The Standard Model... and Beyond


Elias Riedel Gårding wrote this short and sweet article describing the particles that make up the Standard Model of physics. At school, most of us thought that list consisted of electrons, protons and neutrons:
“But atoms are not the end of the story… Protons and neutrons are themselves composed of tiny constituents called up-quarks and down-quarks (a proton consists of two up-quarks and one down-quark, a neutron of one up-quark and two down-quarks).”

Ok, is there anything in the universe not made of electrons and quarks? There’s one answer that is familiar to most people: light. And it is made of photons. With photons, are we done with the list of all particles then? Nope:
“We have discovered a whole slew of them (other particles) in cosmic rays and in particle colliders.”
Here is where things stand today:
“After much head-scratching, it has turned out that they are all different combinations composed from a small set of particles that are – as far as we know today – fundamental (ie, truly indivisible).”

There are 17 of them, explains Gårding:
Nice and colorful, but like me, it probably made your head swim. If so, let Gårding explain the pattern behind the madness of the particle zoo:
-       There are 3 generations (I, II and III above);
-       Each generation consists of two quarks and two something called leptons;
-       The particles in all 3 generations have the same properties as their counterparts in the first generation, except that each generation is heavier;
-       The Red column are the force particles;
-       And finally comes the famous Higgs Boson, which gives mass to things.

Gårding ends his first-in-a-series article by saying:
“The particles shown in the table above, together with Einstein's theory of gravity, account for every observation ever made in physics, with only a small handful of exceptions (mostly in astronomy).”

I loved Gårding’s article, except for that last part about there only being a “small handful of exceptions” that can’t be explained by the Standard Model. Because those exceptions include dark matter (25% of the universe) and dark energy (70% of the universe). Do the maths, and you realize that the Standard Model explains:
100% (total) – 25% (dark matter) – 70% (dark energy) = 5% of the universe!

Whoa! So 95% of the universe cannot be explained by the Standard Model?! Which is why the scientists on the Infinite Monkey Cage podcast titled “What Particles Remain to be Discovered” wondered, which (or both) components of the Standard Model are incomplete?
-       Are there more particles waiting to be added to the Standard Model?
-       Does Einstein’s theory of gravity need to be updated?
(It’s also possible that an entirely new edifice of explanation comes up, what is termed Physics Beyond the Standard Model).

Regardless of how it plays out, the next stage of answers should be interesting.

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