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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."
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".
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.
Just to clarify this paragraph because I've realized it's confusing.
Alice and Bob both randomly decide to measure the H/V polarization or the +/- (45 degree) polarization.
Then they get together and compare results. Where one has measured H/V and the other +/- then they throw the results away because they don't tell them anything useful, but where they've made the same measurement they find they always get the same (or opposite) results.
It's when they make the measurement that neither they, nor their equipment or photon can "know" what the other is doing.
There's also something called Bell's inequality that basically proves that the results of all of Alice and Bob's possible cannot be "known" by the photon ahead of time. (no local hidden variables).
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
I've never quite understood why this conflicts with GR. It seems like from Alice's perspective, when they both make their measurements, Bob is the superposition of having the same result or the opposite result. It is only after they communicate (restricted by the speed of light) that his results can be compared with hers and his superposition collapses. In other words, there are two measurements done by Alice, one of her photon, one of Bob, and they don't require any faster-than-light communication.
Am I missing something here?
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.
For all the naysayers of ISS science, here is the list of past and present experiments for your review:
ISS Experiments by Expedition
Please note the count of experiments currently stands at 561, and the focus ranges from virology, to fluid mechanics, to relativity, to astronomy, and even engineering validation (not simply of space station components, but also of fully independent technologies). That's nothing to sneeze at.
And while a fairly large portion of them are relatively minor or PR projects like sleep habits in 0g and the Buzz Lightyear "teaching from space" program, there is an ample number of experiments designed specifically to take advantage of the unique environment the ISS offers and with a variety of potential future applications.
And don't forget the majority of these so far were conducted prior to the installation of the two primary laboratory modules on the ISS: Columbia, launched late last year, and Kibo, which is 2/3 delivered as of last week. These have also been done mainly by 2 or 3 man crews, with occassional help from shuttle crews. Once the ISS switches to a 6 man crew rotation, the rate at which science work is completed will be greatly enhanced.
But of course, carefully planned, executed, and generally useful science isn't as fun to talk about as broken toilets, so we'll just continue ignoring the successes of the ISS and focus only about the cost overruns, deleted components, and occassional operating problems.
Mostly-naive question: What are your thoughts on the reboost potential of the SpaceX Dragon (assuming they get it up and running)?
Also, what ever happened to the possibility of using solar-powered electrodynamic tethers to reboost the ISS?
Thanks for the link lurv. I did write up an extensive description of this as best I could. It's a weird experiment!
*** Phil Plait, aka The Bad Astronomer http://www.badastronomy.com
No, "hidden variables" refers to information being carried with that which is observed, the particle. That's why they say "local variable". What I am referring to is particles in physically different locations having shared state (ie, the variable referenced exists outside of normal space and time, ie it can be thought of as a function of a simulation). Or, in other words "spooky action at a distance".
In pretty much every case imaginable the programming model corresponds to quantum mechanics, including pointers. Yeah, it's not predictive so it doesn't help answer the questions about the universe, but it can help to ask the right questions.