How Do We Know The Universe Is Accelerating?

The video explains the expansion of the universe and how astronomers measure it using distant galaxies and supernovae. By observing redshift and brightness, scientists can determine the speed and distance of celestial objects. The discovery of the universe's accelerating expansion led to the hypothesis of dark energy, an unknown force driving this acceleration.

What does a straight line on the graph of the universe's expansion indicate?

What is dark energy and how is it related to the acceleration of the universe's expansion?