PhilGoetz comments on Particles break light-speed limit? - Less Wrong

9 Post author: Kevin 23 September 2011 11:00AM

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Comment author: PhilGoetz 24 September 2011 02:33:14PM *  0 points [-]

My question is whether he meant to say

  • moving from A to B faster than the speed of light in one reference frame is equivalent to moving from B to A faster than the speed of light in another reference frame

or

  • moving from A to B faster than the speed of light in one reference frame is equivalent to moving from B to A slower than the speed of light in another reference frame

both of which involve moving faster than light.

Comment author: Owen 25 September 2011 04:35:04AM 1 point [-]

I meant the first one: faster than light in both directions.

You can think of it this way: if any reference frame perceived travel from B to A slower than light, then so would every reference frame. The only way for two observers to disagree about whether the object is at A or B first, is for both to observe the motion as being faster than light.

Comment author: shinoteki 24 September 2011 02:53:28PM *  0 points [-]

He's not talking about impossibility

I know Owen was not talking about impossibility, I brought up impossibility to show that what you thought Owen meant could not be true.

both of which involve moving faster than light.

Moving from B to A slower than the speed of light does not involve moving faster than light.