The Standard Model of Physics – Simplified


The standard model, as it is known, is the sum of every theory we understand in physics to be provable and, at the same time, completely resistant to falsification.  This is a very basic definition of the Scientific Method.  For a theory to be scientific, it must accurately model something (predict) AND withstand falsification.  An unproven theory is a hypothesis, something which is yet to meet these two primary criteria.

PROOF: In simple terms, using a theory or set of theories within the standard model, we can predict with astounding accuracy the outcome of physical events AND construct those physical events and check and prove in physical terms, the predicted outcome’s functional accuracy.

FALSIFICATION: Using a theory correctly to make an incorrect prediction as evidenced by physical experiment and outcome.

Let’s start at the very building blocks of our universe as understood in the Standard Model.  Whilst you will get a reasonable idea in the explanations here, I will use illustrations or statements which give the right idea, whilst not necessarily adhering totally to the properties of the thing being described in every detail.  This is meant to be the simple explanation.

There are two classes of building blocks to everything in the physical universe, fermions and bosons. 

Fermions are the units of mass. Fermions are the ‘building blocks which make stuff’. 

Bosons are units of force.  Bosons are the currency, the mechanisms of interaction and exchange.  You and ‘Fred’ exchange money to interact; fermions exchange bosons to interact.

We need to define what force is here, but don’t get too wrapped up in it all right now.  There are four forces in the Standard Model, but only three of which are explained (accurately described) by it:

Electromagnetism – light, magnets, electricity etc.

Strong (nuclear) Force – Holds the building blocks of matter together

Weak (nuclear) Force – keeps atoms together to make bigger stuff (includes radioactivity)

Very nearly everything in your body, and the ‘touchable’, physical universe is made up of just three fermions, two types of quark and an electron.  There are more fermions, but we are going for simple and these three bits of matter account for all but a miniscule bit of mass in our known, physical universe.

The two quarks in question are labelled ‘up’ and ‘down’.  Each carries a specific charge. 

Up quarks carry a positive two thirds charge (+2/3).

Down quarks carry a negative one third charge (-1/3). 

Electrons carries a ‘whole’ negative charge (-1).

In high school, you probably heard of two types of particles (in addition to the electron), the proton and the neutron, which are described as the common building blocks of an atom.  Let’s look at the proton and the neutron’s construction.  Both are made of three quarks. Remember that the electron is a fermion and is not made up of anything smaller.

Depending on how these three quarks are arranged, you can arrive at a particle with no charge (neutron) or a whole positive charge (proton).  Let’s have a quick look at this now.

Protons are made of two up (+2/3) + (+2/3) =+4/3 and one down (-1/3) quarks.  Combining the third charge of the down quark means you take the negative charge from the positive charge, ending up with a whole unit of positive charge (+4/3) + (-1/3) = (+3/3) =+1

Neutrons are made of one up and two down quarks.  Let’s combine these to see how we arrive at no charge. (+2/3) + (-1/3) + (-1/3) = 0

Now we know that particles and atoms interact with other particles and atoms, right?  This is where bosons come into play.  When two electrons interact, they repel each other, exchanging photons.  This is the electromagnetic force we described earlier.

Other bosons communicate Strong and Weak forces, with ‘heavy’ bosons expressing the weak force and Gluons (another type of boson) expressing the strong force.  We do not need to get more involved than this for a simplified over-view of the Standard Model.

So far, we have three basic particles, a proton with a full, positive charge (+1); an electron with a full negative charge (-1); and a neutron with no effective electrical charge. 

These three particles, in various combinations, make up pretty much everything that has mass (can be touched) in our physical universe.  One electron ‘orbiting’ around a single proton is the most basic atomic structure we know of, Hydrogen, which also makes up the vast bulk of our universe.  To get every other element, and everything else, just add protons, neutrons and electrons!

When atoms interact, they exchange bosons of one type or another.  They can also break. One atom might interact with another atom, breaking away a part of one or both, combining with part or all of the other, and so on. 

When atoms combine parts to form bigger atoms, this is called fusion.  Atomic fusion only happens naturally under the influence of intense pressure found in suns.

When atoms break apart to form smaller atoms, this is called fission. The first atomic bomb split the atom, releasing immense levels of energy as atoms split into lighter or smaller configurations.  This is why these first bombs were called fission bombs.

(Later, scientists used the intense energy of a fission bomb to create pressures like those found in the heart of a sun, using other materials to make fusion happen, releasing even more energy.  This is why fusion bombs are bigger and nastier – they release far more energy.)

A lot of the Standard Model gets right into how, and when, and where, and why these particles behave as they do, and the maths is pretty astoundingly accurate.  To understand how accurate, imagine the distance between London and the Moon, plus or minus the width of a hair (not even the length!).  This is a pretty good real-world analogy of how accurate the Standard model is in describing and predicting all that it covers.

Using the standard model of physics, science can tell us where a thrown ball will land, how much energy will arrive at a given point when a torch is shone on a distant object, how radios and televisions make noise and pictures and a whole lot more.  In fact, it tells us pretty much everything; almost.

There are gaps though.  One of the most glaring gaps is that there is no explanation of gravity.  This might sound crazy, but the Standard Model does not describe gravity in the same way it describes what we’ve discussed so far.

Now we come to the next stage in our very fast tour of introduction to physics, the brilliance of Einstein and the weirdness of Quantum mechanics.

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