Is Spacetime Curvature Real? - Take 2

[Dale]

Spacetime curvature is sufficient to explain tidal forces, but not necessary.

OK, but don't forget that every other explanation of tidal forces is necessarily mathematically equivalent to curvature. If A=B then evidence for B is also evidence for A, so I don't really see the distinction you are trying to assert here.

 

[Mentz114]

... don't forget that every other explanation of tidal forces is necessarily mathematically equivalent to curvature.

No it is not. The Newtonian description of tides does not use relativity or spacetime and explains and predicts tidal forces in agreement with experiment. So does teleparallel gravity through the field tensor.

Tidal forces are the spatial derivatives of the field strength and do not require curvature - as you said.

 

[DaveC426913]

Not only is this reminding me of something religious, but even as religious fundamentalism.
...
Have fun weeping and gnashing your teeth as you nitpick apart my post. Laters ;-)

Ah there it is.

The old 'I asked a question and you asked me for clarity that I can't give so it must be your shortcoming and not mine and now I will insult you as much as possible before running away before I get banned' post.

Anyone else been waiting for that penny to drop for about 50 posts?

 

[A.T.]

Ah there it is.

The old 'I asked a question and you asked me for clarity that I can't give so it must be your shortcoming and not mine and now I will insult you as much as possible before running away before I get banned' post.

Anyone else been waiting for that penny to drop for about 50 posts?

I just needed two posts to make the troll loose temper and make the usual frustrated rant. Not like it wasn't obvious before that.

 

[PeterDonis]

Spacetime curvature is sufficient to explain tidal forces, but not necessary.

As I said a few posts ago in response to your original statement along these lines (which was in response to an earlier post of mine), GR does not say that tidal gravity is evidence for spacetime curvature, or that it "explains" spacetime curvature, or that spacetime curvature explains tidal gravity; it says that tidal gravity *is* spacetime curvature. It's more like a definition than a conclusion. As I said in my earlier post, the definition is justified by the fact that the test for tidal gravity works exactly the same as the test for curvature of a surface (initially parallel geodesics do not stay parallel).

 

[Dale]

Tidal forces are the spatial derivatives of the field strength

Yes, tidal force is the derivative of the field strength, and spacetime curvature is also the derivative of the field strength. They are equivalent, as I have said. You can call it a tidal force or you can call it curvature, they are mathematically and experimentally equivalent.

I don't understand the point you are trying to make. If I took a conservative system and wrote a Lagrangian I could determine the equations of motion without ever writing down the forces. Would you therefore say something like "then you can't use the equations of motion to argue for the existence of forces"? If you would say that then I think you are at least being consistent in your approach, but your approach neglects the equivalence of the two.