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I Don't Understand Quantum Physics

https://www.southampton.ac.uk/~doug/quantum_physics/index.html
66•rramadass•1h ago

Comments

rramadass•1h ago
Author: Prof. Douglas Ross of Southampton University - https://www.southampton.ac.uk/~doug/
polotics•1h ago
me neither! How does the Einstein Rosen Podosky Paradox work? can the unknown that's being collapsed not be a pre-determined value that therefore is not traveling faster than the speed of light?
T-A•51m ago
https://en.wikipedia.org/wiki/Hidden-variable_theory
superluserdo•39m ago
>can the unknown that's being collapsed not be a pre-determined value that therefore is not traveling faster than the speed of light?

This is known as a "hidden variable theory". People will tell you that a local (things can only affect their immediate surroundings) version of the theory is impossible because it would be a violation of Bell's inequality, but there is a loophole that requires accepting the idea of "superdeterminism". This is the idea that where what measurement a scientist chooses to measure is predetermined and correlated with what the particle being measured is going to do.

So if a particle lands on a screen according to distribution p when going through a double slit, but with distribution p' when one of the slits is measured at, conventional QM says that the measurement "collapses the wave function". But a superdeterministic local hidden variable theory would imply that the choice of whether to measure at the slit or not was already set in stone at the same time that the particle "decided" which path to take to land on the screen, more or less.

atemerev•58m ago
When I learned about causal sets program and algebraic quantum field theory, I finally (somewhat) understood quantum physics.

Tl;dr spacetime does not exist as a global background where things are "placed", it is not ontic. "Things" are first, and spacetime is derived from interaction statistics of "things". This eliminates nearly all naive paradoxes like double slit etc. Now, these "things" are somewhat complicated and non-intuitive (e.g. there are no individual "particles", they are a limit of discrete distributions), but that's a good start.

cgio•53m ago
Sorkin is great. I think causal sets make some things simpler but other more mysterious. I also found t’ Hooft’s automata and Spekkens toy illuminating in different ways.
atemerev•46m ago
"Was", unfortunately. He died this September. What a loss, he earned a Nobel long ago.
isolli•53m ago
In a podcast, Alain Aspect (Nobel Prize winner) explained that he does use the power of visualization and his imagination to generate new ideas, but that he always needs to check them with actual calculations because no mental picture can be an accurate representation of quantum physics.
chistev•50m ago
"I think I can safely say that nobody understands quantum mechanics."

- Richard Feynman

ahartmetz•48m ago
I also like "If you think you understand quantum mechanics, you don't understand quantum mechanics" which is supposedly also from Feynman.
atemerev•39m ago
Quantum _mechanics_ cannot be understood, it is full of paradoxes. It contradicts classical EM and special relativity, among other things. A toy theory that was an important step to what came later.

Feynman's own QED is a part of QFT, but this is no longer quantum mechanics. Special relativity and quantum physics are reconciled since then. Now, we only need to reconcile GR and QFT, but this leap was so far beyond our attempts to scale it. Yet, QED/QFT/SM can be "understood" as there are fewer obvious paradoxes that plagued QM.

chistev•30m ago
I think it's one of those famous quotes that was never said. The one I quoted was what he apparently said.
stratos123•10m ago
Whether this was even true in Feynman's time, it's much less true now.
quietFerry94•36m ago
That pre-determined value idea is exactly local hidden variables, and Bell's inequality rules it out, Aspect's 1982 CHSH experiment measured the violation.
caturopath•14m ago
To be precise, Bell's inequality rules out a local hidden variable theory. Pilot wave theories/Bohmian mechanics is an attempt to describe a nonlocal hidden variable theory of quantum mechanics.
antonvs•8m ago
To be even more precise, it rules out hidden variable theories that satisfy Bell locality, i.e. the assumptions that the theorem makes.

Superdeterminism and retrocausality both allow for local hidden variables - it’s just that they don’t satisfy Bell’s assumptions.

antonvs•13m ago
If you saw that in section 15, the very next paragraph covers Bell.
asystole•32m ago
This piece looks great, adding to my ever-growing "to read" collection on Zotero.

If anyone is interested in self-studying quantum physics, QFT for the Gifted Amateur [1] is very well regarded.

1: https://academic.oup.com/book/36442?login=false

frumiousirc•28m ago
I take issue with "understand". I agree QM can not be understood in terms of everyday experience. One must build experience, language and proper metaphor for the understanding. For example, in the intro Ross uses the example of explaining a waterfall to someone who never saw it. He says that can be done but he relies on implicitly the listener knowing what people on Earth may take for granted. That understanding of a waterfall can only happen if the listener already has some understanding of fluid flow and gravity. We do, but say a newly found alien friend from a dry environment that had never experienced fluid flow would not have the mental building blocks to understand it. Feynman gave a famous interview where he said, essentially, "no, I can't explain it to you because you are too ignorant" (he said it more politely). Going the other direction, Physics steeped enough in quantum theory do understand QM enough to have meaningful discussions free (at times) of rigorous math. They do this because they have a shared language, vocabulary, metaphor. Sure, they must rely on math and experiment to ground that understanding in truth but I guarantee they do not communicate understanding (solely) in math and measurement data.
charcircuit•20m ago
Why can AI generate pictures of waterfalls if it has never lived on Earth?
bozdemir•28m ago
So do the rest of us.
dtj1123•18m ago
We understand quantum mechanics well enough to build machines that depend almost entirely on quantum principles.

It sounds all superior and mysterious to quote Feynman here, but the fact is many people absolutely do understand quantum mechanics.

Razengan•13m ago
Or we understand only just enough to make things that work on (and up to) the layer that we understand.

Ancient humans could build boats 5000 years ago and expand throughout the planet, but they didn't know about water being made up of hydrogen+oxygen, or the tides being caused by the moon, etc.

Their calculations served them on the layer they operated on.

bobvanluijt•16m ago
Somewhat related: a book that really helped me is Picturing Quantum Processes by Bob Coecke. It's a visual representation of quantum processes, which really helped me understand the concept
noduerme•15m ago
My question is, if I just refuse to believe in quantum physics, that makes it go away and/or be inapplicable to me, right?

Uh oh, some people have no sense of humor =\

mkesper•6m ago
(2018)
lkm0•5m ago
"IS QUANTUM PHYSICS CORRECT AND COMPLETE?" is reductive, there are more quantum denominations: Copenhagen, QBism, RQM, consistent histories, Many-worlds, Bohmian mechanics, and various spontaneous collapse people. I might've missed a few.
phpnodejspwn•2m ago
2 things to understand about science:

It's useful, not metaphysically real. (Hot take btw) This is called Instrumentalism. The belief that it's real is called Scientific Realism. However over and over again, science can't cover edge cases, and we find better fitting models. The Copernician revolution is a good example of this dichotomy.

2. Academia basically forces you to believe the doctrine or you fail the class. From philosophy to physics to sociology. If you read the philosopher survey, you will find trendy things being quite high. It's a religion in itself.

Bonus 3: Philosophical Pragmatism and Instrumentalism generally solves this, but is intellectually a dead end. There is a reason analytic philosophy continues despite gaping holes in linguistics (late Wittgenstein) that ruin it. But at the same time, best fits might be missing a new paradigm. I wish I could tell people to ask AI to explain Hegel to understand, but I think people need to read it themselves.

Tl;dr: quantum mechanics is the best we have. It's definitely wrong, but it's the most useful we have.

I Don't Understand Quantum Physics

https://www.southampton.ac.uk/~doug/quantum_physics/index.html
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