A New Map of All the Particles and Forces (2020)

https://www.quantamagazine.org/a-new-map-of-the-standard-model-of-particle-physics-20201022/

by frutiger • 4 years ago

121 48 4 years ago

est31• 4 years ago

The article is two years old, and one of the links, the one pointing to https://www.cpepweb.org/cpep_sm_large.html is already dead.

Thankfully the internet archive has a backup: http://web.archive.org/web/20200521151158/https://www.cpepwe...

bsedlm• 4 years ago

why is the absolute overwhelming majority of stuff in the universe (and 100% of things outside of special lab settings) made up from 1st generation matter?

why is it that all stuff made from charm, strange, top, and bottom, quarks decays right away?

frutiger3• 4 years ago

why is the absolute overwhelming majority of stuff in the universe (and 100% of things outside of special lab settings) made up from 1st generation matter?

The first generation have the lowest mass, and there are interactions between generations. Since physical systems like to explore the local energy space and find the lowest one, it follows that more energetic systems will quickly stabilize to lower energy configurations.

You might rightfully have two follow up questions at this point:

1. Why do the first generation fermions have the lowest mass?

2. Why do physical systems like to find the lowest energy configuration?

I don't believe anyone has the answers to those - so far as we can tell this is just the way the universe is. Maybe some day someone will figure out why.

ncmncm5• 4 years ago

Does thermodynamics not suffice for (2)? Or does that just restate the question, somehow?

I learned many things about the SM from this presentation I had never before retained.

Wondering now to what degree string theory seems to exactly require all of this, vs. merely be apparently compatible with it, insofar as it can be "solved" at all. Where it is too hard, maybe it is not known whether certain SM features are compatible, and everyone just hopes?

AnimalMuppet3• 4 years ago

The first generation ones don't come with a little number "!" on them. They are "first generation" because they're the ones we found first. Why did we find them first? Because they're the most common ones. And why are they the most common? Because they're the ones with lowest mass.

I mean, you could still ask why the different generations have different masses at all, but if they do, it follows that the "first generation" has the lowest mass.

superposeur• 4 years ago

Indeed, 1. is a mystery. But, 2. is a consequence of 2nd law of thermo. Specifically, the lighter the mass of a decay product, the larger the number of possible final states in the kinematical phase space (in general). For instance, if there is just enough energy to make a pair of particles, then only one final state is possible: particles sitting at rest. On the other hand if energy is “left over” in addition to rest energy, then there are many possible final states corresponding to the pair flying outward in different directions. Hence, the decay to the lighter products are entropically preferred. This is mathematically encapsulated in Fermi’s Golden Rule.

green_on_black• 4 years ago

why are there generations at all? why 3?

ncmncm5• 4 years ago

Might we just not wield enough energy to evoke a 4th generation?

frutiger3• 4 years ago

No one knows. For what it's worth, we thought there were only 2 generations until well into the 20th century.

evanb• 4 years ago

We know why SM particles come in "whole generations": a mathematical consistency condition known as anomaly cancellation [0]. We also know that with only 2 generations we cannot get violation of charge-parity symmetry [1] via the Cabibo angle [2] alone; to get CP violation we need at least a 3x3 CKM matrix [2]. CP violation is one of the Sakharov conditions [3] that is required to get matter/antimatter asymmetry from early universe dynamics.

This is not an a priori reason, per se, but it does waggle its eyebrows up and down in a sort of anthropic way.

[0] https://en.wikipedia.org/wiki/Anomaly_(physics)#Anomaly_canc...

[1] https://en.wikipedia.org/wiki/CP_violation

[2] https://en.wikipedia.org/wiki/Cabibbo%E2%80%93Kobayashi%E2%8...

[3] https://en.wikipedia.org/wiki/Sakharov_conditions

PaulHoule5• 4 years ago

What I like of the right-hand, left-hand split is that it emphasizes the mystery of neutrinos.

We know neutrinos have a mass, we don't know how much. We don't know how to incorporate the neutrino mass into standard model. Other fermions come in left-handed and right-handed forms but we only see left-handed neutrinos.

One idea is that right-handed neutrinos do exist but are highly elusive. In fact they are a good answer to the dark matter and other physics mysteries

https://arxiv.org/abs/1303.6912v3

ncmncm5• 4 years ago

That the total mass of neutrinos is commensurate with / exceeds all the hadronic mass is rarely mentioned. With so many interactions emitting neutrinos, does everything end up as neutrinos, finally (neglecting expansion)? Or does something consume neutrinos and yield net hadronic stuff?

PaulHoule5• 4 years ago

Particles like protons and electrons can never turn entirely to neutrinos because electric charge is conserved. Protons and bound neutrons seem to be the only stable configuration of quarks & gluons, ultimately there is quark charge that is conserved that prevents quarks from going away unless protons really do decay... which would have to happen at a very low rate if it does.

philipov• 4 years ago

I believe no matter what else, everything eventually ends up as black holes.

dotancohen• 4 years ago

  > We know neutrinos have a mass, we don't know how much.

How small is the possible range? Just last week I read - but possibly misunderstood - that the W-boson mass could not be directly measured so the researchers were using the masses of other decay particles to measure it. One of those other decay particles was the neutrino.

tejohnso• 4 years ago

Is this model actually taught in high schools at this point?

I remember being taught about electrons with their valence shells, protons, and neutrons. That's it. I didn't hear about a boson or a neutrino until well into adulthood.

timthorn• 4 years ago

The Standard Model was covered in A Level Physics syllabus in the late 1990s - I remember being taught it. The top quark was experimentally confirmed in 1995, so this was exciting stuff.

It's still in the specification. AQA Physics is outlined here: https://filestore.aqa.org.uk/resources/physics/specification... And OCR here: https://www.ocr.org.uk/Images/171726-specification-accredite...

yesenadam4• 4 years ago

A Level

For those not in the UK, apparently this means the last year of high school.

joshvm• 4 years ago

Yep, at A level (2007 ish) we had a college trip to visit CERN while it was being built. It was cool to see ATLAS before they joined up the beam lines.

My college physics department was otherwise very underwhelming and I'm amazed they had the imagination to plan it.

AnimalMuppet3• 4 years ago

I understood most of this. But ELI20: Why does the electroweak symmetry breaking give rise to the Higgs field?

l33tman• 4 years ago

It's the other way around, the Higgs field is the field introduced to break the EW symmetry. It can do this because it is particular in that it has a non-zero vacuum potential, that in essence picks out a "direction" in EW-space at each spacetime point that becomes special.

It's like the underlying EW theory has an internal space and the equations don't care about the "origin" in this space, if you made a simulation of this and moved the origin everything would look the same. But as soon as you introduce another all-encompassing field that interacts with EW that has a specific absolute value, the equations lose the symmetry - you can't move around the origin anymore as in effect you have now fixed the numbers.

AnimalMuppet3• 4 years ago

Username checks out... ;-)

Thanks.

transfire• 4 years ago

Where’s the antimatter?

danwills• 4 years ago

The article mentions that antimatter is explicitly excluded to keep the diagram/model simpler. It sounded like it would be basically another whole copy of the same shape, bit I have no idea how it would be connected, which would be interesting!

benditlike• 4 years ago

What's a good resource that will introduce me to this topic? Back in high school, we only up to (down to?) protons, neutrons and electrons.

sgtnasty• 4 years ago

Why does it seem like the further they explore into these particles and the particles that make them the model gets more and more complicated? It seems they are getting further away from the unified model and still have far to go. In my mind I would think that as they got closer to this unified grand theory of everything the "fundamental" particles and their model would be simple, not complex. Am I totally off base here?

A New Map of All the Particles and Forces (2020)

Related Stories