Why is the expansion of the universe speeding up?

The video discusses the unexpected acceleration of the universe's expansion, first observed in 1998. Scientists hypothesize that a mysterious force called dark energy might be responsible, though its nature remains unknown. Alternative theories suggest modifications to Einstein's theory of relativity could explain the phenomenon. The video highlights the ongoing research and the role of observers in providing data to refine these theories.

What was the surprising observation about the universe's expansion mentioned in the text?

What is the term used to describe the unknown energy that is believed to be causing the acceleration of the universe's expansion?

What are some possible explanations for the acceleration of the universe mentioned in the text?

How do theorists approach the problem of dark energy according to the text?

What role do experimentalists play in the search for understanding dark energy?