Why Scientists Are Talking About a Revolution
Physics looked in danger of stagnation. That might be about to change.
Recent weeks have seen a flurry of excitement in the world of particle physics. Two experiments — one in America, one in Europe — have strengthened earlier signs of unexplained physics. Though neither set of results is yet strong enough to claim a certain discovery, physicists seem reasonably confident more evidence will arrive before long.
This is big news for particle physicists. The field has long looked in danger of stagnation. The current fundamental theory — neatly summed up as the “standard model” — works almost perfectly, but has some gaping holes. Those holes, which include things like gravity and dark matter, indicate that the theory is probably wrong somewhere.
Quite where, though, has remained elusive. Outside of those gaps, the standard model has been remarkably successful. The things it describes — fundamental particles like quarks and electrons — behave exactly as it predicts. The things it can’t explain — black holes, gravitons and big bangs — are hard to measure in a laboratory.
Two decades ago physicists were convinced that more powerful experiments would reveal its weaknesses. In anticipation, theorists went wild. They came up with dozens of theories, from string theory to supersymmetry, which could replace the standard model. Most of these ideas predicted various things — new particles, forces or interactions — that the standard model forbade.
The Large Hadron Collider, switched on in 2009, provided the most powerful test of the standard model yet achieved. Armed with their new theories, scientists confidently predicted all sorts of things would turn up, from black holes to extra dimensions.
The result was disappointing. No matter how much engineers increased the power of the collisions — the LHC now operates at twice the power it did in 2010 — the standard model remained stubbornly intact. No black holes have appeared, nor any higher dimensions. Apart from the Higgs Boson — a particle predicted by the standard model — few other big discoveries have been made.
All that has made theoretical physicists look a bit foolish. The idea of supersymmetry — once considered the strongest contender to replace the standard model — has faded away. No clear frontrunner has emerged to replace it.
Instead physicists have been probing oddities in experimental results, in the hope of finding some discrepancy with the predictions of the standard model. Now, two signs of such discrepancies have cropped up together. The first was found at the Large Hadron Collider, where quarks appeared to decay in a strange way. The second, at Fermilab in Chicago, concerns muons, a heavier sister to the electron.
The details are complicated, and too long for this post. If you are interested, check out good descriptions here and here. For now, though, it suffices to say that these results do seem to contradict the standard model. They might, in other words, give physicists an opening to prise out a more fundamental theory of nature.
We have been here before. The stagnation in particle physics has left many scientists feeling a bit desperate. Previous claims of new physics have led to similar flurries of activity, including a period in 2015 when hundreds of papers were published over a claim that turned out to be a statistical fluke. Is this time any different?
So far it is hard to say. Neither experiment has yet produced results that fully confirm their discoveries. Both still have a lot of data to analyse, and that may see the discrepancies confirmed or, perhaps, fade away. Even if the results are confirmed, it doesn’t necessarily mean a problem with the standard model.
The experimenters may have done something wrong, or messed up one of the fiendishly complicated equations of the standard model. If so, the data will be worthless. But if not, the results open the door to new physics. That might mean new particles, new forces and new ideas. Given the dearth of such opportunities over the last two decades, physicists can perhaps be forgiven for getting excited.
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