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Electrons and photons are fundamental, while chairs and tables are not. Some theories of physics also state that space or time or both, are not fundamental. But what does that mean, "fundamental"? Electrons, photons, chairs, tables, and space and time are all real, existent entities, but only some are fundamental. Is there a rigorous definition of "fundamental" somewhere? Also, I am very interested in whether philosophers of physics (or even just philosophers more generally) have talked about this issue, and maybe even tried to give a rigorous philosophical definition or clarification of the concept of "fundamental". I would like to see some references on this.

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    For starters, there's an SEP article on fundamentality (see also the entries on metaphysical grounding and supervenience). Dec 17, 2023 at 2:03
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    I don't have a reference handy, but in very short for how physicists mean it: that system, observable, or model is fundamental which is not emergent. That system, observable, or model is emergent which is an approximate description of how some other system(s), observable(s), or model(s) behave, alone or in combination. A system, observable, or model is more fundamental than some other system, observable, or model, if it is one of the system(s), observable(s), or model(s) whose behavior, alone or in combination, is approximated by the other.
    – g s
    Dec 17, 2023 at 5:12
  • To say that e.g. quanta are more fundamental than tables is to say that you can, given a sufficiently large pile of horrendously overcomplicated math, describe what tables do in terms of what quanta do, but you can't describe what quanta do in terms of what tables do, no matter how much math you do, because the "table" representation is an approximation.
    – g s
    Dec 17, 2023 at 5:15
  • Likewise e.g. Einsteinian mechanics is more fundamental than Newtonian mechanics because the former model can predict everything that the latter can, more accurately, and more besides.
    – g s
    Dec 17, 2023 at 5:19
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    If you own a restaurant, chairs and tables are fundamental. Electricity is fundamental, but electrons are not. It all depends on your frame of reference.
    – user4894
    Dec 17, 2023 at 22:24

3 Answers 3

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I cannot provide a reference, I am ashamed to say, but I can explain the general idea. Much progress in the natural sciences has been in the direction of explaining a wide range of complicated phenomena in terms of a very much smaller set of simpler building blocks. For example, the breathtaking variety of life forms are combinations of more-similar cells; the workings of the cells are the result of interactions between molecules; the molecules are interactions between atoms; the atoms are interactions between electrons and nuclei; and so on. At some point you reach the current end of the decompositional road, where what you are left with is a collection of things you can't explain in terms of anything simpler. Those things and their few properties are what we call fundamental. Note that the labelling is inherently provisional, since it is possible that we might find a way to explain what we currently consider to be the fundamentals in terms of some underlying phenomena as yet hidden from us.

Space and time are currently at the interesting border between being fundamental and possibly being explainable in terms of something else. There are various developing ideas- associated with resolving incompatibilities between General Relativity and quantum theory- about how space and time may be quantised, but they remain speculative as yet.

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  • Descartes doubted physical reality in order to come up with his fundamental "I am", as Antoine Thomas paraphrased: dubito, ergo cogito, ergo sum ("I doubt, therefore I think, therefore I am"). Kant followed up with pure reason of the cogito and Heidegger scoped out its foundation. These philosophers don't treat in theoretical physics for what is fundamental. Dec 17, 2023 at 10:32
  • @ChrisDegnen indeed, and there lies one of the distinctions between physics and metaphysics. Dec 17, 2023 at 10:35
  • @ChrisDegnen Yet, the general idea of "something that cannot be explained in terms of other things/concepts but serves as explanatory for all phenomena" remains true for all of them.
    – Philip Klöcking
    Dec 17, 2023 at 19:42
  • @PhilipKlöcking Quite so, we are bookended by mysteries. 'Something' gives rise to experience, in which we look at the cosmos and wonder what 'something' gave rise to it. Fundamental 'somethings', but necessarily not 'things', (otherwise we would have to seek their causes too). Dec 17, 2023 at 20:10
  • @PhilipKlöcking Perhaps they are fundamental principles. Dec 18, 2023 at 7:01
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  1. In physics the electron and the neutrino are named fundamental or elementary particles. Because until now, no one found an internal structure of these particles. Moreover, one does not expect that these particles have internal components.

    In this sense, not being composite is named fundamental.

    The photon of electromagnetism, the bosons from weak interaction and the gluons from strong interaction are fundamental in the same sense. While particles like proton and neutron are not fundamental in the above sense, because they are composed of quarks.

    For a first introduction see Elementary particle. For information in deep, see physics textbooks for graduate students.

  2. Of course, concepts like space and time cannot be named fundamental in the above sense, because they are not particles. These concepts are often named fundamental because nearly all physical theories use them as their basic concepts. The specific observables of these theories are expressed as functions of time and space, more precisely: time and space are the coordinates of the phase space.

    Nevertheless we know from the Special Theory of Relativity that both concepts are relative. Only the concept of 4-dimensional spacetime has an invariant meaning. Hence spacetime, but neither space nor time, can be named a fundamental concept.

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  • @simonatrcl Thanks, I meant "neutrino".
    – Jo Wehler
    Dec 17, 2023 at 15:25
  • :} I'll delete the comment now it's superceeded, and this one in a little while. Cheers - Dec 17, 2023 at 15:41
  • I love neutrinos, they are so fascinating. In the titanic eruption of a supernova, where 1 star can outshine an entire galaxy, 99% of the power output is neutrinos. Look up the detection of the 1987 supernova.
    – Scott Rowe
    Dec 18, 2023 at 11:48
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Take this with a huge grain of salt, but this is how I interpret the word:

Many people like to imagine the universe as operating a lot like a computer program, a simulation involving rules, and calculating future states based on those rules. Now, I'm not here to argue that that's the "correct" way to view the universe, but I am here to say that if you're at all inclined to accept that that could at least be analogous to how the universe operates, then here's what "fundamental" might mean in such a context:

If the universe is a computer program simulation, then the things which are 'fundamental' in that simulation are the things which have either direct, strong referents, or at least indirect but obviously implied referents, in the source code itself.

So, the "universe" of conway's game of life has, as a fundamental entity, a "cell" or "pixel". Those cells are strongly referenced in the source code, and the source code calculates the future of the Conway's universe by operating on those cells.

Gliders, while being an immediate consequence, aren't purely fundamental because they aren't referenced in the source code - however, they're so close to being fundamental that it wouldn't be surprising if an intelligent being who lived in Conway's universe discovered them and thought they were fundamental.

When someone says something isn't fundamental, to me that means that it's not at the lowest level of reality, it's not a building block of reality that's strongly referenced in the source code - instead, that thing is the consequence of the source code running.

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  • It is kind of tempting to imagine the universe as having rules, cells, an initial state and values of the cells. But at the level where it might work, it is not something relatable, the values end up being quantum superpositions and so on. The explanation winds up so alien that it doesn't do anything for our understanding.
    – Scott Rowe
    Dec 18, 2023 at 11:45
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    @ScottRowe that's why I treat it as a loose analogy at best rather than just the full literal truth. It gives us a solid basis for understanding what "fundamental" could mean, even if the analogy is imperfect.
    – TKoL
    Dec 18, 2023 at 11:51

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