Quantum Entanglement: the strange and the spooky

In William Shakespeare’s Hamlet, the titular protagonist famously tells his loyal friend that “There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy.” Shakespeare’s words would prove prophetic for the early 20^th century, when a group of iconoclastic Physicists shattered the long established Newtonian view of science by discovering the weird world of quantum mechanics.

The first Physicist to prove that Newton’s laws were incomplete was Albert Einstein. In 1905, while working as a patent clerk, Einstein released 3 groundbreaking papers on Special Relativity, Brownian Motion, and the Photoelectric effect. All three would act as the bedrock for the theory of quantum mechanics which would be developed over the next few decades.

Quantum mechanics is the fundamental physical theory that describes the behaviour of matter at the subatomic level. The theory is notoriously difficult to understand. Some of its implications include the fact that matter and light exists simultaneously in a particle and wave state, and that quantum objects can exists in two states simultaneously (known as a superposition). Perhaps the most unsettling consequence is quantum entanglement.

Entanglement is a phenomenon in which particles become correlated so that the state of one cannot be fully described without reference to the other, regardless of the distance between them. In their 1935 paper “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?”, Einstein, Podolsky, and Rosen raised concerns about this feature of quantum mechanics. Einstein argued that no physical influence should travel faster than light, yet entanglement seemed to imply instantaneous connections between distant particles. He famously referred to this as “spooky action at a distance.” A term more commonly associated with the supernatural, like the ghostly apparition of Hamlet’s father, it reflected Einstein’s unease that the quantum world might be far stranger than human intuition allows.

But unlike poltergeists, ghouls, or gremlins, this spooky phenomenon is an observable fact. In 1964 John Bell came up with his famous Bell inequalities to test the predictions of entanglement. In 1981 the first experimental test of Bell’s ideas took place, he was proved correct, and has been proven correct many times over.

Entanglement has vast implications for the future of technology, particularly in the world of quantum computing. Quantum computing relies on qubits (as opposed to regular bits) which exist in a superposition of 0 and 1 (on and off simultaneously). The entanglement property allows for potentially rapid processing across vast distances which could revolutionise cryptography and the entire computing industry as we know it.

If all of this leaves you somewhat perplexed, fear not. Richard Feynman once said that “if you think you understand quantum mechanics, you don’t understand quantum mechanics.” So despite our lack of understanding, we can rest assured that we are in good company.