Re: Faster Than Light Travel (sorry, kinda long...)

>Andy Skinner writes:
>
>@:) Transmission as tachyons?	I don't know anything about tachyons
>@:) except they were supposed to move faster than light.  I don't even
>@:) remember whether they were theoretical, hypothetical, or
>@:) fictional.
>
>  They used to be mostly theoretical and I think now they're
>considered mostly fictional.

This is true. Some physicists in the '30s IIRC showed that there is the
mathematical possibility within the laws of quantum mechanics for
particles
that travel faster than light. However, even those theories conclude
that
tachyons, if they exist, could not penetrate the light barrier. Thus it
would
be impossible for them to slow to below light speed. This is a direct
result
of the theory of relativity that claims that such a process would
require
an infinite amount of energy for any particle with mass.

To say that they are considered fictional is not entirely true either.
The word tachyon doesn't describe a single type of particle, but a
family
of particles. There is now a small movement that thinks that some
neutrinos travel faster than light. Neutrinos have traditionally been
one
of those families of particles that have caused physics a great deal of
problems as they are extremely difficult to detect. And there seems to
be far fewer than predictions indicate there should be. If it is
possible
to show that some of them _are_ tachyons, then it could explain a great
deal, hence the attraction of the theory.

>@:) Aren't the effects of gravity supposed to be effective immediately
>@:) across distance?
>
>  Actually no, or at least that's what I hear.  Gravity is probably
>transmitted by particles like the other forces.

Another horrible particle: the "graviton". There is absolutely no
real evidence that gravity is transmitted by particles. Again, it
is an attractive theory, so gets much attention. Especially from
people who believe in the Grand Unified Theory (GUT). However, it
is equally likely that gravity is unique among the fundamental
forces. In answer to the original question, gravity "travels" at
the speed of light. If the sun were to suddenly disappear, the earth
would happily continue on course for about 8 minutes, so pack your
bags now ;-).

>@:) So could you postulate some sort of gravitational signal that
>@:) would be instantaneous?
>
>  No but - there are certain weird situations in which things appear
>to happen faster than light.  In particular there's this quantum
>thingie (can you tell this isn't my field?) where you take apart an
>object (usually a particle) and the parts retain a certain
>relationship to each other that they got from being the same particle
>(spin or charm or something - I get the impression it's a conservation
>law).	Anyway the idea is that this relationship is continuously
>maintained no matter how far apart the particles are moved.  So if you
>move them a billion light years apart, and change one, the other
>changes as well, instantaneously.  Sounds like FTL communication to
>me.

An even more bizarre effect is the transmission of light. In order for
light to be transimtted within a closed universe, there must exist
both transmitter _and_ absorber. So how does the emmitter "know" there
is something there before it sends its signal? R.P. Feynman developed
a theory for this mechanism, but I can't exactly recall it. A professor
of mine had the priviledge of meeting him and asked him about it.
His comment was "Oh, that stuff is just crazy, I don't know what I was
thinking". So who knows...

I think that it might clear some things up if I explain something of
modern physics. There are three major theories that have withstood
all tests of their validity, and upon these nearly all physics is
based: General Relativity, Quantum Mechanics, and Thermodynamics.
Refutation of these theories must be done with the utmost care, for
people will go to great lengths to challenge any theory that invalidates
them. To simply state that great people have been wrong before is, IMHO,
not enough. I'm not saying that these theories are unassailable, just
that you must be very sure of what you are doing in the attempt. I also
want to stress that they by no means explain everything, but everything
they have tried to explain has withstood serious scientific scrutiny.

>  Unfortunately it's not.  But don't ask me why I just read this stuff
>in Scientific American - I pay taxes for other people to understand
>it.  If anyone here is a quantum physicist and can tell me why no
>information is transferred in the above situation I'd love to know.
>
>@:) I really gotta be quiet.  I don't know what I'm talking about.
>
>  Never stopped me.
>
>-joachim

Me neither. Discussion is a very important part of learning.

Tony.