What is the universe made of?
Astronomers don’t seem to know what 95% of the universe is made of. Atoms and physical matter, which form everything we see around us, only account for a measly 5%. Over the past 80 years it has become clear that the substantial remainder is comprised of two shadowy entities – dark matter and dark energy. The former, first discovered in 1933, acts as an invisible glue, binding galaxies and galaxy clusters together. Dark energy, Unveiled in 1998, is responsible for the universe’s accelerated expansion.