Topic
Expansion
2 questions tagged Expansion — spanning every one of the seven Ws.
why
Why do galaxies move away from each other as the universe expands?
Space itself is stretching, so distant galaxies are carried apart even if they are not moving through space like thrown objects. This expansion was first measured by Edwin Hubble in the 1920s.
CosmologyExpansion
what
What is the Hubble constant?
The Hubble constant is the number that describes how fast the Universe is expanding per unit distance. It is usually given in kilometers per second per megaparsec.
CosmologyExpansion