regarding the speed that beam is travelling.

If it is instantaneously teleported a distance then according to simple laws of motion v=d/t, then the velocity would prove to be faster than the speed of light, but aparently it is impossible to travel faster than the speed of light. How can this be explained? Is there another theory I am unaware of?

Marty

2. Feb 10, 2010

### Fredrik

Staff Emeritus
The "teleported" photon doesn't actually travel to the destination. What happens is that its polarization state is transferred to another photon. The process changes the polarization state of the original photon, so the polarization state isn't being copied. It's transferred. The reason why this can be called "teleportation" at all is that photons are indistinguishable, so the end result is the same as if the original photon had actually moved to the the destination, while another photon was moved from the destination to the starting point (probably with a changed polarization state...not sure about that).

The "transfer" isn't instantaneous, because after you have performed a measurement at the site where the original photon is, you actually have to send some information to the destination site by some other means (pigeons? ), so that the experimenter at that site knows what interaction he's supposed to subject his photon to, in order to reproduce the original photon's polarization state.

I probably gave you the impression that what I'm describing is "measure the polarization of the photon at A, and than give the photon at B the state that's the result of that measurement". That's not what happens. A measurement of the polarization of the original photon would change its polarization state, so we'd end up giving the photon at B the wrong state. We want the photon at B to end up in the state that the photon at A was in before we did anything to it, so the measurement performed at A needs to be something more clever than just a measurement of the polarization of the photon that we want to "teleport".

3. Feb 10, 2010

### Aero_Marty

Haha... pigeons, awesome.

Ah I see, so nothing is actually transported at all.

If I'm getting this right, then the analogy to teleporting a human say, would be that an exact copy of their physical form at that current point in time would have to be given to an existing "blank" body at another location (obviously considering this possibilty hypothetically). Their consciousness would then have to be somehow uploaded, transported and then downloaded again into the other body.

I know this is a bit 'out there' but its something I've been wondering about. Basically, even if all the technology was around for this to happen, teleportation as I would think of it (instantaneous transportation) is not possible?

Thanks for your reply, I was unsure of the details of that experiment.

Cheers, Marty