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Quantum Teleportation Achieved Over 16 km In China
Laxori666 writes "Scientists in China have succeeded in teleporting information between photons farther than ever before. They transported quantum information over a free space distance of 16 km (10 miles), much farther than the few hundred meters previously achieved, which brings us closer to transmitting information over long distances without the need for a traditional signal."
Don't feel bad, this is a pretty common mistake. People read about non-locality and how what happens to one half of an entangled pair affects the other half instantly no matter how far away it is. There does remain some philosophical debate over what entanglement and non-locality really are, but one thing has been supported very well by both theory and experiment: You can't transmit information or power faster than c. In the case of entangled pairs, actions on one half can have a non-local effect that propagates faster than c, but it's not possible to transmit information or power using that effect. In order to make sense of the results and actually observe the effects of non-locality, you typically need to send additional information classically.
So, this will not lead to lag-less communication over vast distances. What it will lead to is quantum crypto networks. Long distance entanglement swapping or quantum teleportation are one of the key ingredients to building a scalable network.
To further clarify what I meant:
- Charlie entangles Particles A+B
- Charlie sends Alice Particle A over fiber
- Charlie sends Bob Particle B over air
- Alice measures A and sends Charlie information about measurement (classic part needed for actual information transfer)
- Charlie sends classic information to Bob
- Bob measures Particle B, combines result with classic information, and voila, Bob can reconstruct the information "sent" by Alice
Clearly no way to transfer information securely or fast, but a proof that entanglement in Particle B for Bob can survive long transfer through air.
That's because in China they just make up results like this to please political bosses.
Actually... http://en.wikipedia.org/wiki/Photons#Experimental_checks_on_photon_mass they're still not sure :P
Buanzo Consulting - 15 Years of GNU/Linux experience, for you.
Light can travel at the speed of light, things with matter can't.
What a bunch of BS. China has about 300 million "regular" people, that is, decent incomes and they shop for food at grocery stores. China has ONE BILLION desperately poor peasants and workers, whose lives are not getting better at all. "Eating bitterness" is an idiom that they use to describe their lives. They are as docile as cattle. They won't be clamoring for freedom anytime soon.
Oh, and Newsweek is a discredited, partisan source. Didn't anyone get the memo?
Shutting down free speech with violence isn't fighting fascism. It IS fascism!
Yes, information can only be transmitted at light speed. (Except [gravity] information [..])
No, that would break the universe. Gravity is also limited by by c. http://en.wikipedia.org/wiki/Speed_of_gravity says: The speed of gravity in general theory of relativity is equal to the speed of light in vacuum, c.
Yes, information can only be transmitted at light speed. (Except information pertaining to gravitational fields, which must be transmitted instantly over vast distances in order for planets and moons to stay within stable orbits. Run the numbers for yourself -- see if you can get the planets to stay in orbit when the force points towards where the *current* light-speed gravitational waves say the massive object is.)
Who modded this "interesting"? It is nonsense. The use of the term "force" in the context of gravity indicates that the poster is is talking about classical, Newtonian gravity. And there is no speed-of-light-limit in Newtonian gravity. Neither is there anywhere else in Newtonian mechanics.
You want to do gravity relavtivistically (i.e. correctly, in agreement with actual, modern-level observations) you'll have to use general relativity. Which just so happens to work just fine. You'll find that there's no "force" (or other absolute vector) in there at all. The whole thing is essentially geometry-free, only the differential of any vector ever plays a role. As it should be, in a properly relativistic physics.
We're all born with nothing.
If you die in debt, you're ahead.
The work was done by Jian-Wei Pan, one of the leaders in the field and a very impressive researcher. You can bet that the result is accurate if his name is behind it. Furthermore, it's being published in Nature Photonics. Besides, the result is impressive, but not ground breaking. Extending the distance of the protocol requires some fancy techniques and a good deal of skill and expertise, but the results aren't surprising.
So if this is the future...where's my jet pack?
Half of it nobody understands anyway.
"I think I can safely say that nobody understands quantum mechanics." --Richard Feynman
"I don't care about the Constitution!" --Bill O'Reilly, November 17, 2009
How did this get moderated up? This poster clearly has no idea what he's talking about.
The whole point of quantum entanglement is that prior to the measurement, there's no basis in which the state is definite. This means it's not just that "you cannot predict which of the two [states] you will measure"; the whole point is that there is no defined classical state the system is in. There's no classical analog for that, so it's really hard (maybe impossible?) to explain without math.
If you don't even know the most basic stuff about quantum mechanics (as is clear from the post), please educate yourself before writing about it or even moderating stuff about it.
Okay, I'll bite.
So just because you measure the speed between them as c doesn't mean they are each moving at half-c. They are still both moving at c, in opposite directions, for an effective 2c with regards to their eventual position.
No. Your conclusions stem from a fundamental misunderstanding of relativity. It makes no sense to talk about "eventual position" in the way you are, because it requires talking about an absolute time. There is no absolute time. You may have heard this sentence being thrown around before in special relativity, but perhaps you haven't appreciated the full meaning of it.
Let's talk about "eventual position". What you're saying is, we measure the positions of A and C, then wait some time t, then measure their positions again, and, lo and behold, if we divide the distance travelled by the time taken we are left with the impression that A and C are moving apart at 2c. This is true if you measure t and the distance in B's reference frame, but not from A's or C's reference frames, even though these are equally valid.
Once again, there is never one way of looking at things that is just a little bit "truer" than the others, even if your intuition may tell you that, since B's reference frame is at rest, it should provide a less distorted and more objective measurement than A's/C's. Truth is, you could look at the same problem in a different way, where A is at rest. Then B is moving away from it at nearly-the-speed-of-light, and C is moving away at even-more-nearly-the-speed-of-light, at a speed defined by the equation on this page.
We have no definition of which of the above observations is the "correct" way of looking at things, because they are physically indistinguishable from each other. They are, in fact, the same thing; different realities exist for different observers, which is why the name "relativity" is so fitting.
Here's a better example. The furthest objects in the universe are about 13b light-years away. The light they emitted 13b years ago is getting to us now. Do you think, in the past 13b years, that they haven't moved any further??
Sure, 13b light-years away must mean that a photon arriving on earth right now must have been emitted 13b years ago, right? From our perspective it does. From the photon's perspective, it made the journey in less than the blink of an eye. Does this mean the photon travelled many multiples of the speed of light to get here? No, it just shows, once again, that different realities exist for different observers.
Of course I didn't RTFA.
Gravitational waves emerge from the Einstein field equations, part of the mathematical formulation of General Relativity. Since we never measured any of them directly, we have no direct evidence of their existence, let alone their speed. But we do have good indirect evidence that they exist. All experiments/measurements we can come up with match GR to a very high degree.
If gravitational waves could go faster than the speed of light, that would break causality. This means that you could find some reference frame moving at a constant velocity (special relativity) or constant acceleration (general relativity) from/to the source of the gravitational wave, for which you would first detect the gravitational wave, and only later see the event that generated it. Which basically reverses the flow of time. Relativity forbids this (see here for SR: http://en.wikipedia.org/wiki/Relativity_of_simultaneity).
Stretching of space-time (metric expansion of space) is a non-local phenomenon, meaning it falls outside of the scope of SR, but in the domain of GR. It's a very very small effect, that can only be seen at galactic scales. It means space-time is created in between two connected points of space-time, which is not what is happening in your case. Even in expanding space, no signal goes faster than light, and causality is preserved. The light itself keeps moving at c, it only undergoes a red-shift because the space it travels through stretches.
So basically we just have a bunch of theories that tell us how the universe works, and those theories seem to hold up during experiments. They don't tell us why there is an upper speed limit, only that because the speed of light is constant and limited, no information can move faster, or causality would break, and the universe would be an even stranger place.
To really know why this is so, and what exactly causes metric expansion of space, we need to find a working model of quantum gravity. GR doesn't seem to work very well at quantum scales. Several candidates exist, but they don't produce enough predictions to allow for conclusive testing. There are indications that the continuous space-time breaks down into a fractal pattern of small units of space-time (strings, loops, pentachoron depending on the theory) that form ever changing interconnections, a bit like water molecules in a drop moving around without the overall shape changing, but this in 4 or more dimensions. Since this all occurs at the Planck scale (about 10^20 times smaller that the diameter of a proton), and basically is the foundation of all space-time and thus reality, that makes it very hard to perform experiments that tell us anything more about it.
On the quantum level we have the same problem: we have complicated field theories (quantum chromodynamics) that tell us how particles interact, but they don't tell us why they do so, or why they even exist with the mass/charge/color they have.
One day we might find some unified theory that will answer all this, and from which everything will emerge naturally, but until then we'll have to do with what seems to work (SR/Newton for normal scales, GR for galactic scales and large masses, QM/QCD for quantum scales).