Astronomy
Why the Universe's Expansion Is Accelerating
Quick fact
The discovery that the universe's expansion is accelerating won the 2011 Nobel Prize in Physics. It implies that about 70% of the universe's energy is made of something completely unknown—dark energy.
Why this is interesting
You've probably heard that the universe is expanding, but what if I told you it's not just expanding—it's speeding up? Astronomers expected gravity to slow the expansion, but the opposite is happening, and the cause remains one of the biggest mysteries in science.