Light takes more than three nanoseconds to travel a meter. Today’s technology can measure times down to the tens of picosecond range (a 100 times less) and probably better if we worked at it. (Actually, technology of twenty years ago could do it pretty well). Consider that just a 2 GHz CPU gets 6 clocks in before light travels a meter.
Nonetheless that is almost instantaneous; it’s just that humans are able to measure things that are almost instantaneous pretty well.
ANU’s own explanation of the experiment is not overly technical, and explains that you do have to send the transformation information at less than light speed. Also, I don’t think the distance teleported is of any consequence either. In theory, you should be able to separate the particles as far from each other as you like.
I’m not surprised they didn’t explain it. This is one of those crazy, mind-bending aspects of quantum physics. You do something to this particle over here, and the same thing happens to that particle over there. How does that particle over there know what happened? No clue. But it does.
To expand on absimia’s post, the communication would be secure because the information would not be interceptible; that is, the signal would go from one place to another without ever going “between” the two places. You can see how this sort of thing can do funny things to one’s mind.
RR
Thanks absimia and Necros for explaining that. That makes a bit more sense. We’re basically dealing with something like gravity, which appears to work instantaneously independent of distance.
So basically you need to find a pair of these “matched” particles to be able to use them. How easy/hard is that?
Then I guess once you found a pair, you could then invent some sort of subatomic motion protocol to transfer data. So you could manipulate one end, and the other would be manipulated the same (or opposite) and you could transfer data that way.
Actually gravity is not instantaneous but rather propogates at the speed of light. It used to be thought that gravity was instantaneous (Action at a Distance) but no longer (I think).
I doubt this will be a serious issue any time soon, but if and when it does become an issue, I imagine the only way to resolve it would be to apply a version of the Turing Test. In other words, if, during unlimited interrogation, there is no perceptible difference between the ‘old’ Tranquilis and the ‘new’, then we would have to accept that we are dealing with the same consciousness or that the difference is literally imperceptible.
Personally, I’m rather disappointed that Trek-style teleportation of people doesn’t seem to be getting very near, very soon. It would make life so much easier.
BTW, has any sci-fi writer come up with a decent take on the early days of such technology being invented and deployed, and the effect it has on society?
The canonical “teleportation” experiment goes something like this:
[list=1]
[li]Create a pair of “entangled” particles–call them A and B. (At this level of explanation, what that means isn’t important.) Move one of the particles to each end of the teleporter.[/li][li]Make a measurement of the particle X to be teleported, together with one particle (A) of the entangled pair, and throw both of these particles away.[/li][li]Based on the results of this measurement, make some modifications to the other particle (B) of the entangled pair. The resulting state of this particle is the same as the state of the original particle (the one you wanted to teleport).[/li][/list=1]
Note that between steps 2 and 3, information has to be transmitted between the two ends of the teleporter. The measurement in step 2 does something analogous to creating a one-time pad: the measurement result is completely random (giving no information about X) and the state of the other entangled particle B is also completely random, but the measurement result can be combined with the state of particle B to exactly recreate the state X.
Since there’s no information available about X in the state of B after the measurement, there’s no FTL communication going on. The reason this can lead to a “secure” protocol is that the measurement result tells you nothing about the state of X. It could be broadcast, and any spy copying it down would have only a list of random numbers. A spy would also have to steal particle B in order to get any useful information. But it turns out that quantum particles can’t be “copied” exactly, so this theft can in principle be detected.
A little more detail on the FTL issue: In quantum mechanics, measurements are often considered to “collapse the wavefunction.” In the teleportation experiment, the relevant wavefunction for the measurement of (2) is the wavefunction for all three particles (X and A because they’re being measured, and B because it’s entangled with A). Wavefunction collapse is often assumed to be instantaneous (and so FTL). But it turns out that the collapse of a wavefunction itself carries no information, so there’s no way to transmit information FTL or back in time. It also turns out that once you use one of these entangled pairs, they become unentangled. So you need one of these pairs for each particle you want to teleport.
Newton was very unhappy by this supposedly instantaneous action at a distance, but he couldn’t think of any other explanation for the orbits of the planets. If the gravitational field didn’t point directly to the mass’s present position (versus its retarded position) the orbits couldn’t be stable.
The same type of problem existed in electromagnetics, without instantaneous action at a distance there could be, among other things, no electromagnetic wave. When special relativity came along this problem was solve without the need for action at a distance. It turns out that nature has a built in correction to this retardation that solved both problems. The E field had a correction to retarded velocity, and the gravitational field has a correction to both retarded velocity and acceleration. This can also be explained via the potential formulation, but the SR explanation is much easier to understand.
Light takes about 1 nanosecond (10^-9 s) to move 1 foot, so it should take about 3 ns to move a meter, certainly within the range of modern timing technology. After all, physicists generate pulses of much shorter length (10^-15 s) with some frequency
Most modern microprocessors have internal clocks with periods in the nanosecond range, as you would expect since the speed (in MHz or GHz) is simply the reciprocal of the primary internal clock period. E.g. a 1 GHz CPU has an internal clock period of 1 ns, a 2 GHz has a clock period of 0.5 ns, etc.). Note that these extremely fast clocks are usually generated on the chip itself; the chip will be fed by a slower (in the tens or hundreds of MHz) signal, which special circuitry on the chip can use to create a faster signal. This is done because it’s very tricky to run high-frequency signals over any appreciable distance – at these frequency ranges, circuit board traces act as broadcast antennas, wreaking havoc on nearby electronics.
Actually, how do you know that the “you” who woke up this morning is the same “you” who went to bed last night? Leads into a discussion about consciousness.
I don’t remember the authors, but two stories stand out.
One dealt with a teleportation device that sent people between planets (I think). Prior to entering the device, it was important that the travellers take a strong sleeping pill which knocked them out for the trip (which, to the outside world seemed instantaneous). A curious youngster did not take the pill, and only pretended to be knocked out. When he came through the other side, his hair was white, and he was insane, having just spent what seemed like many, many years as a concious entity in a white, silent space. “It’s longer than you think,” he shrieked . . .
The other one dealt with a society that used teleporters for all travel. To school, to work, to the market. One day a families’ teleport device is broken, and a boy has to leave the house and walk to the neighbor’s house to use their device. After that day he becomes reluctant to use the device again. The parents and teachers wonder what is the matter, has he gone nuts, is he in trouble? It turns out that the “outside” is a beautiful parkland, tended by largely forgotten robots, and never visited by humans at all (they all teleport everywhere, why go outside). The boy just has fallen in love with the outdoors and nature, and doesn’t want to teleport everywhere.
Both great stories, both deserving of much better synopsi (?) than I’ve given them.
This sounds like “The Jaunt,” a short story by Stephen King. A family is at a “jaunt station” on Earth waiting to go on a trip to Whitehead City, Mars, and while they’re waiting for the nurse to come around to anesthetize them for the trip, Dad is telling the kids all about how teleportation was invented way back in the late twentieth century when gas prices were soaring to twenty bucks a gallon. The story tells about the initial invention, tests on animals and convicts, and how it was learned that you have to be unconscious when you pass through or bad things happen. Cool story. And you’ve already revealed the big spoiler!
Entanglement can occur naturally. For example, in the decay of a neutral pion into two photons, the states of the photons are “entangled.” This means that it’s not meaningful to talk of the “state” (position, momentum, spin) of one photon, independent of the state of the other one. It can also be created by bringing the particles together and performing some joint operations on them.
Entanglement is a kind of correlation between the states of the two particles. The idea is that by looking at (making a measurement on) one particle, you get some information about the state of the other particle. This in itself isn’t so weird; you can imagine doing this classically. Put a penny in one box and a dime in another. Now by opening one box and seeing what kind of coin is in it, you know what kind of coin is in the other box as well.
The thing that makes entanglement different from these classical correlations is that quantum mechanics allows you to make more kinds of measurements than the classical case. (It’s difficult to come up with an analogy that makes any sense, because the quantum case really is nonclassical, so reasoning about dimes and pennies won’t help.)
To continue what shelbo started on I liked some of the things with teleportation that came out of Dan Simmons’ Hyperion. The ‘teleporters’ in this book were a bit different. They were merely doorways to other places. On one side of the door was, say, one planet and on the other side of the door was a completely different planet. You could see right through from one to the other.
The really cool idea here was an extremely wealthy guy who built his house (mansion) with each room on an entirely different planet! Walking around the interior of the house was just as simple as you walking around your house except each window opened onto an entirely different planet’s landscape. Maybe it’s just me but I think that’d be fantastic and just too cool.
