The nature of dark energy
Something is pushing the universe apart, faster and faster. We have no idea what.
What makes this fascinating
The universe is accelerating — Discovered in 1998 (Nobel Prize, 2011): cosmic expansion is speeding up, not slowing down.
It dominates everything — Dark energy makes up roughly 68% of the universe — yet has no agreed explanation.
Off by 10¹²⁰ — The simplest guess — the energy of empty space — disagrees with observation by the worst margin in physics.
Frequently asked questions
- What is dark energy?
- A mysterious influence driving the accelerating expansion of the universe. It accounts for roughly 68% of the cosmos, yet its nature is unknown.
- How was dark energy discovered?
- In 1998, observations of distant supernovae revealed that the universe's expansion is speeding up rather than slowing — implying something is pushing space apart.
- What could dark energy be?
- The simplest idea is a cosmological constant — the energy of empty space — but its predicted value clashes wildly with theory; alternatives include a dynamic field called quintessence.
More summits in Physics
Quantum gravity
Our two best theories of reality contradict each other. Uniting them is physics' deepest quest.
The nature of dark matter
85% of the universe's matter is invisible and unidentified. What is it?
The quantum measurement problem
Why does a particle's haze of possibilities snap into one outcome when we look?
High-temperature superconductivity
Some materials carry current with zero loss — and we still can't explain why.
Ready to climb?
Learn it the whole way up — from the fundamentals to the frontier.