Quantum Field Theory|What is universe really made of?

 

What is the universe really made of? What is truly fundamental in the reality that we perceive? In 400 BC, Greek philosopher Democritus came up with the idea of atoms as being fundamental. He believed that these were solid pieces of matter which could not be divided any further.2,300 years later, in 1897 JJ Thompson discovered something smaller than an atom called the electron. And in 1912, Ernest Rutherford discovered that Atomshad nuclei.

Then we found that nuclei were composed of protons and neutrons.These were thought to be the fundamental components that all things are made of,until the 1960s, when we found that neutrons and protons were composed ofeven smaller things called quarks - two kinds - up quarks and down quarks. Today,everything that you can see around you is thought to be made up of just thesethree particles - electrons, up quarks, and down quarks. That's what all atoms aremade of - your phone, your desk, your skin your grass, everything. At least, this iswhat most people are taught in science class. The only problem is - it's not true.And physicists have known this for decades. These particles are really notfundamental.

The best theory in physics tells us that there really are noparticles at all. Nature is made of fields. Reality isfundamentally many different fields. These things we call particles aremerely waves in the field - not that kind of field though. So what in the heck arethese fields? And what do they tell us about the nature of reality? The idea of particles, even the particles that I've talked about numerous times composing the standard model, is not whatthe universe is actually made of.

The particles are fiction. They're convenient representations that are not really the best understanding of the universe today.The fundamental nature of the universe are not particles but fields. These arefluid-like substances that can be perturbed. They can vibrate andexperience excitations. What exactly are fields? Mathematically, a field issomething that takes a value at every point in space. They're not really madeof anything other than that from a strictly physicist's point of view. Think of it this way, If you have a fireplace in a room, the temperature at every point in that room would have a value. This would be a field of temperature. This isanalogous to the universe's fundamental fields. And these fields in nature areeverywhere. You can't escape it. If you take a strong metal box, and removeeverything from it - all the gases, all the atoms, all the photons, what will be leftin that box? This is what we think of as a vacuum - like the vacuum of empty space. But in fact, this vacuum is alive with fields. And they're constantly moving andchanging. The Heisenberg uncertainty principle means that a quantum fieldcannot sit still. Instead, they're moving and vibrating and changing their valueover time.

This is a computer simulation of empty space. All the bubbles that yousee popping and bursting are perturbations of empty space.Particles are constantly being created and destroyed in this emptiness. Butthese particles are really excitations of fields that pervade all of space. Whatyou can see in the world around you are excitations of these fields. In fact, allyou can see is really only the excitations of four of the fields. Youcan see photons, or light, which are vibrations in the electromagnetic field.Electrons are vibrations in the electron field.

Up quarks and down quarks make upthe protons and neutrons in the nucleus of all atoms. They are vibrations in theup quark field, and down quark field, respectively. Amazingly, everything thatyou can see around you - your phone, your desk, flowers, and trees - the earth belowyour feet, everything is composed of just these four fields. But there are more thanjust these four fields. In fact, everything that we designated asparticles in the standard model, the best theory of physics we have, are reallyexcitations or vibrations of their own fields. The total number of fields wouldbe 17, including the Higgs field. Note that space-time itself is thought to bea field, but so far has not been able to be incorporated in quantum field theory.It would be the 18th field. All the so-called particles are really waves.

Andwhen I say wave, I don't mean a wave like an ocean wave. The 2d models are just avisual aid. But the waves would actually be three-dimensional. Can you see any ofthese fields? Not really. But you can kind of get an idea by putting a magnettogether with some metal filings. The lines that you see are really themagnetic field lines changing due to the magnet. Another way to visualize fieldsis to imagine the volume of the universe being filled with water, as if we wereliving in an ocean. Now, imagine that instead of water, the ocean is filledwith multiple fluids - about 17 different kinds of fluids, and these fluids are ofdifferent colors. This may look really spectacular and weird. But this issomewhat analogous to what our universe actually looks like, except that youcannot see these fields. Why is this theory better than the idea of particles?The key thing that this field eliminates is the idea of action at a distance.

Sofor example, in Newtonian gravity, you have to concede that the gravity ofthe Sun somehow affects the earth, which is a 120 millionkilometers away. How can something affect something else so far away withouttouching it? This is action at a distance. Even Newton thought that action at adistance was absurd. He said, "it is inconceivable that inanimate brutematter should, without the mediation of something else,which is not material, operate upon and effect other matter, without mutualcontact. Einstein's theory of general relativity eliminated the idea of actionat a distance, by replacing space with something called space-time, which is afield that pervades all of reality. And he showed mathematically, that gravity isreally due to a bending of this field of space. Whatever happens anywhere to aparticle in space is governed by what is happening in the field near the particle.In order for something to propagate over distances, it has to affect its fieldlocally, then propagate from the local point to another distant point, thenaffect the field locally at that distant point. This is similar to the way a wavewill propagate in water if you throw a rock in it, from the rock to the shore,and effect sand on the shore. Fields can also explain how particles can becreated and destroyed.

So for example, when a neutron decays to a proton andelectron, and an anti-neutrino, how does this happen? Was the electron hiding inthere? Where did it come from? Fields have the property that they can give theirvibrations or energy away if you strike the field hard enough. They will affectother fields. So in this decay, the energy of the quark field of the neutron can betransferred to the quark fields of the proton, plus electron field, and antineutrinofields. In addition, particles and antiparticles are excitations in thesame field. They're just described as equal andopposite excitations of the field. This is represented by two opposing waves.When these waves come together, they annihilate each other. You are affectedby these fields every day. When you call someone on your cell phone, you'reputting excitations the field, and affecting the electronicswithin the cell phone of the person you're calling. This is action at adistance in practice, except it's not action at a distance.

Your cell phone iscreating excitations in the electromagnetic field, that ispropagating from you, to the cell tower, and eventually onto the receiveron the other end. But there appears to be a dilemma here because you have learnedin school and in my videos too, that quantum mechanics is all about discretethings. That's why it's called "quantum." But fields are continuous not discrete.So there appears to be a conflict here, between the idea of the discreteness ofparticles as presented in quantum mechanics, and the continuous nature offields. So how are these two ideas reconciled? The combining of field theory withquantum mechanics is called quantum field theory, or QFT. So essentially, allthe excitations of fields happen only in chunks of energy.

The energy of the waveis determined by the mass of the particle. What is a mass? A mass of aparticle is just the energy needed to vibrate its field. Energy, if you recall,is equivalent to mass using Einstein's famous equation, E = MC^2 . Thefield will simply not accept energies below a certain threshold. Once you tapthe field hard enough however, a particle is created. This discrete unit of energythat the field can accept, is what we call the rest mass energy of theparticle. In a field, it is the fundamental amount of energy that mustbe added to the field in order to create a particle. So for example, one electronis created when an electron field is excited by 0.511 mega electron volts,which is the mass of one electron. If you add energy equivalent to 0.4 megaelectron volts, no particle gets created. If you put in 1.1 mega electron volts,then two electrons get created, and so on. This works for all the particles. All theelectrons in your body and my body are waves in the same underlying field. Thefield is fundamental. The electrons are not. Also present in this room, and in yourroom, are the up quark field, and the down quark field. And all the atoms in yourbody are composed of particles which are ripples in these three fields.It's the same feel that you, I, and everyone on earth is in. In fact, it's thesame field that all the other planets and the Sun are in. We are basicallycomposed of ripples in the same three fields everywhere in the universe.

Now,there's no indication that ripples in my field can communicate with the ripplesin your field, but it's one continuous field. And everything is connected to it.Fields don't tell us everything though. It does not tell us what dark matter is,what dark energy is, or how the Big Bang occurred, or why there is more matterthan antimatter in the universe. So, there's still work to be done.Now, how are waves in the field related to the probability waves of quantummechanics, and the Schrodinger equation? When we say that an electron is a particlewith a position and velocity, this is wrong. And it's not because we can'tmeasure its position in velocity. It's because there's no such thing as aposition and velocity. All there is is a wavefunction. It is spread all throughoutspace, and it only tells us what the position and velocity will be if wechoose to measure it. So for example, the shape of the electromagnetic field isthe wave function of photons.

The shape of the electric field is the wavefunction of electrons, and so forth. The wave function is what really exists.And when you observe the electron, you don't see the wave function, because thewave function has collapsed into a discrete value. This can be predicted bySchrodinger's equation. The fields are vibrating and modulating, but when you measure them, they resolve into individual packets of energy calledparticles. So quantum mechanics says that fundamentally, reality is different whenyou measure it versus when you don't. Every particle in the universe is a tinyripple in the underlying field, moulded into a particle by the machinery ofquantum mechanics. The quantum fields vibrating at every location in space andthroughout time are the fundamental building blocks of nature. So the age-oldquestion of whether light is a particle or wave can be answered. They are waves. A particle is just what manifests when we measure the wave. Who discovered fields?It should be noted that Michael Faraday came up with the idea,and actually use the word "field" in his notebook in 1845. Are fields a real thing, or are they just mathematical constructs? Even though a field is made of nosubstance that physicists know of, fields are considered real physical stuff. Thisis because they exist in space and have energy. In addition, their properties canbe calculated and accurately predicted by experimental results. Now we get backto the question, "Are these fields fundamental?"  Well, I think it'sfundamental in the sense that it is the limit of our understanding. But it couldvery well be that these fields are just an approximation of a deeper level ofreality, because ultimately there should be some fundamental reason why thesefields have the properties that they do.

Why does the electron field have aminimum requirement of 0.511 mega electron volts? Why does it obeymathematical rules? Will we ever know the answer?Unlike many physics lover, I think we will. We may not even be asking the rightquestions. In the famous words of a certain Secretary of Defense, there areknown unknowns, and unknown unknowns. And I think the answer will come when wehumans know enough to ask the right question.