In this century, progress in fundamental physics has been slow. The Large Hadron Collider hasn’t yet found any surprises, attempts to directly detect dark matter have been unsuccessful, string theory hasn’t made any successful predictions, and nobody really knows what to do about any of this. But there is no shortage of problems, and clues. Watch the talk I gave at the Cambridge University Physics Society for some ideas on this! Warning: this is for ordinary folks, not experts.

There are some squeaky sounds on the video at first, but they seem to go away pretty quick, so hang in there! You can also see my talk slides here:

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13 Responses to Unsolved Mysteries of Fundamental Physics

Good evening and Happy New Year. I am hoping this “reply” to your group email will actually get delivered. I thought it was high time we were in direct contact since we share a number of very good friends, and I have been a long time member of your mailing list – and therefore a long time admirer of your work.

I don’t know if you are (still) in the UK but if so then please do let me know.

I think our closest mutual friend is Bob Coecke so if you are a little unsure about provenance please do check 😊

Hi, Ilyas! I know who you are. Thanks for all you’ve done for the journal Compositionality! I was only in England for a week in October; it took a few months for the videos of my talk in Cambridge to be uploaded. I’ll be in Edinburgh in July 7-13 for the big annual category theory conference, and in Oxford July 15-26 for Applied Category Theory 2019, which Bob and I are helping organize. If you are near either of those, please say hi!

I’m glad you enjoyed those slides, Bruce! It’s interesting to compare them to the earlier edition Mikko pointed out. That earlier version was from 2006, and I think a lot of the distress that “fundamental physicists” are feeling these days can be seen from how little has changed since then. Some things we hadn’t seen yet but were expecting—like gravitational waves—we have now seen. But the hard problems seem only slightly changed in the last 12 years. We have different puzzles concerning neutrinos and high-energy cosmic rays, but no breakthrough discovery yet.

I wonder if today the problem of fundamental physics could be, rather ironically, (i) ‘too much’ knowledge, meaning that one has to find a theory that fits to many more known facts simultaneously, than in previous times, and (ii) a bias in actively pursuing the search for the universal theory, instead of solving seemingly unrelated problems, which still could make the difference?

With the latter I mean, thinking of Planck, that he was not primarily occupied with the goal to find quantum theory (how could he, of course). He ‘just’ wanted to solve the riddle of black body radiation. A quite restricted problem. Quantum theory more or less ‘happened’ to him.

I wonder, again, if there could be ‘small’ fundamental problems in very different fields of physics, say solid state physics, which could give a clue on a (more) universal theory, in a way as it happened in Planck’s case? For instance, if one could imagine an atomic effect, in which both electromagnetism and gravity play a strong role, and thereby find something like Planck’s formula bringing some light about their connection on a deeper level? Or think of Bekenstein’s approach to black hole entropy, coupling, with a quite simple formula, and for a quite restricted problem, very different fields of physics to each other, facilitating a new view or point of attack for the quest for a universal theory?

There are ‘small’ fundamental problems that, when realized and resolved, will usher in the theory of everything and a drastically more complete understanding of our universe. But looking in other areas of physics will not be helpful because they suffer from the same lack of realization. To wit, it is our understanding of mathematics and how we apply it that is skewed at the foundational level. The unskew will cascade rapidly through all of the sciences and ultimately result in a great simplification and unification of previously thought disparate phenomena.

if one could imagine an atomic effect, in which both electromagnetism and gravity play a strong role, and thereby find something like Planck’s formula bringing some light about their connection on a deeper level?

I agree with your overall point, and I agree with this example: if such an effect were known it would be a very interesting way to learn more about how electromagnetism and gravity are related. Unfortunately nobody knows such an effect. The main problem is that gravity seems to have a negligible effect in atoms: for atoms, the electromagnetic force between proton and electron is about 10^{40} times bigger than the gravitational force, and indeed nobody has even been able to measure the gravitational force here!

It’s hard to do experiments measuring the gravitational force on short distance scales, and this has led to a flourishing of surprisingly-hard-to-disprove theories in which gravity does weird things on sub-millimeter scales due to extra dimensions of space curled up in shapes that have about this size. This size is incredibly large compared to those we normally study in particle physics, so it opens the prospect that quantum gravity effects kick in at incredibly low energies. Try:

The first paper is experimental and shows how hard experimentalists work! The second paper is theoretical and shows how good theorists are at coming up with far-out ideas. I’m not a fan of these particular ideas.

I think the avenue I mentioned in my talk—continuing to study the strange anomalies associated to neutrinos—is a bit more promising. A lot of people are working on this! Try this for starters:

I would consider it unfair to say that 22 of 25 of the SM constants relate to the Higgs. 12 definitely (9 non-neutrino fermion masses, W mass, Z mass, Higgs mass). Presumably the three you exclude in 22 of 25 are the three SM coupling constants. (I assume you have 25 rather than 26 because you can derive the W mass knowing Z mass of visa versa, giving you 11). But, it is hard to see how the CKM matrix and PMNS matrix parameters are related to the Higgs, and the relationship of the 3 neutrino masses to the Higgs is at least debatable. Was the slide perhaps a typo that was intended to be 12?

There are different possible explanations of the CKM and PMNS matrices, but in the current most standard version of the Standard Model they involve the Higgs:

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Dear John,

Good evening and Happy New Year. I am hoping this “reply” to your group email will actually get delivered. I thought it was high time we were in direct contact since we share a number of very good friends, and I have been a long time member of your mailing list – and therefore a long time admirer of your work.

I don’t know if you are (still) in the UK but if so then please do let me know.

I think our closest mutual friend is Bob Coecke so if you are a little unsure about provenance please do check 😊

Wishing you the very best

Ilyas

Hi, Ilyas! I know who you are. Thanks for all you’ve done for the journal

Compositionality!I was only in England for a week in October; it took a few months for the videos of my talk in Cambridge to be uploaded. I’ll be in Edinburgh in July 7-13 for the big annual category theory conference, and in Oxford July 15-26 for Applied Category Theory 2019, which Bob and I are helping organize. If you are near either of those, please say hi!I just read the slides — they are extremely clear and interesting!

If you like those, you’ll probably like the earlier edition, too: http://www.math.ucr.edu/home/baez/where_we_stand/

I’m glad you enjoyed those slides, Bruce! It’s interesting to compare them to the earlier edition Mikko pointed out. That earlier version was from 2006, and I think a lot of the distress that “fundamental physicists” are feeling these days can be seen from how little has changed since then. Some things we hadn’t seen yet but were expecting—like gravitational waves—we have now seen. But the hard problems seem only slightly changed in the last 12 years. We have different puzzles concerning neutrinos and high-energy cosmic rays, but no breakthrough discovery yet.

Fantastic helicopter view of the state of things, especially for slobs like me who are several galaxies from the cutting edge.

Thanks! The closer you get to the cutting edge, the more blood and guts you see. But the view from high up is not so messy.

Very nice talk.

I wonder if today the problem of fundamental physics could be, rather ironically, (i) ‘too much’ knowledge, meaning that one has to find a theory that fits to many more known facts simultaneously, than in previous times, and (ii) a bias in actively pursuing the search for the universal theory, instead of solving seemingly unrelated problems, which still could make the difference?

With the latter I mean, thinking of Planck, that he was not primarily occupied with the goal to find quantum theory (how could he, of course). He ‘just’ wanted to solve the riddle of black body radiation. A quite restricted problem. Quantum theory more or less ‘happened’ to him.

I wonder, again, if there could be ‘small’ fundamental problems in very different fields of physics, say solid state physics, which could give a clue on a (more) universal theory, in a way as it happened in Planck’s case? For instance, if one could imagine an atomic effect, in which both electromagnetism and gravity play a strong role, and thereby find something like Planck’s formula bringing some light about their connection on a deeper level? Or think of Bekenstein’s approach to black hole entropy, coupling, with a quite simple formula, and for a quite restricted problem, very different fields of physics to each other, facilitating a new view or point of attack for the quest for a universal theory?

There are ‘small’ fundamental problems that, when realized and resolved, will usher in the theory of everything and a drastically more complete understanding of our universe. But looking in other areas of physics will not be helpful because they suffer from the same lack of realization. To wit, it is our understanding of mathematics and how we apply it that is skewed at the foundational level. The unskew will cascade rapidly through all of the sciences and ultimately result in a great simplification and unification of previously thought disparate phenomena.

This is what everyone with a big new idea hopes. About 99.9% of these people are wrong, but luckily not 100%.

Wolfgang wrote:

I agree with your overall point, and I agree with this example: if such an effect were known it would be a very interesting way to learn more about how electromagnetism and gravity are related. Unfortunately nobody knows such an effect. The main problem is that gravity seems to have a negligible effect in atoms: for atoms, the electromagnetic force between proton and electron is about 10

^{40}times bigger than the gravitational force, and indeed nobody has even been able to measure the gravitational force here!It’s hard to do experiments measuring the gravitational force on short distance scales, and this has led to a flourishing of surprisingly-hard-to-disprove theories in which gravity does weird things on sub-millimeter scales due to extra dimensions of space curled up in shapes that have about this size. This size is incredibly

largecompared to those we normally study in particle physics, so it opens the prospect that quantum gravity effects kick in at incrediblylowenergies. Try:• C.D. Hoyle, D.J. Kapner, B.R. Heckel, E.G. Adelberger, J.H. Gundlach, U. Schmidt and H.E. Swanson, Sub-millimeter tests of the gravitational inverse-square law, 2004.

• Nima Arkani-Hamed, Savas Dimopoulos and Gia Dvali, Phenomenology, astrophysics and cosmology of theories with sub-millimeter dimensions and TeV scale quantum gravity, 1998.

The first paper is experimental and shows how hard experimentalists work! The second paper is theoretical and shows how good theorists are at coming up with far-out ideas. I’m not a fan of these particular ideas.

I think the avenue I mentioned in my talk—continuing to study the strange anomalies associated to neutrinos—is a bit more promising. A lot of people are working on this! Try this for starters:

• Adam Falkowski (aka “Jester”), Other neutrino anomalies,

Résonaances, 2012.I would consider it unfair to say that 22 of 25 of the SM constants relate to the Higgs. 12 definitely (9 non-neutrino fermion masses, W mass, Z mass, Higgs mass). Presumably the three you exclude in 22 of 25 are the three SM coupling constants. (I assume you have 25 rather than 26 because you can derive the W mass knowing Z mass of visa versa, giving you 11). But, it is hard to see how the CKM matrix and PMNS matrix parameters are related to the Higgs, and the relationship of the 3 neutrino masses to the Higgs is at least debatable. Was the slide perhaps a typo that was intended to be 12?

There are different possible explanations of the CKM and PMNS matrices, but in the current most standard version of the Standard Model they involve the Higgs: