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I am currently researching the nature of interactions in philosophy. I am a novice to physics and am here to learn about the latest developments in physical sciences. What do quarks need to exist? What are their conditions of existence? Which I have tried to make more specific:
Is everything composed of quarks? If not, then why not?

  1. It is no secret that philosophy (the community of people working within it, at large) is quite outdated with the ways in which it portrays the world. I'm going through the latest philosophers of physics to understand the developments as well.
  2. Will look into leptons, quantum field theory and symmetries.
  3. The relation between data, observation and theories. Thank you!
Sahana Rajan
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  • Do you mean why couldn't a universe be made with elementary hadrons, or which empirical observations motivate quarks as an explanation? Please edit your question to clarify. – J.G. Jun 01 '18 at 07:04
  • @J.G. Hi! Thank you for replying. I am a novice. My question is neither. If we suppose that quarks exist due to a certain set of empirical observation, then within those observations, what are those conditions without which a quark cannot come to be? I am sorry I am finding it a bit hard to explain in clearer terms. – Sahana Rajan Jun 01 '18 at 07:29
  • Comment to the title question (v2): For starters. there are also leptons. – Qmechanic Jun 01 '18 at 07:58
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    The revised question sounds like you are now asking for the ontology of field theories. "Why is there field/interaction X?" is typically explained in terms of symmetries, but that then leads to the even harder question "Why does the world follow symmetry group Y?" (plus, "why a field theory?") – Anders Sandberg Jun 01 '18 at 10:22
  • @AndersSandberg Thank you. When I came to the question, I was thinking about situatedness. More specifically, that any kind of organization (a structure of components with certain capacities) requires a certain kind of environment to sustain itself. And was thinking if one could say that quark is also that way. In most philosophical discussions, there is the idea that quarks are fundamental and it seems to lead to the conclusion that they don't depend on anything else for their existence. – Sahana Rajan Jun 01 '18 at 13:31
  • @SahanaRajan - The situatedness makes sense. Protons exist when energy levels are low enough so that their three quarks are confined, but when you heat up things the protons dissolve in a quark-gluon plasma. So we can say low temperature is a condition for protons. I don't think there is something exactly similar for quarks, unless there are preons. – Anders Sandberg Jun 01 '18 at 15:01

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Quarks are described by the standard model of physics, which is a field theory: it describes particles in terms of more fundamental fields and symmetries. It is in a sense these fields that actually exist, and each individual quark is just an excitation of the relevant quark field. How these fields interact is described by the standard model Lagrangian, which is largely set by a set of symmetries between different particles and forces.

I interpret your question as what conditions there are for the appearance of quarks in the model. Most primarily there has to be a world the model applies to: without spacetime or a world implementing the "rules" of quantum field theory for example the model is not applicable. One could also imagine that there could be particle fields with no excitations ever showing up; such fields would need to be unconnected in the Lagrangian to all the other fields (right now only some particle fields are unconnected to some of the other fields, e.g. how neutral particles don't "feel" the electromagnetic force and leptons do not "feel" the strong force). But quark fields are connected to more or less everything.

There are likely some more complex conditions described in quantum chromodynamics that determine when quarks can show up too.

But I think the question basically boils down to "why the standard model, and its symmetries?" A very good question I don't think we have any satisfying philosophical answer to (the physical answer is of course "because it fits the observations well").

Anders Sandberg
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