Five Brilliant Ideas For New Physics That Need To Die, Already
Ethan Siegel

Most of these theories have been around for a long time, and they haven’t gotten us anywhere. They don’t need stakes through their hearts, but it’s time to look at some newer ideas or to simply accept the universe as it is. As a reader of Sabine Hossenfelder’s Backreaction blog, I’ve been increasingly drawn to her point of view, that so many of these theories are motivated by things other than trying to understand the universe, usually by aesthetics.

Why is there any concern about the gap between the Planck mass and the mass of the standard particles? It’s a matter of pretty. Aesthetics argues that the ratio should be about one, not ten to the blah-blah-blah. There is no data or mathematics behind this. One is pretty. Ten to the blah-blah-blah is not pretty. It won’t get the cute guys asking it to dance.

The argument about the initial conditions at the birth of the universe seems pointless. Coming up with some theory, like inflation, to explain the initial flat universe just produces a new set of initial conditions that in turn have to be explained. What is this all about? The current initial conditions aren’t pretty enough. The hope is that if we look a bit further back in time, the conditions might be prettier. That’s the heuristic. Go back in time until there is pretty.

WIMP theories sound fascinating with their exotic particles, pairs of particles, even a shadow universe, but why? Recent work measuring the tenuous clouds of gas connecting galaxies has been revealing an awful lot of ordinary matter. Maybe we don’t need exotic matter. Maybe we need better ways of detecting already existing matter. Those strands of gas and lumps of stale intergalactic pizza are just not as pretty as exotic particles.

Some years back, Science magazine had an article about the “haunting beauty” of the Kaluza-Klein synthesis of unified gravitation and electromagnetism. The math was beyond me, but I could understand the haunting sensation. The solution seemed so close, as if hidden by a thin lace curtain, kind of like the dear departed at a seance. As at a seance, the curtain has proven thicker than anticipated.

Again, I’m not saying we should abandon the search for new physics wholesale. We know that general relativity and the standard model are incomplete, maybe even wrong. We do need to stop and take inventory. We also need to consider the fact that the answer might not be as pretty as we would like.

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