But light does travel at other speeds eg. in water. Does causality have to slow down for it?
Good point.
So... from all the reading links provided, it seems to me that the big excuse that nothing can travel faster than light is that nothing has been observed to do so, therefore, we assume that causality itself is travelling at a speed and thus that speed is wrapped up in the definition of space itself. That if you move far enough away, you've moved in time as well because literally, anything you see out there in the universe is what's happening at this very time in relativity to your own frame of observation and the speed of light is defining the speed of time's passage per distance.
I'm not sure I buy it, no matter how verifiable the experiments may seem to be. If light takes time to travel, then it's not the speed of causality imo. The speed of causality is instant. There is a current moment taking place universally everywhere. Time is a 4th dimension that is not the same as space and is instead an entirely different axis to spacial distance.
I may be wrong. Probably am, but it doesn't seem so full of self contradictions that way.
Sure, massless energy seems to have a constant rate of speed, ok, cool, now we know what the rate of speed of a massless energy is. Neat. I see no reason it cannot be exceeded without breaking causality where something can travel c without being automatically capable of moving backwards in time. It just reaches its destination before light does. That's really not that complicated.
Light always travels at c, it seems to be slowed because photons are kept being absorbed and re-emitted in random direction when travelling trough some medium.
Yeah so this doesn't always make sense here - I mean if you are travelling at .5 c in a direction then you shine a light backwards, how does it then travel at 1.5 c to make up for the momentum you have moving the other direction? (This may be what Yudi was trying to say in other words.)
Or is it that to an observer to the side of the person moving and shining the light backwards, both the light that's approaching from the original point to the person moving and the light moving backwards are moving at a speed relative to the speed of the origin of the light sources themselves? Thus it takes a light from the Earth to reach that person moving twice the normal speed of light and it takes the light returning to Earth from that person moving twice the normal speed of light for the distance as opposed to exactly the same distance in light years as the person is/was when the racing lights were sent? But if the person were fixed in space (unmoving) and the Earth was fixed in space, the light would take the normal rate of time to reach both Earth and the traveller?
Yeah, looks like the part I have a hard time swallowing as real would be this stuff:
https://en.wikipedia.org/wiki/Relativity_of_simultaneity
Seems like an incredibly unnecessary convulsion of thought as a whole. That space itself manipulates time doesn't seem to be necessary to explain anything unless you're trying to somehow explain that the speed of light = the speed of causality, rather than all causality is instantaneous.
I say all this knowing I'm probably wrong here because the examples and thought experiments are often baffling in the way they are expressed - there are symbols for mathematical meanings in use on these pages I have no idea what they mean and I don't have the patience at the moment to reread over and over until it starts to make any sense in many other attempted examples.