Recent content by PeterDonis

I have no idea what you are basing that on. Newtonian gravity, the theory, says nothing whatever about what mass distributions are "reasonable". It doesn't even have things like the energy conditions, which as @Dale pointed out are conditions in the GR context that are used to judge whether a...

@renormalize I deleted the post you just responded to.

How does the "scalar" ##\Phi## in this theory have to transform when you change frames, in order for the tensor ##T^{\mu \nu}## that it contributes to to transform as a tensor, as it must? Note that the "Newtonian" potential ##\Phi = - M / r## obviously does not transform as a Lorentz scalar.

For rest mass, you should really say "invariant mass"--the magnitude of the object's 4-momentum vector. For binding energy, if you're careful to define it in terms of the appropriate invariants, yes. But note that it's not as simple as "just take the difference in invariant masses". You also...

Can you give specific references for these statements?

@danieltanfh95 the reference you provided in response to @Sambuco is (a) your own work, and (b) only just published this year, meaning it is too new to be a valid reference, since there has not been sufficient time for the relevant scientific community to review and respond to it.

This isn't possible; that's not how SPDC works. Either you get a pair of entangled photons triggered by the input "pump" photon, or you just get the "pump" photon passing through the apparatus and doing nothing. You can't "tune" the apparatus to pick whether you get pairs of entangled photons or...

That's correct. Also please bear in mind one of the things that is said in the guidelines for this subforum, that the kinds of discussions we have here are about things that can't be resolved by experiment, so they come down to people's opinions, and if different people have different opinions...

Just looked, it's actually a series of three problems, Exercises 7.1, 7.2, and 7.3.

Which also, of course, is not a complete theory (although it is useful as an approximation in the weak field regime), since it also leads to inconsistencies. MTW has a homework problem in one of its fairly early chapters which leads you through building a simple scalar and then vector model of...

But we also observe the homogeneity and isotropy of space. Those are experimental facts as well: that the same experiments done in labs at different places and with different orientations give the same results. And they affect everything, not just light, so they at least seem more general on the...

I think a deeper understanding of the physics comes from looking at a more modern derivation based on spacetime symmetries, such as @PeroK referenced. This shows that Einstein's 2nd postulate was really not necessary; you can get to the existence of an invariant speed which must be independent...

In Newtonian physics, perhaps. But we are talking about GR. GR is not Newtonian physics, and does not work the same. No, he is saying that GR is not Newtonian physics.

Now fixed.

In the original version by Einstein, yes, I think something like that was implicitly being assumed. The more modern derivation from spacetime symmetries, as in the reference @PeroK gave, also requires that no medium is present when you get to the point of deriving that light moves at the...