Re: Simple four velocity question

On Feb 27, 11:58 am, Edward Green <spamspamsp...@xxxxxxxxxxx> wrote:
Since the definition of four velocity involves proper time,  e.g.

http://en.wikipedia.org/wiki/Four-velocity#Definition_of_the_four-vel...

how do we define the four velocity of light, for which there is no
proper time?

Does it seem awkward to anybody else to take the the derivative of the
"four-position" with respect to tau instead of with respect to t?

This pretty much assures that for all objects, you'll get the same
first coordinate (c*gamma*t)/d(tau) = d(c*tau)/d(tau) = c, and as Mr.
Green said, you don't have a well-defined four-velocity for light.

Is that not correct? Is the wikipedia article error?



.

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