Viewing a single comment thread. View all comments

nicuramar t1_j284u3s wrote

Reply to comment by bobtheblob6 in How fast does the Milky Way spin? How far does Earth move through space in a year? by Sabre-Tooth-Monkey

> “if speed can only be measured relative to something else, what if our ‘absolute speed’ in the universe […]

The fact that speed can only be measured relative to something else implies that there is no absolute speed. Also, the flow of time is always normal for yourself. It’s only that you see others, moving at very different speeds, to have dilated time, compressed space.

2

bobtheblob6 t1_j28b6qh wrote

Isn't the speed of light a limit on your "absolute" velocity though? I figured it must exist in some form

2

tnaz t1_j29hqqs wrote

The laws of physics do not specify an absolute velocity, and the speed of light is a maximum that any observer can measure any object going, no matter how fast the observer is going relative to some reference point.

The important context here is that velocities do not compose by simple addition, but by a Lorentz transform. If I see two objects moving away from me in opposite directions at half the speed of light, those two objects will see each other moving away at less than the speed of light. This is where you also see phenomena such as time dilation, length contraction, etc... come from.

1