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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?

Qmechanic
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good_ole_ray
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  • Related: http://physics.stackexchange.com/q/35781/2451 and http://physics.stackexchange.com/q/41676/2451 – Qmechanic Jun 02 '13 at 13:16

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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.

anna v
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  • 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"? – good_ole_ray Jun 02 '13 at 05:44
  • @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. – Brandon Enright Jun 02 '13 at 05:49
  • @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. – anna v Jun 02 '13 at 05:54
  • @annav but if it can be turned into somthing else, doesn't that imply that it has some common composition with that something else. – good_ole_ray Jun 02 '13 at 06:10
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    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. – anna v Jun 02 '13 at 06:19
  • @annav i understand what you mean about no other particles, but can the elementary particles be considered composite of energy somehow – good_ole_ray Jun 02 '13 at 06:20
  • @annav I agree, I didn't mean to imply that the reason you could turn one thing into another is because it's composite. I meant to imply that you can because all energy is the same. – Brandon Enright Jun 02 '13 at 06:28
  • Energy per se is formless has not attributes that can be built up into the complex system we know as elementary particles. It is part of the space time fabric on which everything rests. A building is composed of bricks, but the energy of the bricks or the location (x,y,z) do not characterize the building as composite. It is the bricks that make it composite. – anna v Jun 02 '13 at 07:20
  • @annav but if it can manifest into matter, then it must have some kind of connection to matter/form, no? – good_ole_ray Jun 02 '13 at 10:30
  • Lets put it another way: energy is a continuous variable , the fourth component of the energy momentum vector. All matter, including elementary particles can be described by a four momentum vector. All particles can be described by a four space vector (x,y,z,t). Do not confuse content with context. Energy momentum, time and space are context for the content of all we see, and down to the nuclei (protons, neutrons) we see compositeness,(subparticles with their own x,y,z,t and p_x,p_y,p_z, E . Below that level we see point like entities as seen on the table.. – anna v Jun 02 '13 at 10:40
  • can we say that light is an "intermediate" between energy and matter, hence it has properties of both (particle/energy wave) – good_ole_ray Jun 03 '13 at 05:19
  • when light is at the single photon level it is no different than any other elementary particle in the table. All the elementary particles in the table and their composites/resonances are both particle like and probability wave like when the dimensions are of order hbar. When individual photons form a statistical ensemble we call light then macroscopically the ensemble is described by the maxwell equations smoothly. have a look at http://motls.blogspot.com/2011/11/how-classical-fields-particles-emerge.html – anna v Jun 03 '13 at 05:24
  • @good_ole_ray no, you cannot. Energy is a property of an object, like speed or mass or position. It is in no way equivalent to matter. By the way, I'd suggest taking this discussion to [chat] since it seems like it could get rather involved. – David Z Jun 03 '13 at 19:05