Grand Unification may be a dead-end for Physics
“It may still turn out that grand unification is correct, and that it’s an important step on the road to a Theory Of Everything: the ultimate holy grail of many theoretical physicists. But it may also turn out that nature doesn’t unify at high energies, and that our biases towards simplicity, elegance and more unification is completely wrongheaded and has nothing to do with our physical Universe. In science, as in all things, we cannot afford to be driven by our own preconceptions of how things ought to be. Rather, we owe ourselves to view the Universe exactly as it is, and to listen to the story it tells us about itself.”
One of the greatest discoveries of the 20th centuries was not only that there were just four fundamental forces describing all of nature, but that two of them — the electromagnetic and the weak force — unify into a single “electroweak” force at high energies. Given the equivalences between electric charges in the strong nuclear force sector and the electroweak sector, could there be a grand unification between those as well? In a great theoretical development, Grand Unification Theories (GUTs) became all the rage, making bold predictions like additional bosons, flavor-changing neutral currents, and proton decay. But in the more than 30 years since their inception, the ideas of GUTs have all fallen flat, implying the question of whether the entire concept of unifying forces and interactions into larger groups and structures is completely wrongheaded.