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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."
I posted this next week and it's still the first post.
America, Home of the Brave.
Apparently the entangled photon link they were using to host the webpage couldn't hold up under the strain of Slashdot.
Scientist used Entangle!
It's super effective!
Photon capture device go!
You entangled a photon!
It was added to your photondex.
Knowledge is power. Knowledge shared is power lost.
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
As I understand it, a quantum entangled photon is very fragile. I don't understand how or why it's fragile, but wouldn't that make this extraordinarily difficult to do? The trip to the ISS is pretty bumpy.
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
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.
Please don't break reality. It's where I keep my stuff.
But the ISS is not only about science, it's also about engineering and learning how to live for long periods off the world (the MIR was pioneer, but its design and MO would be too dangerous to use beyond Earth's orbit). The next target will be the Moon and then probably Mars, but we had to learn how to walk before we can run.
There's a hidden treasure in Python 3.x: __prepare__()
Classical physics tells us that if you know the angle of polarization of a photon, then its chance of passing through a polarizer is the square of the cosine of the difference in angles between the photon and the polarizer. If you have a 45 degree photon, it will always pass a 45 degree polarizer, have a 50% chance of passing a 90 degree polarizer, and will never pass a 135 degree polarizer.
QM tells us that when you have two entangled photons and measure both of their polarizations, the chance the results will correlate is the square of the cosine of the difference in angles between the two polarizers . If you measure them at the same angle, the results always correlate. If you measure them at 45 degrees apart, the measurements correlate 50% of the time. If you measure them 90 degrees apart, the measurements never correlate (the results are always opposite). No matter how you look at it, this means either the results are predetermined at the time the photons are created based on the angles the polarizers will be at the time the measurements are taken, or that one measurement somehow influences the other later so the past isn't immutable.
Either way you look at it, it means the universe doesn't work the way we expect it to. If you're a glass-half-full person you want to believe in FTL and time travel, and if you're a glass-half-empty person then you think maybe the universe is deterministic.
That's why this stuff gets everyone who understands its implications all in a tizzy.
Fun with Anagarams! LADS HOST, SHALT DOS. HAS DOLTS. AD SLOTHS, HATS SOLD. ASS HO, LTD.
they actually are both H and V polarized at the same time. you can think of them as just being "unknown" for the sake understanding why you cant use it to communicate faster than light, but it isnt what's actually going on.
we know this because in a quantum superposition, different possibilities in the superposition can interfere with other possibilities, making certain results more or less likely. this is shown by the double-slit experiment. shooting photons at a screen through two slits produced not two stripes like you'd expect, but several stripes. this is because each photon went through 2 waves of possibilities, one through each slit, and the waves then collided with each other, making certain ares of the screen more likely to be hit than others.
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.