>> Ok, sanity check time.  I've had another one of those disturbing 
>> thoughts..

>> ... So how can a "timeless" particle interact with anything?  It 
>> would either
>> always be interacting, or never be.

> DAVID!
> I think you are catching what Russell has..

I am honoured by the compliment!
It was a compliment, wasn't it?

And Dave has touched on one of the great beauties that I return to 
marvel at from time to time. And fail to understand, frame of 
reference wise or otherwise. viz: All photons are joined together in 
an instantaneous intercommunicating 'web' throughout the universe. 
They all dwell in the eternal now. They know no time or essentially 
space. It is far easier to make slightly (or very) incorrect 
statements about them which help to illuminate, or confuse, or both at 
once, than to make categorical statements of fact. Well educated 
particle physicists (whose ranks I am far from, and will never be 
counted amongst) may believe differently. They may just possibly be 
correct. Just possibly. A photon leaving Alpha Centauri Proxima 
(second closest star to earth, one of the two pointers to the Southern 
Cross for fortunate Southern Sky viewers, and another leaving Sol 
(closest star to earth) at the same "time" will arrive at a viewer at 
the same 'time' as each other and instantaneously, and will never 
actually 'go' anywhere, as everywhere is everywhere else and there is 
no here and there and there is no time - all from their own 
perspective of course, and is there a more valid one? For us there 
will be a time difference between their arrivals of about 4 years.

There. Was that poetic enough for such an occasion ? :-).
I just know someone is going to complain about at least one part of he 
'physics' back there.

And fwiw and AFAIK and IMHO and I'm happy to be corrected if wrong - 
re other statements made:

All massless particles always travel *AT* C, never near it. They can 
only travel at C and MUST do so to be massless. They all have zero 
rest mass and their apparent masses are related to their energies in 
any frame of reference except their own. (! :-)).

Just because the speed of light varies in different media it doesn't 
mean it isn't constant in the way that constant is meant by those who 
use the term usefully :-). Cerenkov radiation (which even budget 
equipped amateurs can detect and measure from incoming gamma rays) is 
the result of photons (usually the ones termed Gamma rays)(photons on 
speed) desperately adjusting their terms of reference to conform to 
reality. (ie extra lower energy radiation 'shed' to allow the high 
energy photon to 'slow down'. ) It's also the cause of the nice 
actinic blue glow in radioactivity storage pools (as simulated in 
suitably budgeted movies) as photons adjust themselves to the 
discovery of the pool.

C and the speed of light are one and the same. Declaring that they are 
different may make everything make a lot more sense, but reality 
doesn't know about this :-).

Photons are 'real' particles - but they have no mass so they (like 
particles which have rest mass) cannot be accelerated to the speed of 
light BUT with photons they are already there and with the others they 
can never get there.

Expansion of the universe or no (shaky ground here) nothing moves 
faster than C relative to anything else in out universe *in a manner 
that can be usefully or meaningfully expressed in terms which 'make 
sense' in our reality*. ie you can (and apparently do) have particles 
which are coupled instantaneously at any distance and you can make 
measurements which prove that this has been the case or even that this 
is currently the case or even that it will be the case BUT you cannot 
use that knowledge to make any use of the FTL or instantaneity of the 
coupling.

Some (or all) flavours of Neutrinos *may* have negative rest mass, and 
I hope that they do. If they do then they must travel faster than 
light. There have been various measurements made from time to time 
that suggest that this may be the case but the results tend to fade 
away like the grin on the Cheshire Cat when attempts are made to 
verify observations.

Exercise for fun:
Those with glazed eyes may wish to stop reading about here :-).
Usefulness of anything beyond here is highly likely to be zero for 
many values of zero.
It is easy to plot classical energy of a particle (or starship or ...) 
with relativistic mass as it's velocity increases from zero through 
the speed of light and beyond. Note the energy minima at V > C and how 
the energy then climbs again and how there are 3 points at each energy 
level - one below C, one slightly above C (AFAIR in the 1-3 C range 
and another at around ?20 C. Think about what would happen if you 
could quantum tunnel from below C to either of these two equal energy 
points. Ignore the imaginary nature of the mass for practical 
purposes. Note that there is a velocity below which there are no two 
 >C "jump points. This is the McMahon quantum hyperdrive stages 1 and 
2. (Not to be confused with Niven's similarly named system which had 
no explanation given).

Note that the velocity difference between the equal energy points for 
<C and 1st >C decreases as one approaches C and becomes vanishingly 
small as C is approached. How to achieve the tunnelling is left as an 
exercise for the student.

Note that to accelerate above C from the first >C jump point you need 
to *decrease* energy, and to decrease speed you need to increase it. 
One could become 'lost' at > C if energy was lost after jumping. 
Objects which jump and then lose energy all increase velocity until 
reaching the energy minimum point at about ?2C, so one may expect a 
lot of tachyon traffic at about that point.

As the first "jump point" isn't reached until about 0.6C (AFAIR - long 
time since I worked this out) this effect will never be discovered 
accidentally in everyday life ;-).

Enough :-)


        Russell




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