Are The Elementary Particles Truly 'Elementary'?

[HopCat]

I would like to know what your, and the general physics community think about whether the elementary particles we recognise today such as fermions, bosons and leptons are truly indivisible or are just made out of something smaller.
People named the atom 'the atom' because it mean indivisible, are we just at another stage of not knowing what comes next?
Thanks in advance for your opinions

 

[Bill_K]

While it's clear that something further must underlie the Standard Model, it's not at all clear that this comes in the form of compositeness of the particles. Such "preon" models have been proposed, but there's no evidence for them. If anything, the LHC is suggesting that the next layer of the onion lies at even higher energies than we currently explore.

 

[DrDu]

AFAIK, "elementary" is not a concept of modern theory any more. Noninteracting particles are purely fictional and real particles can at best be described as a mud of infinitely many interacting particles. All that remains are some basic properties of the particles like charges, spin and mass.

 

[Bill_K]

Underlying the mud is a quantum field theory, and elementary particles are by definition the ones whose fields appear in the Lagrangian.

 

[DrDu]

Ok, but is the "decomposition" of interacting particles into non-interacting ones appearing in the un-renormalized Lagrangian unique and does it have physical significance?

 

[Conde]

I teach pre physics and chemistry to private high school students in central nj. I am looking for someone that has worked with atoms to speak to my classes on an elementary level. Any ideas?

 

[Nabeshin]

I think that at this point, and certainly for a long time into the future, it's best to think in terms of effective field theory. That is, the standard model is an approximation to some higher energy theory, and so what look like elementary particles when probed up to the TeV scale may not turn out to be in the higher energy theory. But it's not really a question of 'reality', since this theory may be subsumed by another, and so on and so forth. If you're willing to think of these theories simply as ever better approximations to reality, then the correct thing to say is, "Our current best description describes electrons, quarks, bosons as fundamental particles."

 

[Vanadium 50]

This is a question that has only one possible logical answer, "we don't know".

It cannot be answered "yes", only "we have seen no evidence that they are not".
It cannot be answered "no", because that would lead to the question, "so, is the next level down elementary"?

 

[mfb]

"we have seen no evidence that they are not".

The absence of such evidence is some evidence that the particles might be elementary.
Electron and muon g-factors, for example, are extremely close to the predicted value for elementary particles, while protons and neutrons (which are known to be composite) have completely different values.

 

[Vanadium 50]

Yes, but that only provides - and only can provide - an upper bound.

 

[Charm Quark]

Please do not be quick to pounce if this is an irrelevant question, I am still in High School, and still have much to learn. This is directed at the original post: when the question of, 'whether elementary particles are divisible...' I couldn't help but think of Superstring Theory, or potentially, (but not necessarily,) 11 Dimensional Supergravity. But I don't know if these are applicable, or if the Original Post wanted an answer in The Standard Model, or if my understanding of Supergravity and Superstring theory are even correct. Feel free to give me feedback.

 

[DrDu]

In relativistic QFT it does not make sense any more to speak of a single particle. If you look close enough at e.g. an electron you will see that it is surrounded by electron positron pairs and you cannot even distinguish which one is the original electron and which one belongs to the pairs. This is the main topic of renormalisation theory.
Hence it also makes no sense to think of an elementary particle as some indivisible point particle.

 

[K^2]

DrDu, yes, the only thing you will ever measure are quasi-particles that consist of, as you called it, mud of elementary fields. But the description is still that of collection of elementary particles, which is supported indirectly by how well the model describes the system, as well as available degrees of freedom. While any meson will act as if it consists of an entirely mess of quarks, it will act as an entire mess of quarks that are themselves behaving as elementary point particles. If these particles did not behave as elementary at energy scales we are used to, these would manifest in additional degrees of freedom, which would alter the parton distributions of mesons, which would ultimately manifest in Deep Inelastic Scattering and Drell-Yan type experiments.

In other words, our accelerator data, so far, supports existence of elementary particles that make up the quasi particles we observe, consistent with standard model.