For a long time, scientists thought our universe was headed for a Big Freeze. Dark energy was believed to drive this endless expansion, making galaxies drift apart until stars burn out and everything turns cold and empty. However, new ideas are challenging this view.
Theoretical physicists from Cornell University, led by Henry Tye, suggest that the universe may not expand forever. Instead, they believe it could have a lifespan of about 33.3 billion years. This change in perspective is significant.
The main clue comes from the cosmological constant, denoted by λ. Introduced by Albert Einstein, this constant represents the energy density of empty space. For about 20 years, scientists assumed it was positive, meaning it pushes the universe to expand endlessly. But recent large-scale surveys, like the Dark Energy Survey in Chile and the Dark Energy Spectroscopic Instrument in Arizona, are shaking things up. Tye points out that this new data hints the cosmological constant might be negative after all.
“For the last 20 years, people believed that the cosmological constant is positive, and the universe will expand forever,” Tye states. If it’s negative, it could mean the universe will start collapsing instead of expanding.
So, why is the universe still growing if the cosmological constant is negative? Tye and his team propose the existence of an ultralight axion field. Axions are hypothetical particles that are challenging to detect because they only interact with normal matter through gravity. According to their study published in the Journal of Cosmology and Astroparticle Physics, this axion field initially behaves like a positive constant, which is why we still see expansion. But over time, it loses strength, allowing the negative cosmological constant to take over. Tye describes this as “much like a stretched rubber band snapping back.”
So, when could we expect a collapse? Their model suggests that our universe might last around 33.3 billion years in total. Since it’s currently about 13.8 billion years old, we have roughly 20 billion years until things start to change significantly. The crunching phase could begin in about 11 billion years, leading to the Big Crunch about eight billion years later.
Interestingly, what happens after that is still a mystery. Some theorists mention a potential “Big Bounce,” where a new Big Bang happens after the collapse. However, Tye is careful not to commit to that idea. “Here, we predict the end of our Universe, but precisely how it ends remains an open question,” he explains.
This theory relies heavily on data from ongoing projects like the European Euclid space telescope and the Vera C. Rubin Observatory. If future observations align with the standard model of cosmology, the Big Crunch idea might lose credibility. But new data is on the horizon. As Tye notes, while the idea of a negative cosmological constant is not new, estimating when and how the collapse might occur is a fresh and exciting development.
