It was 1964, before man had gone to the moon, when Peter Higgs first published a paper proposing a mechanism detailing how the property of mass came about in the Universe. Nearly half a century passed before there was any experimental verification of his ideas, and it took the biggest and most complicated machine ever built to procure it. It is perhaps the single most important confirmed breakthrough in Physics this century. But what exactly is this “Higgs Boson” that captured attention the world over?
Basically it’s a quantum excitation on the Higgs field, which is one that breaks certain gauge symmetries of the electroweak field. Simple.
For those who have absolutely no idea what that means, the following is much more accessible explanation that doesn’t require a degree or two in theoretical Physics.
In particle physics there are 16 well established fundamental particles – fundamental here meaning that they cannot be broken down into any further particles and these 16 particles can combine in a variety of ways to make up everything in the entire universe. Together with one equation which governs exactly how these particles interact, they comprise the excitingly named Standard model, which describes everything in the Universe, the way it moves and essentially everything – except Gravity. Both the Standard Model and its problems are themselves worthy of stand-alone pieces but that’s for another time.
The properties of these 16 fundamental particles and where they come from are all very well understood, with the exception of mass. Before Higgs, there was no established mechanism showing where particles got their mass from, it just was. Trying to explain exactly why stuff that just seems to appear out of nowhere can exist and where it comes from is not a bad definition of Physics, so naturally people began working out some mechanism by which particles, and by extension everything in the universe, could have mass. Peter Higgs is the man credited with being the first to solve this problem, though like so many other famous problems, there were several others who figured it out at very similar times.
In practice of course the mechanism is exceptionally complex and is governed by similarly complex equations. It can be simplified somewhat to give an understanding of what’s going on without all the maths parts. The central part of the theory is an all permeating field that spans all the Universe. This may sound like a strange idea and it is, put it’s fairly common in Physics. The most common example is probably the Earth’s magnetic field: for every point on and around the Earth there is an associated number, which is tells your compass where to point. Another possible way of looking at the concept of a field is a room. At every point in this room there is naturally a temperature. Collectively, all the data on the temperature at each and every point is a temperature field. The Higgs field is fairly similar except that it spans the entire Universe and deals with mass rather than magnetism or heat.
So now we have a set of fundamental particles and a field that covers the whole Universe, but how do these two ideas lead to particles having mass. Well, one analogy of the Higgs field involves syrup. Imagine a room full of syrup. With nothing better to do, and presumably lacking pancakes, you decide to walk through the room. As you set out on your walk, you begin to feel the syrup resisting your attempts to pass through it, dragging you backwards and slowing you down. It is as if you are heavier; i.e. have a greater mass than normal. That’s a very simplified picture of how the Higgs field interacts with particles, slowing some down more than others to give some particles more mass than others. It is important to note that in reality the Higgs field does not work by slowing down things that are moving, but on all particles in the field. The field of course spans the whole Universe, so it acts on all particles everywhere, and all objects, including the screen you are reading this on and you yourself, which is why everything in the Universe has mass.
Except that last part isn’t quite true. There are two particles, the photon and the gluon, that do not interact at all with the Higgs field, so they are massless particles. This in turn means they travel at the speed of light, which is handy in the case of the photon as photons constitute light.
So there it is, particles have mass as they interact with an all permeating Higgs field in a way that can be thought of as objects moving through syrup, except without the particles doing any of the moving part. Hang on a minute though, this piece isn’t titled the Higgs field, it’s called the Higgs Boson, so what’s that?
To answer this, a slightly closer look at those 16 fundamental particles is required. 12 of these particles are termed fermions and it these particles that make up everything you have ever known. But without the other 4 particles the Universe would be a pretty boring place – just a load of particles sat about, not forming atoms, stars or moons for humans to go walk on, or possibly the Universe would be entirely devoid of any form of matter. These 4 particles are known as Bosons, and they each mediate a fundamental force. The photon and the gluon together represent the electroweak force (previously thought of as the electromagnetic force and the weak nuclear force which were subsequently shown to be two aspects of the same thing), while the Z and W particles represent the strong nuclear force.
Like the Higgs field, these forces have fields. Excitations in these fields are what cause the bosons to spring into being to mediate the force associated with the field. The Higgs boson is the same in this regard; it springs into being when the Higgs field is sufficiently excited. Note that excitation here does not refer to a literal state of being excited but rather is a term commonly used in Physics relating to the energy level something sits at.
So there it is – the Higgs Boson.
As for why it took so long to verify this model experimentally and find the Higgs Boson, the reason can be explained fairly easily. To produce particles, it is necessary to smash other particles together at sufficiently high speeds and in just the right manner. For the Higgs Boson, the energy levels required for this process are far larger than for any other particle previously discovered, as the Higgs Boson has a much much larger mass than almost all other particles, some 126GeV, compared to say an electron at 0.000511GeV (eV, or electron volt, is a unit of mass used for subatomic particles, while G is the prefix for giga or 1x10^9. 1eV = 1.78x10^-36 kg = 0.00000000000000000000000000000000000178kg).
Of course there are many things we still do not know about the Higgs, including its exact mass, whether or not it has multiple manifestations just to name a couple. There are also numerous questions left unanswered questions of the Standard Model itself, and it is these that Physicists at the Large Hadron Collider at CERN are now turning their attentions to. Those asking what practical applications the discovery of the Higgs are have missed the point of Physics and are likely going to be disappointed for a while to come, as there are no obvious ways that the Higgs can be used practically. That most certainly does not mean there won’t be any, after all Heinrich Hertz, the man credited with discovering radio waves, famously said “I do not think that the wireless waves I have discovered will have any practical application”. Of course they turned out to be one of the key building blocks in the formation of the modern world.
Hopefully, somewhere along the way, this has provided a reasonably clear explanation of what the Higgs Boson is, where it comes from, what it does and how it fits into the wider framework of the Standard Model of particle Physics. Perhaps that first technical definition of the Higgs Boson looks a much more manageable now, but if it doesn’t its worth knowing anyway, as it’s a great way to pass yourself off as intellectual at dinner parties.