The universe may not expand forever as scientists once believed. According to new calculations by Cornell physicist Henry Tye, the cosmos is approaching the midpoint of its 33-billion-year life and could eventually collapse in a catastrophic “big crunch.”
The prediction comes from fresh data collected by dark-energy observatories in both the northern and southern hemispheres.
Tye, the Horace White Professor of Physics Emeritus, used these observations to update models involving the cosmological constant, a concept introduced by Albert Einstein over a century ago.
“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.”
Universe could collapse in 20 billion years
The universe is currently 13.8 billion years old and expanding. According to Tye’s updated model, its future depends on the sign of the cosmological constant. A positive constant would mean eternal expansion.
A negative constant, however, would cause the universe to stop growing, reach a maximum size, and then contract until it collapses to zero.
The physicist’s calculations indicate the latter scenario is likely. “This big crunch defines the end of the universe,” he wrote. The model estimates this collapse will occur roughly 20 billion years from now. The universe, in effect, would snap back like a stretched rubber band, returning to a single point.
Dark Energy observatories provide critical data
This year’s major advance comes from the Dark Energy Survey (DES) in Chile and the Dark Energy Spectroscopic Instrument (DESI) in Arizona.
These observatories measure dark energy, which makes up 68% of the universe’s total mass and energy. Their observations suggest dark energy is not just a simple cosmological constant.
Tye and his collaborators proposed a hypothetical low-mass particle that acted like a cosmological constant early in the universe’s history but behaves differently today. This model aligns well with the new data and points to a negative underlying cosmological constant.
“People have said before that if the cosmological constant is negative, then the universe will collapse eventually. That’s not new,” he mentioned. “However, here the model tells you when the universe collapses and how it collapses.”
More observations are coming
Hundreds of scientists are now measuring dark energy by studying millions of galaxies and the distances between them. DESI will continue its observations for another year.
Additional projects, such as the Zwicky Transient Facility in San Diego, the European Euclid space telescope, NASA’s SPHEREx mission, and the Vera C. Rubin Observatory, will also contribute new data.
Tye finds the ability to estimate the universe’s lifespan encouraging. “For any life, you want to know how life begins and how life ends – the end points,” he stated.
“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.”
The findings were published in the Journal of Cosmology and Astroparticle Physics.