Why is the universe expanding faster today than it used to?
Quick Answer
Distant supernova observations showed in 1998 that cosmic expansion is accelerating, likely because of dark energy. Dark energy seems to act like a property of space itself.
The Full Story
For much of the 20th century, astronomers expected gravity to slow the expansion of the universe. But in 1998, two teams studying distant Type Ia supernovae found that the expansion is actually accelerating. The leading explanation is dark energy, a mysterious component that makes up about 68% of the universe’s total energy content in modern cosmology. Its exact nature is still unknown, but it behaves very differently from ordinary matter and radiation. This discovery won the 2011 Nobel Prize in Physics.
Key Facts
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