Okay, real quick… I just want this confirmed or denied. If you take two rocket ships in space, and sent one off in one direction travelling at 51% of the speed of light, and sent on off in the opposite direction, also travelling at 51% of the speed of light, from the point of view of either ship, would the other appear to be travelling faster than light?
Nope.
Relativistic speeds don’t add that way.
(They are additive, but not linear.
51% + 51% is about 64%, if memory serves. I left
my calculator in my other brain…)
Trinopus
Here’s a link to doing relativistic velocity addition if you want the math. As Trinopus hinted at you can never add velocities in such a way for any observer to view another object as exceeding light speed. If you do see an object exceeding light speed then some trick is at work or the object is not real (e.g. a shadow can be made to exceed light speed but a shadow is a physical thing).
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html#c1
I’d like to know how you can make a shadow move faster than the speed of light. If you can do that, you can send information FTL, which violates relativity.
First off I should correct my earlier post and say a shadow is not a physical thing.
As to the question above here is your answer (note that other ‘things’ such as the spot of a laser can manage the same feat).
The key to this paradox is to note that you, the observer, see the spaceships separating at 1.02c, but neither of them is moving at a speed greater than c relative to you. Thus you never observe any material object moving at a speed greater than c.
I’ve been trying to envision how you came up with that idea, but for the life of me I can’t do it. How do see a shadow communicating information FTL?
It can’t. That was the whole point. I was trying to get the poster to expand on his/her point, which he/she did.