ScienceDaily (Dec. 8, 2010) —
Under just the right conditions — which involve an
ultra-high-intensity laser beam and a two-mile-long particle accelerator
— it could be possible to create something out of nothing, according
to University of Michigan researchers.
The scientists and engineers have developed new equations that show
how a high-energy electron beam combined with an intense laser pulse
could rip apart a vacuum into its fundamental matter and antimatter
components, and set off a cascade of events that generates additional
pairs of particles and antiparticles.
"We can now calculate how, from a single electron, several hundred
particles can be produced. We believe this happens in nature near
pulsars and neutron stars," said Igor Sokolov, an engineering research
scientist who conducted this research along with associate research
scientist John Nees, emeritus electrical engineering professor Gerard
Mourou and their colleagues in France.
At the heart of this work is the idea that a vacuum is not exactly nothing.
"It is better to say, following theoretical physicist Paul Dirac,
that a vacuum, or nothing, is the combination of matter and antimatter
— particles and antiparticles.Their density is tremendous, but we
cannot perceive any of them because their observable effects entirely
cancel each other out," Sokolov said.
Matter and antimatter destroy each other when they come into contact under normal conditions.
"But in a strong electromagnetic field, this annihilation, which is
typically a sink mechanism, can be the source of new particles," Nees
said, "In the course of the annihilation, gamma photons appear, which
can produce additional electrons and positrons."
A gamma photon is a high-energy particle of light. A positron is an
anti-electron, a mirror-image particle with the same properties as an
electron, but an opposite, positive charge.
The researchers describe this work as a theoretical breakthrough, and a "qualitative jump in theory."
An experiment in the late ’90s managed to generate from a vacuum
gamma photons and an occasional electron-positron pair. These new
equations take this work a step farther to model how a strong laser
field could promote the creation of more particles than were initially
injected into an experiment through a particle accelerator.
"If the electron has a capability to become three particles within a
very short time, this means it’s not an electron any longer," Sokolov
said. "The theory of the electron is based on the fact that it will be
an electron forever. But in our calculations, each of the charged
particles becomes a combination of three particles plus some number of
The researchers have developed a tool to put their equations into
practice in the future on a very small scale using the HERCULES laser at
U-M. To test their theory’s full potential, a HERCULES-type laser would
have to be built at a particle accelerator such as the SLAC National
Accelerator Laboratory at Stanford University. Such infrastructure is
not currently planned.
This work could potentially have applications in inertial confinement
fusion, which could produce cleaner energy from nuclear fusion
reactions, the researchers say.
To Sokolov, it’s fascinating from a philosophical perspective.
"The basic question what is a vacuum, and what is nothing, goes
beyond science," he said. "It’s embedded deeply in the base not only of
theoretical physics, but of our philosophical perception of everything
— of reality, of life, even the religious question of could the world
have come from nothing."
A paper on this work is published in Physical Review Letters.
Sokolov is a research scientist at the Space Physics Research
Laboratory in the Department of Atmospheric, Oceanic and Space Sciences.
Nees is an associate research scientist at the Center for Ultrafast
Optical Science and an adjunct associate professor in the Department of
Electrical Engineering and Computer Science. Mourou is the A.D. Moore
Distinguished University Professor Emeritus of Electrical Engineering
who is currently with the Institut de la Lumiere Extreme in France. Also
contributing is Natalia M. Naumova, with the Laboratoire d’Optique
Appliquee in France.
This research was supported in part by the Department of Energy.