Einstein's Equivalance Principle and the Curvature of Spacetime

[@WEPayne]

Sean Carroll has a wonderful lecture where he explains Einstein's Equation and I actually got

[@WEPayne]

In school I never learned tensor math to understand Einstein Field Equation. A year ago I watch Sean Carroll explaining it at Royal Institute an start to catch on to tensors. It truly opened my eyes. Once a reporter asked Einstein "what if you are wrong?" Einstein thought a moment and reply "Then I would feel sorry for the dear Lord." Yes. It is truly That Beautiful.

[@edd.]

I love learning about GR!!

[@JasonKendallAstronomer]

Glad to hear it!

[@brendawilliams8062]

@@edd. I love trying to to.

[@mialotusmusic]

Stellar work! I'm learning so much watching your videos! Thank you! 💫

[@graham2105]

Fantastic video...cheers

[@paulmicks7097]

Great topic, thank you Kendall

[@cleon_teunissen]

There is historical information that may well be of interest to you. Source: article by Dennis Lehmkuhl: 'Why Einstein did not believe that general relativity geometrizes gravity'. Dennis Lehmkuhl explains why Einstein held that point of view. Among the evidence for Einstein's point of view: In 1927 Einstein had (presumably on request) written a review of a book by Émile Meyerson 'La déduction relativiste' Lehmkuhl writes that Einstein's review was very positive, with one exception [start of quote] Meyerson sees another essential correspondence between Descartes' theory of physical events and the theory of relativity, namely the reduction of all concepts of the theory to spatial, or rather geometrical, concepts; in relativity theory, however, this is supposed to hold completely only after the subsumption of the electric field in the manner of Weyl's or Eddington's theory. I would like to deal more closely with this last point because I have an entirely different opinion on the matter. I cannot, namely, grant that the assertion that the theory of relativity traces physics back to geometry has a clear meaning. The fact that the metric tensor is denoted as “geometrical” is simply connected to the fact that this formal structure first appeared in the area of study denoted as “geometry”. However, this is by no means a justification for denoting as “geometry” every area of study in which this formal structure plays a role, not even if for the sake of illustration one makes use of notions which one knows from geometry. Using a similar reasoning Maxwell and Hertz could have denoted the electromagnetic equations of the vacuum as “geometrical” because the geometrical concept of a vector occurs in these equations. [end of quote] Of course, the physics community doesn't have to follow Einstein's lead in everything. Still, the reasons for rejecting the geometrization interpretation are interesting, and worth knowing.

[@JasonKendallAstronomer]

Thanks for the comment. I think I found that reference: www.sciencedirect.com/science/article/pii/S1355219813000695

[@cleon_teunissen]

@@JasonKendallAstronomer I didn't put the link in my comment because sometimes a comment with a link in it disappears. (Presumably due to false positive in youtube anti-spam.) I had verified that the name and the title of the paper are sufficient to find it, and that it is not behind a paywall.

[@derndernit8275]

@cleon_teunissen Can one ask, and can one answer, what in reality is not physical geometry? Just that if the gravity field is referred to as such, it should not be forgotten it is not merely pencil on paper 2d geometry the common colloquial thought one might first think when hearing the term geometry, but the "shapes" of a massive-energetic moving "body" called "the gravity field" among other things.

[@davidhand9721]

The comparison to Maxwell's equations being geometrical is way off. The reason GR is called geometrical is that free fall paths are geodesics; we expect that the metric tensor _is_ the single structure of spacetime and therefore _all_ physical phenomena will be subject to it. There is no physics that is not embedded in spacetime. If it uniquely determines the behavior of all straight lines, it's hard to think of the metric as anything other than geometric.

[@andycremeans]

Thank you for this

[@JasonKendallAstronomer]

My pleasure!

[@kn9ioutom]

THE UNIVERSE IS WEIRD ! PEOPLE ARE WEIRDER !!!

[@lotusflowerrr]

Hello, lads :)

[@paulmicks7097]

Photons are being bent by the geometry of space/time (gravity)

[@astronomy-channel]

Excellent- as usual!!

[@VictorHernandezVH1]

The Philosopher's Stone

[@chadb9270]

Does the equivalency principle survive extreme conditions or does it break there? As in just above the event horizon of a black hole or traveling at almost the speed of light. 1. I feel that if you were traveling at almost the speed of light, just under, and you tried to accelerate something forward the energy it would take to accelerate that object would be different at relativistic speeds than it would be standing on the surface of the Earth. That difference in energy could be measured, therefore breaking the equivalence principle at the extreme. 2. If you could hover just above the event horizon of a stellar size black hole you would be able to measure the title force difference between the floor of your ship and the ceiling of your ship. This would be another verifiable measurement to distinguish gravitational field versus acceleration as acceleration would be uniform across the ship. These aren’t bad, Newton’s laws break at the extreme then relativity takes over. I’m just wondering if that’s what happens?

[@chadb9270]

11:20 OK, I just landed on another point. If you were free falling in a room towards a black hole, spaghettiifacaiton would still occur. This will be a measurable change in the gravitational field. Wouldn’t that be a giveaway?

[@gyanprakashraj4062]

YOU NEED MANY BIRTHS ....KHAO PEEYO....