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.

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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.

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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.

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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

But:

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.

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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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