Re: Length Contraction

[Marlyn Jakub <mjakub@PHYSICS.OTAGO.AC.NZ>]

At 01:18 PM 12/14/00 -0700, you wrote:
> I am wondering if someone could tell me what experimental evidence there has
> been to confirm length contraction stated in Einstein's Special Theory of
> Relativity. Thanking you in advance.
> - Abby Abul Kalam
> Community College of Denver
One application of "length contraction" is to the permanent magnets designed
for the Wiggler (coherent light amplifier) of the Free-Electron Laser
devices. Since the energetic electrons can be made to emit some of their
energy by accelerating them, the wiggler uses a series of alternating
magnetic fields to accelerate a cluster of electrons, thereby causing the
"synchrotron-emission" of light waves. If the electrons see a seed laser
light and the corresponding frequency of magnetic fields, then they amplify
the coherent frequency light of the seeding laser.

The calculations required the permanent magnets to be a few millimeters
thick, as seen by the electrons travelling near the speed of light. However,
by using the electrons from an accelerator which makes them very close to
the speed of light, the magnets are able to work in spite of being many
centimeters thick. The electrons are "seeing" the many centimeters as just a
few millimeters ...thanks to their relativistic speed and the
length-contraction phenomena.

There was an article in Scientific American in l989...it's the issue with
the wiggler shown on the cover.

Marlyn Jakub