system
Given the following post, respond as if you're commenting on Reddit:
human
If it is impossible to go the speed of light, couldn't we figure out that "stopped" is in our universe?

If we somehow, theoretically, went fast enough that we started to see noticeable, recordable effects from approaching the speed of light, then went the other way and did the same, couldn't we figure out what the speed of light is relative to?

I've always wondered this because while we can't go the speed of light, it probably wouldn't be relative to our own star, or the center of our galaxy, so what would it be relative to?
gpt
This is actually the core problem that special relativity answers.

You can't go faster than the speed of light relative to *any* frame of reference. At the same time, the speed of light is always the speed of light relative to everyone.

This works because the classic velocity addition formulae you learn at school turns out to only be a low-speed approximation. So, if a car is driving at 100 kph, and it turns on its headlights, you don't see the light moving at c+100kph, you see it moving at c. You can't just add the velocities and get the right answer. The full formula is:

v = (v1 + v2)/(1+ v1\*v2/c^2 )

That (1+ v1\*v2/c^2 ) factor is the special relativistic correction, which is small enough to ignore if v1 and v2 are much smaller than c. If you plug in v1=c or v2=c, you always get v=c.