Relativistic velocity

I would have another question. If I travel at the speed of light (or 99.9999999999....% of the speed of light) in a spaceship and i begin to run from the back of the spaceship to the front in direction of the spaceship movement, will I be moving faster than the speed of light?

arildno
Homework Helper
Gold Member
Dearly Missed
Nope.
As measured from the Earth frame (in which the spacecraft has the velocity indicated), you'd be measured to have a velocity strictly below c.

You cannot just add velocities to get total velocity. Use:
w = (u + v)/ (1 + uv/c2)
If you define all the velocities in terms of light speed by dividing each one by “c” the formula is simpler and becomes:

w = (u + v)/ (1 + uv)

You’re more accustomed to living and working with speeds less than 0.0005
Where doubling that speed gives you
.001 / 1.00000025

You’ve just never needed the accuracy of dividing by such a small number at those small speeds. And just used the .001 part or (u + v).

But as one of the speeds becomes high, say above .25
Then using the whole formula and dividing becomes important.

krab