Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.space
Subject: Re: Speed of Light and beyond
Message-ID: <5608@utzoo.UUCP>
Date: Sat, 18-May-85 19:33:43 EDT
Article-I.D.: utzoo.5608
Posted: Sat May 18 19:33:43 1985
Date-Received: Sat, 18-May-85 19:33:43 EDT
References: <415@ho95b.UUCP>
Organization: U of Toronto Zoology
Lines: 20

> >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.

Sigh, I knew about Cerenkov radiation, and if I thought people would be
this picky [I know, I know, I've done it myself sometimes...] I would
have qualified all references to "speed of light" with "in a vacuum".
I thought it was reasonably clear from the original posting that the
question referred to spaceships, i.e. operations in a vacuum.  Now, if
somebody can tell me whether an FTL starship would emit Cerenkov radiation
in a vacuum, *that* would be interesting.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry