Why aren't standard rods and clocks affected by LC and TD?

[FieldTheorist]

Not exactly. It is because the assumption about physical validity of ideal clocks and rods unaffected by LC/TD is undoubtedly confirmed empirically by the stability of atoms and their spectra that we can do that "reverse engineering".

I'm sorry, but this post is incoherent. Could you please rephrase this in a way where the central equations/concepts/reasoning are made explicit, rather than implicit? I'm afraid I can't answer a question (or know if I have the requisite knowledge to even attempt to answer the question) if the question is vague and unclear.

 

[loislane]

I'm sorry, but this post is incoherent. Could you please rephrase this in a way where the central equations/concepts/reasoning are made explicit, rather than implicit? I'm afraid I can't answer a question (or know if I have the requisite knowledge to even attempt to answer the question) if the question is vague and unclear.

I don't find it incoherent on rereading but perhaps it needs to be read after post #16 to understand it. Sorry for assuming you read the whole thread.

 

[Dale]

Not if you include rototranslations and those are motions found in physics.

Those motions don't correspond to any Lorentz transform. Any motion which corresponds to a Lorentz transform (more generally any Poincare transformation) can be achieved through Born rigid motion only.

How dou you interpret Einstein's concern in that quote

I interpret it as the concern of a person before the symmetry approach had been developed.

 

[PeterDonis]

H-N theorem says what you write between parenthesis only.

Yes, but the fact that any rigid motion at all in SR must be Born rigid was already known, so H-N didn't need to state it explicitly. In more technical language, any rigid motion in SR must be described by a congruence of timelike worldlines with zero expansion and shear (which is what "Born rigid" means); that was known before H-N proved their theorem. The H-N theorem gives the conditions required for a congruence of timelike worldlines to have zero expansion and shear.

This was already settled by Laue in 1911 when it showed that rigid bodies cannot exist in SR

No, that's not what he showed. You need to spend some time actually looking at the science instead of reading pop science.

 

[PeterDonis]

An ideal measuring rod is one that keeps its shape while being (gently accelerated)

Technically, no, an ideal measuring rod is one that is not being accelerated at all. As I noted in a previous post, the geometry of Minkowski spacetime can be constructed using only inertial frames, i.e., only rods and clocks in inertial motion. Adding accelerated measuring rods with the property you describe is a useful convenience, but is not fundamentally necessary.

 

[PeterDonis]

The OP question has been answered. Thread closed.