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In philosophy there is a principle that anything composite cannot have existed eternally, since it is preceded by its parts and whatever forces assembled it.

Is everything in the physical world composite in one sense or another or is there something not composite?

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The study of the component parts of nature ends up into what we now term "elementary particle physics". Our experimental studies up to now and the mathematical theories that fit the data are encapsulated in the Standard Model.

This model has a basic assumption/axiom that elementary particles that are not composite exist and on these and their interactions the whole edifice is built up.

Here are the particles that our experimental exploration up to now finds as elementary

elementary particles

Of course somebody aware of the history of science from Demokritos' time 2500 years ago to the present knows that science calls elementary the level it has explored which does not show compositeness with the instruments and methods of the time. We have very sophisticated instruments and believe we are exploring in depth what has not been possible the past centuries. Still, to avoid hubris, I would qualify the statement with :these particles are elementary as far as we know now.

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  • $\begingroup$ if the elementary particles are destructible as we see they can be converted to photons, does that mean they are composed of some kind of more fundamental "energy"? $\endgroup$
    – good_ole_ray
    Commented Jun 2, 2013 at 5:44
  • $\begingroup$ @good_ole_ray there is only one type of energy. As long as you conserve various properties such as momentum you can (in principle) turn anything into anything else. $\endgroup$
    – Brandon Enright
    Commented Jun 2, 2013 at 5:49
  • $\begingroup$ @BrandonEnright "turning into something else" is not the same as being composite. Composite has the sense of "building blocks" within. There is nothing within the electron, the elctron is a point particle according to the standard model. Or in any of the others in the table. $\endgroup$
    – anna v
    Commented Jun 2, 2013 at 5:54
  • $\begingroup$ @annav but if it can be turned into somthing else, doesn't that imply that it has some common composition with that something else. $\endgroup$
    – good_ole_ray
    Commented Jun 2, 2013 at 6:10
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    $\begingroup$ NO. the whole study of elementary particles is a self consistent edifice, theory and measurements, and they tell us that the elementary particles are point particles, they contain nothing within them. The energy and momentum they carry may create other point particles or they may decay into other point particles but that does not mean that within an elementary particle there exist other elementary particles in contrast to the nucleus, which is composed of neutrons and protons, or the nucleon which is composed of quarks. Quarks have attributes, but are point like. $\endgroup$
    – anna v
    Commented Jun 2, 2013 at 6:19

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