If you mean small, like teeny wheeny… then fundamental particles are the smallest thing composing the universe. These are basic building blocks of the universe. The particles make every other particle in the universe. The particles it makes are things like atoms and then atoms make up every living thing, every physical thing in the universe.
But in the universe, if you put all the matter together it would only add up to 5% of what the universe is. What could the other 95% of the universe be?? Time? It can’t be more space because that is made up of these particles?
This is because we think of planets as big because they are made up of a lot of matter, which is the physical thing of everything, even us – is very empty lol A lot of matter has a lot of space in it…so if we scrunched up a human and squeezed all the matter out of it….we could fit inside a sugar cube 😛
It’s thought that most of the mass in the universe can’t actually be seen – it’s called Dark Matter.
We see matter in the universe because of its ability to reflect or absorb light, or emit or absorb radiation of some kind. But Dark Matter doesn’t do any of this! We only think that it’s there because the matter than we CAN see (from every atom to a planet) cannot create all of the gravitational pulls that we see in the universe. Physicists realised that there must be more matter that we can’t see to be causing such big forces. They think that 84.5% of the matter in the universe is Dark Matter.
bizarrely most of the universe is made of nothing, it is literally space. Even our bodies are mostly space. We are made of atoms which have electrons in them and a nucleus and they in turn are made of smaller bits of stuff with funny names like muons, leptons and quarks. But the fact remains that between all these particles is nothing. It’s amazing really that we’re solid at all.