# Feynman Path Integral's Meaning

#### edpell

Stephen Hawking for one, makes a very convincing argument for a "Sum Over All Histories" aka Path Integral for particles, but without unification... who knows?
I am not take up on QM; what does "without unification" mean? Thanks.

#### Frame Dragger

I am not take up on QM; what does "without unification" mean? Thanks.
Sorry, that's my bad, I mean the unification of Relativity (a geometric view of gravity, spacetime, etc) with Quantum Mechanics.

#### edpell

All paths seem a lot like LQG (Loop Quantum Gravity). That is a foam of quantized spacetime. So I guess the question is how big is the object (say an electron) relative to the plank spacetime interval? It almost seems like some kind of temperature comes in here to make the position of the electron (if point like) uncertain (diffuse). Or at least a QM zero point energy that makes the electron not point like.

We should keep in mind Feynman's all paths is effectively all paths very close to the classical path far away paths oscillate so fast that they cancel.

#### Frame Dragger

All paths seem a lot like LQG (Loop Quantum Gravity). That is a foam of quantized spacetime. So I guess the question is how big is the object (say an electron) relative to the plank spacetime interval? It almost seem like some kind of temperature comes in here to make the position of the electron (if point like) uncertain (diffuse). Or at least a QM zero point energy that makes the electron not point like.

We should keep in mind Feynman's all paths is effectively all paths very close to the classical path far away paths oscillate so fast that they cancel.
No diagreement here... I think the major issue is discovering how this behaviour "Stops" at the macroscopic level, or most lilkely how it DOESN'T. That said, this isn't a small mystery, it's an absolute kick in the nuts of QM and has been since day one. You see it as a possible answer, and I can't say it isn't, but to me it just seems... incomplete. Do the paths cancel on PAPER, or in real life? If the former, it's a tool in the math, and the latter requires some new theory or interpretation which has not gained sufficient standing to convince the scientific community.

You also mentioned the oscillation, which is another problem that goes back to a need to understand what's happening @ & below the Planck Scale. If a particle can "test" all paths, why doesn't it TAKE all paths? That is the argument made by proponents of the MWI, and it's hard not to resort to something like that to reconcile the "Big" with the "Small".

#### edpell

If a particle can "test" all paths, why doesn't it TAKE all paths?
Super good question.

I do not know. It is great to know that there are still areas in physics still to be understood. :)

#### Frame Dragger

Super good question.

I do not know. It is great to know that there are still areas in physics still to be understood. :)
Thanks, I wish I was the guy/gal who thought of that question! I would say that we can live safely in the knowledge that barring massive alterations to humanity, we'll die with many myteries still unsolved. I find that oddly comforting.

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