The universe is a vast expanse full of untold mystery and endless surprises… but,
in the twenty-first century, we might finally be beginning to understand its innermost workings.
We might finally be getting to grips with why some things are and some things aren’t.
This is Unveiled, and today we’re exploring the extraordinary question;
Did scientists just prove that light creates matter?
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In his 1905 seminal work, “Does the Inertia of a Body depend Upon Its Energy Content?”,
Albert Einstein further outlined to the world his theory of relativity - completely overturning the
laws of physics at the time, and our view of the universe. Among the many statements
the great physicist made, he’s perhaps most well-known for the equation E = mc2,
describing how mass and energy relate. Of course, that equation - and how the world viewed
it - would go on to be shaped by events at the end of World War Two… where, through atomic bombs,
we saw how a tiny amount of mass could trigger the release of an incredibly large amount of energy.
But, for today’s video, we’re focussing on the flip side of that, and we’re instead making mass
from energy. Albeit a tiny amount of mass, from an incredibly large amount of energy.
Scientists at the Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (otherwise known
as the RHIC) have reportedly shown how this could be possible if we look into the light.
The prospect of creating matter by smashing light particles (or photons) together
has intrigued scientists for years. It was first theorized in 1934 as the Breit-Wheeler process,
by the American physicists Gregory Breit and John Wheeler. At the time it was believed impossible
to prove it, however, as an experiment to do so would be extremely difficult to set up and
even more difficult to execute… but close to a century later, and it’s perhaps no longer quite
as impossible as it had at one time seemed. In fact, there have now been various setups
aiming to show how the Breit-Wheeler process is achievable… although, still,
scientists debate whether we’ve ever truly seen it in action here on Earth. But more on that later.
At the centre of almost all Breit-Wheeler-seeking experiments is the use of particle accelerators.
These incredible machines have triggered more and more headlines in recent times, and for good
reason. Specifically here, they enable the high energy conditions required to potentially set off
the process of turning light into matter. Simply put, a particle accelerator (unsurprisingly)
accelerates elementary particles, such as electrons, protons, and photons, at extremely
high energies. The powered-up particles travel inside a vacuum, inside a huge pipe,
while detectors within the accelerator then record and reveal what happens when the beamed particles
either hit a target or collide together. In 1997, researchers at the Stanford Linear
Accelerator in America would demonstrate one of the first examples of light
seemingly being converted to matter. The team propelled electrons along a straight beam line
to create high-energy photons. These photons, after multiple collisions, then created electrons
and their positive counterparts, positrons. The photons had, in effect, created matter.
The slight controversy surrounding the experiment, though, is one that has followed most others ever
since… with questions raised over how the photons used were generated to begin with.
Ideally, the Breit-Wheeler process expected the creation of matter from photons alone,
no prior electrons necessary. Direct experimental proof of this type,
however, has remained elusive as it requires the photons to be extremely energetic,
on the level of gamma rays. But we just don’t see that kind of energy on Earth,
and a gamma-ray laser is one technology that we’re currently lacking. So, scientists have continued
to seek ways around this stumbling block. For example, one design of a particle accelerator that
could theoretically smash genuine photons together was proposed by a team at Imperial College London,
in 2014. It involved shooting charged electrons into a slab of gold to create high-energy (but
this time sperate) photons… and then smashing those photons into each other,
to again create subatomic matter. The experiment was reportedly started in 2018, but there are as
yet no reports of a successful observation. And now, physicists at Brookhaven National
Laboratory believe that they’ve beaten their contemporaries to the punch… and that they
have achieved the first direct evidence of matter created from light. At the centre of
the Brookhaven experiment are heavy ions of gold (meaning, particles of gold that have
been stripped of their electrons, to create a powerful positive charge). In the experiment,
the full details of which were made public in July 2021, the charged ions were accelerated to 99.995%
the speed of light… inside the Relativistic Heavy Ion Collider. An offshoot of this process was that
what’s been labelled a cloud of photons appeared around the gold ions… and, so, when the ions
passed close enough by one another, those extreme high-energy photons did collide. The collisions
themselves weren’t actually detectable, but the resulting generation of electrons and positrons,
the resulting creation of matter, was. And, therefore, the claim is that the Breit-Wheeler
process has finally been demonstrated. Although, again, not everyone agrees.
The problem still rests with how the Brookhaven method generated the photons it used... because
some scientists believe the photons produced here aren’t necessarily real. They’re considered,
by some, to be virtual… as, when triggered in this way (following the acceleration of heavy
ions of gold) they pop in and out of existence only very briefly. The Brookhaven experiment,
then, according to some, still isn’t an example of two standard photons colliding, even if the
process has been shown to create matter. Naturally, the Brookhaven team has defended
its method, and what’s more has shown how the photons they’ve recorded can justifiably
stand in for so-called real photon particles. One reported way to do this is by measuring the angles
between the electron-positron pairs (between the particles of matter) that are created. In short,
the angles can be translated to reveal how real or virtual the photons are… and, when physicists at
Brookhaven painstakingly zoomed in on more than six thousand of their electron-positron pairs,
they found that they were consistent with what we’d expect to see from real photons.
Nevertheless, the scientific community has remained cautious about the results.
We’ve taken another significant step towards demonstrating the Breit-Wheeler process,
for sure… but not everyone is convinced that we’ve truly proven it. Particle physicist
Lucian Harland-Lang of the University of Oxford, for example, has commented that
the experiment is “strictly speaking… one step removed” from the true Breit-Wheeler process.
As such, the debate on the validity of this experiment has skirted toward an arguably even
bigger topic than the creation of matter, moving instead towards the definition of reality itself.
What’s real and what’s not? From a scientific perspective, and just in general? The results
from Brookhaven appear to prove how we can smash photon into photon to create genuine matter…
but because the nature of those photons can be called into question, that incredible occurrence
is perhaps still not as pure as it could be. Regardless, we’re still considerably further along
toward capturing the Breit-Wheeler process once and for all. And the experiment has added to our
growing knowledge. Because, ultimately, the quest to show beyond doubt this phenomenon in action…
this emergence of matter from light… is also a bid to recreate what was happening in the
first moments at the birth of our universe. We of course know that matter did arrive,
that something did come from seemingly nothing, and there are plenty of reasons and theories as to
why (and how) that unfolded. But it’s thought that the Breit-Wheeler process accounts for at least
part of the story, birthing some of the earliest electrons and positrons into the cosmos.
Moving forward, the coming years are set to be crucial as we further flesh out our understanding
of the subatomic world that guides everything, and the most fundamental laws of physics. But perhaps
the most significant change for this field, in particular, won’t happen until we develop gamma
ray lasers. These would truly represent tech of the future, but only then will we be producing
light that’s as genuinely real as the light allowing you to view this video, while also
harbouring the extreme energy required to trigger the Breit-Wheeler process at all. And so, the work
continues… but that’s how scientists - on some level - have proven that light can create matter.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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