Re: does light travel forever?


"David Ewan Kahana" <dek@xxxxxxx> wrote in message
news:1137616521.350064.65220@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Denis Loubet wrote:
>> "John Vreeland" <vreejack@xxxxxxxxxxx> wrote in message
>> news:67rps1hmmvltmvko3qb0n9ui20lj1nbt36@xxxxxxxxxx
>> > On 16 Jan 2006 23:11:38 -0800, ck19bla@xxxxxxx opined:
>> >
>
> [snip]
>
>>
>> I hereby present a stupid question:
>>
>
> There are no stupid questions, only stupid answers.
>
>
>> 1. I assume a photon experiences time dilation just like any object
>> traveling near the speed of light.
>>
>
> Only another photon could notice it however.
>
>> 2. Since the photon is traveling AT the speed of light, in a vacuum, I
>> assume it's time dilation is total, and it experiences no passage of time
>> whatsoever.
>>
>
> Yes. Proper time vanishes along the path of a photon.
> If you could travel along such a path, then there would
> be no passage of time.

Ok, cool! I'll pretend to understand that!

>> 3. 1 and 2 being the case, how can a photon lose energy? From the
>> photon's
>> point of view, there's no time for it to lose energy.

> It loses energy from the point of view of observers who are
> not comoving with the photon. Instead they are comoving
> with the expanding universe.

You seem to be saying that the different frames of reference (I'm saying
that as if I understand it) make a difference to changes in energy? One
frame -- the non-comoving one -- sees a change, and the other doesn't? (I
might say the other *can't* because no time is passing for it, but I don't
know if that's the reason.)

This doesn't make sense to me yet.

> As far as an observer who is comoving with a photon
> is concerned, a photon has no energy to lose.

Errr, okayyy....

Is the observer experiencing the passage of time? If he isn't, does that
place a logical hurdle in the way of his ability to observe?

And I'm assuming that comovement at lightspeed and its subsequent time
dilation is a special case that violates the effect that no matter what your
frame, light is seen to travel at lightspeed. (He said, exposing his
ignorance.)

> Its rest mass is zero, so if you could move together with it,
> its frequency would also be zero, since no proper time passes.
> Hence its energy is also zero from E=h*nu.

Oy! You're hitting the brick wall of my conceptual abilities.

But "no proper time" = "No frequency" makes sense. Hmmm.

Ok, I'll stand out in front of my conceptual wall and take another hit: I've
been led to understand that when a photon strikes matter it releases energy.
In what form is the energy of a photon for the zero time it's in transit.

I'm almost afraid of the answer...


--
Denis Loubet
dloubet@xxxxxx
http://www.io.com/~dloubet
http://www.ashenempires.com


.

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