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# Re: Universal Constants (this is getting a bit long and going a bit off topic...)

From: alun.thomas@c...
Date: Fri, 13 Feb 1998 12:24:50 +0000
Subject: Re: Universal Constants (this is getting a bit long and going a bit off topic...)
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Tony Christney <acc@uvic.ca> on 12/02/98 19:15:45 wrote:

> If the speed of light is constant, then what is the speed of light
when
> measured by a photon?, ie, how fast does a photon "feel" like it is
going?

Special relativity: the photon isn't accelerating - therefore it feels
like
its
stationary.

> For example, it takes a finite time for a photon to go from A to B,
> but since the photon is travelling at the speed of light the distance
> between A and B is zero, time stands still, and the photon takes an
infinite
> amount of time to go from A to B, which contradicts the fact that it
does
> get to B (very quickly, I might add!).

No, In the photon's frame of referance, the distance between A and B is
zero,
hence (in the photon's frame of referance) it takes no time to travel
between the
two.

In our frame of referance A and B are separated by some distance which
the
photon crosses at (by definition) the speed of light.

No contradictions anywhere, just two different frames of referance.

> Quantum Mechanically, the photon is actually everywhere in the
universe
> at the same time, until it is detected in a particular place. This has
to
> be so, because for a photon to be emitted, it also has to be absorbed
> (we can't have a "leaky" universe, can we?). Hence it has to "know"
that
> it will be absorbed before it can be emitted! Again, another
> If nothing can travel faster than light, then how does that little
bugger
> know about its absorber when it is , say, 10 million light years away?
[...]

Again, there are 2 different referance frames here:

In our frame, the photon is emmitted from A at time Ta and is absorbed
at B
at time Tb. Where the distance between A and B is 10 million light
years,
and
the time between Ta and Tb is 10 million years.

In the photon's frame, A and B are the same point, and Ta and Tb are the
same
instant.

> As for the immortal Pi, try drawing a circle on a sphere! Then Pi
changes
> for every circle of a unique radius! [...]

'fraid not - the sphere just prevents you from measuring the radius (you
can't
get to the centre of the circle without cutting away chunks of the
sphere).

> (Just when you thought I was done, ha ha ha!)
> Even atomic decay rates are not constant. Its impossible to slow them
down
> enough! And when they are slow enough, they have already decayed down
to
their
> lowest possible energy! Interstingly, the atomic clocks used in orbit
for
> GPS (among other things) keep different time than identical clocks on
Earth!
The different rate at which the GPS clocks run is due to predictable
relativistic effects
(they're higher up the Earth's gravity well, and moving at a different
rate
than their
Earth-bound duplicates).

(If anyone wants to carry on with this, can I suggest we take it to
private
e-mail ?)

Alun.
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