Re: [asa] LHC, TOE, and the limits of knowledge

From: George Murphy <>
Date: Wed Sep 17 2008 - 09:27:12 EDT

A few comments on this -

1) Here's an amusing, though relativistically simple, question. (In fact I was asked it during my grad school oral comp.) Since the source for electrons at an accelerator like SLAC are emitted at random, & since the target is a few km away down a pipe only a few cm in diameter, how does any significant fraction of those electrons manage to make it to the target?

2) A slightly pedantic comment on "increase of mass with velocity": That is an old-fashioned, though not "wrong," way to speak about relativistic dynamics. But if it's to be used it's necessary to remember that in such a formulation the "longitudinal mass" of a particle differes from its "transverse mass." The former is mG^3 while the latter is mG, where m is the rest mass and G = 1/(1 - v^2/c^2)^(-1/2). Many popular discussions incorrectly use the transverse mass when talking about straight line motion.

(It's also worth noting that use of the increase in mass with speed to explain the fact that a particle can't be accelerated to speeds greater than c is, while not completely off base, misleading. Actually this is a purely kinematic consequence of the Lorentz transformation.)

3) On Burgy's earlier comment, I'm not sure that it was Clarke who first suggested multi-stage rockets. I need to dig out Willy Ley's book on the history.

  ----- Original Message -----
  From: Don Winterstein
  Sent: Wednesday, September 17, 2008 4:44 AM
  Subject: Re: [asa] LHC, TOE, and the limits of knowledge

  As I recall, Larry Johnston also told us that the klystrons in the Stanford Linear Accelerator are made to operate as if the speed of electrons at injection is exactly the speed of light. If it were not, the particles would not be accelerated. "Accelerated" in this case does not mean increase in speed but in mass. In other words, the electron speed differs from the speed of light all along the 2-mile traverse by a negligible amount.


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Received on Wed Sep 17 09:28:06 2008

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