What is the Universe?

Part of Hall of the Universe.

Universe and What is the Universe AMNH/D. Finnin

The universe is all the matter, energy, and space that exist. We can observe only a part of it - the observable universe. The entire, universe, including the part we cannot see, may be infinite.

location (universe)
Earth centered view
In antiquity, the universe was widely thought tobe a globe of fixed stars that turned around Earth at its center. Ptolemy's writings assumed that the Sun, Moon, and planets also circled Earth.
Sun centered view
In 543, Nicolaus Copernicus published De revolutionibus, which placed the Sun at the center of the universe and demoted Earth to the status of a planet.
galaxy centered view
Telescopes revealed the Milky Way to be a vast system of stars. In 1918 Harlow Shapley showed that the Sun was not at the center of the Milky Way Galaxy, but neared its edge.
universal view
In 1923 Edwin Hubble showed that the Milky Way was just one in a universe of galaxies. His later discovery that galaxies all appear to move away from one another established that the universe is expanding.
space
Space is not mere emptiness. It is more like an invisible three-dimensional "fabric" that stretches and warps in the vicinity of matter.
light
Light is a form of energy that travels through space in waves. There are various kinds of light, differing from visible light in wavelength and energy.
matter
Matter is the physical substance of things--of stars, planets, people, and atoms.