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B Travelling faster than the speed of light?

  1. Oct 9, 2016 #1
    I know that no object can travel faster than the speed of light, but if two objects travel in the opposite direction, both at almost the speed of light, then would one object be travelling faster than the speed of light relative to the other?
  2. jcsd
  3. Oct 9, 2016 #2


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    Velocities do not add linearly. If the two objects are moving near light speed with respect to you, you will see the distance between them falling at slightly less than 2c. However, each object will condider itself at rest, and see you and the other object approaching at near c (the other object slightly faster than you).

    If, in your frame, the two objects are doing velocities u and v then the one doing v will see the other doing $$u'=\frac {u-v}{1-uv/c^2} $$Remember that your objects are going in opposite directions so one has a negative velocity. Note that for everyday speeds, ##uv/c^2## is tiny and the formula above becomes ##u'\simeq u-v##, which is what you expect from Newtonian physics.
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