Since 1998 we have known that the expansion of the universe is speeding up. Whatever drives it is called dark energy. In the simplest picture its strength stays the same forever, and the universe slowly runs down into a cold heat death. But in 2003 three physicists asked what would happen if dark energy instead grew stronger over time. Their answer was the Big Rip.
Phantom energy
Physicists describe dark energy with a number called w. If w is exactly −1, dark energy is a cosmological constant: its density never changes. If w is less than −1, Robert Caldwell, Marc Kamionkowski and Nevin Weinberg showed in a paper titled “Phantom Energy and Cosmic Doomsday”, its density would increase as the universe expands, becoming infinite in a finite time. Expansion would then overpower every force that holds things together.
The countdown
The paper worked through an example with w = −1.5. In that universe the end comes 22 billion years from now, and the order of events follows the strength of what holds each thing together:
- About a billion years before the end, clusters of galaxies come apart.
- About 60 million years before, the Milky Way is torn apart, its stars flung away from each other.
- About three months before, the planets come loose from the Sun.
- About 30 minutes before, the Earth itself explodes.
- About 10⁻¹⁹ seconds before, atoms are torn apart.
Then everything ends at once.
What the measurements say
The countdown depends entirely on w. The Planck satellite measured it as −1.028 ± 0.031, very close to −1. Even taking the most pessimistic end of the measurements, a Big Rip would be at least about 200 billion years away. Still, a Big Rip is very difficult to rule out completely, because a value of exactly −1 can never be measured with infinite precision.
Recent results point the other way. In 2025 the Dark Energy Spectroscopic Instrument (DESI), mapping millions of galaxies, found growing hints that dark energy is weakening, with w today greater than −1. The same analysis allows phantom behaviour in the distant past, but not now. If those hints hold up, the universe is heading away from a Big Rip, not towards it.