Is General Relativity Merely a Classical Framework for Calculations?

[stevendaryl]

There is a perfectly valid classical analogue to that as well. The value of your lottery ticket, and simultaneously the value of all other lottery tickets distributed throughout the country, will (within your mind) suddenly collapse from their expectation value to their prize value once you learn the results of the drawing. Or more "physical" if you observe that perfume molecule at some point in the room you will update (collapse) your probability density function to one centered at the observed location and starting with 0 deviation (delta function).

Everyone keeps explaining collapse in terms of that analogy, even though Bell's theorem can be interpreted as saying that that analogy is false. It doesn't have to be interpreted that way, but it is hard to see how that analogy can really work in light of Bell's theorem.

 

[Zafa Pi]

I'm mastering this paper shared by Bhobba over a hundred times. http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

This is from the 1st paragraph of chapter 1:
"According to the Superposition Principle, any two state vectors in a Hilbert space of a quantum mechanical system, can be linearly added together to form another valid state of the system: for |ψ⟩ , |φ⟩ ∈ H

|Ψ⟩ = a |ψ⟩ + b |φ⟩ ∈ H (1.1)

where a, b ∈ C . This causes the occurrence of many purely quantum mechanical effects, such as interference in the double slit experiment"

This gave me quite a chuckle. It's like saying Newtonian Mechanics is what makes things move. Prior to The Principia there was a profound silence and the world was still.

 

[bluecap]

I want to learn to see things in quantum way. For example when a baseball is flying through the air.. I want to see it as quantum baseball.. should I use quantum mechanics or quantum field theory in imagining it's internal state? How do you tell whether to use QM or QFT on everyday objects you see? And to shift from qm to qft back to qm visually quickly.. is it like replacing the positions by operators so the positions of the baseball needs to replaced by operators (in QFT)? So when the baseball flying, should I think of it in terms of operators and state vector (QFT) or position and state vector (QM)

 

[bhobba]

I want to learn to see things in quantum way

It written in the language of math. That's the language you need to use and study.

Generally speaking you use QM and only go to QFT if it fails eg you can't account for spontaneous emission in QM - so you go to QFT and it works.

For the baseball its classical so you look at it that way.

Why is the baseball is classical and how does Newtonian physics follow on from QM? The simplest way is to derive the Principle Of least Action from QM and use that to develop Newtonian Mechanics. That is done by Landau in his book I have already mentioned.

Thanks
Bill

 

[bluecap]

I've been thinking a lot before I ask anything so it won't sound silly.

About the Bohmian pilot wave that is supposed to be deterministic and set the initial conditions. But isn't it possible a randomizer field is piggy back to the pilot wave that makes it random and the randomizer is the source of the born rule in BM? any papers?

 

[bhobba]

It's like saying Newtonian Mechanics is what makes things move.

It's actually key to many quantum effects rather than the somewhat misleading wave-particle duality. For example it is one of the keys to the double slit which depends in the uncertainty and superposition principle rather than the wave-particle duality as is told in popularization's and beginner texts:
:https://arxiv.org/ftp/quant-ph/papers/0703/0703126.pdf

But yes since it basically expresses the vector space structure of quantum states it does look a bit like - well so? The key is seeing how you apply it like in the double slit.

Thanks
Bill

 

[PeterDonis]

Can you take the analogy to General Relativity? Can we say that in GR, the world is still classical and the Einstein Equations are just for calculation purposes?

"Classical" in this context just means "not quantum". So GR is a classical theory.

This thread is wandering over a very wide field because the original question was vague (and based on a misconception--see above). I suggest that you take some time to learn more about QM and GR so you can formulate more specific questions. Thread closed.