Question: What Is the Universe Made Of?

Michael Nolan answered on 15 Nov 2013:

Nice question Alanah.

For many years we were sure the Universe was composed of particles with which we are familiar, those like electrons and protons that make up the matter that we can see.

However, this is not the case. First it was discovered that the rotation of outer arms of galaxies was bigger than thought even though these areas have less matter and should rotate slower – there must be something else that we cannot see that interacts through gravity, we call this Dark Matter and we still dont know for sure what it is as we cannot probe it with the usual forms of radiation.
To quote prof Matt Strassler:
“something that gravitates and clumps, but doesn’t shine, either in visible light or in any other form of electromagnetic waves”

About 4.9 % of the mass + energy in the Universe (remember mass, m, can be converted to energy, E, by Einsteins equation E = m*c*c) is what we call matter, as I described above
A further 26.8 % is Dark Matter

The rest is called Dark Energy

Of the matter, then around 75% is dark matter and 25 % is the normal matter.

Figuring out what Dark Matter and Dark Energy are is a very active and hot topic. This has all happened really in the last 20 years or so.

you can see a decent description on wikipedia for example.

M