Illustration by ZME Science.
We’ve been told by science that the universe is expanding relentlessly, driven by a mysterious force called dark energy. Eventually, galaxies would drift so far apart that the night sky would go black, stars would burn out, and the universe would end in a “Big Freeze” — an eternal, heat-dead whimper.
But a new study by theoretical physicists at Cornell University suggests we might need to rewrite that ending. Instead of fading away into infinite darkness, our universe could be destined for a dramatic, violent implosion known as the “Big Crunch.”
According to calculations by Cornell physicist Henry Tye and his colleagues, the cosmos may be nearing the halfway point of a total lifespan of roughly 33 billion years. If their model holds up against scrutiny, we aren’t drifting into a void. We are living in a universe that acts less like an endless balloon and “much like a stretched rubber band snapping back.”
The Dark Energy Plot Twist
To understand why the forecast has shifted from “freeze” to “crunch,” we have to look at the “cosmological constant.” Introduced by Albert Einstein a century ago, this constant (λ) represents the energy density of empty space.
“For the last 20 years, people believed that the cosmological constant is positive, and the universe will expand forever,” says Tye, a professor emeritus at Cornell. A positive constant acts like a foot permanently stuck on the gas pedal, pushing the universe apart faster and faster.
However, recent massive astronomical surveys — specifically the Dark Energy Survey (DES) in Chile and the Dark Energy Spectroscopic Instrument (DESI) in Arizona — have thrown a wrench in the gears. Their data, which maps millions of galaxies to measure cosmic history, suggests that dark energy isn’t as steady as we thought. It seems to be evolving.
“The new data seem to indicate that the cosmological constant is negative, and that the universe will end in a big crunch,” Tye says.
Graphic by ZME Science based on data from Tye et al, Journal of Cosmology and Astroparticle Physics, 2025.
In this scenario, the universe is currently expanding because of a temporary boost from other forces, but the underlying negative pressure of the cosmos is waiting in the wings. Eventually, it will hit the brakes. “This big crunch defines the end of the universe,” Tye writes in the study published in the Journal of Cosmology and Astroparticle Physics.
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The Elusive Axion
But if the cosmological constant is negative — which naturally pulls things together — why is the universe currently flying apart? Tye and his co-authors, Hoang Nhan Luu and Yu-Cheng Qiu, propose a culprit: an ultralight “axion”.
Axions are hypothetical particles (meaning they’re not yet proven to exist) that are notoriously shy. They “only interact with normal matter via gravity, making them very difficult to detect in a lab.” In Tye’s model, an incredibly light axion field permeates the universe.
“It’s simplest to assume that dark energy comes entirely from the cosmological constant,” Tye says, but the data from DES and DESI imply a more complex reality.
Here is how the physics plays out: Early in the universe’s history, this axion field mimicked a positive cosmological constant, driving the expansion we see today. But unlike a true constant, the axion field is rolling down a hill of potential energy. As it rolls, its pushing power diminishes.
Eventually, the axion’s influence will fade. When it does, the true nature of the cosmological constant — the negative λ — will be revealed. The expansion will lose its steam, and gravity will take the wheel.
A Universe with an Expiry Date
The team’s model allows them to put a tentative expiration date on existence. The universe is currently 13.8 billion years old. Tye’s calculations estimate a total lifespan of 33.3 billion years.
That means we have roughly 20 billion years left. But the party doesn’t end all at once.
“The Universe’s expansion is still accelerating now in our theory,” explains co-author Hoang Nhan Luu. The shift will be gradual.
“The Universe’s expansion only slows down when the so-called ‘crunching’ phase starts, which may happen in the next 11 billion years, as a rough estimation, followed by a Big Crunch around eight billion years afterwards”.
So, for the next 11 billion years, the cosmos will continue to grow. Then, it will pause. Finally, it will begin to contract, shrinking for billions of years until all matter, energy, and spacetime collapse into a single point.
Beyond the Event Horizon
What happens after the collapse? This is where physics hits a wall. “Unfortunately, our model can’t give much prediction after the Universe collapses,” Luu admits.
The issue is a classic conflict in modern physics: the clash between general relativity (which governs gravity and the big stuff) and quantum mechanics (which rules the subatomic world). As the universe shrinks to a singularity, these two rulebooks have to merge, and we don’t yet know how to read that language.
Some physicists speculate about a “Big Bounce” — a scenario where the crunch immediately triggers a new Big Bang, creating a cyclical universe that breathes in and out for eternity. Tye is more cautious. “Here, we predict the end of our Universe,” he told BBC Science Focus, “but precisely how it ends remains an open question. Just as one can predict a person’s life expectancy without predicting the circumstances of the death”.
This prophecy of doom is far from settled science. It relies heavily on the data from DES and DESI, which show dark energy behaving strangely — specifically, that its equation of state, ω, is not equal to -1. If future data snaps back to the standard model, the Big Crunch theory could vanish as quickly as it appeared.
Fortunately, we won’t have to wait billions of years to find out.
More Data to Study the Universe
A fleet of next-generation observatories is coming online to double-check the math.
“People have said before that if the cosmological constant is negative, then the universe will collapse eventually. That’s not new,” Tye notes. “However, here the model tells you when the universe collapses and how it collapses”.
Upcoming data from the European Euclid space telescope, the Vera C. Rubin Observatory in Chile, and NASA’s SPHEREx mission will test these predictions with unprecedented precision. If they confirm that dark energy is evolving, we may have to accept that our universe is mortal.
“For any life, you want to know how life begins and how life ends — the end points,” Tye says. “For our universe, it’s also interesting to know, does it have a beginning? In the 1960s, we learned that it has a beginning. Then the next question is, ‘Does it have an end?’”.
It seems the answer might be yes. And while 20 billion years is a long time, it’s a good reminder that even the cosmos itself might not be too big to fail.