So, I was sat on the loo and thought...

"Mark McIntyre" wrote in message
...
On 31 Mar 2006 22:37:16 GMT, in uk.sci.astronomy ,
(Richard Tobin) wrote:

(mildly rearranged to let me respond in order)

photons do not move from one spot to another.
Different photons, successively emitted, travel to the different points.
They just travel out from
the source in different directions.

Indeed, but a photon arriving at point B would have, relative to a
photon arriving at point A, some velocity component perpendicular to
photon A's path. That vector would have an apparent magnitude greater
than c, according to simplistic analysis performend in a third frame
of refefence. I believe this to be a flaw in the maths.


Perhaps you are still misunderstanding the scenario:

To be honest, I've long since given up caring. My view is as follows:
1) nothing with rest mass can travel faster than c.
2) stuff with zero rest mass can travel at c.
3) even if you can devise a though experiment to show a theoretical
process by which some non-tangible thing can travel faster than c, you
can't observe it and it can't convey any information (which amounts to
the same thing).

In this thread, people have talked about taking photos with
"instantaneous" cameras, superluminal particles etc. Thats great -
invent some new physics and you can do anything.


Mark,
You seem to assume that Richard is proposing FTL material speeds, but he is
not.

The reason why superluminal scissor blades are impossible still stand (no
parts of the blades travel at c speed), but are irrelevant in the
discussion of the locus of the moving spacetime 'point' of intersection of
the crossing of the two blades.

As regards the 'beam' scanning across the moon, each photon is precisely
radial to the source and moving at precisely c. There is precisely NO
problem with this in some hypothecated 'third frame of reference'.

If I may add my £0.02:

Surely there is a distinction between "things" moving at c and loci
(such as scissor-blade intersection or laser intersection with Moon)
moving at c? In the case of loci, I don't see where the problem is, as
a locus is no-thing, so SR is not contravened.


Best,
Stephen

Remove footfrommouth to reply

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Mark McIntyre wrote:

On 28 Mar 2006 22:10:52 GMT, in uk.sci.astronomy ,
(Richard Tobin) wrote:

You could shine a beam of light onto the moon, and if you moved it
across the disk in 1/100 second (which you could do by hand if you had
a powerful enough hand-held laser) the spot would move faster than
light.

Er, no. Again you're applying newtonian mechanics. The light beam
would in fact /bend/ in such a way that the end moved at, at most, c.

Surely not. The light beam is merely a collection of photons that are
aimed at separate points on the moon. There's no relationship between
any of them.

Any half decent oscilloscope can generate a sweep that exceeds the speed
of light. There's no distortion in the trace or displayed waveform.

--

Peter

On Tue, 4 Apr 2006 13:40:33 +0100, in uk.sci.astronomy ,
(Peter Hayes) wrote:

Mark McIntyre wrote:

On 28 Mar 2006 22:10:52 GMT, in uk.sci.astronomy ,
(Richard Tobin) wrote:

You could shine a beam of light onto the moon, and if you moved it
across the disk in 1/100 second (which you could do by hand if you had
a powerful enough hand-held laser) the spot would move faster than
light.

Er, no. Again you're applying newtonian mechanics. The light beam
would in fact /bend/ in such a way that the end moved at, at most, c.

Surely not. The light beam is merely a collection of photons that are
aimed at separate points on the moon. There's no relationship between
any of them.

Thats the point - the beam wouldn't be straight, successive photons
would head off in different directions.

Any half decent oscilloscope can generate a sweep that exceeds the speed
of light. There's no distortion in the trace or displayed waveform.
Mark McIntyre
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