From: Daniel Fabulich (daniel.fabulich@yale.edu)
Date: Fri Jun 12 1998 - 18:00:30 MDT
On Fri, 12 Jun 1998, Ian Goddard wrote:
> It is stated that the speed of light is
> not instantaneous, and as such, the light
> from distant galaxies is "old light."
>
> I believe that that idea is illogical.
> It is an accepted fact that at the speed
> of light, there is no time, time is fixed
> at 0, and thus the idea of an "old photon"
> is inherently illogical.
You're confusing your definitions again. When people say that the light
is old, they mean this: if a photon is emitted by a star 20 ly away at
the time t=0 in our own reference frame, we will observe 20 years
difference between t=0 and the time it hits our detector, t=T. This
statement says nothing about the photon's perspective: this distinction,
indeed, is meaningless from the photon's reference frame. Nonetheless, we
can still make the "partial" statement that in our own reference frame,
the difference between T and 0 is 20 years. When we say "old light," that
is what we mean. And we are not wrong nor illogical to say so.
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