Particles approach each other with .8c

Question

Two particles travelling with velocity .8c (observed from ground frame) each approach each other. What is their relative velocity wrt ground frame. According to me they should be added. I am very much aware that their relative velocity wrt each other is smaller than c i.e is velocity of one particle wrt other.

What is the relative speed of two near-light speed particles headed towards each other?

Ben51 · Accepted Answer · 2019-09-19T15:03:55.137

1

I agree with you: just add the velocities (or rather, subtract them: one has velocity $0.8c$, and the other $-0.8c$). In the ground frame, the distance between the particles decreases at a rate of $1.6c$. This does not violate any laws of physics.

edited Sep 19 '19 at 15:03

answered Sep 19 '19 at 14:56

Ben51

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Particles approach each other with .8c

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