[geijoenr]

Yeah well, we don't really know what happens at high speeds. Probably biochemistry stops working at 0.3c? It doesn't seem structural materials would remain solid at 0.95c... who knows.

[inasio]

High speeds relative to what? The earth orbits at 30 km/s, our galaxy arm is at over 200 km/s (say 0.1% c), I'm not sure relative speed matters at all

[monkeydreams]

I am not a physicist but I suspect that we are already moving at significant speed relative to other bodies. We have no special frame of reference that defines our "real" speed.

[gpm]

That's not quite right. There's the cosmic background radiation "rest" frame, which can reasonably be taken as 0 velocity.

The laws of physics don't change in different frames (Einstein's assumption), but that doesn't mean that all frames are equivalent in other respects.

[geijoenr]

The speed of light is the frame of reference. It remains constant for any observer no matter at which speed is moving.