Re: The world as seen by a photon

["John S. Denker" <jsd@MONMOUTH.COM>]

James Mackey wrote:

> One question was, what does the world look like from the frame of a
> photon ?

It doesn't look like anything.
There is no such frame.

> I assume for a photon, that since it travels at c, it's interval is
> always zero, so the photon can get anywhere in zero time
> relativistically. If true, what does that mean?

A photon exists for zero _proper_ time.

Whether or not it can get "anywhere" in that
time is an unanswerable question, because the
would-be "frame" of the photon has no notion
of distance for the same reason it has no notion
of time.

> The second question stems from the first. In relativity I recall
> transforming from one frame of reference to another, and requiring
> that the results be symmetric, i.e. no preferred reference frame. If
> one of those frames is the frame of a photon, is this still true?

Since the photon "frame" does not exist, the
situation is certainly not symmetric.

More generally, the universe can be divided into
the future light-cone of a particular event, the
past light-cone, and the outside-the-cone regions.

All observers whizzing past the given event,
regardless of the observers' velocities, agree
as to this three-part division (and agree as to
where the boundaries are).

Given any two frames, both have their timelike
axis inside the future light-cone.  And there is a
certain symmetry between them.  They are members of
a certain equivalence class.  Any attempt to put the
timelike axis on or outside the light-cone clearly
steps outside that equivalence class.