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

JRS: In article , dated
Wed, 29 Mar 2006 10:13:41 remote, seen in news:uk.sci.astronomy, Mark
McIntyre posted :

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.


That cannot be right.

Approximate everything by circular motions with a common axis, which
clearly does not affect things. The moon's orbit has a circumference of
about eight light-seconds.

Stand at the North Pole with a perfect torch pointed at the moon's
orbit, and rotate continuously about the pole at one rev/sec.

The spot of light will clearly traverse the Moon once per second, and
must pass across the middle of the disc at about 8 c.

If someone now stands a megamile above the North Pole, and takes an
instantaneous flash photo using hyperlight (infinite speed, and reflects
off torch photons), he will record the beam as a spiral with about 1.28
turns between Earth and Moon.

In fact, the spiral will make an angle of about 1/8 radian with the
Moon's orbit, and the light will hit like a wave on a perfect beach
would meet a ship that had run aground by heading 1/8 radian shorewards.

The photons move outwards at c, but the impact point moves sideways at
8c.

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That cannot be right.

Approximate everything by circular motions with a common axis, which
clearly does not affect things. The moon's orbit has a circumference of
about eight light-seconds.

Stand at the North Pole with a perfect torch pointed at the moon's
orbit, and rotate continuously about the pole at one rev/sec.

The spot of light will clearly traverse the Moon once per second, and
must pass across the middle of the disc at about 8 c.

If someone now stands a megamile above the North Pole, and takes an
instantaneous flash photo using hyperlight (infinite speed, and reflects
off torch photons), he will record the beam as a spiral with about 1.28
turns between Earth and Moon.

In fact, the spiral will make an angle of about 1/8 radian with the
Moon's orbit, and the light will hit like a wave on a perfect beach
would meet a ship that had run aground by heading 1/8 radian shorewards.

The photons move outwards at c, but the impact point moves sideways at
8c.

I like that.

Also, there may not be a problem with "the impact point" moving at c because
the effect cannot be used to transfer information between two remote points
at c.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.livejournal.com/userinfo.bml?user=fleetie

On 29 Mar 2006 22:41:13 GMT, in uk.sci.astronomy ,
(Richard Tobin) wrote:

In article ,
Mark McIntyre wrote:
[...]

Well, let's have one more try,

Lets not. The experiments you describe have been more than adequately
described elsewhere, together with explanations of why, irrespectiveof
what one can simplistically calculate with 'normal' maths, the
conclusion that the beam moved faster than light, is wrong.
Mark McIntyre
--

On 30 Mar 2006 00:58:12 -0800, in uk.sci.astronomy , "Martin Brown"
wrote:

Mark it is you who does not understand special relativity.

All things are possible.

There is no
conflict at all with SR in the superluminal scissors "paradox".

The word paradox is fairly important here.

Nothing
physical is moving faster than the speed of light. You might be able to
grasp this if you imagine what observers on a pair of exactly parallel
blades would observe when they crossed.

I already did, and I noticed that they can't actually observe anything
useful, for a variety of reasons.
Mark McIntyre
--

In article ,
Mark McIntyre wrote:

Well, let's have one more try,

Lets not.

I find it suspicious that you stop just at the point where you would
have to show a specific error. Especially when I have gone to the
trouble to spell out the steps to reduce the scope for confusion.

To be blunt, I believe that you are not answering because you cannot.

The experiments you describe have been more than adequately
described elsewhere, together with explanations of why, irrespectiveof
what one can simplistically calculate with 'normal' maths, the
conclusion that the beam moved faster than light, is wrong.

You have changed my words. I did not conclude that *the beam* moves
faster than light. The illuminated spot moves faster than light. No
real body can exceed the speed of light, but non-physical things such
as the intersection of two blades or an illuminated spot can.

-- Richard

On 30 Mar 2006 00:58:12 -0800, in uk.sci.astronomy , "Martin Brown"

wrote:

Mark it is you who does not understand special relativity.

All things are possible.

It is now absolutely certain. Your grasp of special relativity is
entirely superficial.

There is no
conflict at all with SR in the superluminal scissors "paradox".

The word paradox is fairly important here.

It is called a paradox because it appears to do something that is
forbidden by a naive interpretation of the rules of SR. It provides a
very good test of whether or not someone actually understands
relativity.

Nothing
physical is moving faster than the speed of light. You might be able to
grasp this if you imagine what observers on a pair of exactly parallel
blades would observe when they crossed.

I already did, and I noticed that they can't actually observe anything
useful, for a variety of reasons.

Which are? You clearly do not understand what you are talking about.

BTW John Stockton's analysis of the laser pointed at the moon elsewhere
in this thread is also correct.

I suggest you try asking for enlightenment on sci.physics.relativity
you might find someone there with enough patience to explain this to
you in a form that you can understand.

Regards,
Martin Brown

On 30 Mar 2006 22:21:08 GMT, in uk.sci.astronomy ,
(Richard Tobin) wrote:

To be blunt, I believe that you are not answering because you cannot.

Thats fair enough, i accused you of the same thing earlier. And to be
fair, I couldn't do the maths any more.

You have changed my words.

Not deliberately, it is however how I understood what you'd written.

I did not conclude that *the beam* moves
faster than light. The illuminated spot moves faster than light.

Consider that for this to happen, the photons would need to have a
transverse velocity vector greater than c

Mark McIntyre
--

On 31 Mar 2006 00:46:54 -0800, in uk.sci.astronomy , "Martin Brown"
wrote:

On 30 Mar 2006 00:58:12 -0800, in uk.sci.astronomy , "Martin Brown"

wrote:

Mark it is you who does not understand special relativity.

All things are possible.

It is now absolutely certain. Your grasp of special relativity is
entirely superficial.

I see. On the basis of a throwaway remark, you feel able to analyse my
grasp of a pretty complex subject. Out of interest, whats your
qualification in relativity? I'm no expert, though I did do a degree
in Physics, specialising in high energy physics and nuclear physics in
my 3rd year.

I suggest you try asking for enlightenment on sci.physics.relativity
you might find someone there with enough patience to explain this to
you in a form that you can understand.

Thanks for the condecension. I'm sure someone with your intellect and
wit finds it hard to stoop to the level of mere mortals.
Mark McIntyre
--

In article ,
Mark McIntyre wrote:

I did not conclude that *the beam* moves
faster than light. The illuminated spot moves faster than light.

Consider that for this to happen, the photons would need to have a
transverse velocity vector greater than c

Perhaps you are still misunderstanding the scenario: 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.

-- Richard

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 McIntyre
--