What would happen if you attempted to break an elementary particle—especially a force-carrying particle such as a photon, which carries the electromagnetic force—into smaller pieces?
According to physicists’ common understanding of these fundamental building blocks of the universe, it shouldn’t even be possible, since it was long held that they can’t be broken down any further. But that wasn’t the case for physicist Johannes Skaar and colleagues, who in a new study appearing in Physical Review Letters, argue that something rather strange would happen if one were to try breaking this rule of physics.
Based on the team’s findings, attempting to slice up a photon into two halves wouldn’t just create two smaller photons: it would potentially lead to the creation of many more of them—perhaps even an infinite number—seemingly out of nothing.
Splitting Elementary Particles
Elementary particles are the tiniest bits of stuff that make up our universe, and they come in two varieties: matter particles (or what scientists call fermions), which include the various manifestations of quarks and leptons, and force carriers (Bosons), such as gluons, the enigmatic Higgs Boson, W and Z Bosons, and, of course, photons.
Given that such fundamental particles exist both as a single particle and as a wave, it has long been insisted that splitting them would be impossible. This prompted a unique question for Skaar and his team: even if it seems impossible, what might happen if one were to try to slice an elementary particle in half, and succeed?
To help envision the answer to this question, the researchers worked off the premise of a photon passing through a kind of optical shutter involving a mirrored system turning on and off at extreme speeds, which would allow it to block only part of a single pulse of light.
In theory, if the pulsing mirror system could operate at fast enough speeds, it could catch a single photon in mid-pulse, thereby slicing a portion of the particle’s extended wave. Logically, they then wondered what would happen next.
A Deep Dive into Infinity
Answering that question took Skaar and his colleagues into the realm of infinite superposition. By applying quantum equations that correspond to the electromagnetic field associated with the photon, and how it behaves at the quantum level, the researchers were able to gauge the response of the photon’s quantum state to its close encounter with the fast-switching shutter.
Then things got really weird.
Rather than just splitting the photon in half, a superposition of different states—each containing an infinite number of photons at once—was the result. To explain why this occurred requires a look at one of the many unusual and seemingly counterintuitive aspects of quantum mechanics.
Specifically, quantum mechanics informs us that there is far more to empty space than the nothingness we perceive: within such voids are an ongoing series of electromagnetic fluctuations. Hence, as the mirrored shutter is rapidly operated between states, it interferes with the natural, invisible fluctuations, which generate entirely new photons.
“The result is neither another photon nor a mix of a photon and a vacuum,” Skaar and his colleagues write. “Instead it is a superposition and mix of photon numbers up to infinity.”
Despite this odd phenomenon, merely looking at the areas to either side of the shutter’s location of operation would reveal nothing out of place, at least on the surface. Nothing, that is, apart from a single photon on one end, and what would appear to be nothing on the other.
“This state is rather complicated,” Skaar and colleagues note, “but nevertheless locally equivalent to a single photon or vacuum to the left and right, respectively, of a narrow transition region.”
The High Strangeness of the Quantum World
For Skaar and his team, the experimental results of their investigation provide a unique look at how differently the quantum world behaves when compared to our everyday experiences, where solid, Newtonian physical rules apply.
More fundamentally, the new research also points to more intriguing questions, such as how information is contained within a space, and also with regard to the measurement of quantum systems.
Going forward, the team hopes to look at similar conditions that might give rise to unusual physics, including what the outcome of a similar system involving more than one photon might be.
The team’s recent paper, “A Truncated Photon,” was accepted for publication in Physical Review Letters, and a preprint version appeared at arXiv.org.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.