Guest Post by Stefano Marcellini
What is the most romantic physics tattoo? Dear readers, you all clearly love physics (right?) and perhaps you even love another person to the extent you want to symbolise that love forever.
We see it often: the Dirac equation pulled in to symbolise that undying love. But be careful before you commit to it on your skin, as it is not quite as you see it described online… Here’s a little extract of a phenomenon we see repeated across different websites:
‘She said: ‘Tell me something nice!’ He replied: ‘(δ + m) ψ = 0’.
It is the Dirac equation, the most beautiful equation in physics. It describes the phenomenon of quantum entanglement. The principle states that: ‘If two systems interact with each other for a certain period of time and are then separated, they can no longer be described as two distinct systems, but somehow become one system: what happens to one of them continues to influence the other, even if they are kilometres or light years apart'.
According to Dirac's reasoning, if two people enter into a relationship, over time growing close romantically or platonically, and are then separated, they cannot be defined as two different subjects but somehow become one. Even after their separation, they will continue, for better or for worse, to retain within themselves a part of the other. Forever. Regardless of the distances, experiences of each individual, people who have interacted with each other will influence the other ‘till death do us part’. Is Dirac's equation therefore the scientific formula for eternal love?
Where has this come from? Dear readers, this is nothing but a copypasta of epic proportions! Let us untangle this particular knot for you:
Until a few years ago, the Dirac equation was known only to physicists. It is indeed a beautiful equation, and it describes the behaviour of 1/2 spin particles taking into account the theory of relativity. One of its most famous consequences is the presence of negative solutions, which led to the theoretical prediction of the positron, which is the antimatter equivalent of the electron with a positive charge. It was discovered experimentally a few years later.
Quantum entanglement is one of the most fascinating and strange phenomena among the consequences of quantum mechanics. Two particles originating from a single initial state manifest a correlation between their properties that only manifests itself when a measurement is performed on one of the two particles. At that point, instantaneously, no matter how distant the two particles are, the other particle also assumes a corresponding state.
Believe us - we would know! It is a phenomenon we study a lot, and in 2024 CMS and our sister experiment ATLAS published some groundbreaking work on the entanglement of top and anti-top quarks, the heaviest of the fundamental particles - you can read a little more about that here.
Dirac's equation, therefore, has nothing to do with quantum entanglement at all: it is a completely made-up combination. Aside from anything else, it is the equation for a single particle, and entanglement implies by definition the presence of more than one particle. It takes (at least) two to entangle-tango.
Furthermore, IF this were to be all true, why should the holism of the Dirac equation always be positive? Why is it assumed to be an ~entanglement~ of love rather than any other emotion?
Indeed, given the varied dynamics of couples, why should only love remain forever, regardless of distance, and not the mutual throwing of plates and glasses, the shouting in anger, and all the variegated vocabulary that goes with it? Does that mean that the mythical Dirac equation would not work? Would there be no ‘we are and will always remain one’, in that case?
If we were to be pedantic about it, quantum entanglement applies to quantum (microscopic) systems in very specific circumstances, and disappears very easily when these systems interact with the macroscopic world. In short, entanglement doesn't apply to you!
But don’t be upset, dear reader, all this should reassure you! It means that there is no other equal to you, anywhere in the universe - and that should be embraced.
