What is the universe made of?

The suprising fact is that we don't know.

Stars and gas

Stars and gas in the Galaxy (and in other galaxies) are made of hydrogen (about 75%) and helium (about 25%) plus a small amount (~1%) of heavier elements.

Is there anything else?

Let's see how to measure mass.

Measuring the mass of galaxies.

What could it be?

Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA soper@bovine.uoregon.edu