QFT: What is the universe really made of? Quantum Field Theory visualized
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Many thanks and shout-out to David Tong's lecture on Quantum Fields for inspiring this video. I highly recommend his free lecture series. In my opinion, he and Richard Feynman are two of the best educators in physics.
What is the universe really made of? What is truly fundamental in the reality that we perceive? This video is about QFT: Quantum field theory - simplified.
Everything that you see is thought to be made of up of particles. This is what most people are taught in science class. The only problem is it is not true. And physicists have known this for decades. Particles are really not fundamental. The best theory in physics tells us that there really are no particles at all, only fields. Particles are merely waves in the field.
Fields are fluid-like substances that can be perturbed, vibrate, and experience excitations. What exactly are fields? Mathematically a field something that takes a value at every point in space. They are not really made of anything other than that from a strictly physicist’s point of view. 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 is analogous to the quantum fields.
The vacuum of space is alive with these fields. The Heisenberg uncertainty principle means that a quantum field cannot sit still. Instead, They are vibrating and changing their value over time. All you can see is really only the excitations of 4 of the fields - Electromagnetic, electron, up quark, and down quark fields. But there are more. The total number of fields is 17, including the Higgs field. Space-time itself is thought to be a field, but so far has not been able to be incorporated in quantum field theory. It would be the 18th field.
One way to visualize the fields is to Imagine the volume of the universe being filled with about 17 different kinds of differently colored fluids instead of water.
Fields eliminate is the idea of action at a distance. In Newtonian gravity, the sun affects the earth which is 120 million kilometers away without touching it. Even Newton thought this was absurd. Einstein’s theory of general relativity eliminated this idea of action at a distance by replacing space with space-time, which is a field that pervades all of reality. In order for a force to propagate over distances, it has to affect its field locally, then propagate from the local point to the distant point, then affect the field locally at the distant point.
Fields can also explain how particles can be created and destroyed. When a Neutron decays to a Proton, an electron, and an antineutrino, it does this by giving its vibrations or energy away to the quarks fields of the Proton, electron field and antineutrino fields.
When you call someone on your cell phone, you are putting excitations in a field and affecting the electronics within the cell phone of the person you are calling. This is field excitations in practice.
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But quantum mechanics is about discreet things yet fields are continuous. The combining of field theory with quantum mechanics is called quantum field theory or QFT. This means the excitations of fields happen only in chunks of energy. The energy of the wave is determined by the mass of the particle. The mass is just the energy needed to vibrate its field. The field will simply not accept energies below a certain threshold.
This discrete unit of energy that the field can accept is what we call the rest mass energy of particles in a field.
Fields are related to the probability waves of quantum mechanics and the Schrodinger equation by their shape. The shape of the electric field is the wavefunction of electrons, for example.
The wave function is what really exists. A "particle" is created when you measure the electron wave. This is when the wave function has collapsed into a discrete value. This can be predicted by the Schordinger equation. A particle has a location, but a field is spread out everywhere.
Who discovered fields? Michael Faraday came up with the idea and actually used the word “field” in his notebook in 1845.
Are fields a real thing, or are they just mathematical constructs? Most physicists believe them to be physical reality.
Are these fields fundamental? - only in the sense that it is the limit of our understanding. Fields may be just an approximation of a deeper level of reality.
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