Henry Tye, Emeritus Professor of Physics at the College of Arts and Sciences, has reached a fascinating conclusion by revising a long-standing model centered around the "cosmological constant," a concept introduced over a century ago by Albert Einstein. This idea has been pivotal in shaping contemporary theories regarding the universe's future.
"For the past two decades, it was widely accepted that the cosmological constant is positive, indicating an endless expansion of the universe," Tye explained. "However, recent data suggests that the cosmological constant may actually be negative, implying that the universe could ultimately face a big crunch."
Tye is the lead author of "The Lifespan of our Universe," featured in the Journal of Cosmology and Astroparticle Physics.
Big Crunch Versus Endless Expansion
The universe, currently estimated to be 13.8 billion years old, continues to expand. Standard cosmological theories propose two main scenarios: If the cosmological constant is positive, expansion will persist indefinitely. Conversely, if it is negative, the universe could halt its growth, reach a peak size, and subsequently contract until everything collapses back to a singular point.
Tye's revised model supports this latter scenario.
"This big crunch represents the universe's conclusion," Tye noted, predicting that such a collapse might occur in approximately 20 billion years.
Dark Energy Data From DES and DESI
Crucial evidence stems from new findings released by the Dark Energy Survey (DES) in Chile and the Dark Energy Spectroscopic Instrument (DESI) in Arizona. Tye highlighted that the results from these two observatories, situated in opposite hemispheres, show remarkable agreement.
Both initiatives aim to deepen the understanding of dark energy, which constitutes about 68% of the universe's mass and energy. Their objective is to determine whether dark energy is merely a constant feature of space. Recent data, however, indicates that the reality may be more intricate. The universe does not seem to be influenced solely by a straightforward cosmological constant; additional factors might be affecting dark energy's behavior.
To address this complexity, Tye and his team proposed a theoretical particle with an exceptionally low mass. In the early cosmos, this particle would have functioned similarly to a cosmological constant, but its impact would have evolved over time. This adjustment aligns with the latest observations and suggests a shift of the cosmological constant into negative territory.
"The notion that a negative cosmological constant could lead to the universe's eventual collapse isn't new," Tye remarked. "However, our model specifies when and how this collapse would occur."
Ongoing Observations and Future Tests
More data is on the horizon. Hundreds of researchers are examining millions of galaxies and measuring their distances to refine dark energy estimates. 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 recently launched SPHEREx mission, and the Vera C. Rubin Observatory, are also contributing to this effort.
Understanding the Beginning and the End
Tye finds it promising that scientists can calculate the universe's total lifespan in quantifiable terms. Knowing both its inception and eventual conclusion aids cosmologists in piecing together the grand narrative of cosmic history.
"For any form of life, understanding how it begins and ends is crucial," he stated. "For our universe, it's equally compelling to explore whether it has a beginning. The 1960s revealed that it does. The next logical question is, 'Does it have an end?' For years, many believed it would continue indefinitely. It's reassuring to know that, if the data holds true, the universe will indeed have an end."
Tye's co-authors include his former doctoral students from the Hong Kong University of Science and Technology, Hoang Nhan Luu and Yu-Cheng Qiu.