Faster than light data transmission

[Neil]

We truly do live in amazing times! - http://www.legitreviews.com/quantum-...mission_143076 Imagine if/when our probes dive into Europa's sea, if we can communicate with the probe immediately rather than waiting 40 odd minutes! Now consider our first probes to other stars? Why wait for years for the data to be sent back, when it could be instant! Indeed! Maybe the reason we haven't heard any alien transmissions, is because they don't bother with slow light speed based communications!

[Publius]

My first reaction was: OMFG, why isn't this front-page news all over the world? But then I started trying to read more sources. The information available on how exactly this experiment worked is pretty sketchy but a lot of people commenting on articles about the experiment claim that it can't be used for FTL communication. One example: If this setup can be used to send information, then it is effectively the ansible of SF. There are still some limitations as follows: 1. One of the electrons must be physically carried away to the receiving station in advance of the communication session, and without suffering decoherence in the process. That is, AFAIK, quite challenging; quantum superposition states are notably fragile. 2. If this is successful, then the electron pair can be used to transmit one bit of information instantaneously or nearly so (at vastly superluminal speed at any rate). To transmit more, you need more entangled electron pairs. As you can see, this is not unlike the scheme used to communicate with messenger pigeons---the pigeons native to the destination must first be land-transported to the origin, and each pigeon can be used for transmission once. Except that here you are dealing with superluminal pigeons. :-) This is pretty exciting if true, but alas, I am afraid that it doesn't quite work this way. You see, what the article says is that you can flip the first electron's spin, and when you check, the electrons still have opposite spins---the other electron flipped as well, at the same time. That's nice, but to actually send information you need to make the original electron point a specific way: say, up for 1 and down for 0. But the article does NOT say that you can do that. All it says is that you can _flip_ the original spin, _without knowing_ what it was to begin with*, and which way it will end up. That is _not_ the same as making it point up on demand (thus encoding a 1) and no information can actually be transferred. But on the other hand, the laboratory's own press release about the experiment quotes the lead scientist as saying: "We're able to set the spin (rotational direction) of these particles in a predetermined state, verify this spin and subsequently read out the data." I don't know how to read "predetermined state" without interpreting it as meaning they can "make it point up on demand" (to use the terms of the comment quoted above), and if that is so I can't understand why this could not be used for FTL communication. I'm very confused.

[MoonSylver]

Indeed! Maybe the reason we haven't heard any alien transmissions, is because they don't bother with slow light speed based communications! Or maybe because they don't WANT the primitive primate nutters on this mudball listening in...

[Publius]

Or maybe because they don't WANT the primitive primate nutters on this mudball listening in... Haha, true. Seriously, though, even without exotic communications technologies, it's unclear why we would expect advanced civilizations to be randomly broadcasting their signals out into space like a 20th-century radio station. That's just a waste of signal strength, and we're moving beyond that kind of approach ourselves. Maybe all the cool kids in the galaxy communicate with things like tightly-focused laser beams, so all of your signal energy is directed right at your intended recipient's receiving antenna. It'd be a lot harder to pick up something like that by accident.