There are a few equations in physics that are somehow able to make their way into mainstream media. E=mc^2 may be the most known of the A-list celebrity equations. The concept behind this equation may be a bit less well known. 

Einstein realized that energy and mass are two forms of the same thing, with the speed of light acting as the conversion factor between the two. This is a fancy way of saying that if you, like the neutrino particle, had the ability, you could convert a bunch of your mass to energy and take off at an amazing velocity. 

Energy takes a lot of forms. There is the energy of motion, and there is potential energy like what is stored in a stretched rubber band or a child at the top of a slide. When particle colliders like CERN collide fast-moving particles together, it is from the mass of those particles and the energy of their motion that researchers are able to convince rare particles like the Higgs boson or the top quark to pop into being. In the moment of the collision, all the motion and all the mass becomes a tightly confined bundle of energy available to make new stuff.

Over the decades, researchers have slammed particles together in a number of different ways to try and understand both what particles can exist and what holds particles together. In general, there are fundamental particles – like the electron, the neutrino, and the quark – that can’t be broken down into anything any smaller, and there are particles like the proton, neutron, or pion that are made from combinations of quarks. Particles that are combinations of quarks have additional energy: the binding energy that holds them together. This makes those protons, pions, and neutrons appear to weigh more than they should because their mass is actually made up of the mass of their quarks and the energy holding those quarks together.

Does your brain hurt yet?

This is where E=mc^2 gets weird. Mass and energy together describe a particle, and sometimes mass gets measured in units of energy, and sometimes that energy appears as units of mass.

Back in the 1950s, it was postulated that a three-way exchange – what’s called a triangle singularity – can be used to explain how pions, which are made of a quark and an antiquark, can snap apart in a collision and transform into new particles with the final result being a new pion and a new four-quark particle called a tetraquark. This is a three-step process with known energies and outcomes, and in new experiments at CERN, researchers smashing pions into hydrogen atoms were able to see the exact predicted reaction.

This is one of those times where the science has everything; it feels like magic to see energy and matter interchange. It is always amazing when a theory turns out to be true. And there were amazing crashes.

More Information

University of Bonn press release

“Triangle Singularity as the Origin of the a1(1420),” G. D. Alexeev et al., 2021 August 18, Physical Review Letters