[ExI] speed of light at the speed of light

[Adrian Tymes]

On Aug 22, 2013 4:43 AM, "Gordon" <gts_2000 at yahoo.com> wrote:
> I understand it is problematic to speak of massive objects actually
travelling *at* c, but it seems me that *in the limit* as I approach c (as
above), c is still a constant in my frame of reference. And how is this any
different from saying that if my ship is travelling at c, the light from my
flashlight still travels in my direction of travel at c relative to my
flashlight?

What you're missing is time dilation.  That is, you appear to react slower
to the universe/the universe speeds up from your point of view.  In both
perspectives, the light from your flashlight proceeds ahead at c, but your
clock (by which you measure meters per second) slows down.  (IIRC, there's
also distance compression along your axis of motion.)

This only works so long as there is some gap, however small, between your
velocity and c.  However, you also gain mass as you near c, so conventional
means of acceleration can never quite boost you all the way.  (That is,
something gets pushed backward - slowing down and in this case thus losing
mass - to boost your momentum a little bit more.  It's akin to Zeno's
paradox.)
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