Philosophy has long asked the question “What is Reality?” While it’s daughter, physics has been more precise by asking instead: “What is it made of?” The answer, as we shall see, takes us into quantum field theory.
One of the first answers to this question was supplied by the philosopher Democritus nearly 2500 years ago when he espoused his metaphysic of atoms in the void. The father of atomism, he set up the still prevailing view that material objects occupy space, building on the notion that space itself is a kind of container.
Today, however, the view supplied by modern quantum field theory paints a much different picture. No longer are material objects situated in space, but rather, material objects are the macroscopic effect of properties or conditions of space. For as we shall discover, with regards to quantum field theory, space itself has properties that manifest as physical effects. Now what’s positively fascinating about fields is that their essential “immaterial” nature far more resembles mind than that of matter. If you’ve ever considered any form of philosophical idealism the intuition of what fields are may come easier to you.
The Fundamental “Object”
Quantum field theory tells us the fundamental object(s) of the universe is unbounded fields or rather, a single unified field made up of many distinct but superimposed, interpenetrating, and cooperating in parallel fields. These fields are ubiquitous and pervade the entire universe. It may help us to think of them as separate sheets or fabrics but we must remember they do not stack atop one another but are instead enmeshed within one another.
All of the material objects that we see and all of the fundamental forces we know, are the result of the complex interrelationships of charge distributions and energy-momentum fluctuating in these quantized fields. Now, I’ve used a lot of fancy language and I still haven’t even defined a field yet…. or a quantum for that matter.
A field is defined as a property or condition of space that has physical effects. So, the magnetic field, as the father of fields Michael Faraday would say, is a property of “mere” space. The very fabric of reality is a magnetic field that allows “lines of force” to transmit energy and momentum across “thin air,” through nothing, but not nothing because it’s a field. Not only is the fabric of existence a magnetic field, but it’s also a gravitational or metric field, an electromagnetic field, a Higgs field, a gluon field etc. I’m sure you get the picture.
Quanta
In QFT there is no such thing as empty space as a kind of container, but rather space itself has properties that manifest as physical effects. Now you might be wondering what happened to the atoms of Democritus. Well, atoms are composite entities made up of smaller, more basic sub-atomic energy-momentum fluctuations that are but (somewhat) localized vibrations confined to their particular field. In fact, these minimal excitations of the field are called quanta. A single one is called a quantum. People tend to think of quanta as particles but they are certainly not particles.
A quantum is a discrete, minimal unit of energy that, wave-like is a spread-out vibrating oscillation of the field. The word quantum does not refer to the size or magnitude of the field vibration but rather emphasizes its discrete nature. Although it is spread out and everywhere it remains a single unit and so must act as one. It is discrete because it is its own unit and lives and dies a life of its own.
Further, these quanta are described by what’s called a wave-function and consulting the wave function can tell you all of the properties of that quantum, but with a little uncertainty because in QFT you can only calculate probabilistic results of interactions. And also, there was this guy named Heisenberg who illustrated an intrinsic and undeniable indeterminacy with regards to a quantum’s position and velocity.
Interacting
Should a single quantum — spread out in its field — encounter an atom with which it wishes to interact, it must do so as a unit, no matter how spread out it is and it must do so instantaneously. This is called quantum collapse and is governed by the probability that it should interact and the appearance of which makes it “look like” a particle is present. But with a fields-only view we should think of this moment as nothing but the spatio-temporal location where the energy-momentum of the quantum transfers between fields or interacts with other quanta within its own field.
Further, a fields-only view solves the incomprehensible wave-particle duality because no particle exists! and the entanglement paradox is understood by illustrating that entangled quanta also act as a unit, instantaneously, regardless of distance between them for the simple fact that the two are no longer two, but entangled, have become one, a single quantum.
So that’s the basics of quantum field theory. A mere scratching the surface. There exist properties of space that allow quanta of energy-momentum to spin and dance about, to respond to charges and manifest macroscopic phenomena. No particles exist but the necessary behaviour of quanta can give the impression that particles exist….. But they don’t!
Some excellent books on the topic: TheLightness of Being by Frank Wilczek: http://amzn.to/2oG2d4K
A beautiful Question by Wilzcek: http://amzn.to/2oFSStL
I’m currently reading Tales of the Quantum by Art Hobson. I highly recommended it. I had to order it from Amazon as my local Chapters wasn’t carrying it despite it being released only a few months ago. Splurge for your library and get the hardcover: http://amzn.to/2qB8tz7