4
$\begingroup$

In the beginning of "Quantum Field Theory for the Gifted Amateur," there is the statement:

Every particle and every wave in the Universe is simply an excitation of a quantum field that is defined over all space and time.

To an naive (not gifted) self-studier, this came as quit an eye-opener. Over the course of a non-physics education, one tends to get so used to the existence of atoms, protons, electrons,etc., even subatomic particles, that it is easy to overlook where they came from.

So the above remark is a nice resolution. Then my question is, where do these quantum fields come from.

Further, with a subsequent assertion that, e.g., all protons are perfectly alike, as mentioned on pdf page 9 of Prof. Tong's notes:

http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf

in that "there is a sea of proton stuff filling the universe," if this sea fills the universe, then where do the seas of other particles fit in - and how do they keep things straight amongst themselves.

Maybe this is too broad a question, or, more likely, I am inadequately versed in these matters. But I would appreciate any help or reference suggestions.

Thanks

$\endgroup$
5
  • 2
    $\begingroup$ possible duplicate of What is a field, really? $\endgroup$
    – ACuriousMind
    Jul 28, 2014 at 20:17
  • 1
    $\begingroup$ @ACuriousMind nice link -thanks. Yet it seems that those discussion of a field tend to portray it as a derivative to describe what is happening. Yet, my impression from my modicum of exposure to QFT is that the field precedes the particle. $\endgroup$
    – user41976
    Jul 28, 2014 at 20:32
  • 1
    $\begingroup$ If you read dmckee's answer carefully, I think it says that what precedes what is a meaningless question. The formalism says its the fields, but what you observe is the particles, but what you explain it with is the fields... The question "What is a field?" has exactly one answer: "An assignment of values (be they scalars, vectors, operators) to points." All else is (from the pure theory viewpoint, unnecessary) interpretation. $\endgroup$
    – ACuriousMind
    Jul 28, 2014 at 20:37
  • $\begingroup$ @ACuriousMind Thank you for the emphasis and pointing thing out. I appreciate it. Regards, $\endgroup$
    – user41976
    Jul 28, 2014 at 20:46
  • 1
    $\begingroup$ "where do these quantum fields come from." If quantum fields are fundamental then this isn't a valid question. And, if they aren't fundamental and if someone gave an alleged answer "quantum fields come from X", I would think that you might pause, furrow your brow, and then ask "but where does X come from?". $\endgroup$ Jul 28, 2014 at 22:45

1 Answer 1

3
$\begingroup$

The "is simply an excitation" might be a bit overstated, as it if it were that simple you probably wouldn't have needed to ask this question. It might be better stated as "can simply be modeled mathematically as an excitation".

The "fields" are part of a mathematical model that attempts to explain our observations. Saying "where does a field come from" is a bit like saying "where does everything in the Universe come from" or "what happened before the Big Bang", which may seem intuitively sensible to humans, but are not necessarily well-founded questions.

Some "fields" may have emerged shortly after the Big Bang due to symmetry breaking, so it may be possible to unify some of the "fields" to a simpler state with fewer "fields", if that makes sense. Evidence suggests (as well as a scientific bias toward simplicity) that the closer you get to the Big Bang, the simpler the models can be. Unfortunately, this also makes the process of modeling things more complicated in part since we can't make direct observations of what the Universe might have looked like back then to test theory.

$\endgroup$
3
  • $\begingroup$ So if I'm right. Once we assumed atoms, then we assumed particles and waves, and now we assume fields? $\endgroup$ Mar 6, 2020 at 23:33
  • 1
    $\begingroup$ @VeronicaNoordzee We've never assumed that atoms exist, that wave/particle duality exists, or that fields exist. We determine these things via observation and the scientific method. Theories use models to describe observations. In physics, these models are mathematical in nature. In quantum physics the models are necessarily mathematical because no common-sense physical interpretation can explain observations. Philosophers still argue over whether reality is mathematics, or if the math just attempts to describe a deeper reality. I believe the former due to what I said two sentences ago. $\endgroup$ Apr 30, 2020 at 19:08
  • 1
    $\begingroup$ I like the first word of your comment: "We". We, human beings. We, scientists, We, physicists. $\endgroup$ May 6, 2020 at 14:28