Audio Guide：

Astronomer Edwin Hubble found that the velocity of galaxies receding from the observer is approximately proportional to their distance. This phenomenon is known as Hubble’s Law and is a basic principle in modern cosmology. It is also considered to be an important piece of evidence for the Big Bang model and proof that the universe is expanding. Scientists proposed various models of the expanding universe based on its possible geometric properties, including the closed, flat, and open universe. In 1998, astronomers observed type Ia supernova explosion and found that the universe is most likely expanding at an accelerated rate. This major finding was awarded the Nobel Prize in Physics in 2011 and prompted more research into dark energy.