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BobbyTables2 | on: I don't understand quantum physics (2018)
The math is one thing, but I find the idea that the fundamental pieces of reality aren’t particles a little unsettling.

The classic double-slit experiment is kinda bizarre when one considers the “single electron” case.

fpoling | parent | next
Particles do exist for practical purposes. If one can distinguish individual photons, then the picture is nothing but a bunch of particles with only averages producing wave-like pictures. But the puzzle is that they do not travel in straight lines and we cannot predict individual point where they will hit.
diedyesterday | parent | next
The fundamental claim of QM is essentially a claim about the shape and size of the state space: That states were not limited to the edges (axes) of that high (or infinite-dimensional) space (as classical mechanics thought) and that the whole interior points were available. This is essentially the central claim of QM (imagine it as not being limited to the edges of a very high dimensional cube and that you can choose points in its interior as your states).
throwaway894345 | parent | next
It’s crazy to me that reality is just waves in quantum fields that interact to create the illusion of particles, which interact to create atoms and chemistry and biology and neurology and society.
yatopifo | root | parent
This is the best mathematical model in existence but I’d be cautious equating it with reality. There are lots of gaps that may eventually necessitate that we switch to a more convenient formalism. It has happened many times already.
namero999 | parent | next
"Particles" don't exist in the naive sense. What a particle is, is an excitation of a field. A "particle" is a dynamic pattern.
themgt | root | parent | next
But that just kicks the can.

The modern record for a matter-wave superposition stands at a nanoparticle composed of roughly 7,000 sodium atoms (about 8 nanometers wide), achieving a massive "Schrödinger's cat" state at the scale of a small virus.

So then particles don't exist, and viruses also don't exist? Is "reality" just a dynamic pattern that doesn't exist in the naive sense? As astute stoics we should not worry ourselves with such matters, "shut up and calculate"?

There is something about quantum theory that is different in character from any physical theory posed before. To put a finger on it, the issue is this: The basic statement of the theory—the one we have all learned from our textbooks—seems to rely on terms our intuitions balk at as having any place in a fundamental description of reality. The notions of “observer” and “measurement” are taken as primitive, the very starting point of the theory. This is an unsettling situation! Shouldn’t physics be talking about what is before it starts talking about what will be seen and who will see it? Perhaps no one has put the point more forcefully than John Stewart Bell:

> What exactly qualifies some physical systems to play the role of ‘measurer’? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system . . . with a PhD?

https://arxiv.org/pdf/1003.5209

soon_to_be_sb | root | parent
> But that just kicks the can.

"reality" is just a picture painted on consciousness. A particle exists because consciousness, for some reason, perceive a particle. Physicists should stop looking for smaller particles, and look into space and time as something that emerge out of consciousness...

loading story #50237641
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throwaway894345 | root | parent
This is a bit like saying the universe is made of tiny pink elephants, and arguing that this is only untrue in some “naive sense” because we redefined “tiny pink elephant” to mean “excitation of a field”. It doesn’t seem more naive to me to admit that the world is not in fact made of tiny pink elephants than it is to argue “yes it still is made of tiny pink elephants [but only because we redefined the term to match the evidence]”.
My_Name | parent
Not if you imagine the single electron going out from the emission point along every path the apparatus allows and back again, forwards and backwards in time, with the whole sequence taking no time at all. Each trip goes through one slit, so the electron goes through both slits on different trips, and the trips combine where they meet at the screen, which gives the fringes (bands). It never turns into a wave and back. It ends up as one dot when one trip doesn’t make it back, because it was absorbed at the screen. The equations of physics are time-symmetric to a very good approximation, and Feynman read antiparticles as particles running backwards in time, so nothing in the maths forbids it. To me it’s the simplest explanation of a lot of “quantum woo”.