Is speed of light relative to "eather" flow?

schiz0ai

If 2 rockets fly from earth in opposite directions.
Both end up flying at 60% the speed of light.
Does that mean they flay faster then the speed of light, compared to eachother?
Or is it relative to spacetime or eather or whatever?

jtbell

No. In relativity, velocities don't "add" the same way as in classical physics.

http://hyperphysics.phy-astr.gsu.edu...iv/einvel.html

The result is always less than the speed of light.

schiz0ai

so would an observer standing on 1 rocket be able to see light coming from the other rocket?

Doc Al

Why not?

schiz0ai

how fast would light travel from 1 rocket to the other? and compared to what? the earth? the rocket emitting the light? or the one recieving it?

HallsofIvy

The basic concept of relativity is that the speed of light is the same in any coordinate system. So the answer to all of your questions is "c".

schiz0ai

so does that mean that when we think we shot something at 90% speed of light.
That seen from the center of the universe, the earth was moving so fast to begin with, that the thing we shot went only little bit faster?

Doc Al

Something like that. Say we shoot a spaceship at 90% of the speed of light with respect to earth. Then those on that spaceship shoot a rocket in the forward direction at 90% of the speed of light with respect to the spaceship. According to us on earth, that rocket is moving at about 99% of the speed of light (not 180%).

phinds

There is no "center of the universe".

schiz0ai

i thought the radius of the universe was the speed of light times the time since the big bang, and asumed herefor it had a calculatable center, but something tells me i really need to do some serious years of school to understand that kinda stuff. And hopefully some day il get the time to dive into it.

phinds

Try this for a start:

www.phinds.com/balloonanalogy

tensor33

That is correct. However, it is true for any point in space. There is no special point that is the center of the universe, any point in space can be considered the center. This is called the cosmological principle.

phinds

No, it is NOT true. You are using sloppy terminology. What you have described is NOT "the universe", which is what the statement was about, but the "OBSERVABLE universe". There is a big difference.

tensor33

You're right. That was a sloppy choice of words. Let me rephrase that. Any point in space can be cosidered the center of the universe it can observe (The observable universe)

phinds

Excellent recovery

Austin0

I am not sure I understand the distinction you are making here.
It would seem that unless there is an assumption that our observable sector of a total universe is somehow privileged that it would follow that we (or any other point) are effectively at the center of the whole shebang whatever it's extent.
What am I missing?

phinds

Yeah, I think I got carried away by the use of the terms "radius" and "universe" together and immediate said to my self, NO ... that's the OBSERVABLE universe (which HAS a radius), not "the universe" which does not have a radium, but you are of course correct. Any point anywhere is the center of its own observable universe