The Higgs Boson: A journey, not a destination.
Preliminary ideas: Watch for the way these crop up in what follows.
Every story has a precursor so it always hard to know quite where to start but I will begin this story with the story of light.
Isaac Newton (1642-1727) had reason to believe that light consisted of particles but by the end of the 18th century there was much stronger evidence to suggest that light was waves. (it diffracted and interfered as waves do). But waves require a medium to wave in eg sound travels through air but not through a vacuum. Throughout the 19th century two stories coalesced to deal with this medium. One was the search for the “Ether” (also “luminiferous ether” and also aether). The other was the rise in our understanding of electricity. Another background story was the business of how forces could act “at a distance”, eg gravity acts without touching as do magnets and electric charges.
Michael Faraday (1791-1867) was academically uneducated but a wonderful investigator. He proposed the idea (model) of a field. This was the idea that space was filled with a region of influence. Thus he could speak of a gravitational field, an electric and a magnetic field. James Clerk Maxwell (1834-1879) gave a mathematical structure to this idea and showed that all light was in fact perturbations in the electro-magnetic field. He was also able to predict the existence of light that could not be seen (the full electromagnetic spectrum including infra red, ultra violet, radio waves and X-rays).
So at the end of the 19th century light was firmly established as waves (and radio was invented). At about this time the photoelectric effect was being investigated. This means that when light of certain frequencies was shone onto certain metals, electrons were ejected from the surface. This phenomenon had some disturbing features which were explained by Einstein in 1905. It required that light seemed also to possess a particle nature. The particles of light came to be called photons. It was not that light was no longer a wave, but that it also showed particle properties. The simple model of light being a wave or particle was too simple. Light appeared to be both things.
In 1923 Louis deBroglie (1892 -1987) suggested that if light showed a particle nature maybe particles, especially electrons and other subatomic particles would show a wave nature.
Yet another strand of the story, not mentioned so far is, “what is the nature of matter”. At the end of the 19th century most were convinced of the existence of a limited number of different types of atom. The elements of the periodic table were the alphabet from which everything in the Universe was made. That atoms had internal structure became evident in 1897 with the discovery of the electron. In 1911 Rutherford proposed the nucleus and in 1929 Chadwick found evidence for the long suspected neutron. Rutherford and Bohr and the community of Physicists developed our current understanding of the atom. It required de Broglie’s insight of the wave nature of particles. Wave-particle duality.
Just as Physicists were settling to the existence of protons, neutrons and electrons an apparent “zoo” of odd new fundamental particles began to make themselves known. (pions, positrons and others).
In 1935 Hideki Yukawa (1907-1981) proposed a different model for forces that acted across space (previously modelled by fields). His model involved the idea of “exchange particles” (that came to be known as gauge bosons). Thus, a repulsive force was mediated by the repelling objects, throwing particles at each other and attractive forces by the mutual grabbing of the exchange particles. The idea was that if perturbations in the electromagnetic field could be modelled as particles called photons, maybe the other field forces could have their own particle nature.
The endeavour to find a structure to this slew of particles and forces resulted in what has become known as “The Standard Model”. This model was built by several theorists during the 60’s and 70’s. It has been very successful because it has made predictions that have found experimental support. The model has predicted that the various particles will have certain masses. Since, from Einstein, mass is equivalent to energy, the task of revealing these particles has required the slamming together of the sub-atomic particles with sufficient energy to break them apart and expose them. The experimental support has come from the giant atom smashers like the LHC at CERN.
In the early 1960’s the question of why objects have mass was debated. In particular the property of inertia which is the “difficultness of getting goingness” and the reluctance to stop, of objects. Peter Higgs and others proposed that all of space was filled with a field rather like honey that had the property of resisting changes to motion (no ordinary honey). The details of this Higgs Field are buried in the mathematics of the proposal but it was described as a scalar field because it acted in any direction whereas the other, more well known fields acted in one direction (eg gravity acts towards the Earth.) If such a field existed then it too should have its own gauge boson. This became known as the Higgs particle. In recent weeks the LHC has revealed a particle that has the predicted mass of the Higgs.
When predictions from theory are supported by experiment the confidence in the validity of a model grows. Because the discovery of the Higgs appears to be real, the implications for the deeper study of gravity are immense. There are also implications for the nature of Dark Matter. Our current observations of the mass in galaxies and their centripetal motion convince us that there is more to know about their mass and or gravity. Because the Higgs field speaks of space and of mass there may also be implications for both Special and General Relativity.
Studies of the macroscopic world can lead to useful applications. Water running downhill can lead to irrigation, pendulums can lead to clocks. Applications of the sub-atomic world could never be imagined prior to the search to uncover those mysteries. Computers and mobile phones would be magical to the people of the 19th century. Our desire to know will always precede our ability to utilise that knowledge. In finding the Higgs we have given support to a model but questions remain. We have reached the end of a chapter, but the book contains more chapters. We can properly ask what a Quark is made of and find ourselves on the edge of a chasm of ignorance that swallows us for we too are made of the same stuff of the Universe that is torn apart in the LHC.