The standard model is a theory developed in the 1960s and 70s to describe the physics of all of the known particles and most of the known forces. It was cobbled together as a provisional theory until, presumably, something better came along, but to most physicists’ surprise, it has withstood 40 years of experimental testing, and celebrated the triumph of the discovery of the Higgs boson, the one particle whose existence it predicted.
The theory has known limitations. The one force it does not incorporate is gravity, and it can not account for either dark matter or dark energy. A complete theory of the universe would have to bring together these elements also. But every experimental measurement related to the Standard Model has confirmed it…
...Until quite recently. Recent analysis of some observed particle decays have shown evidence of a breakdown in a tenet of the standard model—though it’s not the breakdown physicists were looking for. More below the fold.
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There are four known fundamental forces in the universe: The strong nuclear force that holds atomic nuclei together; the weak nuclear force responsible for nuclear decay; the electromagnetic force, responsible for holding electrons on atoms, holding atoms together in molecules, and most of the ordinary phenomena we experience every day; and gravity. The standard model managed to incorporate all of these, except gravity. (Theorists are still struggling to find a way to reconcile gravity with quantum theory; perhaps general relativity was Einstein’s most durable practical joke on quantum physicists?)
Physicists knew from the beginning that the standard model could not be the full story because of the exclusion of gravity. Further, when dark matter was discovered, it was recognized that it could not consist of any particles predicted to exist by the standard model. Despite these known flaws, as well as physicists’ efforts to try to find break points in the theory, it has managed to explain all observations made at particle accelerators for decades.
Now, a new analysis has found a possible point of disagreement between the theory and experiment, but it has come from an unexpected direction: the leptons. Leptons are particles that respond to the weak nuclear force (and electromagnetism, if the particles are charged), but not the strong force. The electron is a lepton, and there are two other particles that behave just like the electron in most aspects, except that they are more massive. These are the muon and the tau particle. Unlike the electron, both are unstable.
In the analysis of the observed decay of a particle called a B-meson, the decay can proceed by either producing muons or taus. In comparing the decay of the two particles, it was observed that the tau particles were living longer than expected. This defies a fundamental assumption of the standard model that all the leptons behave exactly alike.
While this observation has been reasonably consistent, it has not yet achieved the ironclad standard that physicists require to definitively confirm a new particle or phenomenon (that standard being 5 sigma), and nobody should consider dancing on the grave of the standard model before that point. Many proposed phenomena have evaporated before they got to the 5 sigma standard, and this one may, too. But if it does survive, it may pose a threat to the standard model.
However, the lifetimes of the leptons have no clear bearing on the new phenomena that everybody knows the standard model does not explain (i. e. dark matter, quantum gravity, etc). As such, it’s weird that the standard model might be felled by an inconsistency in lepton lifetimes—like the Roman Empire might have collapsed from an epidemic of athlete’s foot.
But you never know. Somewhere in this inconsistency there might be a thread to pull that will lead to a solution to the newer mysteries of the universe.
On to the comments!
Top Comments (September 6, 2017):
From MikeTheLiberal:
Yeah, the news has been depressing…
But, in Chris Reeves’ article, AaronMc nails the definition of conservatism.
(This comment was also nominated by allergywoman.)
From HeyMikey:
Bob Love tosses off this bon mot.
Top Mojo (September 5, 2017):
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Top Photos (September 5, 2017):