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# Re: Universal Constants [OFF TOPIC ]

From: "Steve Pugh" <mafb90@p...>
Date: Thu, 12 Feb 1998 21:04:47 +0000
Subject: Re: Universal Constants [OFF TOPIC ]
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> 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?

The measured speed of light is independent of the motion of the
source or of the observer. That's one of the underlying postulates of
Special Relativity. So the photon would measure the speed of light to
be the speed of light.

On the second point: the photon would believe itself to be standing
still: The other basic postulate of Special Relativity is that
Absolute Motion can not be detected. So how would the photon detect
it's own motion except relative to something else? "Am I moving at
light speed past all these objects? Or are they moving at light speed
past me? I can't tell."

> For example, it takes a finite time for a photon to go
> from A to B,

Finite time as measured by us, not moving at light speed.
Remember that measurement is relative.

> but since the photon is travelling at the speed of
> light the distance between A and B is zero,

Length contraction. As you approach the speed of light lengths along
your direction of motion contract and at the speed of light they
become zero.

> time stands still, and
> the photon takes an infinite amount of time to go from A to B,

Time dilation and you got it backwards. You age less as you approach
light speed and so at light speed you would experience zero time
passing. So zero amount of time not infinite amount of time. Note
this is zero time in the photons frame of reference.

> which contradicts the fact that it does get to B.

Nope: It's all relative. Repeat until you feel calmer.

Steve
+---------------------------------+----------------------------------+
|			Stephen Richard Pugh			     |
|		     steve.pugh@dial.pipex.com			     |
|	    http://dspace.dial.pipex.com/town/estate/ax16/	     |
+---------------------------------+----------------------------------+

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