Question: What are things made of? We thought we knew the answer with atoms. Then we found substructure to atoms. Then we found substructure to nucleons. Now we're contemplating superstrings. Where will it end? Or will it?
Most scientists agree that there’s something smaller than quarks (which is what makes up nucleons) but that we just haven’t got there yet. There are lots of theories like superstring theory (which a lot of scientists think is rubbish) but no ones really sure. Most people agree that eventually it will all essntially boil down to a specific arrangement of energy.
The question here is what is the minimum number of different things you need to explain everything we’ve ever observed. If there is such a thing as a set of elementary particles (this is what the standard model puts forward – the Higgs particle is the last piece in the puzzle, which is part of the reason why finding it is so important) then we need go no deeper than that. If the universe is made of vibrating strings in some high dimensional space, then the strings would be the most basic thing – and there would be no reason to go deeper than that.
The real issue is that until we’ve successfully put together a theory explaining all 4 forces together (electromagnetic, strong, weak, gravity) and accounted for all the observed matter (including finding out what dard matter is) there will always be a possibility we’re missing something and need to dwell deeper.
So far, as far as we know everything is made up of 29 different ‘fundamental’ particles (not counting the Higgs boson, which we think should be there but we’ve never seen it yet. And not counting variations due to something called ‘colour charge’).
Here’s a diagram of the particles: http://en.wikipedia.org/wiki/File:Standard_Model_of_Elementary_Particles.svg
The green and purple particles all have partner anti-particles (antimatter), and the W+ and W- particles are shown together in the same box.
All the particles in the green and purple boxes make up matter, and the particles in the red boxes are responsible for the different forces (electromagnetic force, strong force, and the weak force). Gravity isn’t included since we don’t know how that works in a particle (quantum) way.
In fact pretty much all the matter around us is just made up from electrons, up quarks and down quarks. Two up quarks and a down quark joined together makes a proton. Two down quarks and an up quark joined together makes a neutron. combine protons, neutrons and electrons and you have atoms.
Now that’s all we know so far. Lots of scientists wonder if these particles are made up of smaller things. People have come up with theories to explain how this could be possible (string theory for example), but so far no one has been able to prove anything.
So the truth is we really don’t know! There are a lot of puzzling questions that make us think there could be some sort of underlying structure (why are there 3 generations of matter, for example), but all we can do is for theoretical particle physicists to keep coming up with theories to try to explain things, and for experimental particle physicists to keep testing those theories and searching for new things.
It’s all a big mystery, and as physicists we get to try and find out the answers 🙂