Re: Question about light clock and derivation of time dilation

Ken S. Tucker says...

>Using the light clock, the time axis "t"
>is the path of the light-ray as it's used,
>and that's fine.

Hmm. Usually, the time axis is chosen to be a timelike vector.
I've heard of coodinate systems using lightlike vectors as
basis vectors, but I don't know much about them. In 2-D spacetime,
you can let

u = x + ct
v = x - ct

then

ds^2 = -c^2 dt^2 + dx^2
= 4 du dv

So, in these coordinates, g_uu = 0,
g_vv = 0, g_uv = g_vu = 2.

Okay. I guess off-diagonal metric comes into play when you
use lightlike coordinates.

--
Daryl McCullough
Ithaca, NY

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