Really! Astronomers first noticed part of the universe was missing in the '30s when they looked at the movement of a cluster of galaxies. Galaxies near the edge were moving a bit too fast for the amount of mass that was visible. Then in 1975 a researcher found that the stars in the halo around individual galaxies were rotating much too fast which meant over 50% of the mass that should have been visible was missing.
Today, ordinary mass in the universe, the stuff we can see, is estimated to be only about 4% of everything that's out there! About 22% of the universe is apparently something called dark matter--matter that doesn't emit or reflect electromagnetic radiation. The remaining 74% is thought to be dark energy, an even stranger component of the universe.
Many lines of evidence point to so-called dark matter as the missing mass. How fast galaxies and clusters of galaxies rotate, gravitational lensing, and the temperature distribution of hot gas in galaxies and clusters of galaxies all show that the missing mass must be dark matter.
In August of 2006, dark matter was directly observed for the first time. Ordinary matter is shown in red in this landmark image of the Bullet cluster, the dark matter is shown in blue.
First we thought Earth was the center of the Universe, then we discovered the Sun is just the center of our solar system. Now we know the Milky Way galaxy is teaming with planetary systems, the Universe is comprised of hundreds of billions of galaxies, and that everything we can see is only a minuscule part of what's out there thanks to dark matter and dark energy. What's more, recent research suggests that our Universe is just one of perhaps an infinite number of Universes populating a multiverse that has existed forever and will go on forever.
The human species, like individual human beings, is slowly growing up. No longer do we have an naive self-centered view of the world. If we can let go of childish fantasies, and if we survive our adolescent behavior, we might find go on to really understand the real wonders of the universe.