Faster Than Light
OK, I’m having trouble coming to grips with the following question.
PersonA and PersonB share a teleportation device which will pass one bit of information between them, signifying, I don’t know, whatever. They synchronize their watches which can read down to, say, nanoseconds. One jumps in a spaceship. At t=0, the spaceship takes off and accellerates to acheive a speed of 0.9c. PersonB, ten minutes (by his watch) later, sends the single bit of information via our teleporter.
What time did PersonA (by personA’s watch) receive it?
Sorry to bump this, but i really want to know the answer. I thought FTL travel allowed time travel, and not only that, but this is something they could possibly test (since they’ve done the FTL travel and they’ve demonstrated that clocks slow down).
I hope they didn’t just shine a torch at a wall and say “look! we transported light from this torch to that wall!” I guess I better follow the link and find out.
bye.
The rocket ship person’s watch will read 2358 seconds.
There’s nothing moving faster than light. There’s some sort of quantum mechanical non-local action at a distance going on, but this can have no effect on the non-quantum world.
Teleportation requires information to be transmitted (in this case, from PersonB to PersonA), as I mentioned in an earlier post. As far as we know, information can’t be transmitted faster than light, so the best PersonB can do is shine a light beam (transmitting Morse code, say) toward PersonA. The teleportation is not complete until PersonA receives the Morse-code message and performs an operation on his entangled particle. You can calculate the elapsed time for PersonA pretty easily knowing this; it’s no different from standard relativity.
To reiterate, there’s no “useful” FTL going on in quantum teleportation. Teleportation still requires you to send information between the source and destination, so unless you have some magic device for sending information FTL, you can’t teleport FTL. The reason teleportation is still considered interesting is that it allows transmission of a quantum state with no direct quantum channel (there still needs to be a way of distributing the entangled pairs, but that can be done beforehand). This can’t be done by just looking at the quantum object and describing it, because such observations can’t give a complete description of the quantum state. With teleportation, you can send someone the quantum state without ever knowing what it was.
But what?? 
I thought the state changes happened instantly. That’s faster than light IMNSHO.
So if we keep the original, we’ve got a replicator too, right?
As an Aussie, I for one am very proud. Over the last 50 years in particular, Australian researchers have often been at the forefront, if not leading the world in certain areas esoteric scientific advancement - in particular in the fields of medicine.
Sadly, unlike North America and Europe, due to Australia’s relatively small population there has often been a lack of corporate funding into such esoteric research and many of Australia’s leading minds often left Australia to continue their research overseas - never to return.
For example, between 1955 and 1970, fully two thirds of Australian science graduates from universities here left for North America and Europe and never came back - such was the brain drain.
I’m told that NASA in particular hired hundreds of 'em.
In fact, I’m pretty sure that the world’s 4th computer was built and designed down here and that is was superior to all that came before it - but then the project died.
Also, I’m pretty darn sure that more than a substantial part of UNIX, the computer operating system had it’s genesis down here as well.
Ultimately, the advancement of human knowledge shouldn’t be a contest for nationalist jingoism, but it’s good to be a little proud now and then! I remember walking thru a hallway at MIT in Boston and seeing plaque after plaque dedicated to Nobel Laureates who had won various gongs for advancements in physics and chemistry etc and thinking to myself - ahh, what could have been.
Regards to everyone!
OK, so, if I understand this correctly, the entangled particles have to be physically transported to the location where you wish to ‘teleport’ your beam of light, and once you’ve used an entangled pair, they’re no longer entangled…?
So, what we have isn’t for use in open-ended FTL exploration, but you could place entangled particles on a spacecraft, with their matching particles here on earth, and then communicate back-and-forth essentially instantaneously, until you run out of entangled pairs, and then you’re back to plain ol’ light-speed communications. Is this correct…?
In other words, the devil is in the details, like always.
erislover, thanks for the link!
Yes, and yes. But…
No. You can’t communicate FTL with quantum teleportation. You have to send information (by some other means) to perform the teleportation, which means the speed of the teleportation is limited by the speed that you can already send information.
erislover, the quantum state changes instantaneously, but it changes in a way that can’t be used to send information FTL.
I don’t see, but I will quite honestly take your word for it. It just sounds like they’ve achieved a macro-version of the (possibly implied) non-locality of Bell’s inequality.