How the universe will end depends mainly on dark energy, the mysterious component that is making the expansion of space speed up. Nobody knows for sure, but current observations point toward a long, cold fade.
The discovery that changed everything
In 1998, two teams studying distant Type Ia supernovae found that they were dimmer than expected: the expansion of the universe is accelerating. This work earned the 2011 Nobel Prize in Physics. The cause was named dark energy and makes up roughly 68 percent of the universe’s content, see dark matter and dark energy.
The main scenarios
Big Freeze (heat death). If dark energy stays constant, galaxies outside our local group will recede beyond view, star formation will end as gas runs out, and the last stars will burn out after trillions of years. The universe will become cold, dark and nearly empty. This is the scenario favored by most current data.
Big Rip. If dark energy grows stronger over time, the expansion could eventually tear apart galaxies, stars, planets and even atoms. Observations do not currently favor this.
Big Crunch. If dark energy weakened and reversed, gravity could pull everything back together. Recent results from the DESI galaxy survey hint that dark energy might be changing over time, which has revived interest in such scenarios, but the evidence is not conclusive.
A timeline for our neighborhood
- About 1 billion years: the Sun will be bright enough to boil away Earth’s oceans.
- About 5 billion years: the Sun becomes a red giant, then a white dwarf, see how stars evolve.
- Billions of years: the Milky Way may merge with the Andromeda Galaxy.
- Trillions of years: red dwarfs, the longest-lived stars, burn out.
- Far beyond: white dwarfs cool into black dwarfs, and black holes may eventually evaporate through Hawking radiation, see black holes.
Why we are not sure
Predictions rely on knowing what dark energy is, and physicists do not. Future surveys such as ESA’s Euclid mission and the Vera C. Rubin Observatory aim to measure the expansion history more precisely. See the evidence for the Big Bang for how the story began.
