mostly nothing i think! It has relatively small amounts of “stuff” which can be found burning in stars, or hanging around in the nothingness as planets, moons, comets and asteroids… but i think shane or aggelos can probably jump in on this!
The universe is made from atoms and molecules (Who are themselves made of subatomic particles.. we’re still figuring out about them) The most abundant element in the universe is hyrdrogen. Stars are the engines that make all the other elements. The universe is ‘held together’ by the four fundamental forces. these are 1. Gravity. the weakest of all four, but the one that acts over the largest distances. 2. the electromagnetic force. caused by the interaction of charged particles (like electrons) – it can push charges together and force them apart. 3. the strong nuclear force (Great name). this holds the nuclei of atoms together (it only applies over VERY short distances though (like the diameter of a nucleus (which is 0.0000000000000001 meters wide)). 4 the weak nuclear force (associated with nuclear decay).
The universe is made of mystery. As far as I can make out, most of the universe is empty space, and a lot of scientists – mostly physicists – have a lot of interesting theories about what the universe might be made of and how it all holds together, but for the most part these are just theories. A lot of people are either frightened of science or imagine that it’s boring because they think it’s very black and white and that there’s no room for imagination – in fact science is incredibly creative and imaginitive. It would be a boring world if we already had all the answers.
Everything in the entire universe is made from the particles that were formed just after the big bang. I think that is SO cool, even just thinking about the variety of animals and plants on our Earth – not to mention whatever kinds of life might exist elsewhere – that everything is made up of the same bits.
There’s still a lot of theories about how the big bang actually happened. If I could travel back in time, I think that’s what I’d pick to go back to (or maybe the time of the dinosaurs…that would be super cool too!)