The building blocks of reality

What are the fundamental building blocks of reality?

1 Until the 1970s it was assumed that protons and neutrons were the fundamental particles. Then it was discovered that protons and neutrons consist of quarks and nothing smaller was ever discovered.

2 A model based on fundamental particles is easy to learn, but it's not true.  The fundamental building blocks of nature are actually more nebulous and abstract. They are fluid-like substances spread throughout the universe, which ripple in strange and interesting waves. These fluid-like things are called fields.

3 A field is:

• like a fluid which ripples and sways throughout the universe
• spread everywhere throughout the universe
• takes a particular value at every point in space and time.

4 This is not a new idea. It originated 200 years ago, thanks to Michael Faraday and his experiments with electricity and magnetism. He described the electric and magnetic fields as invisible "objects" spread throughout space. This was one of the most revolutionary ideas in science.

5 We become familiar with fields as children when we play with magnets and feel the force that exists when they repel.  Faraday realised that even though the space appears to be empty, there is something real there which is responsible for the force.  We call it the magnetic field.

6 Faraday demonstrated how moving magnets can induce an electric current, as shown by the movement of a needle in a galvanometer.  This astounded audiences in the 1800s. You were making a needle move without touching it or going near it. We take this for granted now. The point is that the field is physically real – we can affect things far away using the field.

7 Faraday’s legacy

The world does not consist of particles – there is an underlying fabric of reality, consisting of fields, spread throughout all of space.  In 1846, Faraday suggested that these invisible magnetic and electric fields that he’d postulated were literally the only thing we’ve ever seen. In other words, light consists of ripples in the electric and magnetic field.  To appreciate Faraday’s genius, note that it took 50 years for Maxwell and Hertz to confirm this.

8 The concept of fields turned out to be even more important than Faraday realised. In the 1920s, Heisenberg and Schrödinger realised that at the subatomic scale, the world is much more mysterious and counter intuitive than the description given by the classical physics of Newton and Galileo. This was the birth of the theories of quantum mechanics.

9 Quantum Field Theory

Energy is not continuous – it is parcelled up into small discrete lumps known as quanta (quantum means discrete, or lumpy)

If we take the ideas of quantum mechanics (which is discrete and lumpy) and combine them with Faraday’s ideas of fields (which are continuous smooth objects waving and oscillating in space) we get quantum field theory.

Waves of the electromagnetic field are what we call light. When we apply quantum mechanics, we find light waves appear as particles which we call the photon.

That same principle applies to every particle in the universe. Space is permeated with several fields. So, as well as the electromagnetic field, there is the electron field. As with all fields, the electron field is like a fluid, filling space throughout the universe. The ripples and waves in this fluid get tied into little bundles of energy which are what we call the electron.

Like photons, electrons are also not fundamental – every electron in the universe is a wave in the in the same electron field, just like the waves on the Pacific coast of the USA are part of the same underlying ocean as the waves on the Pacific coast of Australia.

There are also two quark fields (there are two types of quark) - these fields give rise to the up quark and down quark.

So to summarise Quantum Field Theory:

There are no particles in the universe.

The building blocks of reality are fluid-like substances we call fields.

[Click here for more detail on quantum fields] 

10 Nothingness

Start with an empty container.  Although it looks empty it is full of molecules of air and a bath of infra-red light from its warm environment. It also contains ambient electromagnetic radiation from our surroundings, and even streams of cosmic particles. So, take every, single thing that exists out of the container – all the particles, all the atoms. Shield it from passing cosmic particles. Cool it to absolute zero. The container then contains empty space. We then discover empty space is not nothing. 

This is what nothingness looks like at the sub-atomic scale:

This is the state of empty space, the simplest thing we can possibly imagine. What we see is that in the absence of particles, a field exists. As with all fields, it is governed by the rules of quantum mechanics, specifically Heisenberg’s uncertainty principle which explains nothing in reality can be still.  This vacuum state is the quantum state with the lowest possible energy. It contains no physical particles. This zero point energy is the energy of a system at a temperature of zero.

Hence we see that nothing is a field full of bubbles and activity - we call these quantum vacuum fluctuations. 
Quantum fluctuations are not just theoretical – they have been measured, they are real (and give rise to the Casimir effect).

11 How Many Quantum Fields Exist?

Let's start with the particle fields. There are twelve particles that comprise everything we have ever seen or detected.

The top row represents the particles we experience every day. The others only appear in extreme conditions, such as in particle accelerators.  Even though we refer to them as “particles” - they are not really particles: Each particle arises from a field and it is the twelve fields shown above that give rise to what we perceive as particles.

These twelve fields interact with each other through four different forces... 

Two of these are familiar (gravity and electromagnetism) but there are two other forces that only operate on small scales of a nucleus – the strong nuclear force which holds the quarks together inside protons and neutrons, and the weak nuclear force which is responsible for radioactive decay and making the sun shine among other things.  Each of these forces is associated to a field.

·       The electromagnetic field is associated with electromagnetism

·       The gluon field is associated with the strong nuclear force

·       The W and Z boson field carries the weak force

·       There is also a field associated with gravity. This turns out to be space and time itself.

So... twelve fields that give matter and four other fields that are the forces. The universe is a combination of those sixteen fields acting together in interesting ways. The universe is filled with these fields, which are fluid-like.

12 How do the fields interact?

Consider an example: Say one of the matter fields starts to ripple, for example, the electron field starts to wave up and down. That could kick off the electromagnetic field which in turn will also oscillate and ripple producing light.  That will react with the quark field which in turn will oscillate and ripple and so on.  We end up with a harmonious dance between all these fields, interlocking with each other, swaying and moving this way and that way. That image represents the fundamental laws of physics.  

13 The theory which underlies all this is the pinnacle of science, the greatest theory human beings have ever come up with. It’s called the standard model and mathematically, it looks like this:

There is one extra field, which became famous recently and that is the Higgs Field.  It was first suggested in the 1960s by Peter Higgs but experimental evidence did not appear until 2012 in the Large Hadron Collider, which made a Higgs Boson particle appear by creating a ripple in the Higgs field.  The particle is incredibly short lived - it only lasts for about 10⁻²² seconds. It is important for two reasons:

a) It is responsible for mass in the universe. Properties of particles are actually a statement of how their fields interact with other fields. So the property we call the electric charge of an electron is actually a statement of how the electron field interacts with the electromagnetic field.  The property of its mass is a statement of how it interacts with the Higgs field.

b) It was the final piece of the standard model jigsaw.   It took 50 years to discover and it behaves precisely as predicted by the theory.

14 The theory of everything (so far)

Refer again to the equation for the standard model (see paragraph 13).  This equation correctly predicts the result of every single experiment we’ve ever done in science. Everything is contained in this equation.

·       The first term comes from Einstein and describes gravity. You can predict how far an apple falls from a tree, or why the planets orbit in ellipses, or what happens when black holes collide, or how the universe itself expands.

·       The second term comes from James Clark Maxwell and it tells us everything about electromagnetism, the results of Faraday’s experiments, lasers, etc. 

·       The next term governs strong nuclear and weak nuclear forces. 

·       The part that describes matter comes from Paul Dirac

·       Finally the Higgs Boson equations produced by Peter Higgs.

(Z is the Partition Function)

We have yet to find a way that this equation stops working, however:

15 What does the equation NOT explain?

Three things:

a) The standard model equation is the best thing we currently have but we know there is stuff out there in the universe that is not explained by this equation, such as invisible particles (dark matter). We can’t see dark matter particles but we can see their effects, for example on how galaxies rotate or how light bends around galaxies.

b) There is also dark energy spread throughout space, which is probably some kind of field but not one we understand. It causes everything in the universe to repel everything else.

c) Evidence suggests there was an unimaginably rapid expansion that occurred prior to the Big Bang (the Big Bang is the aftermath of what occurred at the end of that inflation). That rapid phase of expansion is called inflation. Inflation is also not explained by the equation.

We need to understand those in order to determine the next laws of physics.

16 Inflation

The universe is 13.8 billion years old. During its first 380,000 years it was in  state we refer to as a primordial fireball - a state where atoms could not exist, where matter was distributed as a highly ionised plasma. We know this for sure because we can see the remnants of it, known as cosmic microwave background radiation and it looks like this...

By studying the patterns, patches and flickering in the background radiation, we get a lot of information about what was happening when the universe was born.

17
An obvious question is: What caused the flickering that we see in the fireball? We know that whatever caused this flickering must have happened in the first fractions of a second after the big bang. Immediately prior to the Big Bang, during inflation, the Universe is completely empty. There are no particles, no matter, no photons; just empty space itself. That empty space has a huge amount of energy in it, with the exact amount of energy slightly fluctuating over time. Those fluctuations get stretched to larger scales, while new, small-scale fluctuations are created on top of that (see paragraph 10). These fluctuations became stretched across the universe as it expanded. This is confirmed because the calculations based on our knowledge of quantum vacuum fluctuations match the observation perfectly. 

Which field we are seeing in the background radiation?  We know it is a scalar field, which suggests the Higgs field. Or it could be the graviton. Further experiments are required to determine this, which look at the polarisation of the flickering and perhaps find a pattern of swirls which tells us it was the graviton itself that gave rise to that pattern, that is, quantum gravity.  

18 Is there an even deeper level to reality?

There are patterns that suggest there is something deeper underneath the standard model.

For example, the equation that describes the force of electricity and magnetism is almost the same as the equations that describe the strong force and the weak nuclear force. So maybe it’s not a case of three forces, maybe it’s one force and we are actually looking at that one force from three different perspectives.

The twelve matter fields in the universe each obey the same equation (the Dirac equation). So maybe it’s not twelve fields, but one field, which we see from twelve different perspectives.

These ideas are known as unification.  Electromagnetic, weak and strong forces are three of the fundamental four forces of nature, which are responsible for all of the pushes and pulls in the universe. Finding a single force which underlies those three forces  is called grand unification.   The equations for matter and forces are also very similar. So maybe matter and forces are related to each other, and this idea is called Supersymmetry. 

19 The ultimate step would be to combine all the terms into a single term from which everything emerges: Gravity, Higgs, all the forces, all the particles... everything.  The theory for this is called String Theory. It contains the entire standard model in a single concept.

20 To verify any of this requires experiments. There’s no way to test string theory at the moment, but the LHC is testing the other ideas. However it has not seen anything yet. Three approaches currently being considered to accelerate progress:

• Be patient! Maybe it will see something next year or the year after. (This seems unlikely).
• All our theories are so beautiful they must be right so what we need is a bigger machine. Ten times more powerful. That would cost $10 billion and not many governments want to invest in this, except possibly China. It would take 20 years to happen.
• Maybe the suggestions of unification are red herrings. Maybe if we work harder to understand the standard model equation better (see paragraph 14), other options will emerge.  So maybe we should dig deeper into the equation and challenge some of the assumptions.  There are hints in there of mathematical patterns we haven’t explored.

The above is mainly taken from this lecture by Professor of theoretical physics, David Tong. The timings in the lecture correspond to the paragraph numbers as follows:

1 07:00
2 09:00
3 10:47
4 11:00
5 13:00
6 14:30
7 16:00
8 17:00
9 18:10
10 21:00
11 33:00
12 36:00
13 37:40
14 40:44
15 43:30
16 45:20
17 46:45
18 51:00
19 52:45
20 57:00