Dark-energy evidence suggests the universe will end in a “big crunch” roughly 20 billion years from now.

The universe is nearing the halfway point of what may be a 33-billion-year lifespan, according to new calculations by a Cornell physicist using updated dark energy data. The findings suggest that the cosmos will continue expanding for roughly another 11 billion years before reversing course, contracting back into a single point in a dramatic “big crunch.”

Henry Tye, the Horace White Professor of Physics Emeritus in the College of Arts and Sciences, arrived at this conclusion after updating a theoretical model that incorporates the “cosmological constant,” a concept first proposed by Albert Einstein more than a century ago and widely used by modern cosmologists to describe the universe’s expansion.

“For the last 20 years, people believed that the cosmological constant is positive, and the universe will expand forever,” Tye said. “The new data seem to indicate that the cosmological constant is negative, and that the universe will end in a big crunch.”

Tye is the corresponding author of a recent study about the findings published in theJournal of Cosmology and Astroparticle Physics.

Predicting the universe’s fate

The universe, now about 13.8 billion years old, continues to expand outward. According to Tye, the future depends on the value of the cosmological constant: if it is positive, expansion will continue indefinitely; if it is negative, the universe will eventually reach a maximum size before reversing direction and collapsing entirely. His calculations support the latter scenario—a future in which the cosmos contracts to zero, marking the ultimate end of space and time.

The latter is the conclusion Tye reached with his recent calculation.

“This big crunch defines the end of the universe,” Tye wrote. He determined from the model that the big crunch will happen about 20 billion years from now.

New data from dark energy observatories

The big news this year is the reports by theDark Energy Survey (DES) in Chile and theDark Energy Spectroscopic Instrument (DESI) in Arizona this spring. Tye said these two observatories, one in the southern hemisphere and one in the northern, are in good accord with each other. The whole idea of the dark energy survey of these two groups is to see whether dark energy – 68% of the mass and energy in the universe – really comes from a pure cosmological constant. They found that the universe is not just dominated by a cosmological constant, dark energy. The dark energy actually has something else going on.

Tye and his collaborators proposed in the paper a hypothetical particle of very low mass that behaved like a cosmological constant early in the life of the universe, but does not anymore. This simple model fits the data well but tips the underlying cosmological constant into negative territory.

“People have said before that if the cosmological constant is negative, then the universe will collapse eventually. That’s not new,” Tye said. “However, here the model tells you when the universe collapses and how it collapses.”

Observations and the future of cosmology

There are more observations to come, Tye said. Hundreds of scientists are measuring dark energy by observing millions of galaxies and the distance between galaxies, gathering even more accurate data to feed into the model. DESI will continue observations for another year, and observations are ongoing or will begin soon at several others, including theZwicky Transient Facility in San Diego; the European Euclid space telescope;NASA’s recently launched SPHEREx mission; and the Vera C. Rubin Observatory (named after Vera Rubin, M.S. ’51).

Tye finds it encouraging that the lifespan of the universe can be quantitatively determined. Knowing both the beginning and the end of the universe provides a greater understanding of the universe, the goal of cosmology.

“For any life, you want to know how life begins and how life ends – the end points,” he said. “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?’ For many years, many people thought it would just go on forever. It’s good to know that, if the data holds up, the universe will have an end.”

Reference: “The lifespan of our universe” by Hoang Nhan Luu, Yu-Cheng Qiu and S.-H. Henry Tye, 18 September 2025, Journal of Cosmology and Astroparticle Physics.
DOI: 10.1088/1475-7516/2025/09/055

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