Question: Sticking with the sci-fi theme... is teleportation possible? Have scientists achieved it, if so at what scale?

Susan Cartwright answered on 29 Apr 2020:

I think Lori-Ann’s done a really good job of anwering this. The key point is that what defines a particular photon (or electron, or any other elementary particle) is a set of numbers that tell you its energy, its polarisation state, and so on. If you can modify another photon somewhere else so that it has those exact same numbers, then it is, by that definition, the same particle. Since the interaction that you have to have with the original photon in order to determine these defining numbers actually changes them (imagine trying to find the position of a small ball in a darkened room: the only way to find it is to collide with it, which will cause it to move – so now you know its original position, but it isn’t at that position anymore), you can argue that the original photon has been teleported to the new position.

The problem with “Three to beam up, Scotty!” is that trying to do this with the approximately 60000000000000000000000000000 (6E28) particles that make up a human body is, well, something of a challenge. And you’d have to do it fast enough that the destruction that you caused from the moment that you started did not affect the states of the final particles that you copied – and likewise at the other end. And you have added to that the problem that Heisenberg’s uncertainty principle limits the precision with which you can measure certain pairs of properties. (Star Trek’s transporters were fitted with (hypothetical, of course) “Heisenberg compensators” to deal with this. When Larry Krauss was writing his book “The Physics of Star Trek” he asked one of the people from the show “How do those work, then?” The answer? “Very well, thank you.”)

So, if you accept that two photons with identical quantum numbers are in fact the same photon, we can teleport photons. But macroscopic objects are a different story.