What is the Universe made of?

The universe is mostly made up of hydrogen and helium, which are the two lightest elements. The rest of the elements found in the universe are very rare. Elements such as silicon, carbon and others are concentrated into clouds, stars and planets. The universe is held together by four invisible forces: gravity, electromagnetism, strong nuclear forces, and weak nuclear force. Gravity and electromagnetism are the two familiar forces. The other two operates only inside the incredibly tiny nuclei of atoms, holding the tiny particles together.