Is the Standard Model of Physics Now Broken?

Sabine is very good at telling everyone to calm down. :grinning_face_with_smiling_eyes: I had read another article that quoted a scientist explaining he was so excited he couldn’t sleep.

But I thought this was a really helpful explainer about the standard model and physics generally, in case anyone was interested. She’s good at that too.


20 years for the only real anomaly in particle physics to go from 3.7 sigma to 4.2 sigma – perfectly sums up why I left the field.


I was hoping Sabine would write something about this discovery; thanks for the find @thoughtful ! This helped place the actual significance (no pun intended) of the result in perspective.


No, this result does not show that the Standard Model is broken:

  1. 4.2 sigma is not that high
  2. It’s 4.2 sigma off from a theoretical calculation that we didn’t know whether we did correctly – there are other ways for the calculation to be off than the Standard Model being wrong


There is a myriad of other experiments/observations pointing to the Standard Model being at the very least, incomplete. Most of them are astronomical: dark matter, accelerating expansion of the cosmos, matter-antimatter asymmetry, etc. None of them can conclusively say anything about the SM, but each is evidence against the SM being all there is.


While we have a physicist or two here: Is it clear that dark matter is composed of particles? Does dark matter interact with other dark matter in any way other than by gravity? Similarly, do dark matter particles have a size, i.e. do they repel each other over some distance? What is the density of dark matter particles around here? Is there even a way to investigate those questions? Etc.

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No. The effects of dark matter on galaxies, for example, could potentially be explained by a modification of the gravitational force. In this theory, “dark matter” never existed in the first place.

Maybe – there are theories of an extended “dark sector”, which involves, for example, “dark electromagnetism”. In dark electromagnetism, dark matter can interact with other dark matter via “dark photon”. There is a variety of tests one can conduct to deduce whether dark electromagnetism (or any other “dark forces”) is true or not; so far the tests are inconclusive.

We do not know. Different models of dark matter predict different “sizes” for the dark matter particle.

-) At small scales (i.e., solar system and smaller): we have no idea, again different theories predict different densities

-) At large scales, this can be measured using techniques like “gravitational lensing”, where the gravity of the dark matter bends light that we can observe with telescopes

-) At extremely large, cosmological scales, the prevailing theory is that it has a density of 0.23 times the “critical density”, where the “critical density” is density required to make the Universe flat (it’s just a number that you can compute)

Yes, it’s difficult, but we’re trying our best.

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