Can't Explain

For much of the last 40 years, once the three fundamental forces of the strong and weak nuclear force and electromagnetism could be shown to have enough similarity to suspect that in high-energy conditions they might very well be a single force, physicists have searched for a Grand Unified Theory or a Theory of Everything.

Such a theory wouldn't actually explain everything, but it would combine those three with the fourth fundamental force, gravity. And such a theory might allow for a quantum theory of gravity, something which has also eluded scientists.

Over those years, quite a few theories have been floated, some of which have more plausibility than others. And while many of them are able to make their mathematics work, they have yet to produce any experimental confirmation. Even the exotic concepts of string theory, which posit as many as 12 different dimensions, make some predictions about the observable universe. If such and such a thing happens, a theory suggests, then the theory is a plausible explanation for it. Even stronger evidence would suggest that the theory is the most plausible or even the only plausible explanation.

So far, though, none of the proposals for a Theory of Everything have been able to make such predictions. That hangup either pushes scientists back to the drawing board to start over completely or try to tweak an almost-got-it type of theory to make it work. Sabine Hossenfelder, who is fast joining John Polkinghorne as one of my two favorite physicists, suggests another possiblity. There is no theory of everything and gravity can't be reconciled with the other three forces in any situation which human beings could experimentally create or imaginatively dream up.

Dr. Hossenfelder doesn't say there is no such theory or that no one will ever find or deduce it. She says that a Theory of Everything isn't necessary right now in order to do physics and explore the universe. The standard model accounts for the three quantum forces and General Relativity accounts for gravity and we find ourselves able to observe and explain much of what we see going on according to those frameworks.

As for the quest for a Theory of Everything, it may not be possible to supply one at the current level of human technology. Some kind of dramatic breakthrough might allow us to design and conduct experiments at energy levels magnitudes higher than we can now, but until then the candidates for the Theory of Everything are as much philosophy or even theology as they are science. That last sentence, by the way, is mine and not something Dr. Hossenfelder says. But admitting that we're not there yet in terms of our ability to construct a unified theory could free up a lot of powerful scientific gray matter to tackle other matters. It's just that scientists, apparently like cable news talking heads, won't accept that sometimes "We don't know" is a chronic -- but not necessarily debilitating -- condition.