The dust is beginning to settle – a new particle has been discovered using the Large Hadron Collider. Discovering new particles of nature is not an everyday occurrence and we are reasonably entitled to proclaim that this is the arrival of the Higgs. We aren’t certain, though: more careful examination of the particle’s properties is needed before we can be – we want to know that it has spin zero and that it couples to other particles with a strength that is in proportion to their mass. Answers to those questions and to many others will follow over the coming months and years. This is all very important – but why? Why is the discovery of a new type of particle something to get so excited about?
The best way to appreciate the beauty of a discovery is to get stuck in, learn some mathematics and see those dazzling equations in all their glory. Examples include Einstein’s equation of general relativity, Dirac’s equation for the electron and the Lagrangian at the heart of the standard model of particle physics. But it is possible to get the gist of what a physicist means when they speak of a beautiful theory without the hard work. Before doing that let’s be clear – this is a kind of life-changing beauty. This is not titillation and it is not a conceit of the human mind – it leaves everyone who has studied these things with an overwhelming sense that the natural world operates according to some beautiful rules and that we are very fortunate to be able to appreciate them. To spend time contemplating this is thrilling. We believe that these are universal rules that would also be uncovered by sufficiently intelligent aliens on a distant planet: we are discovering something at the heart of things.
The situation is extreme enough for greats such as Einstein and Hawking to invoke God. But they were certainly using the word to express the intimate relationship between the human mind and the glorious intelligibility of the universe. It feels like a personal thing – like we are relating to something very special. This is the sense in which Hawking once spoke of knowing the mind of God, but it doesn’t really have anything to say about the existence or not of a creator, and Id be surprised if science will ever have anything much to say about that.
A beautiful piece of physics is elegant. An elegant theory has the capacity to explain many apparently different things simultaneously – it means that rather than needing a library full of textbooks to explain the workings of the universe we can manage with just one book. In fact the situation is better than that – the fundamental equations that underpin all known natural phenomena can be written down on the back of an envelope. That is really true – the nature of light, the workings of the sun, the laws of electricity and magnetism, the explanation for atoms, gravity and much more can all be expressed with breathtaking economy. It is like we are in the business of discovering the rules of an elaborate game and we have figured out that they are really very simple, despite the rich variety of phenomena we see around us. Uncovering the rules of the game is exciting, and maybe one day we will know all of the rules accessible to us – that is what people are referring to when they speak about a “theory of everything”. It sounds very arrogant to speak about a theory of everything but those in pursuit of it are not so dumb. They are well aware that knowing the rules is not the whole story. A child can know the rules of chess but exploiting them to produce a classic game is far from easy. This is an illustration of how simple rules can lead to something very complicated. The study of complex phenomena and their emergence is another very exciting area of modern physics.
Beautiful physics is also compelling. It is as if nature possesses a kind of perfection that is guiding us in our pursuit of the rules of the game. The result is that we very often have little or no choice when figuring out what equations to write down. That is a very satisfying situation to be in. It means that when we try to figure out an equation to describe something important, such as how an electron behaves, instead of saying, “Well… the equation might look like this… or maybe it looks like that… or…” we have no choice and nature simply screams out at us: “The equation simply must look like this.” Dirac’s beautiful equation is just like that – it describes the electron and predicts the existence of its anti-matter partner, the positron. Our understanding of the origins of inter-particle interactions (aka force) is like this too – starting from a very dull theory in which particles do not interact with one another (so no stars or people) and the idea that nature is symmetric in a certain way we are absolutely compelled to introduce interactions into the theory – the symmetry forces our hand and dictates how the theory should look. Symmetry is so often the device that leads to elegant and compelling theories. A snowflake is symmetric – if I draw part of one you could probably do a good job of sketching the rest. Likewise equations can be symmetric, which means we only need part of one in order to figure out the rest. In the case of particle interactions, symmetry means we can infer their necessary existence starting from the simpler equations that describe a world without any interactions at all… and that really is beautiful.
The genius of Peter Higgs and the other physicists who proposed the existence of the Higgs boson was to take the idea of symmetry seriously. The same symmetry that gives us “for free” the theory of inter-particle interactions also appears, at first glance, to predict that nature’s elementary particles should all be without mass. That is flatly wrong and we are faced either with ditching a symmetry that has delivered so much (although that was not known when the Higgs pioneers were beavering away in the early 1960s) or figuring out an ingenious solution.
-=-The Higgs idea is that solution – it says empty space is jammed full of Higgs particles that deflect otherwise massless particles as they move – the more a particle is jiggled by the Higgs particles the more it has mass. As a result, the fundamental equations maintain their precious symmetry while the particles gain mass. Faith in the idea that nature’s laws should be elegant and compelling has, yet again, delivered insight. The Higgs discovery is the jewel in the crown of particle physics and a worthy testament to nature’s astonishing beauty.
Read more: www.guardian.co.uk