In early October, the Royal Swedish Academy of Sciences awarded the 2022 Nobel Prize in Physics to Alain Aspect, John Clauser and Anton Zeilinger for their pioneering experiments in quantum science, and in particular a mystifying phenomenon called entanglement. Don’t worry, we’ll start at the beginning.
To understand the weird world of quantum mechanics, one must first accept that different rules apply to things that are extremely small. Subatomic particles like photons and electrons do not behave as macroscopic objects would, and this divide between classical and quantum mechanics has spawned entire fields of research. For example, a critical axiom of classical mechanics is the principle of locality, which states the intuitive knowledge that objects can only be affected by their immediate surroundings. Any impact on one object from a distant one requires some type of physical mediator between them. The discovery of tiny particles that exchange physical forces held consistent with Albert Einstein’s famous result of nothing travelling faster than the speed of light. However, it was Einstein himself in 1935 (along with Boris Podolsky and Nathan Rosen) who co-write the seminal paper predicting quantum entanglement from particles that appeared to communicate faster than the universal speed limit. They referred to their perplexing result as “spooky action at a distance”, and concluded that our understanding of physics was incomplete.
The authors were, of course, right, and since then experiments have attempted to observe this “spooky action”. The basic principle is that information about a subatomic particle can be linked to information about another, such that a change in the state of one triggers a corresponding instantaneous change in its entangled partner. Quantum mechanics is based on the probabilities of what a particle’s state may be, and detecting what actually is requires large equipment operating under classical principles. This ruins the quantum state in a process known as “collapsing the waveform”. This was caricatured with Erwin Schrődinger’s thought experiment involving his famous cat who, were he placed into an opaque and sound-proof box with a lethal-dose of poison to be released at a random time, was effectively simultaneously alive and dead. This was Schrődinger’s exasperated attempt to illustrate the problems with the mainstream “Copenhagen interpretation” of quantum mechanics using macroscopic objects. Only once the box is opened and the fateful feline’s status confirmed would its quantum waveform collapse. As an aside, a strong competitor to the Copenhagen interpretation was proposed by Hugh Everett in 1957 called the “many worlds theory”, suggesting that anytime an objectively real observation is made from a set of quantum possibilities, parallel universes are created to account for all possible outcomes. In this case, Schrődinger’s cat would be alive in one universe and dead in another. This idea has been used copiously in science fiction – think Donnie Darko, Rick and Morty, and Everything Everywhere All at Once. I told you it was weird.
Quantum particles have an esoteric but experimentally interesting property called spin. Spin is described using numbers that indicate its strength and direction, and these must complement each other within entangled pairs. If one photon spins clockwise, its entangled partner must spin counter-clockwise with equal speed. This means that if the spin of one is measured, the spin of the second could be inferred based on the knowledge they must be complementary. This circumvents the need to “collapse the waveform” and preserves the quantum state of the system.
This crudely simulates a transfer of information that technically travels faster than light. Whether it actually does is a topic of debate, as the link between the two spins had to be preconceived. The “hidden variables” theory suggests that the particles always contained some secret information on what spin they (and their pair) have, whereas traditional quantum mechanics suggests they contain all potential spins until measured by an observer. One result of Aspect, Clauser and Zeilinger’s Nobel Prize-winning research was to determine that the latter interpretation is correct.
Entangled particles have been shown to communicate their existing states instantaneously from the surface of the earth to a space station, but encoding new information into the system remains a challenge. One fascinating phenomenon is that of “quantum teleportation”, where an entangled particle collides with a new particle and transfers information on its partner (like passing on gossip), thus entangling particles that have never been in contact. This could significantly increase the range of quantum communication. Quantum computing is under intense research to replace the 1s and 0s of traditional transistors with “qubits” which can take a combination of multiple quantum states simultaneously, thus encoding far more information at once. This speed at which this theoretical machine could operate would break current digital security models, as they rely on practically-unsolvable mathematical operations to obscure passwords on current hardware, which would quickly become solvable on a quantum computer. Researchers in quantum cryptography are searching for new security mechanisms to mitigate this.
The work of these brilliant physicists has been rightfully recognised by the Royal Swedish Academy of Scientists. We’re still finding out everything quantum physics could do for us. But highlighting the most unintuitive, abstruse and bewildering theories from the frontiers of physics can only ignite the childlike sense of wonderment that sustained our desire to cross oceans, develop agriculture and cast bronze. The firelight legends in science are there to ensure our children will always have new stories to write.
