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Unformatted text preview: Name:__________________________________________ Date:__________________________ PHYS 360 Lecture Question #33 Consider the entangled singlet state for the electron and positron pictured above. Assume that both particles pass through separate Stern ­Gerlach “Z filters” that determines if it is spin up or down. Conservation of angular momentum requires that if the electron is spin up, then the positron is spin down, and vice versa. Assume an electron is found to be spin up, and the positron is spin down. Quantum mechanics says that these values were caused by the measurements; they were in the entangled singlet state until the measurements collapsed the spins into the measured values. 1. What if quantum mechanics is wrong (or incomplete, or it leaves out some “hidden” variable…), and the particles were actually “born” with their spin values. There is no way to tell the difference between the quantum mechanics predictions and this theory, because both always give opposite spins, with random probabilities. TRUE FALSE 2. What if the two measurement stations were actually miles apart from each other. Assume the measurement on the electron is made first, and it is spin up. This means the positron must be spin down. Is it possible for the positron to “know” that a measurement was made on the electron that forces the positron to be spin down? YES NO 3. What if the two stations were so far apart that the news of the electron’s measurement would have to travel much faster than the speed of light, which rather looks like a violation of the fundamental principle of special relativity. In this case, is it possible for the positron to have the “wrong” spin, to also be spin up like the electron? YES NO ...
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