PeterDonis's latest activity

Zero or negligible, it's still pointless. You're making it negligible by making the beam itself negligible. Which means we can just...

If you build the object in curved spacetime, hovering against gravity, you can't make the stresses in it negligible, because it's under...

Meaning, you build the object in an accelerating spaceship or something like it in flat spacetime, and then bring it into curved...

A beam of "negligible mass" might as well not be there; you're only getting the result that the stress in it is zero by saying it has no...

The OP specified a piece of paper, not a truss structure. Also, your claims, if they are correct, should apply to any object, not just...

Really? You can externally apply a force to an atom in the center of the object? You can't apply an external force to a part of an...

Btw, for the particular special case under discussion in this thread, we don't even need the Riemann tensor, because we know that the...

I strongly suggest that you do the math. If you do, you will find that your statement here is false. First, the "spatial curvature" you...

Yes, that's true, but... Yes, which is why the stationary congruence does not fall into the first type of congruence that the H-N...

While the theorem was originally proved before GR was even discovered, AFAIK it does not actually require flat spacetime. The two types...

This is also correct. I don't know if we discussed this particular case in previous threads some time back on the Herglotz-Noether...

Yes, this is correct. Since the worldlines in the congruence are integral curves of a timelike KVF, you can derive the result...

The kinematic decomposition is useful, yes, but to obtain it, you have to already know the worldlines. But you need to know the material...

No, that's not correct. Knowing the spacetime curvature does not tell you the deformation, because spacetime curvature only tells you...

No, they didn't. That's because the theory does not, and is not intended to, account for structure on human scales. More generally...