Mike_bb's latest activity

The term "massless" means "mass is undefined". But mass is fundamental property then term "massless" isn't correct in that case.

Photons have mass. The mass is 0. "Massless" is somewhat unfortunate term.

Ibix, That's what I want! Thanks!

I had a suspicion this was about the Riemann tensor. Start with a vector ##V^a## and parallel transport it along a small vector...

Matterwave, big thanks!! I found such interpretation of measuring curvature: Could you explain why "The difference between these two...

Could you explain your notation? Are you using abstract index notation? That is the notation I know that looks like what you used. In...

That would be great. :smile:

I can post a more complete answer later today if nobody else has done so already by then but it'll be a while.

This is not true in general, if it were so you'd have ##\partial_x \partial_y f =0## generically and it's obviously not generically true...

Why?

The del A gives you the rate of change in the A direction. When you apply del B to that you get the rate of change of del A in the B...

Hello, PF! When we use covariant derivative (##\nabla_a## or ##\nabla_b##) we have that ##\nabla_a## or ##\nabla_b## shows how vector...

Why do you watch you tube videos instead of studying physics textbooks?

The construction of a theory is a modeling process. It creates models.

Newton's absolute frame included an absolute time. We know from observation and experiment that that is demonstrably false. If engineers...