John Carlos Baez4d ago

The Higgs boson gives elementary particles their mass, but 98% of the visible mass in the Universe (not dark matter) comes from a less famous mechanism: chiral symmetry breaking. This is why protons and neutrons are so much heavier than their quarks!

Briefly, protons and neutrons act like bags full of a soup of virtual quark-antiquark pairs, which give them most of their mass. This soup, called a 'quark condensate', breaks a certain symmetry that exists outside the bag: 'chiral symmetry', where you change the phase of the clockwise and counterclockwise rotating quarks separately. In the quark condensate, the clockwise spinning virtual quarks are entangled with counterclockwise spinning virtual antiquarks.

https://en.wikipedia.org/wiki/Chiral_symmetry_breaking

Chiral symmetry breaking - Wikipedia

Show threadcpkimber
@johncarlosbaez I know this is google-able, but I want to ask someone who knows more than me- what about bonding energy? I thought bonding energy accounted for a large amount of mass.
Mar 25 at 5:57amWeb
Show threadJohn Carlos Baez4d ago

@cpkimber - if something has binding energy, it has *less* energy and thus *less* mass than it would otherwise have, because binding energy is the energy it would take to pull it apart. For example, when a hydrogen bomb goes off, the hydrogen nuclei fuse into something that has less energy and thus less mass, releasing a lot energy in the process.

https://en.wikipedia.org/wiki/Binding_energy

Binding energy - Wikipedia

Show threadcpkimber4d ago
@johncarlosbaez I knew that some time ago, but now feel like a kid for asking.
Show threadJohn Carlos Baez4d ago
@cpkimber - no prob! I love questions about physics, and that was a good question.
Show threadAlexander Knochel4d ago
@johncarlosbaez @cpkimber It has less energy than when it is separated. But does it have less energy compared to if you turned off the force? Then to zeroth order I'd think it depends on the exponent?
Show threadJohn Carlos Baez4d ago
@Quantensalat @cpkimber - it's a subtle counterfactual question, but I'd say a bound system has less energy than if you turned off the force that binds it.
Show threadAlexander Knochel4d ago

@johncarlosbaez @cpkimber

If it's e.g. an r^2 potential then the virial theorem would suggest that all contributions are positive. In that case wouldn't I have an attractive potential that lifts the energy of the system above the free case?

(Adiabatically switching off might yield different results, i.d.k. if the virial theorem then keeps holding in each instant cooling off the system. I should find out....)

Show threadSnoopJ4d ago

@cpkimber I find it helpful to think of the binding energy you're referring to (i.e. the strong force) as an enhancement of the fundamental masses that were already present due to the Higgs interaction @johncarlosbaez is describing. I.e. you need to "prime the pump" with some starter mass before you can work your way up to e.g. the proton mass in this way.

I was not a particle guy in my past life, so I don't really know if you can support that intuition with formalism (or how), but since the QCD couplings that include a massive particle *do* depend on that mass, I can squint and tell myself it's "good enough".

Show threadJohn Carlos Baez3d ago

@SnoopJ @cpkimber - the Higgs boson gives the quarks masses, and the fact that quarks have different nonzero masses breaks chiral symmetry, so yes there's a real sense in which the Higgs "primes the pump" for the generation of the proton's mass!

However, I want to again emphasize that the proton's mass is not "binding energy": binding energy always contributes *negatively* to mass. All the stuff I said about how chiral symmetry breaking gives mass was not just a ridiculously complicated euphemism for "binding energy". Something else is going on here:

"Briefly, protons and neutrons act like bags full of a soup of virtual quark-antiquark pairs, which give them most of their mass. This soup, called a 'quark condensate', breaks a certain symmetry that exists outside the bag: 'chiral symmetry', where you change the phase of the clockwise and counterclockwise rotating quarks separately. In the quark condensate, the clockwise spinning virtual quarks are entangled with counterclockwise spinning virtual antiquarks."

Show threadSnoopJ3d ago
@johncarlosbaez @cpkimber ah yes, thank you for the correction. I am not aware of a "popsci" term that fits in the place of "binding energy" here but which does not confuse the strong interaction's contribution to mass with the other phenomenon (but there should be one if there isn't!)
Show threadJohn Carlos Baez3d ago

@SnoopJ @cpkimber - the good term, which is not yet popsci, is "condensate". It should remind you of how water vapor condenses into mist when it gets cold enough. The proton and neutron are bags containing 3 quarks, and gluons, but also a condensate of quark-antiquark pairs, and this "mist" contributes most of the mass.

There are other condensates in nature, one being the Higgs field itself, but also others that show up in various materials.

Show threadSnoopJ3d ago
@johncarlosbaez @cpkimber it reminds me of Bose-Einstein condensates, but I guess that's not exactly a coincidence ;)
Show threadJohn Carlos Baez3d ago
@SnoopJ @cpkimber - right, duh, I should have mentioned that example.
Show threadSnoopJ3d ago
@johncarlosbaez @cpkimber as an aside, I think it's also a fun collective noun for a group of physicists!