Do Quantum fields describe reality or are reality?

Question

I have been told that Quantum fields are the real "fundamental" of reality and particles are excitations in these omnipresent fields. I have also been told by no less credible sources that Quantum fields are instead simply a good mathematical "abstraction" and a fine way to quantum mechanically "describe" reality, namely elementary particles - as excitations in the Fock states of their respective quantum fields.

I am not sure if this is a controversy, or even a debate in the scientific community, but I would like someone to elaborate as to whether or not those two views contradict each other, and if the do, to understand why.

Answer 1

This is a highly philosophical question. Usually I try to avoid those, but now I am a bit tempted. I would like to share my thoughts, thoughts that are not in any way special and are taught in introductory courses of quantum field theory. I am not sure to what extend I will cover your concerns, but more experienced people can also comment/reply.

If one imagines flat spacetime as some background on which a set of "quantum fields" live, and all particles that can be thought of as excitations of those fields (fermions as excitations of spinor fields, photons as excitations of gauge fields etc) and their interactions to be happening in a way such that the world we live in occurs (imagine a world without gravity, because attempts are currently going on to interprete gravity as a quantum field, but they are not so successful yet), then one can set up experiments, just like the ones being conducted at CERN to measure specific properties of quantum field excitations or simply particles by making them collide.

A lot of results for the abovementioned measurements of the properties at hand have been verified to a great extend (see magnetic moment of electron for instance). Nevertheless, no one is telling us that the world we live in is a spacetime filled with quantum fields. The "quantum fields" are merely a description, constructed by us, to explain what we see in various experiments. This description is contstructed using a mathematical language (i.e. fields being spacetime functions that obey some algebra relations)...

So, in all I wouldn't say that one perspective contradicts the other. Yes, the framework of quantum field theory is a human construct, but it does not fail to explain the world around us (all the forces of nature except one: gravity). It is formulated in a concise mathematical language, yes, but this does not mean that there is no physical meaning in whatever mathematical objects/structures there exist in that framework... For reference I would advice you to read any quantum field theory textbook (I list some of them below) and be patient, as understanding some concepts may require some time. I also happened to see a nice lecture from David Tong.

Books on QFT (some of them are pretty heavy on mathematics):

1. Peskin and Schroeder: An introduction to quantum field theory

2. Srednicki: Quantum Field Theory

3. Sidney Coleman: Lectures of Quantum Field Theory

4. Weinberg: The Quantum Theory of Fields

Answer 2

There is a controversy about whether quantum theory describes reality, whether such a description is necessary or desirable and whether quantum theory should be modified. This debate is typically but misleadingly said to be about the "interpretation" of quantum theory:

Can an electron move in a well-defined path?

Some people, advocates of the Copenhagen and statistical intepretation, say quantum theory doesn't describe reality and is just a machine for making predictions. Since a prediction is an account of what will happen in reality under particular circumstances so those interpretations make no sense. In addition, without an account of what's supposed to be happening in an experiment there is no criterion for whether the experiment has been set up correctly, so these interpretations are wildly impractical, philosophical mutterings to the contrary notwithstanding.

If you take quantum theory as a description of reality instead of ignoring it or trying to modify it, then it implies that reality on a large scale is described by a structure that looks a bit like a collection of parallel universes. This is often called the many worlds interpretation of quantum theory. Other interpretations require modifying quantum theory in ways that are difficult to reconcile with QFT:

https://arxiv.org/abs/2205.00568

And the Everett interpretation has been used to explain issues such as the propagation of information in entanglement experiments:

https://arxiv.org/abs/2207.09020

If you want to learn QFT there are good and relatively easy to understand books that don't take an explicit position on the interpretation issue such as "Quantum Field Theory in a Nutshell" by Zee and "Quantum Field Theory for the Gifted Amateur" by Lancaster and Blundell.

Answer 3

I have been told that Quantum fields are the real "fundamental" of reality and particles are excitations in these omnipresent fields.

Call it the A belief.

I have also been told by no less credible sources that Quantum fields are instead simply a good mathematical "abstraction" and a fine way to quantum mechanically "describe" reality, namely elementary particles - as excitations in the Fock states of their respective quantum fields.

Call it the B belief.

A is an ancient proposition , which started with the mathematics and philosophy of ancient Greece.

There are the platonists, who, according to Plutarch believed that

ἀεὶ ὁ θεὸς γεωμετρεῖ

Always the great God applies geometry to the universe

This is the point of view of the people believing fervently A, god being substituted by beautiful mathematical theories. They expect that everything flows from mathematics. I would call them Platonists.

B are the people who since the enlightenment have laboriously experimentally studied nature applying the appropriate mathematics to get theories that will describe data and also, very important, be predictive of new data. They use the mathematics with extra axioms that connect measurements and units to the mathematical outcomes, and freely acknowledge that they are using mathematical models, not discovering a mathematical universe. I would call them pragmatists.

Maybe my answer here will help a bit in this.

Now if, and it is a big if, a mathematical theory of everything is found in the future, that is always correct, one could say that the people who believe in A are correct. Until then it is an open question AFAIK.

Answer 4

It depends what you define as reality. Is there some underlying and humanly accessible true description of reality (true in the sense of Plato)? Perhaps.

Is there no such humanly accessible true description of reality (Kant perhaps thinks so)? Perhaps.

The first order question you must then answer is whether you believe in an "absolute truth" or not. I personally don't think this question can be answered.

Answer 5

We can't observe the field directly but we know it's there.