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Testing Quantum Behavior — From Earth to the ISS
KentuckyFC writes "Einstein famously believed that the instantaeous effect of quantum entanglement would allow 'spooky action-at-a-distance' in violation of special relativity. Every test of entanglement on Earth has so far agreed with quantum mechanics but naysayers continue to point out various loopholes that might allow the results of these experiments to be determined in advance rather than instantaneously as QM suggests. Today, an international team of scientists is proposing the mother of all entanglement experiments, to be performed in space. The plan is to send entangled photons between an observer on the ground and one on the International Space Station. By the peculiarities of special relativity, the high relative velocity between the observers means that both will always be able to claim to have carried out their measurement first, thereby ruling out the naysayers' arguments (abstract). The experiment, called Space-QUEST, would be housed aboard Europe's Columbus module and would give the much-derided ISS a stab at doing some decent science for a change."
Remember that Niels Bohr denied that such a test of nonlocality was possible. Einstein had said that this phenomenon was "incredible" in his "EPR" article, thus rejecting his own prediction. And Bohr replied in effect that such things were taboo metaphysics.
Michael J. Burns
Sure it would be nice to do even more, and sure the costs are high (in part due to the STS, a nice but incredibly inefficient LV), but all this group-thinking about the "white elephant" ISS is akin to saying that kernel programming is easy. It's stupid, flat wrong and insulting for the people that get a lot of good work and science done.
There's a hidden treasure in Python 3.x: __prepare__()
I'm not sure what you are trying to suggest, but you can't use entangled photons to communicate faster than light.
I've not RTFA - it's down - but basically the EPR effect allows someone to create two photons and then measure if their polarization is H or V. The result is completely random BUT, both photons will always give the same result.
Now Alice measures her photon first and lets say we get H, then Bob's photon must instantaneously turn into H (previously it was a mixture of H and V - the dead and alive cat) so that when he measures his photon he also gets H.
What's already been done is to ensure that Alice and Bob decide what measurement to do, and make the measurement, so close to the same time that it's impossible for there to be any way for Bob's equipment or photon to "know" what Alice is going to do (or vice-versa) except at superluminal velocities.
But because Alice and Bob are in the same inertial frame there's still, at least in theory, a concept of who did the measurement first and who did it second. (Alice and Bob can have synchronized clocks and record the time they did the experiment. Then they can, using normal communication, tell each other what time they did the experiment and they'll both agree who was first and who was second.)
What this experiment will do is mean that Alice and Bob won't agree about who was first and who was second. Alice and Bob's clocks cannot remain synchronized, so that according to Alice, and people sitting next to her, she did the measurement first, but according to Bob, and people sitting next to him, he did the experiment first. And BOTH will be correct because the two measurements are space like rather than time like.
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
That won't necessarily help with the derision, as nobody denies the fact that interesting experiments are possible in space. The main point of contention will still be if you need to keep live persons there continuously to perform them. It'd have to be shown that a satellite or a simple orbiting mission couldn't have performed the same experiments for a fraction of the total costs. The cost of the ISS program is already ridiculously small, and the #1 thing that gets people interested in space at a young age, and in a lasting way, is the idea of people going into space.
I think it's like a zoo. Maybe the animals inside are being held in some sort of unfair captivity (I tend to think that in modern zoos most animals are pretty satisfied, but let's not go into that), but the interest and money generated by those animals creates the world's largest resource for saving their wild relatives.
Even if the ISS is never used in a way that provides more direct scientific knowledge per euro than unmanned missions, I believe it's worth it in the long term.
"I zero-index my hamsters" - Willtor (147206)
It doesn't (there are other points where GR and QM conflict, but entanglement is not one of them ). Einstein thought it did because he assumed that any such interaction would be deterministic and could hence be used for communication (THAT would break GR ). Essentially Einstein never liked the idea that the universe was based on randomness, hence the famous "god does not throw dice with the universe" quote. As a consequence he repeatedly tried to disprove quantum mechanics by inventing scenarios in which the random nature of QM would conflict with GR. The surprising, and somewhat ironic, outcome of his attempts was however new insights into quantum mechanical interactions that just seem to confirm the random nature of QM.
Also, to be pedantic about it, entanglement doesn't in principle imply that an interaction is quicker than the speed of light. You could alternatively claim that the interaction occurs with the speed of light, but the ENTIRE UNIVERSE ends up in an indeterminate state similar to that of Schrödinger's cat until you receive Alice's message. Thus you can keep interactions restricted to the speed of light ( locality ) but in order to do so you would have to throw out the notion that Alice exist when you do not hear from her ( realism ).
In practice throwing away realism would force you into a rather solipsist interpretation of reality which I think even Kant would have issues trying to accept, and thus most of the time we just stick with the much more comfortable notion of having a reality with instantaneous long distance interactions. If nothing else this is a lot easier to visualize than imagining the entire world entering a superposition of states until you receive Alice's message. From a purely physical point of view the two cases are indistinguishable however, so it doesn't really matter either way.
You have missed something fundamental.
Here is the issue:
If you assume, as you do, that the photon has some predetermined phase A (for angle), then the likelihood of it passing through a filter at another angle B is cos(A-B) * cos(A-B). Experiments testing this by passing photons through a filter at angle A (all photons that make it through have phase A) and measuring how many make it through a filter at angle B confirm it.
BUT, if the photon had an initial angle A, and Alice and Bob both have filters at the same angle B, EVERY TIME the photon with either pass through BOTH Alice and Bob's filter, or NEITHER Alice nor Bob's filter. That can't be explained by your classical model. It can only be explained by "spooky action at a distance".
(It can also be explained by assuming that the universe splits into two cases, one where the photon passes through both filters, and one where it passes through neither, and some mechanism that prevents communication between the universes. This is the many-worlds or relative-state formulation of quantum mechanics, discovered by Hugh Everett in 1957 but unpopular until many years later.)
IHA14YOBSIPBIANAP.
(I have a 14 year old BS in Physics, but I am not a physicist).
That is, unless I'm missing something fundamental.
Yes, you're missing something fundamental.
Going back to one photon.
We'll have four polarization states H, V (the normal horizontal and vertical polarization) and +, - the 45 degree polarizations.
Now Alice produces a stream of H photons and sends them to Bob. Now if Bob measures to see if they're H/V then he will always get H.
But if Bob measures if they're +/- he'll get 50/50 + and -, with each individual photon being + or - at random.
After measuring +/-, if Bob then remeasures H/V he'll again get 50/50 H and V. The measuring of +/- destroys the knowledge about H/V
If Bob measures at an angle other than 45 degrees then he'll get different proportions but he'll get sin^2 theta with one polarization and cos^2 theta with the other polarization.
Now lets consider entangled photons that will always give the same result for Alice and Bob. Initially we'll assume that Alice will always measure the horizontal polarization (0 degrees) Now lets consider that the photon "knows in advance" whether it will go through a horizontal polarizer i.e. it has (an infinite number) of hidden variables. Regardless of what measurement Bob does, an ensemble of photons can distribute values amongst these hidden variables so that Bob gets the expected correlations relative to Alice and the angle of his measurement.
But now let Alice vary her angle as well. Now the correlation depends on the difference in angle between Alice and Bob. But that angle isn't known (and hasn't even been decided) at the point the photon has been created. It could have a big "look up table" saying "If Alice angle is n and Bob angle is m then do/don't go through Alice's filter and do/don't go through Bob's filter BUT the photon that arrives at Bob's detector has to know what measurement Alice will/has done and the photon that arrives at Alice's detector has to know what measurement Bob will/has done.
But because Alice and Bob independently randomly decide what angle to measure "long" after the photon was created and their independent decisions are made so close together in time that neither can know what the other has/will do when they make their measurement due to the speed of light limit then there is no way for the photon to use its "lookup table" and get the correct statistical results.
It doesn't matter how you construct that "lookup table", unless you allow some sort of faster than light communication, using the lookup table will give different results to QM.
If you want the formal maths for that bit of hand waving then lookup Bell's inequality. He actually deduced the inequality that could be tested to prove no local hidden variable theorem was consistent with the results of QM based on measuring particle spins while most of the tests that have been done have used polarization of photons but the underlying theory is the same.
These experiments have already been done, and Bell's inequality has come down on the side of QM. Because Alice and Bob make their measurements so close together in time, not all observers will agree which one is first but (perhaps unfortunately) Alice and Bob will agree who was first and who was second. What this experiment does is close even that loophole - even Alice and Bob will be unable to agree who made the first measurement and who made the second.
Tim
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
And there's the rub, and the reason why people are still trying to prove QM after a hundred years. The equations appear to indicate that one of the following MUST BE FALSE:
1. Quantum Mechanics.
2. Locality.
3. Realism.
All the experiments performed so far strongly support QM, so we can't dismiss that. If locality is false then we have Einstein's spooky action at a distance and a conflict with GR. If realism is false...then nobody knows where the hell we are, or what we are.
But one of them *has* to be wrong. All these experiments are trying to prove is which one.
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
They aren't going to ship the photons in a Sojuz or the Shuttle (in a highly reflective box?), instead they'll probably be using a laser or similar device to send the entagled photon directly to the ISS. The ride is still bumpy with the atmosphere between the sender and receiver, but it's probably manageable, as demonstarated in this experiment, sending photons over 144km. They explicitly mention that this proves the feasibility of the ground to ISS experiment.
Bah, relativity is for macroscopic objects and quantum mechanics is for tiny quantum-scale objects.
Just like spiders can lift 10 times their weight, but humans can't. Different scales mean different rules.