robphy's latest activity

Seen in terms of geometry, it is closely analogous to two cars driving at equal speeds ##v## down straight roads that make an angle...

Although this has some overlap with causal structure and relativity, your specific questions are more about the mathematics rather than...

I use -- in Microsoft Word and it converts to the em-dash there. But how do you do it with this website's interface in Chrome or Edge...

By the way, how you do type that dash ? I can't find it on my keyboard.

So, can you specify by what you mean by "something more primitive" than Szekeres' signal relation S which "is reflexive, but not...

Clearly, we are not all using the same definitions. So there is some ambiguity. And words are imperfect. So, it seems the question is...

I'm surprised that no one has yet to point out that it may not really matter that much. But then again that joke is so low-hanging and...

Probably off-topic, how would one even type an em-dash in the forum software?

In General Relativity, the Einstein field equations read ##G_{ab}=\kappa T_{ab}##, where ##T_{ab}## is the stress-tensor, where all...

I would prefer your thoughts.

@OmniThoughts Please don't post chatbot output here. If any of us wanted to have a conversation with a chatbot then we would just ask...

You can't travel faster than ##c##. So your question is "how should I interpret some maths I've applied in a regime where the same maths...

"Proper time" does not exist for the photon. However, there must be a sense of causality, The Emission-event occurs before the...

I should probably write the relevant formula involving hyperbolic-trigonometry. ##\beta=(v/c)=\tanh\theta ## so...

For a ship (with nonzero rest mass), it cannot achieve "the speed of light" physically. Although your Newtonian intuition suggests that...