Re: more teleportation

Hal Finney (
Thu, 22 Oct 1998 21:52:13 -0700

Damien Broderick, <>, writes:

> >
> > Quantum teleportation allows information to be
> transmitted at the speed of light -- the fastest speed possible -- without
> being slowed down by wires or cables.
> I think the reporter is missing the real boat here - surely quantal
> entanglement allows information to pass from one spacetime location to the
> other *instantaneously*, faster than light. (Of course, you need to have
> the prepared black box states already waiting, in advance, at either end,
> so it won't get us to Alpha Centauri in less than 4.3 years - but it will
> permit people at home to see the pictures in the very same instant the
> explorers arrive [whatever *that* means, *pace* Einstein].)

The unique aspect of quantum teleportation isn't its speed, which is no faster than the particle which must travel between sender and receiver, but the fact that the receiving particle ends up in exactly the same quantum state that the sending particle was in.

This is significant only because of a peculiarly quantum phenomenon: "you can't clone a quantum state." That is, given a quantum particle, it is impossible to create a duplicate which is in the same state. Quantum teleportation exploits a loophole, which is that you *can* create a duplicate if you destroy the original in the process. (Of course it is a matter of semantics then whether it should still be called a duplicate, since there is only one.)

If we had classical physics, the analogous phenomenon to quantum teleportation would be utterly mundane. Measure the state of a system, and send it to the other side, then build a system in the same state. It is the impossibility of this technique in the quantum world which made quantum teleportation such an amazing discovery.

As a matter of fact, teleportation of macroscopic objects like people would almost certainly be done in the classical manner. It is unlikely that quantum phenomena play any role in determining our physical state. Classical measurements of the particles which make up our brains and bodies would be enough to create a remote duplicate. With a sufficiently mature technology, this will allow people to switch between uploaded and physical bodies, and to travel to reception stations throughout the universe, sending themselves as an information stream carried by a light beam. has a description and a picture of how quantum teleportation works.

As was already mentioned, it would not allow people at home to see pictures from Alpha Centauri in real time. Particles would have to travel from there to here to carry any signals which would allow us to see pictures, and those particles would travel no faster than light.