Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site ho95b.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!ho95b!ran
From: ran@ho95b.UUCP (RANeinast)
Newsgroups: net.space
Subject: Re: Speed of Light and beyond
Message-ID: <415@ho95b.UUCP>
Date: Fri, 17-May-85 15:18:51 EDT
Article-I.D.: ho95b.415
Posted: Fri May 17 15:18:51 1985
Date-Received: Sat, 18-May-85 01:37:42 EDT
Organization: AT&T-Bell Labs, Holmdel, NJ
Lines: 43

>> I know this is impossible, but what would happen if...
>> 
>> A ship could exceed the speed of light?  When the space shuttle crosses the
>> sound barrier, there is a sonic boom.  If it were possible to cross the
>> "light barrier", what phenomenon would result?
>
>A lot of heart attacks in the physics community, for one. :-)

>More seriously, as I recall it, the basic answer to this from relativity
>(if we ignore tachyons, which are a messy case) is "does not compute".
>Faster-than-light speeds involve logical contradictions (notably, loss of
>the normal cause-and-effect relationship) according to special relativity.
>This being the case, the theory basically cannot give coherent predictions
>about such a situation.
>
>I'd be very interested to hear this contradicted by somebody who knows
>more about the subject...

It's known as Cerenkov radiation.  It turns out that the speed of light
depends upon the medium through which it travels (the speed in vacuo
is the ultimate limit), so you can have particles going very near the speed
of light in a vacuum enter water (where the speed of light is much slower)
and create a "sonic boom", except, of course, it is light that is emitted.
This slows the particle rather quickly.

Regarding tachyons, the idea first came up about 15 years ago when it
was noticed that the relativity equations had no problems with faster-
than-light if an object ALWAYS went faster then light, so tachyons
were proposed.  Despite possible mechanisms for how a tachyon might
be observed, there is at present NO experimental evidence for their
existence.  Quantum field theory also has a few problems if tachyons
exist, since the mass (imaginary for tachyons) of the particle
defines an integration path in complex space for the calculation
of certain measureable quantities.  I realize the last sentence is
not real clear, but I'm afraid I can't explain it much better.



-- 

". . . and shun the frumious Bandersnatch."
Robert Neinast (ihnp4!ho95b!ran)
AT&T-Bell Labs