5. The Standard Model
— The Common Arrangement of Fundamental Particles —
Breaches in Symmetry
Imagine having your eyes closed and somebody gives you two objects — two cubes, 1 and 2 — in your hands. The two cubes are identical in shape and you understand the two cubes to be similar; you would only need one definition to describe both objects.
But then you open your eyes and one cube appears to be red while the other is green (1a and 2a). Now the two objects are different and you would need two definitions to describe them.
When you had your eyes closed the two objects were the same. We speak of symmetry. When you open your eyes the symmetry breaches and you have two different objects.
Now imagine that you don't have eyes. Nobody has eyes. Nature has not yet produced eyes. In fact, nature has not produced any way to determine the difference between the two cubes. That means that the difference between the two cubes is not yet part of reality, and in a way that sits on a very slippery slope (click here for more on this) we can say that the difference between the two cubes does not exist! And then nature comes up with eyes to see. And in their wake lies the difference between the two cubes. In that same slippery way we can say that when nature produces a way to discern differences, these differences are produced along with it. That is how it went in the Beginning.
According the most plausible theories, the universe commenced in a condition of complete symmetry; we would only need one definition to describe this initial condition. That definition is often called the Grand Unified Theory and it is still unknown to mankind. In other words, we know that the universe commenced as a singularity but we have no idea how that would translate into understandable mathematics.
The various fundamental particles popped out of the quantum foam and, apart from their masses, their differences were not discernible because there was only one force at work in the universe. Imagine having only one sense, like the tactile sense with which we identified the cubes at first. The cube is either there, or it isn't. No further details can be observed. Right after the Beginning, all particles responded to the one and only force and there was no way to identify inherent differences, and so there were none. In retrospect we call this force the Grand Unified Force, only because we know that its symmetry was bound to breach. And when it did there came to exist two forces: gravity and the strong-electro-weak force.
Now particles either responded to gravity by means of their mass or amount of energy, or they responded by means of their strong-electro-weak charge. And the breaching went on.
The strong-electro-weak force spawned the strong nuclear force and the electro-weak force. This caused two major groups of fundamental particles to be identified: quarks that responded to all three existing forces, and leptons that did not respond to the strong nuclear force. In our tactile/visual analogy of the cubes, leptons would be those particles that we can feel but not see, while quarks can be both felt and seen. This caused a significant change in particles dynamics. Also because quarks are generally more massive than leptons. We speak of the mass-dominated era.
The final breach in symmetry happened when the electro-weak force broke apart into the electromagnetic force and the weak force. This breach in symmetry only marked a further difference in the lepton-tribe. Those leptons that had electromagnetic charge followed electromagnetism, and those leptons that did not have electromagnetic charge (the neutrinos) did not follow electromagnetism.
The four forces of nature
When the era of symmetry breaches came to an end there were four forces, and those four identified all the various differences between the existing fundamental particles:
|Gravity||Graviton||Gravity curves space. And it always attracts, never repels. Gravity is the only force to which all particles are subjected.||Infinite|
|Strong Force||Gluon (8 kinds)||The strong force binds quarks into nucleons and nucleons into nuclei.||Limited to the atomic nucleus|
|Photon||Electromagnetism binds electrons to the nucleus. By doing so electromagnetism allows all physical and chemical processes to happen.||Infinite|
|Weak Force||Weak bosons|
|The weak force causes unstable particles and nuclei to decay.||Limited to the atomic nucleus|
As stated before, material particles can be divided into three fundamental groups:
- Quarks, which are electrically charged, either positive or negative, and which form atomic nucleons that contains most of the mass of the visible universe.
- Leptons which either have a negative electrical charge or no charge at all — in which case they are called neutrinos — and which make the universe a lively place in which a lot more happens than simply bumping into each other.
- Bosons, which are bits of force, not real particles.
There are 12 quarks and 12 leptons although some demand that there are only 6 of each. In fact, there are 6 of each and each has an anti-particle; 6 of each plus 6 anti-of-each. But because particles have only a handful of characteristics, a reversed electrical charge (which defines an anti-particle) alters the nature of a particle by such a big percentage that most feel confident to speak of 12 different particles of each kind, even though there's a strong kinship between 6 pairs.
So, here is the Standard Model in its fullness but keep in mind that every quark and lepton has an anti-quark or -lepton that is just as real and corporeal as the normal sibling it was named after (electron & anti-electron or positron; down quark & anti-down, etc).
Of the lepton bunch you should know that every charged one has a sibling that isn't charged, called a neutrino.
The Standard Model:
|— Quarks —|
|— Leptons —|
|— Bosons —|
* These masses are approximate, and given in electron masses. These masses are what you would get if a certain field would be ignored. This force field is always present in nature so these masses don't make a lot of sense. We've just put them here so you can see the incredible differences between quark and lepton masses.
Also: Not all qualities of the particles are listed here. And the graviton is usually not listed in the Standard Model because gravity is negative energy while all other energy is positive. Not very complicated, but read Kip Thorne's excellent book Black Holes and Time Warps if you want to know more.
The evolution of the Standard Model over time:
Supersymmetry and the Higgs particle
For certain reasons, physicists strongly suspect that beyond the symmetries of the Standard Model another incredible symmetry lurks; supersymmetry, and that a particle must exist that is unlike all other particles and which gives all other particles their mass: the Higgs particle.
The theories of supersymmetry — which are very likely true but still unproven to date — demand that every particle and anti-particle of the Standard Model has a supersymmetric partner, also known as a super-partner or simply 'spartner'. Normally these super-particles are named after the particle they accompany and prefixed with an s: electron and selectron, quark and squark. And if these sparticles had survived the early universe there might have been sstars and splanets, perhaps even speople who drink sbeer and tell sjokes. But no, there was to be a greater fate.
As stated before, this initial family of particles was thoroughly thinned out during the turmoil of the early universe. The next chapter will discuss which heinous plague struck this utterly royal family, for never was a story of more woe than this of the Universe and her Standard Mo.Go to the next chapter:
Does the Universe Expand? →
Summary 5: The Standard Model
- A quality only exists if a way to determine it exists. Nature identifies qualities by means of the four forces of nature.
- There are four natural forces: Gravity, Electromagnetism, Strong Nuclear Force, Weak Nuclear Force.
- There are three fundamental kinds of particles: Quarks, Leptons and Bosons.
- All particles listen to Gravity.
- All electrically charged particles listen to Electromagnetism. All neutral particles are deaf to EM.
- All Quarks and Quark-compounds listen to the Weak Nuclear Force. All leptons are deaf to the Weak Force.
- All quarks listen to the Strong Nuclear Force. All leptons are deaf to the Strong Force.