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(Don't) Blame The Messenger

In the course of the theoretical and experimental evolution of particle physics, it was realized that each force not only needs some kind of charge, but also some kind of messenger particle to communicate between the particles that carry the charge. These messenger particles are referred to as the "fundamental bosons" or the "force bosons". If two electrons are placed a short distance apart then they repel due to the nature of like charges in the electric force. But how does each electron know that the other is present to begin with? That's the job of the electric force bosons. It is envisioned that carrying a particular type of charge causes a particle to continually emit the associated bosons of the force in question. This does not cost any net energy, so the particle can do this continually. If a boson of a certain force from a certain particle meets another particle that obeys the same force, then the boson will interact with it and give rise to the force's effect. That second particle would have been emitting its own bosons the whole time too, some of which will interact with the first particle. In this way there is a force signal between the particles which tells them what they have to do to satisfy the force, such as move apart if they are two electrons.

The required force bosons have all been experimentally verified in particle decay data, which supports the theory of all particles and their interactions that has come to be known as the "Standard Model". The electric force is mediated by a boson called the "photon", and the strong force is mediated by a set of bosons called the "gluons". There is also another force which allows certain interactions that are not provided by either the electric or strong forces, which is referred to as the "weak force" and which is mediated by two types of boson labelled as "W" and "Z". An outstanding puzzle is that the most familiar force of all, namely gravity, does not fit in the existing Standard Model picture, but if it can be incorporated then it too will have a mediating boson, which has been preemptively called the "graviton".

Photons and gluons are both massless, but the W and Z bosons are not. In order to explain the mass of these particles it was necessary to propose a further boson in the theory, called the "Higgs boson", which is not associated with any force at all. This boson comes from space itself, and interacts to varying degrees with different particles, not only the W and Z, and gives rise to their attribute of mass. This may not be the mass mechanism for all particles, but it is thought to be so for most of them.

The Higgs boson was proposed in 1964 as an answer to a theoretical problem, allowing for the mathematics of the Standard Model to be cooked up in just the right way. The predicted observations that such a particle would provide were so subtle that the theory creators never believed it would be discovered, given the state and trends of technology at the time. However, about 50 years later it turned out that technology had actually evolved enough for the Higgs boson to be indirectly observed. The announcement was made in 2012 that two detectors, called ATLAS and CMS, which operate at the Large Hadron Collider at the CERN laboratory in Geneva, had strong enough evidence that the Higgs boson was indeed found. This was a resounding success for both theory and experiment, and provided the Standard Model with its crowning keystone.