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Hendrik Casimir predicted the weak force between two plates in a vacuum which
we now call the
Casimir
effect in 1948. Steven Lamoreaux at the Los Alamos National Laboratory
in New Mexico has just succeeded in measuring the force of the effect, using
a torsion pendulum. The result: a force within 5% of the predicted level
was measured, a very good result indeed.
The importance of this is that any
time
machine that we can now predict will need to use two sets of plates
experiencing the Casimir effect. But until we have a working time machine
available to see what happens, the best we can say is that it is early days
yet.
The Casimir effect is only measurable when two parallel plate are set up,
just a fraction of a millimeter apart in a vacuum, and the result is that
a weak force then operates to push them together. Empty space is not really
empty, according to quantum theory. Instead, virtual photons are continually
popping into existence and then disappearing again.
In the narrow gap between the plates, the only photons which can exist are
those with wavelengths which area equal to the gap distance divided by an
integer. All other photons are excluded from the gap, and this means there
are more photons pressing on the outside of the gap than on the inside, producing
the force we call the Casimir effect. According to Lamoreaux, the force he
measured, with a separation of just 0.75 micrometer, was about one billionth
of a newton.
This is the third major breakthrough in physics that has been achieved with
a torsion pendulum, after a wait of almost two centuries. Charles Coulomb
used a torsion pendulum to measure the forces between electrical charges
in 1785, and soon after, Henry Cavendish had used a similar device to measure
the force of gravitation in 1798.
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