Spacecalendar_todayLast updated: Apr 2026
What is Dark Energy?
/dɑːk ˈɛnədʒi/
Dark energy is a mysterious force that makes up approximately 68% of the total energy content of the universe and is causing the universe's expansion to accelerate rather than slow down.
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Everyday Example
Imagine blowing up a balloon and finding that instead of slowing as you get tired, the balloon inflates faster and faster on its own — this is what dark energy is doing to the universe.
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“The discovery that the universe's expansion is accelerating was so unexpected it won the 2011 Nobel Prize in Physics. It contradicted the assumption that gravity should be slowly pulling everything together.”
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Did you know?
Dark energy was discovered in 1998 by two independent teams studying distant supernovae. Einstein had predicted something similar (the "cosmological constant") in 1917 and then famously called it his "greatest blunder."
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Key Insight
We can measure dark energy's effects precisely — we know it makes up 68% of the universe — but we have no idea what it actually is. It is the biggest unsolved mystery in physics.
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