Einstein's dream of a unified field theory accomplished? | Hacker News Reader

Einstein's dream of a unified field theory accomplished?

phys.org

15 pointsMadcapJake14 comments

The title of the phys.org article is a bit more misleading than the article itself (when are they not).

What the authors did is build a unified setup for classical gravity and electromagnetism as the solution of one action, under specific assumptions (Weyl geometry, etc...). Usually we consider gravity as the curvature of spacetime, and electromagnetic forces as the curvature of the electromagnetic field. The authors built something elegant where you can get both in one go.

What this work doesn't do is as important as what it does given the "ambitious" title. The authors' work is interesting, but a casual interpretation of the title would really mislead people into thinking they solved the unification problem.

This work doesn't address other forces or the general particularities of the standard model and how they would also bundle. The second thing it doesn't answer is how to quantize any of these fields (gravity is notoriously difficult to quantize for many reasons).

What would be a better title? "Unifying gravity and electromagnetism in a classical theory"?

That'd be a good start. This article is well anchored within geometrodynamics (the theories which attempt to explain all physics as geometry), so maybe making that clear would avoid confusions already.

>We discovered that on top of the new nonlinear field equations, electric charge is related to the local divergence or compression of spacetime. Charge is therefore a field, which has its own laws of motion.

I wonder if mass could also be represented as a distortion of space-time. Like if charge is the divergence, mass could be the curl?

And I'm in way over my head here, but if charge is the compression of space time in a classical theory, what keeps it in place, instead of diffusing/spreading out? Seems like space-time is very stiff (i.e. speed of light is pretty high). Something to do with the non-linearity built into this new theory? Space time "yields" after a certain point?

Fun stuff to think about anyway!

This is already sort of the case. Of course it's not as immediate a comparison, but in the same way that charge sources the divergence of the electric field (Maxwell's equations), mass-energy are sources of the Einstein equations involving the curvature. It's the same reasoning and something we generally already consider.

But I want to go the other way. In general relativity space-time curves because of mass. But what is mass? Just a given. But maybe mass comes about as distortion of space-time.

This is what I was trying to convey: this is already how we think about it.

In general relativity, mass is not more fundamental than the gravitational field and its curvature. While we generally speak of spacetime curving because of mass, this doesn't mean this is a one way relation. The stress energy tensor is equal to the Einstein tensor (roughly curvature), so the relationship is already two-way.

It's a cool thing to think about of course, just wanted to clarify.

Interesting, I've never heard that before. Do you know of a lay-man's article / book that goes more in-depth into treating mass as a curvature of space-time?

Sadly no, most examples I'm familiar with are within research articles. A typical thing done within such articles is to consider a spacetime geometry, calculate its Einstein tensor and map it to some ansatz like that of a perfect relativistic fluid. It's a neat way to interpret the geometry in question as an energy/matter content.

Hope that helps point you in the correct direction!

Direct link to the paper [0]. Related [1].

[0] https://iopscience.iop.org/article/10.1088/1742-6596/2987/1/...

[1] https://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect

How? The paper barely mentions gravity and completely omits strong and weak forces.

Did Einstein "dream" about unifying the strong and weak forces with gravity? Anyone have a good timeline on what we knew about the weak force and when? Maybe most of the developments occurred after or just prior to his death in 1955? He was already 53 when the neutron was discovered. I kind of thought most of the strong interaction stuff wasn't really figured out until the mid 1960's.

Thank you for your input. I apologize. I was trying to get curious.

Einstein died before we learned that quantum entanglement was not local and occurs over distance. The book "Einstein's Unfinished Revolution"[0] talks about what he knew and what was found after his death. It also talks about where and why modern quantum mechanics diverge from his theories.

[0] https://en.m.wikipedia.org/wiki/Einstein's_Unfinished_Revolu...

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