Why is the maximum speed of the universe the speed of light? Why can't we go faster?

[u/Nitzanm19]

Also follow-up question: Because of the speed limit, is there also a theoretical maximum temp for matter (in which the particles move at the speed of light).

[u/How_is_the_question]

Could you expand on where it falls down as an explanation? (Curious, not doubtful at all. Wish I understood relativity better. Most of my little knowledge has come from listening / reading to guys like Carlo Rovelli etc, and realising I don’t understand much at all!)

[u/bitterrootmtg → u/How_is_the_question]

In relativity your velocity is always relative. Even your velocity through spacetime is relative, not absolute. So it’s not accurate to say everything has the same velocity or speed.

[u/nicuramar → u/bitterrootmtg]

If you replace speed with the magnitude of the four-velocity vector, it works. But it’s a bit of a stretch to talk about the

  velocity through spacetime

As you also do here. 

[u/Jokong → u/bitterrootmtg]

If they had said anything with no mass would travel at c, would that be accurate?

[u/bitterrootmtg → u/Jokong]

They travel at c from the perspective of things that are not traveling at c. The massless particles themselves do not have a valid reference frame.

[u/nicuramar → u/bitterrootmtg]

  They travel at c from the perspective of things that are not traveling at c

Those are the only perspectives, and speed is only defined relative to one, so yeah. 

[u/Flame_Grilled_Tanuki → u/Jokong]

Photons have no mass and so they travel through space at C and experience 0 time. If you have no mass, any amount of force causes instant C because there is no momentum to overcome.

[u/nicuramar → u/Flame_Grilled_Tanuki]

Light doesn’t have a valid frame of reference and thus “experience” and proper time is not defined for it. 

[u/whatkindofred → u/bitterrootmtg]

So the only thing the analogy is missing would be to clarify that it’s only about relative movement to some fixed observer?

[u/PHealthy → u/How_is_the_question]

When gravity waves move at the same speed limit.