If someone breaks a chocolate bar in half, they get two smaller pieces. If you cut a string, two shorter strings appear. But What would happen if we tried to split a photon?
The question seems absurd. A photon is an elementary particle, one of the fundamental building blocks of nature. It is not made up of smaller components that can be separated. However, a team of physicists from the University of Oslo decided to consider precisely that impossible scenario: what would happen if we could cut a photon as it passes through space? The answer, published in Physical Review Lettersit was not what was expected. Instead of producing two fragments of light, calculations predict the appearance of a strange quantum mixture which can contain anywhere from no photons to a potentially infinite multitude of them. From zero to infinity in an instant.
Let’s go in parts, what exactly is a photon? Photons are the particles that carry light. Every time we turn on a lamp, observe a star or receive a signal from our mobile phone, enormous amounts of photons are involved. But in the quantum world a photon is not simply a “sphere of energy”, it also behaves like a wave. This wave-particle duality is one of the most famous and puzzling features of quantum mechanics. and it is precisely that wave nature that allowed the authors, led by Johannes Skaar, to imagine how to “cut” a photon.
The first step was to theoretically analyze what would happen if a single photon passed through a type of ultrafast gate. From our everyday intuition we would expect the result to be a weaker photon or, simply, a certain probability that the photon disappears. But Quantum mechanics had a surprise in store.
When Skaar’s team applied the equations of quantum field theory, they discovered that the “clipped” photon does not transform into two parts. In its place appears an extremely complex superposition of states. Some contain a single photon, others contain several. And, in theory, the mathematical description includes states with an arbitrarily large number of photons. This does not mean that infinitely many observable photons suddenly appear. The probability of finding huge quantities of them is extraordinarily small.
However, the mere presence of these states in the mathematical solution surprised the authors themselves. The key is that the quantum vacuum is not really empty. Although we imagine space as absolute nothingness, modern physics describes a vacuum full of microscopic fluctuations: during minimal intervals of time, particles and fields appear and disappear that cannot always be studied adequately. And, if that were not enough, Closing the gate extremely quickly alters these vacuum fluctuations. Which also modifies any experiment.
But perhaps the most disconcerting result is something else. If an observer looks only at the region in front of the gate, he or she will see something that looks like a normal photon. If you look at the posterior region, you will simply see emptiness. However, When the complete system is analyzed, that intricate quantum mixture formed by a multitude of possible states appears.
It is as if the same reality showed two completely different faces depending on where you look. At first glance it might seem like a mathematical game without practical applications. But Skaar’s team suggests that the new “snipped” photons could help develop theories where cause and effect relationships are better defined. In addition, the study opens the door to studying what would happen when applying similar ideas to other fundamental particles, such as electrons. In the quantum world, Trying to split an elementary particle can end up revealing a multitude of particles that, according to all our intuitions, should never have been there.