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Assume 2 rockets coming towards each other at each other at 99% of speed of light, and so as they pass each other the relative velocity between 2 rockets would be 198% of Speed of Light and so what will the observers in the rockets see happening in the opposite rocket?

  • The problem with your answer is that you added velocities as if it was a classical problem. On special relativity you must be more careful. If I have time I will post a detailed answer – Ivan Burbano Jul 09 '15 at 18:06

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I think I see your mistake: it's the classic mistake. You would think that if you travel in a rocket moving at the speed of light and flash your flashlight out from it in the same direction the speed of the light would be $2c$ (where $c$ = speed of light), but in truth, due to time dilation and length contraction etc, etc, relative velocity would still be $c$. I think. Someone correct me on that if I'm wrong. So from my theory

To answer your question, they would see that the opposite rocket would be travelling at the speed of light, but the opposite rocket itself would be at length $\sqrt{1-(\frac{.99c}{c})^2} L_0 = L$, so their length would be approaching 0 ($L_0 =$ length at velocity 0). But from the opposite rocket, I think that due to relative velocity, the length of the rocket would be $\infty$.

EDIT: For those who were confused at my length contraction formula, my mistake, I accidentally switched my thoughts out from time dilation, etc.

phi2k
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I'm no expert but: you have to assume that you stand still in your initial system. And also because of these contractions it doesn't sum up straight v1+v2 (like the pre-answered said).

There are other thought experiments like when you turn yourself and you look out in the universe, things can then pass way faster than light but only because your angular speed. But in straight line acutally passing room it's limited to the speed of light.

So the speed of light in vacuum is the maximum speed you can reach travelling through space relativ to something but not moving other things around you in respect to your initial system. I'd recommend to study the minkowsky room. It makes clearer what the limits are and how the shifting of the spacetime works.

Hope this helps. Greetings

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