Mass = L/c2. Albert Einstein said so in 1905. A simple replacement of L (light energy) with the letter E (all energy), move “c2” to the other side of the equal sign, and we get “Ta da!” the familiar equation: mc2=E
Or, better yet: E = mc2
Thanks to Gary Larson, Bugs Bunny and elementary school, most people are aware of this bit of physics, and even that Einstein is to be blamed for it.
What does it mean? It means that Mass is ultimately equal to Energy, which was demonstrated in the detonation of the first nuclear bomb. It also theoretically means that Energy can be converted into Mass, but until recently physicists hadn’t been able to figure out how to it. We’re not only years away from a good old-fashioned Star Trek food synthesizer, we can’t even make protons from photons.
In 1934, Gregory Breit and John Wheeler played with the idea that matter could indeed be created from light by smashing together two photons. They might not be able to organize molecules into apples or pears, but the photon car-wreck could create an electron and a positron. It has been 82 years, and physicists at the Imperial College of London have finally put together plans for a “photo-photon collider” — a machine that could actually force two photons to crash into one another. Sort of.
It’s not as easy as you’d think. Photons belong to a class of subatomic particles known as bosons, and bosons are known for their peculiar ability to share the same quantum state. It’s like being able to be in the same place at the same time. In reality, Star Wars light sabers wouldn’t smash into each other, they’d “swish” pass right through one another like good light beams should. Fermions, particles like protons and electrons, aren’t so fortunate. They take up their own space and they don’t like to share it. It’s easy to smash together two particles that take up their own space. It’s not so easy to crash together two particles that can pass right through each other… like a light wave.
Photons do interact with charged particles like electrons and protons, though. Occasionally, a photon can waffle into a particle-antiparticle pair like an electron and positron, allowing one of the mates in this subatomic pair to capture another photon. A soon as the electron and positron recombine (Pow!), they release two photons. This all happens in fractions of a second, and it appears as though two photons just bounced off each other. This “photon-photon scattering” has been observed in the Large Hadron Collider (LHC) at CERN in Switzerland, but nobody’s been able to systematically force the interaction.
A research team led by Oliver Pike at the Imperial College of London has figured out a way to increase the number of photon-derived electron-positron teams that can interact with other particles. Their article in Nature Photonics proposes the building of a machine called the “photon-photon collider” which uses several steps, starting with accelerating electrons with a laser and pounding them into a bar of gold. This first step will create a beam of light immensely more intense than sunlight. The machine would aim this beam at a hohlraum, a hollow cave of gold, to create a thermal radiation field that releases another beam of light that will intersect with the first beam. The electrons and positrons formed during the interaction of the light beams would be detected as they left the hohlraum, and should produce far more pairs of particles than the occasional chance encounter made in the CERN LHC.
The design is out; now the researchers have to build the machine and test it.
“Although the theory is conceptually simple, it has been very difficult to verify experimentally,” Pike said. “We were able to develop the idea for the collider very quickly, but the experimental design we propose can be carried out with relative ease and with existing technology… The race to carry out and complete the experiment is on!”
It’s a massive challenge for physicists, but once they conquer it, their accomplishment will still come several years too late. Organic machines have long been capable of taking light energy and converting it into matter. In fact, these organic machine are capable of organizing molecules into the shapes of apples and pears and figs. These organic machines are called “trees” and they are in many respects similar to the organic machines called “raspberry bushes” that provide delicious materials for jams and ice cream topping.
You’d think that we could throw light, carbon and water together into some sort of food-like substance too, but there will be no vending machines producing foods that were “photo-synthesized” any time soon. As great as our technological advances have proved, manipulating subatomic particles is still the expertise of the Creator alone.
“Observing Light-by-Light Scattering at the Large Hadron Collider” — Physics Review