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In summary, the conversation discusses quantum mechanics and the concept of entanglement. It is suggested that the lack of probability patterns for certain events is what leads to the belief that measuring them is the only way to know their outcome. However, this is not necessarily true, as in the case of a lottery where the probability of different outcomes is known. It is also mentioned that there have been lotteries with design flaws that allowed people to manipulate the game and win. The conversation then brings up Bell's theorem, which states that there are no hidden variables that can predict the behavior of a system in quantum mechanics. This leads to a discussion about entangled particles and how their states are not definite until they are measured. It is explained that if entf

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There have been some lotteries that have had design flaws that allowed folks to game the game and win.

https://www.newscientist.com/articl...wins-come-easy-if-you-can-spot-the-loopholes/

In the case of QM, Bell's theorem says there are no local hidden variables that can predict what the the system will do:

https://en.wikipedia.org/wiki/Bell's_theorem

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However doing this measurement doesn't mean we will always get this answer when they are entangled only that we get the answer with a high probability of the time. This is why we can't say we have superluminal communications between two entangled particles because one measurement doesn't answer the question, we must make many measurements and compare results later on.

Here's a video on Bell's Theorem that you might interesting:

and one on Quantum Entanglement:

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we have yet to establish probability patterns for, say, what the spin of a photon is

Where are you getting this from? We have very detailed quantum descriptions of how photons behave, including their spins, that have been confirmed to many decimal places in experiments.

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I guess what my question boils down to is: How do we know that these particles just aren't in complementary states from the start?

Because the particles don't have definite states until they're measured. Only the overall system consisting of both particles has a definite state.

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If entangled particles had their definite values from the beginning, then spin measurements at angles other than exactly opposite must obey an inequality called "Bell's Inequality". However, quantum mechanics predicts that Bell's inequality will be violated, and experiments have confirmed the quantum mechanical prediction. Therefore, no theory in which the entangled particles have their definite values from the beginning can be right, or can reproduce all the predictions of quantum mechanics.what is to say that they weren't just that way since the time they became entangled instead of what is currently asserted which is that it is the act of observing that brings them from a state of uncertainty and randomness to a solid state?

For more about Bell's theorem, you could start with https://static.scientificamerican.com/sciam/assets/media/pdf/197911_0158.pdf and the website maintained by one of our members: http://www.drchinese.com/Bells_Theorem.htm

Do remember that you only get one measurement: A and B are entangled; I measure A then I know what the result of the corresponding measurement of B will be; but that measurement of A also ends the entanglement so that subsequent measurements will not be correlated.

Thus, the only way to even detect entanglemet is to work with a large number of entangled pairs. I measure A and get spin up and then measure B and get spin down; that might mean that they were entangled, or I might have just gotten lucky - random chance will give me a mismatch 50% of the time. So I prepare another pair of particles the same way and I get a mismatch again. I do this a few thousand times and I get a mismatch every single time. The probability of this happening with random unentangled pairs producing a mismatch every single time is negligible (would you think a coin was honest if it landed heads ten thousand times in a row?) so I conclude that my source is generating entangled pairs.

Variations of this experiment have been done in countless different ways by many different groups in the half-century since Bell first published his inequality. At this point, the evidence is as convincing as anything in science.

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Thank you for the response, this was really helpful! A question I have then is what if you measure them at the exact same time?If entangled particles had their definite values from the beginning, then spin measurements at angles other than exactly opposite must obey an inequality called "Bell's Inequality". However, quantum mechanics predicts that Bell's inequality will be violated, and experiments have confirmed the quantum mechanical prediction. Therefore, no theory in which the entangled particles have their definite values from the beginning can be right, or can reproduce all the predictions of quantum mechanics.

For more about Bell's theorem, you could start with https://static.scientificamerican.com/sciam/assets/media/pdf/197911_0158.pdf and the website maintained by one of our members: http://www.drchinese.com/Bells_Theorem.htm

Do remember that you only get one measurement: A and B are entangled; I measure A then I know what the result of the corresponding measurement of B will be; but that measurement of A also ends the entanglement so that subsequent measurement will not be correlated.

Thus, the only way to even detect entanglemet is to work with a large number of entangled pairs. I measure A and get spin up and then measure B and get spin down; that might mean that they were entangled, or I might have just gotten lucky - random chance will give me a mismatch 50% of the time. So I prepare another pair of particles the same way and I get a mismatch again. I do this a few thousand times and I get a mismatch every single time. The probability of this happening with random unentangled pairs producing a mismatch every single time is negligible (would you think a coin was honest if it landed heads ten thousand times in a row?) so I conclude that my source is generating entangled pairs.

Variations of this experiment have been done in countless different ways by many different groups in the half-century since Bell first published his inequality. At this point, the evidence is as convincing as anything in science.

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The difference is: You're never going to become a millionaire from quantum mechanics.

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It makes no difference which measurement is first or whether they are simultaneous. In fact, since we are typically working with particles that are moving between source and detectors at close to the speed of light, relativity of simultaneity (Google for that if you're not familiar with it already - it's an essential part of Einstein's theory of relativity) often means that there is no unambiguous way of saying which measurement came first or whether they were made at the same time - different observers moving at different speeds relative to one another will disagree about the relative ordering of the two measurements.I have then is what if you measure them at the exact same time?

The quantum mechanical prediction comes out the same either way. We can can explain the observed 100% mismatch by saying that when we measured A and got spin-up, we collapsed the wave function into the state "A is is spin-up and B is spin-down" so of course a subsequent measurement on B will be spin down; but we could just as easily say that it was the measurement of B that caused the system to collapse into that state so of course the measurement of A has to be spin-up. But the only thing that QM says is that when we compare the two measurements after the fact they will always mismatch if the particles are entangled.

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An entangled pair share one wave function - they are always measured at the same time.A question I have then is what if you measure them at the exact same time?

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Not quite... For example I could measure A's spin on the vertical axis and B's spin at an angle of 45 degrees from the vertical, and then I'd find a different correlation than exactly opposite. Again, I'd have to do this with many pairs before the statistical pattern emerges. In any case, once the wave function has collapsed (and it is irrelevant which of the two measurements I consider to be the one that came first and "caused" the collapse) the entnglement is broken and the two particles evolve independently.So once a wave function has collapsed by the observation of A, B is permanently the opposite from then on?

As far as the mathematical formalism of quantum mechanics is concerned - and there's not much else on the table - yes. It's actually even stronger than what you said. "No way to know" implies the possibility that the spin has a definite value but we don't know what it is; it would be more in the spirit of the mathematical formalism to say that there is no value before the measurement, the same way that I have no lap before I sit down.So is this ultimately saying: everything is random until we measure it, then it is a certainty; that there is no way to know anything before?

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If you're setting up an experiment to test spin entanglement, you design your setup so that the evolution of the wave function doesn't change the direction of the spin before the particles reach their respective spin-measuring devices. As a practical matter, this means that the particles are moving through a hard vacuum and we don't have any stray magnetic fields in our apparatus.

(As an aside, note just how hard it is to talk about quantum mechanics without using the math. Both your "if the spin has changed" and my "doesn't change the direction of the spin before [measurement]" are speaking of a pre-measurement spin - and there's no such thing. It would be more accurate to say "doesn't change the probabilities of getting various measurement results at various angles, including the 100% probability of a mismatch if we measure both spins along the same axis")

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Unless you get a Nobel Prize for work in quantum mechanics, perhaps by definitely answering the question where do quantum probabilities come from.The difference is: You're never going to become a millionaire from quantum mechanics.

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Unless you get a Nobel Prize for work in quantum mechanics, perhaps by definitely answering the question where do quantum probabilities come from.

The Nobel Prize is a kind of lottery, you might say.

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It seems to me that so far in quantum mechanics, because we have yet to establish probability patterns for, say, what the spin of a photon is, we have made it some mystical thing that we can only know by measuring it. I

You have received some good answers here.

I just want to say there is nothing mystical about any part of QM.

Thanks

Bill

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