The universe
Absolutely everything, from the building blocks up to galaxies and from the beginning to the end of time.
"In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move."
Douglas Adams in The Restaurant at the End of the Universe
Part 1. The building blocks of the universe
When the Greeks such as Democritus and Leucippus were considering matter, they hypothesised that if you were to continually cut matter in half, you would eventually come to something that is uncuttable. Since A- means not and Tomos means to cut, “atom” means cannot be cut. This gives us, at least hypothetically, the fundamental building blocks of reality. But it wasn’t until 1908-1913 that the observation of Brownian motion by Jean-Baptiste Perrin proved that atoms existed.
Leucippus thought there were Earth, Air, Fire and Water, but in Modern Chemistry there are 92 naturally occurring elements and a further 26 artificially made, extremely short-lived elements. More about these elements in Part 2.
In 1897, J.J. Thomson realised the uncuttable atoms had a substructure in the form of the electron. This really makes the term atom invalid, but we are stuck with it.
Rutherford and Chadwick's work has now taken us into the subatomic world. Atoms can be broken up into Electrons and Nuclei; the nucleus can be further broken into protons and neutrons. Then in 1968, experiments at SLAC showed that protons and neutrons have internal structure, in the form of up and down quarks. So really the building blocks of the universe are three particles: electrons, up quarks and down quarks, one less than the original four elements of earth, air, fire and water.
When we do further particle collider experiments, trying to smash these particles apart to see if they have a substructure, we find they cannot be broken. Electrons and quarks appear to be fundamental, in that they are not made up of anything else.
However, the energy involved in these collisions, instead of breaking the particle apart, ends up creating new, highly unstable, short-lived particles.
We get muons; they are a lot like electrons, just more massive. They quickly break down into electrons. Then there is another particle like the muon again, more massive and more unstable, called the tau particle. Again, these decay very quickly into muons and finally into electrons.
We also get some weird, ghostly, very low-mass, and uncharged particles called neutrons. With an electron, a neutron, a muon, a tau, a neutrino, and a tau neutrino. These six particles form the Leptons. See the orange.
There are a huge number of neutrinos around. They are released in Nuclear reactions, such as those that happen in the centre of the Sun. Hold your thumb up in the direction of the Sun, and 65 billion neutrinos pass through your nail every second. But their ghostly nature means they are barely there, since they interact very, very rarely. Neutrinos would get through a piece of concrete the length of the solar system and not notice it. Even a piece of concrete 5 light-years long, larger than the distance to the next solar system, and only half of those neutrinos would have hit it. Take another 5 light-years of concrete to halve them again;; I think you get the picture.
So we have our six leptons: the electron, muon, and tau particle each with their own type of neutrino. The up and down quarks also have exotic, high-energy, unstable partners. When some particles had a relatively long lifetime, the strange quark was found. Just like the up and down quarks had partners, it was thought that the strange quark had a fourth quark to join it: the charm quark. Then, to complete the symmetry with the six leptons, it was thought there should be a fifth and sixth quark. So when the fifth was found, it made the idea true: the truth quark, and the sixth made the whole beautiful, the beauty quark. Unfortunately, truth and beauty are less common names, and they are more commonly referred to as top and bottom. But I prefer the elegance of those less common names.
With the six leptons and six quarks, we have all the matter in the universe. However, each of these particles also has an antimatter partner, which will annihilate its matter partner when they meet, turning into energy. The reverse is also possible, with energy randomly turning into matter and antimatter pairs, pair production. This is a background effect across the whole universe, with sparticles popping in and out of existence all the time on really short time scales.
As a big fan of board games, I will use the analogy that space is like the board, then the quarks and leptons that form matter are like the pieces on the board. The final piece of the building blocks comes from how these pieces interact with each other. Since we are dealing with the quantum model of reality, where everything is made up of individual quanta or particles, the forces follow the same pattern: forces are fundamentally the exchange of particles between other particles (see the gauge bosons in red above). Each of the four fundamental forces in the universe has its own particles.
The electromagnetic force, or the force between charges, is communicated by charges exchanging virtual photons. The strong nuclear force, which acts between quarks and sticks quarks together, is mediated by gluons and the Pi-zero. This force is also why we never see quarks on their own; they exist only bound to other quarks via the string force, forming baryons and mesons. Finally, we have the weak force, with its W-, W+ and Z0 particles. This interacts with both leptons and quarks, allowing things like radioactive beta decay to happen.
Now, if you were paying attention, you’d notice I have only mentioned three of the four fundamental forces; the fourth force, gravity, hasn’t come up. While everything I have mentioned here is experimentally confirmed and forms the basis of all electricity, magnetism, contact forces, nuclear energy and decay, etc., really everything except gravity. The particle for gravity, the graviton, is only hypothetical, and we don’t have any evidence that it actually exists.
Gravity also plays by different rules; a completely separate theory called general relativity describes how gravity works, and it works really well. Then we also have the Standard Model and quantum mechanics of all these particle which works for everything else. Gravity and Quantum speak entirely different mathematical languages and are entirely incompatible with each other. Quantum mechanics will give us the probability that an event will occur, and its predictions have an amazing degree of accuracy when compared to experiment. Add general relativity and gravity into quantum mechanics, and maths spits out a probability of infinity, which is nonsense.
Most of the time, this doesn’t matter because when we are dealing with tiny sparticles at the quantum scale, gravity is so weak it makes no difference. When we are dealing with really large things, gravity matters, and the quantum effects are so tiny they make no difference. The only time this is an issue is when you have larger amounts of mass or energy confined to quantum scales. This happened at the very beginning of our universe and in the singularities at the centre of black holes. This is why we have absolutely no idea what happens there. We do know what happened shortly after the beginning of the universe, as our particle collider experiment recreates those energy densities, just on a small scale. We get all the particles we mention earlier coming into existence, eventually settling down, and up and down quarks are all that's left from the quarks; they settle into protons and neutrons, the electron later joining them to form atoms, and our building blocks for our universe are made.
But the very beginning of the universe is a mystery. For some, this is the realm of god, and it might be forever unknowable. But I hold out hope that future generations of physicists will unlock the quantum theory of gravity, or theory of everything and tell us more about the beginning of time and space, and what happens inside a black hole, maybe even telling us more about the creation of the universe and fully "know the mind of god.
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In Part 2, we will look at Stars, galaxies and the universe from just after the beginning to its probable end.
Dr Andy Gibson
BSc PGCE QTS MSc PhD
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