CSvax:Pucc-H:ab3@pur-ee.UUCP (10/13/83)
I think the resoluton of "Can you do anything while traveling
at C" may be resolved by giving two answers:
1. Relevant to *your* inertial frame: You can turn on the
headlights, play cribbage, whatever you like; I am assuming (possibly
incorrectly) that you should be unable to observe *anything* within
yur inertial frame that gives a clue as to your velocity. This postulate
certainly holds true for non-accelerating frames at v < C; I really
don't know if it works for v >= C.
2. Relevant to *other* inertial frames: Since you are made
of photons by now, and are therefore "light" ( :-) ), your relative
velocity to any observer is C. From the outside observer's point of view,
no time is passing in your frame, so he cannot observe you doing anything.
Now, I'd like to try to restate two points you made:
"Seems to me, if you were in a C-velocity frame:
o If a positive amount of time passed (as measured your clock), the first
thing you'd encounter would be, uh, maybe the end of the universe. This
would occur instantaneously. I won't even try to speculate where or when
you would be if you and your clock kept going after that..."
I would change the words inside the parenthesis to be
"(as measured by your clock, observed by someone not in your
inertial frame)"
Probably Irrelevant Note: If the universe is closed but unbounded, you'll
spend your time looping around it...
"o If precisely zero units of time passed (again, by your clock), but your
velocity were subsequently (according to someone else's clock) slowed to
less than C, you could have traveled to ANYWHERE in the universe."
Same change in the parenthesis.
The key that keeps either of these statments from making a photon-constructed
spaceship into an instantaneous-transport vehicle is that we are talking
about time on *your* clock measured by an *outside* observer. As far
as he's concerned, you just move by him at C, and it takes you 8 minutes
to go 93 million miles, and so on.
"And does experimental physics show that time does not pass for photons? It
always struck me as strange that they were something, yet had no mass."
Experimental physics does show that certain types of particle decay (which
take a known time to occur) take "longer" from the outside observer's point
of view when these particles are moving at v ~= C in a particle accelerator.
I don't know how you could perform this experiment on a photon; what do
photons do that takes time to occur? And how would you know that they
did it?
"Whether this article is correct or not, we still haven't determined
what things `look like' from a C-velocity frame. I heard somewhere
as your velocity increases toward C, the visual area in the direction
of motion `appears to expand'; does this imply that at C the point at
your direction of motion expands to fill your entire visual field?"
This is an area in which I am somewhat fuzzy; the best demonstration of
this effect was shown on a PBS program where they used "relativistic
motorcycles" to demonstrate a number of principles...anybody remember
the name of this?
I do recall, however, that they stated that the sides, and then the
backs, of objects would become visible to you as you accelerated towards
C...of course, they blue-shifted as well. I really don't know what
would happen at v = C...does anybody out there?
Darth Wombat
p.s. Michael-no offense intended, none taken.
p.s. again: The first book I ever read on the subject (and one which
I'm going to read again if this discussion keeps up!) is
"Relativity for the Million" by Martin Gardner, published by Macmillan
in 1962...it is probably out of print, but it is a wonderful introduction
to the special and general theories of relativity, cosmology, non-Euclidean
geometry, and a number of related topics.mwe@astrovax.UUCP (10/14/83)
The "probably irrelevant point" about looping around the universe is also incorrect. In a closed universe, a photon has just enough time to go around once between the big bang and the big crunch. So "you can't see the back of your head" 8-). web ewell astrovax\!mwe
Shinbrot.WBST@PARC-MAXC.ARPA@sri-unix.UUCP (10/18/83)
Darth, A very fun book on relativity is George Gamow's "Mr. Tompkins in Wonderland." Gamow discusses what would happen in a closed universe the size off a football field, he has a story on what would happen if h were on order of unity, and what would happen if c were very much slower. - Troy