We’re all familiar with the Fundamental Forces of Nature: Electromagnetism, the Weak Nuclear Force, the Strong Nuclear Force and Gravity. They are the Beatles of the Standard Model of Particle Physics and allow us to explain the Universe at the most elementary level. As with the Beatles, each force has their own defining instrument, or as they are better known, their corresponding gauge boson. These bosons, also known as “Force Carriers”, allow the forces to interact with the Universe, just as the Beatles used music to interact with the world. Electromagnetism has the photon, the Strong Nuclear Force has the gluon and the Weak Nuclear Force has the Z and W bosons (that one’s extra talented!).
But, like all bands, there’s one dark horse, one member who doesn’t like to go along with what the band wants. This is gravity, the John Lennon of the Fundamental Forces. Like John Lennon, gravity is the force that is probably the most famous but is also the most controversial when it comes to the forces. This is because gravity doesn’t have an associated gauge boson and this is a problem. See, gauge bosons are particle-like objects that pass between two or more particles to enact forces on each other. They allow for phenomena like magnetism, nuclear fusion and radiation.
But gravity, as we understand it nowadays doesn’t interact with particles this way. Gravitational forces act due to the bending of spacetime. At the Big Bang, all the forces are believed to have been the one force, one band that was going to take over the world, or the Universe for that matter. But as time went on, the Universe’s temperature cooled and its energy decreased and all four forces separated. Physicists have shown that this is probably true through experiments in accelerators such as the Large Hadron Collider (LHC) at CERN being able to approach energies present in the early days of the Universe.
From these experiments, we have been able to unify some of the forces. In 1983, the Electromagnetic and Weak Nuclear Forces were united at energies over 100 GeV. These were the Ringo Starr and George Harrison of the Forces, reliable and easy to get to work with one another without as much effort as the others. At these energies, the forces act as one. LHC experiments haven’t been able to reach the energies required for the unification of the Strong Nuclear Force with the other two yet, but theories, such as the GUT, suggest it is highly possible once we engineer powerful enough accelerators. This is the Paul McCarthy of the Forces, a bit volatile but willing to work when paid enough.
But with gravity, we just don’t know. The energies at the start of the Universe were so monumentally big that we just don’t know if we can do it. We’ve tried to come up with ways we might discover gravitational gauge bosons or “gravitons”. But some theories suggest a Jupiter-sized detector in close orbit of a neutron star would detect only one in the space of ten years. Gravity was the rockstar of physics when Newton proposed his Laws of Gravity but its reputation completely changed when Einstein put forth his Theory of General Relativity. Is Einstein gravity’s Yoko Ono? Will gravity ever be unified with the other forces or is it doomed to never return to how it was in the good old days? Let me know in the comments below.
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A lot of information for this blog was gathered through reading A Brief History of Time by Stephen Hawking and The Sky at Night by Patrick Moore and Chris North.
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