EUR 10.-"Local hidden variable theory" - who can explain the meaning of the following sentences to a novice to the field of quantum mechanics / science philosophy?

Hi posters before me, I have some things to add here:

The paradox, as Hecke explains well, appears when two objects that share a state (technical term: are "entangled") are separated by a large distance. Then both objects' state is measured, at times such that it is impossible for light to leave after one measurement, but arrive at the other before its measurement (both ways) This is the closest one can get in relativity to "at the same time". Now, when at a later time the measurements are compared, they will be found to be each in the same state (both 1 or both 0). So far, no problem. Maybe they already *were* 1 before the measurement, but we didnt know it yet. This is called a 'hidden variable theory' eg. there is some information we dont have, but which is still already true before measurement.

Bell's inequality is a mathematical argument that proves that such a 'hidden variable' cannot give the same results as quantum mechanics if it is local (roughly speaking local means 'not faster than light').
Experimentally it has been verified that quantum mechanics is better than local hidden variables. If you want a reference I can try to find it.

Now the problem is: how do the particles independently know which state to choose when measured? This is the EPR paradox. The resolution to this question is that there need not be a faster than light exchange of information. There is a correlation between two measurements, that can only ever be checked *after* sufficient time has passed to interact slower than light. The tricky thing is that our language is ill equipped here, because it is actually incorrect to think of this as "two qubits" as separate entities. They are "a universe that contains two qubits, with certain correlations", and that those correlations persist if they are separated is weird from every day experience, but perfectly fine with relativity: Relativity only makes statements about observable effects faster than light, and those don't appear in the EPR paradox.

My apologies for the longwinded explanation, but I don't know what your background is so I try to explain everything I use.

cheers,
Leo

Dear Cap, dear Alex,

i guess, that your problem, cap, is the concept of entanglement. As a fan of quantum computing i had a lot of encounters with computer science guys not understanding the phenomenon.
In quantum mechanics, an object, say qubit in my case, can exist in a superposition of different states. That means, it can be as well |1> and |0> at the same time. This can be in differing amounts, let's say.
If you have two qubits, they share a two-dimensional state, which again can be a superposition. Now you can prepare the system such that both qubits are either |1> or |0> each. That means if you measure, you have with probability (again assume equal distribution) 1/2 a measurement of |11> or |00> but with certainty you do not get |01> or |10>. Clear so far? great.
Now take very carefully one of the qubits and transport it to australia. If you were carefully enough, the state of both qubits is preserved. Meaning that there is still no way of having a state of |01> or |10> when measuring. If you now ask the australian guys to measure their qubit, they will see |0> or |1> with probability 1/2. Nothing special so far. But a difficult thing for quantum novices: If you measure a system, you change it (OK, OK, this is a buzzphrase everybody knows) in our case, if the australians measure |1> the two-qubit state |0> is extinct. Therefore, the qubit on your table is with certainty in state |1> as well. This happens at the very same moment, the australian has done his measurement. Therefore the debate on faster-than-light information transport. But the major argument in favour of Einstein is, that you had needed quite some time to get the second qubit to australia, and this is when the information was passed. Not the moment of measurement. There were a lot of attempts for a communication protocol that uses this feature, but they all failed.
There was actually a swiss team stating that 'if the interaction is not instantaneous, it is at least very very fast:-)
http://www.gapoptic.unige.ch/HomeExtras/SalartNewsandViews.pdf

have fun
Hecke

Dear Alex, Thanks for the comments.
You write:
"1. Based on the first paragraph of two difrent theories stating oposing (oposite) views the second paragraph states that using "local hidden variables" method is flawd due to those two theories.

2. the two theories stated int eh first paragraph are in teh context of the 4 dimentions of space, and as withing black holes, or naked singularities which reach infinate density thus warp space (and since space has a 4th dimention of time it warps too) certain events can be occuring at the same time due to other events (the idea here is that since space is warped an event that is a billion light years away can be at the same time happening at the other warped side of a black hole)

3. (3d peragraph)The theores are based with the understanding of the known particles or "energies" the physics that these particles follow break down at their level and these physics break down at naked cingularities, black holes, worm holes, and begining univers at the big bang. since the physics break down people can only speculate to what can be going on so there is no real answer or proff for these theories they are only valid with RELATIVITY. Relativity to time, space and events."

Actually, to me as a novice, your explanation contains several concepts I do not understand. Wouldn't it be possible to explain the phenomenon with very simple words not referring to an outside article? Maybe that would help.
Thanks a lot!

Hey, If anyone else wants to take a hit at this question, then go right ahead :)

Hi Alex, I have the impression, that there are not so many difficult and hard to understand things - unless the theory/concept is not yet mature enough. Is there a way to condense the "theory" so that I do not need to read an entire book? I am sure there must be a way to express this in a few sentence - what do you think?

OK, if Alex decides not to help when he is back, drop me a line, i would be glad to help too.

Hey, I will answer this when i get back in 2 days...
(need to write quite a bit and I am about to leave)

The passage describes two different theories,
and Einstein has been proven wrong a few times, to understand the jest of this the easiest thing to do is read a few books by Steven hawking.