why is faster than light travel impossible?

Question

I’m wondering if interstellar travel is possible. So I guess the starting point is figuring out FTL travel.

In: 1302

Answer 1

One of the reasons we think it’s impossible is that the speed of light is less about light itself and more about information. In order for *things* to happen information needs to be passed around to allow other things to respond and, in the case of life, perceive. If you could exceed the speed of light, you would be sharing information faster than information can be shared. Cause and effect would break down because other things should have reacted to your presence, but couldn’t because you arrived before you arrived.

EDIT: This blew up. A number of people have asked some good questions, so I’ll cover off two of the recurring and related ones: are black holes faster than light because light gets trapped, and how do we know that the maximum speed limit isn’t just higher?

Black holes are not FTL. They don’t trap light because they’re stronger. They trap light because light is running around the lip of a really steep bowl, and eventually light gets tired and slows down, and begins to spiral in to the centre, [like a penny in a wishing well collector](https://youtu.be/XTipCQxJ6Ak?si=kgE-mmxp-007qSEH). Light is too slow to climb back out, but not because the black hole is FTL.

Knowing this, we can answer the second question. We do have evidence that suggests the maximum speed isn’t higher: nothing else seems to exceed the speed of light either, but does move at it, such as gravity. If everything that can move at light speed seems to stick to that speed as the maximum, it seems odd to suggest that they could move faster but don’t. You then have to ask: if the maximum speed limit is higher than the speed of light, why are multiple phenomena that aren’t light moving at the **same** speed as light? If we find something that does you can guarantee that we’ll update the textbooks, but the more we understand, the more we seem to find phenomena that don’t go faster than light, which is suggestive.

For anyone asking “why isn’t the speed of light N+1?”, take it up with God. I can only really either refer to design or to random chance with regard to universal constants (I favour the latter personally, but that’s just me). Its presently not a question we can even hope to test, so any answer will be either pseudo or fully religious.