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Did Einstein really say "God Does Not Play Dice" when referring to quantum mechanics? And what did he actually mean by it? Did he hate quantum mechanics, or believe in God?
In this video we will look at Albert Einstein's actual quote about quantum mechanics and understand his discomfort with this area of physics. He apparently did not believe in a personal or religious God, but rather referred to the as yet unknown forces driving the universe as "God".
Let's remember that in quantum mechanics, any system is described by a wave function, which can be used to calculate the probabilities of getting any allowed measurement result when we study a system. This applies to the positions of particles in space, or the energy level they will be found in, or any other possible measurement result. Quantum mechanics, or rather the Copenhagen Interpretation of quantum mechanics, also says that before making a measurement, the system itself is in a superposition or blend of all possible allowed quantum states. And once we make a measurement, it randomly collapses into one of the allowed states (with probabilities given by the wave function squared). This is quite different to the system already being in a particular state, and then us just finding out this information when we make the measurement. In fact, this video shows how the two scenarios are mathematically different, and that experiments can be done to show the latter is not true: • Pure vs. mixed quantum...
So what did Einstein actually say about quantum mechanics? Here's an excerpt from a letter he wrote to Born in 1926: "Quantum mechanics is very worthy of respect. But an inner voice tells me this is not the genuine article after all. The theory delivers much but it hardly brings us closer to the Old One's secret. In any event, I am convinced that He is not playing dice". This shows that Einstein respected quantum mechanics a lot, but felt it might be incomplete.
He was uncomfortable with the idea of a system randomly collapsing into a state when a measurement was made. This is because this idea breaks the principles of determinism and locality, both of which are extremely important in Einstein's theories of Special and General Relativity. We see what is meant by determinism (realism) and locality, as well as how the Copenhagen Interpretation breaks both principles. For example, we can see how weather forecasts could be perfect in a deterministic world, if we could gather enough data. Also, we understand locality is related to causality, and how events can only affect each other if we allow enough time for light (or some slower signal) to pass between them.
Quantum mechanics breaks both principles because the random collapse is not deterministic, and a pair of entangled particles separated by large distances could break locality. This is because a measurement on one particle could result in an instantaneous collapse of the other (due to the wave function describing both particles in the system). This is a simplified description of the EPR Paradox.
Einstein proposed hidden variables to resolve the EPR paradox. These variables would not be accessible to observers, but would deterministically and locally drive quantum systems in a way that would appear random to us. However a few years later, John Bell came along and developed Bell's Theorem. This quantified the difference between the Copenhagen Interpretation, and Einstein's Deterministic Local Hidden Variable theory. This allowed us to conduct experiments to see which of the two was likely. And Einstein was proven... WRONG?!
Well, at least partly. Hidden variable theories that were both local and deterministic were ruled out. However hidden variable theories that were deterministic and non-local are still possible. And the Copenhagen Interpretation is still possibly correct.
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Timestamps:
0:00 - This Quote from Einstein is Famous - WHY?
0:55 - Basic Principles of Quantum Mechanics
4:06 - Einstein's Opinion on Quantum Mechanics
6:07 - Important Principle #1 - Determinism
7:35 - Hidden Variable Theory
8:00 - Important Principle #2 - Locality
9:22 - EPR Paradox
11:32 - Bell's Theorem
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