1948: Casimir effect - The book of science

Casimir effect
One atmosphere
“Sewing Vacuum”
Commentary

Hendrik Casimir, Dirk Polder quantum mechanics

Casimir effect

Van der Waal forces
Conductors and dielectrics
Quantum harmonic oscillators
Virtual photons
Hendrik Casimir
and Dirk Polder
studied what happens
between two conductive plates
extremely close together
in a vacuum.
The energy inherent
in empty space
results in the Casimir–Polder force,
a physical force
that pulls the plates together
or pushes them apart.

One atmosphere

When the plates are separated by only ten nanometers
the Casimir-Polder force is equal to about one atmosphere.
If you think one mere atmosphere
is only a small amount of pressure, consider
Otto von Guericke’s Magdeburg experiment
in which two copper hemispheres
put together and pumped free of air
could not be pulled apart by teams of horses.

“Sewing Vacuum”

Space isn’t ever empty.
Out of perturbations of a quantum field,
invisible particles appear,
and before they merge and disappear,
sew wedding dresses
and knit baby blankets, bibs, and booties.
What pulls these particles
from the fabric of timelessness?
What sufficiently perturbs
nothing at all
if only temporarily
into something old, something new,
something borrowed, something blue?
The answer to this mystery
is probably not the shop
on Fifteenth Avenue and 56th Street
that sells sewing machines
and vacuum cleaners.

Empty space is empty only in that all excitations of the quantum field—all spins, polarizations, energies, masses, and momentums—eventually cancel each other out; however, in the short term, between two plates close enough together, we see that the term “virtual particles” describes particles that may be transient but are as real as other particles.