What does it take to make everything there is in the whole universe? Had we not known about atoms and subatomic particles, then we would probably assume that for every single thing that exists there must be something that makes up what it is. So there’s a chair and it is made of this unique substance called ‘wood’ – not any type of wood, but just this one particular type unique to that particular chair. Next there’s this cup made of plastic, not just any plastic, but one that’s unique to that cup. And it goes on like this, every single thing in the universe, every single entity there is, whether solid, liquid or gas, whether living or dead, whether old or new, they are all composed of unique ‘stuff’, their own proprietary substance. Imagine if that were the case then there would be billion, trillions, a whole universe’s worth of stuff to make everything that there is, that there ever was, and that there ever will be. A truly complicated universe. As we’ve found out, things aren’t that complicated. In fact, it is deceptively simple. And amazingly elegant. Let me explain how.
Through the ages, we’ve dug deeper and deeper into the constituent of matter. From molecules to atoms to nucleons and, finally, quarks. And let’s not forget the electron, the tiny negatively charged elementary particle central to our understanding of electricity. There was a time when we thought that the atom was indivisible. We were wrong. We can, and we have, split the atom. The atomic bomb is a notorious example of our ability to do so. Inside the atom we have the nucleus which is composed of protons and neutrons. Protons are the positive counterparts of the negatively charged electrons. However, in terms of mass, a proton is close to 2 000 times the mass of an electron. Neutrons are similar to protons in terms of their mass but they carry no charge and are therefore neutral. Typically, there are the same number of protons and electrons in an atom, regardless of the number of neutrons, so that the atom is electrically neutral.
Now, the protons and neutrons are themselves made up of smaller particles. These particles are called quarks and there are two kinds of quarks that make up the protons and neutrons. There is the ‘up’ and ‘down’ quark. The proton is composed of 2 up and 1 down quark. The neutron is made up of 1 up and 2 down quarks. The electron just as the quarks are not made up of any smaller particle, as far as we know. This is why we call them fundamental particles.
So you need three boxes, one containing a large number of up quarks, the second one, down quarks and the third, the electrons. That’s it. That’s all you need, 3 boxes. And by arranging those different particles together in different combinations you’ll be able to make every single kind of matter there is in the universe! Isn’t that astounding? 3 fundamental building blocks are all you need to make a chair, a cup, the oceans, lemon juice, you, me and everything else there is! It’s not one kind of particle for every different entity as one might assume given the varying properties and characteristics of every stuff there is. We are all made up of the same building blocks.
On top of these 3 fundamental particles, we’ve also catalogued the existence of a fourth naturally occurring particle. It’s called a neutrino. (To be exact, it’s called an electron neutrino.) This neutrino comes from radioactively decaying elements. So there you have it. All that we call matter in the universe has to do with just 4 things: up and down quarks, electron and the neutrino. That’s all there is to the seemingly complicated stuff in the universe.
Isn’t that an elegant model? Isn’t that a truly clever way to make up all of the stuff there is? Isn’t that just amazing that if you were to design a whole universe of stuff with all its galaxies and stars and planets and plants and people and poodles and stuff, all you would need is only 4 building blocks? I find this truly extraordinary.
If you can think of the LEGO blocks as the units for building any thing you want, then all you need are 4 kinds of LEGO blocks, no more, no less. With these, you can make anything you want. Fine, you’ll need a lot of them to make a planet and not so many to make a pin but, still, all that’s required is those 4 kinds of blocks. Truly incredible!
Just as you can make a model of a car using LEGO blocks, you have to bear in mind that the four fundamental particles that constitute all of matter is our model of the universe. We are not claiming that this is exactly how the universe is. Far from that. What we’re saying is that, if we had to make sense of the universe, if we had to understand what it is and what it’s made up of then the best model to explain all of this would be the one where you need those 4 fundamental particles. Best in terms of how close we are to being able to explain and make predictions about the behaviour and physical nature of the universe. So far, the best model is called the Standard Model. That’s the closest we’ve come to explaining the true nature of matter. So to state that all we need is 4 fundamental particles to make a universe so complex and diverse and rich is not far-fetched at all. It is the best we can do so far.
The Standard Model in fact describes the existence of 16 building blocks. Four of them are what constitute all of matter. These four particles are the first generation of a total of three generations of particles. The second generation is composed of the ‘charm’ and ‘strange’ quarks, the mu and its neutrino. The third generation has the ‘top’ and ‘bottom’ quarks, the tau and its neutrino. For some reason we cannot yet explain, only the first generation is what occurs naturally in the universe. The second and third generations exist but only as a product of our smashing together of particles inside particle colliders of the kinds we have at CERN in Geneva. They have no part in making up matter as we know it. Yet they do exist and we know their properties and how they interact with each other.
Altogether, therefore, these make up 12 particles. What about the remaining four which the Standard Model describes? The other four have to do with the three fundamental forces or interactions which govern how the 12 other particles behave. Each of the fundamental forces are transmitted by their respective particles. Perhaps the best known is the photon, the carrier of the electromagnetic force. The gluon is responsible for the strong force, the interaction between quarks. The other two have been labelled the ‘W’ and ‘Z’ particles and are responsible for the so-called weak interaction which dictates how radioactive decay works.
So there you have it, the 16 building blocks of the universe. The up, down, charm, strange, top and bottom quarks, the electron, mu and tau, their respective neutrinos, the photon, gluon, W and Z. Four to make all of the known matter in the universe, four for the forces and the rest, well, the added flavours, if you will, of what is in our elegant universe.
I think it’s neat that one can fit our understanding of the composition of the whole universe into a box with 16 compartments arranged in a 4 by 4 grid. This by no means diminishes the magnificence of our universe; on the contrary, it confirms that we can make sense of its complexity and beauty using simple rules. The fact that we know that a cake is made up of flour, egg, butter and sugar doesn’t imply that the cake loses its flavour. Similarly, by reducing the whole of the universe to four ingredients, in this case the up and down quarks, the electron and the electron neutrino, doesn’t debase it or reduce our sense of complexity to being insignificant. At least for me, it adds another dimension to my view of the world, it makes me realise that we are all connected and we are all composed of the same stuff.