"Quantum mechanics and quantum entanglement are becoming very real. We're beginning to be able to access this tremendously complicated configuration space to do useful things."I do not think these explanations are helpful. He says the theory was not practical until recently, when quantum computers started being built.In just 22 minutes, physicist and professor Brian Cox unpacks the subatomic world, beginning with the theories as we understand them today.
15:13 Now you go back a few decades 15:16 then I think you could say that the interpretations 15:21 of quantum mechanics 15:23 are very interesting and very important, 15:28 because we're talking about the nature of reality. 15:30 But you might say, well, it doesn't really matter 15:33 so much practically, right? 15:35 If that now, I have a lot of colleagues in physics 15:38 who would, I think rightly hate that description 15:41 because what we're trying to do 15:42 is understand reality, what physics is. 15:45 But now particularly, I think, with the possibility 15:50 of building quantum computers, 15:52 this attempt to understand how large systems 15:55 of quantum mechanical objects behave 15:57 is becoming extremely important, 15:59 because a quantum computer 16:02 is a device which is built out of qubits.No, the annual world economy has about a trillion dollars based on quantum mechanics. The theory is essential for transistors, silicon chips, lasers, led lights, solar panels, cameras, digital displays, and many other technologies. So the theory has been very practical for 70 years. On the other hand, no one has demonstrated any utility for quantum computers.
He spends time explaining that quantum physics involves probabilities, wave effects, and predictions from conservation laws. But none of these are unique to quantum mechanics. I do not think he explained the subject at all.
The most important new ideas in quantum mechanics are that (1) observables are non-commuting operators; and (2) electrons, and everything else, have wave properties but are observed as eigenvalues. Those are the quantum mysteries.
All the other stuff, the probabilities, the Schroedinger cats, the supposed nonlocality, the entanglement, the superpositions, etc., just are not that mysterious. Cox is a leading Physics expositor, and he can do better.
Physicist G. tHooft got a Breakthrough Prize and he was interviewed about his strange quantum ideas.
Quantum mechanics is the possibility that you can consider superpositions of states. That’s really all there is to it. And I’d argue that superpositions of states are not real. If you look very carefully, things never superimpose. [Erwin] Schrödinger asked the right questions here: You know, take my cat, it can be dead; it can be alive. Can it be in a superposition? That’s nonsense!He believes in superdeterminism as a way to save locality. He complains that no one takes him seriously.And he was quite right. People shouldn’t continue to insist that a dead cat and a live cat superimpose. That’s complete nonsense ...
What I’m saying is: we must unwind quantum mechanics, so to speak, as to see what happens underneath. And until the quantum technologists start doing that, I believe they won’t make really big progress.
His ideas are too silly to take seriously. He says QM is just being able to consider more than possibility. What is quantum about that? Classical mechanics allows considering multiple possibilities. And superdeterminism is really kooky.
Physicist Ethan Siegel is usually pretty good, but he rambles about the multiverse in his latest video.
At 1:18:50, he says particle spin has just a discrete degree of freedom, because it is just up or down, in each of the three dimensions. But decay into fixed-energy photon has a continuous degree of freedom, because photons can go in any direction. I did not follow that. Spin can also be in any direction. Spin is different from momentum in that different directions do not commute, and spin magnitude can only have discrete values. But in his example, both the momentum and spin have a known magnitude. So I think he is making a mistake here, but I could be wrong.
My real objection is to all the multiverse junk.
Cox is not a good expositor. He was on a radio show in the UK once telling everyone the phases of the moon are caused by the Earth's shadow.
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