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Why Quantum Mechanics?

scottaaronson.blog

121–130 of 248 posts

Re: Why Quantum Mechanics?

#121
post #66
post #63

Earlier quoted context omitted.

You seem to be asserting the anthropic principal, but in doing so you're assuming that quantum mechanics is required for consciousness. But that's not really an answer to this post -- he explicitly calls that out as a possible answer, but why is QM required for consciousness?

Because since we dont understand consciousness, we cannot assume qm to be irrelevant for it, being the basis of the universe, which were just a part of?

Nothing follows from the assertion that we do not understand consciousness. Nothing at all.

Re: Why Quantum Mechanics?

#122

> why complex values amplitudes? If you multiply the left and right sides of schrodingers equation by its complex conjugate, do you still get an equation that the real valued square of the wave function solves? Can you do QM with just the real valued probability distribution? If you can, why not say that that’s the “real” thing, and factoring it is just a convenient way to solve it, same as imaginary solutions to qua…

You might enjoy this: https://www.nature.com/articles/s41586-021-04160-4

Re: Why Quantum Mechanics?

#123
post #78
post #71

Show me a simpler theory that can explain chemistry. Without QM, slow electrons would just drop into the nucleus all the time. The question is odd and makes it seem almost like Aaronson knows all about theoretical QC, but little about actual physics.

I think you misunderstand the post, he's not arguing against QM in any way at all, this isn't QM denial. He's just asking _why_ the universe is built that way.

I think you may have misunderstood GP's point. Isn't asking "why" equivalent to asking "what if not"? There is indeed a subtle, but still a difference, from "arguing against."

Re: Why Quantum Mechanics?

#124
post #27

Earlier quoted context omitted.

That's why physicists are so opposed to super determinism because like you say it would make life 'utterly meaningless' (I dont agree, a bit dramatic). Super determinism is the unpopular answer that solves many problems in quantum mechanics and relativity. It also makes a lot of sense if you think of the universe as pre-rendered, just like you would a CGI movie. Determine where all the particles land upfront througho…

Physicists don't largely choose physical theories on whether they make life meaningful or not. I think you're thinking of religious people.

Not sure why this was downvoted. I'm not attacking religious people, so apologies if I gave any offence.

Just observing that historically religion tends to select theories of the physical world that align with its moral and religious belief.

Re: Why Quantum Mechanics?

#126
post #11

Randomly found a link to this video on super determinism from his blog and found it super interesting. 100% agree, what is 'free will' anyways? A concept with no scientific definition. Why is it even used to explain anything in quantum mechanics? https://www.youtube.com/watch?v=ytyjgIyegDI

I think the question of free will is even simpler. It doesn't come down to determinism vs indeterminism because either way it's not "you" making a decision. At the lowest level (neuron or whatever) when a decision is "made" it is either deterministic (determinism) or probabilistic (indeterminism) based on physics but either way, where is the "you" in the process? Only way free will makes sense is if something superna…

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Re: Why Quantum Mechanics?

#127
Q1: Why didn’t God just make the universe classical and be done with it? What would’ve been wrong with that choice?

Why mention God? If you're attempting a scientific stance, starting your initial question with an unproven deity who doesn't want us to eat meat on Fridays part of the year, why? Why include that, it's an instant turnoff to any evidence-based reader.

Re: Why Quantum Mechanics?

#128

Im just taking the easy course of QM by Suesskind. He had an example like you have two coins and give them randomy to your kids. The they move far away. Then one kid discovers what it got, it knows what the other has. So what I dont get is why QM you could argue that there is some hidden shared state. Guess this is a typical question. But anyway I‘m somehow not convinced that it is really random.

That example cannot describe the 'spooky action at a distance'. Because it involves 'local variables' which have been dis-proven by the bell-inequality in actual experiments.

Taking the standard example of an entangled pair of photons. Those must have opposite spin. We then move the photons rather far apart measure the spin on one side. Then because of entanglement and conservation, the spin someone will measure on the other side is guaranteed to be the opposite.

A 'local variable theory' explains this by saying that the moment the entangled pair of photons is created it is already determined what the two spins are. This variable (the pre-determined spin) then travels with both photons (hence being 'local' to the photon). And the one measurement does not affect the other measurement.

The bell inequality shows this to be false. Crucial to the bell inequality is that, when measuring spin, You don't get back the 'angle'. Instead you choose a reference plane, and measurement will tell you whether the spin is pointing above or below that plane.

Now in the bell experiment. You measure in two different planes at the two different ends. If you pick two planes at a 180 degree angle. You will always find the same result on both sides (perfect correlation). If you pick two planes at a 0 degree angle, you will always get the opposite results (perfect anti-correlation). If you pick the planes at a 90 degree angle, the results will be totally independent, and this completely uncorrelated.

On these 3 angles (0, 90 and 180), quantum mechanics and a 'local variable theory' agree on the correlation coefficient between the measurements. (-1, 0 and 1 respectively). Bells inequality concerns the other angles. In those cases quantum mechanics predicts a stronger correlation (either more positive or more negative) than the local variable interpretation can predict. This discrepancy is strongest around angles of 45 degrees. Where a local variable theory means the correlation cannot be above 0.5, but quantum mechanics allows a correlation of up to ±1/√2 = ±0.7071.

These correlations were measured experimentally, and something close to the QM maximum of 0.7071 was measured. Hence disproving there are local variables.

Re: Why Quantum Mechanics?

#129

Q1: Why didn’t God just make the universe classical and be done with it? What would’ve been wrong with that choice? Why mention God? If you're attempting a scientific stance, starting your initial question with an unproven deity who doesn't want us to eat meat on Fridays part of the year, why? Why include that, it's an instant turnoff to any evidence-based reader.

I think you're reading far too much into that. Anecdotally, I'm as atheistic as they come, and I don't have a problem with that. It even echoes Einstein's famous quotation "God does not play dice with the universe".

Re: Why Quantum Mechanics?

#130

Q1: Why didn’t God just make the universe classical and be done with it? What would’ve been wrong with that choice? Why mention God? If you're attempting a scientific stance, starting your initial question with an unproven deity who doesn't want us to eat meat on Fridays part of the year, why? Why include that, it's an instant turnoff to any evidence-based reader.

Many evidence-based readers don't mind when a bit of poetic language creeps into technical or scientific writing.
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