In the early 1920s, American astronomer Edwin Hubble made some of the most important astronomical observations in history. He discovered that galaxies are moving away from each other at high speed and that the farther away they are, the faster they move. These discoveries led to a revolutionary idea – that our Universe is expanding!
This theory was first proposed by Belgian priest Georges Lemaître in 1927. Lemaître suggested that the Universe began as a single point, or “primeval atom,” which exploded and started the expansion. This event became known as the Big Bang.
Over time, the Universe has continued to expand and cool down. As it expands, matter is spread out thinning out the density of matter and energy present throughout space-time. The leftover radiation from the Big Bang fills all of space today and can be detected using radio telescopes.
The distance between galaxies continues to increase as they move away from each other at high speeds. Observations show us that this process is Accelerating due to an invisible form of energy filling all of space called Dark Energy . Scientists believe that dark energy makes up about 68% of everything in our Universe!