Question: What is the universe made of?

Jarvist Moore Frost answered on 13 Mar 2012:

Well, we don’t really know to be honest!
Currently we think that the majority of mass in the universe is something we can’t see we’ve named ‘dark matter’. It’s not just that it’s black or doesn’t reflect light, it doesn’t interact with light (or radio waves, or X-Rays, or gamma rays!) at all, so is entirely transparent. There’s loads of different theories about what it is.

We think it has to be there, as when we tot up all the matter we can see in nearby galaxies, there must be some extra mass to stop the galaxies flinging themselves apart.

Of the matter we can see, most of it is relatively normal things 🙂 – the fermions, electrons neutrons and protons. Most of it has formed neutral atoms, particularly lots of Hydrogen and Helium was formed as the universe cooled down soon after the big bang. These formed big diffuse clouds (only a few molecules per metre cubed of space!), and in some places collected together into big balls so massive that they spontaneous started nuclear fires (we call these things stars).

Perhaps the most interesting thing is that you and me are made out of heavier atoms. These atoms didn’t form in the Big Bang, instead they formed in massive stars that burned billions of years ago and then EXPLODED throwing out all these heavy atoms that accreted into the solar system and our own sun. We’re star dust!