Physicists at Brookhaven National Laboratory have achieved a groundbreaking experiment, creating matter from light by demonstrating the Breit-Wheeler process. Using the Relativistic Heavy Ion Collider, they accelerated heavy ions to generate nearly real photons, leading to the formation of electron-positron pairs. This experiment showcases Einstein’s E=mc² equation in action, aligning with predictions for transforming energy into matter. While these virtual photons act similarly to real ones, the experiment is a crucial step towards proving the process with real photons when technology advances to create gamma-ray lasers.
Physicists
have reportedly created matter from pure light for the first time, showcasing
one of Einstein’s most renowned equations in action.
Albert
Einstein’s well-known E=mc² equation suggests that by colliding two
sufficiently energetic photons, or particles of light, you could produce matter
in the form of an electron and its antimatter counterpart, a positron.
This
phenomenon, first described by American physicists Gregory Breit and John
Wheeler in 1934, has long been one of the most challenging to observe in
physics — largely because the photons involved would need to be extremely
energetic gamma rays, and gamma ray lasers are not yet available. Alternative
experiments have shown matter being formed from multiple photons, but not in
the direct one-to-one way necessary to definitively prove the effect.
However,
researchers at the Brookhaven National Laboratory in New York now believe
they’ve discovered a workaround. Using the lab’s Relativistic Heavy Ion
Collider (RHIC), they’ve been able to generate measurements that closely align
with predictions for this unusual transformation.
“In their paper, Breit and Wheeler already realized this is almost impossible to do,” Zhangbu Xu, a physicist at Brookhaven Lab, said in a statement. “Lasers didn’t even exist yet! But Breit and Wheeler proposed an alternative: accelerating heavy ions. And their alternative is exactly what we are doing at RHIC.”
Instead
of accelerating photons directly, the team accelerated two ions — atomic nuclei
that have been stripped of their electrons and thus carry a positive charge —
in a large loop, guiding them past each other in a near-collision. Since these
ions are charged particles moving at nearly the speed of light, they carry an
electromagnetic field with them, filled with not-quite-real ‘virtual’ photons
“traveling with [the ion] like a cloud,” Xu explained.
Virtual
particles are temporary particles that momentarily appear as disturbances in
fields between real particles. They differ from real particles as they can have
mass (whereas real photons do not). In this experiment, when the ions nearly
collided, their clouds of virtual photons moved so rapidly they behaved as
though they were real. These virtually-real photons then collided, resulting in
a very real electron-positron pair that the scientists observed.
To
verify the Breit-Wheeler process as closely as possible using virtual
particles, the researchers needed to confirm that their virtual photons were
acting like real ones. They did this by detecting and analyzing the angles
between more than 6,000 electron-positron pairs generated in their experiment.
When
real particles collide, the resulting products should emerge at different
angles compared to collisions of virtual particles. In this experiment,
however, the secondary products of the virtual particles scattered at the same
angles as those from real particle interactions. This enabled the researchers
to confirm that the particles they observed were behaving as if they were
generated by a real interaction, successfully demonstrating the Breit-Wheeler
process.
The
team also measured the energy and mass distribution of the systems. “They are
consistent with theory calculations for what would happen with real photons,”
Daniel Brandenburg, a physicist at Brookhaven, said in the statement.
Still,
despite appearing to act like real particles, the virtual photons in the
experiment remain undeniably virtual. This raises the question of whether the
experiment truly demonstrated the Breit-Wheeler process, but it remains a
crucial first step as physicists work toward developing lasers powerful enough
to demonstrate the process with real photons.