Dark energy isn’t constant: CASSA scientist authors groundbreaking paper on the fate of the universe

A new research paper authored by Anowar Jaman Shajib, an Associate Member of the Center for Astronomy, Space Science and Astrophysics (CASSA) at Independent University, Bangladesh (IUB), challenges a long-standing assumption about the nature of dark energy. It presents evidence suggesting that dark energy may not be a constant after all, opening up new possibilities for understanding the fate of the universe.

The paper, titled "Scalar‑field dark energy models: Current and forecast constraints", was published in the Physical Review D journal on September 8. It is authored by Anowar Shajib, who is also an Einstein Fellow at the University of Chicago, and Prof. Joshua A Frieman, an Emeritus Professor at the University of Chicago.

The dominant theory for more than two decades has been that dark energy is constant – the so-called cosmological constant first proposed by Einstein and others. But recent astronomical surveys are now indicating that this energy might actually evolve over time.

This has profound implications. If dark energy weakens over time, it could affect the future trajectory of the universe. Instead of ending in a catastrophic "Big Rip" or collapsing in a "Big Crunch", the universe may cool and fade slowly into a "Big Freeze".

If dark energy continues to grow stronger over time, then in the distant future, everything from galaxies to atoms and particles – even the fabric of space and time – will be torn apart and scattered. This catastrophic scenario is known as the Big Rip.

On the other hand, if dark energy weakens and the expansion of the universe comes to a halt, then gravity will pull galaxies and matter back toward each other. Eventually, the entire universe will collapse into a single, dense point – essentially the reverse of the Big Bang. This is called the Big Crunch.

But as suggested in the research by Shajib and Frieman, if dark energy evolves very slowly, the universe will continue to expand indefinitely. Galaxies will drift farther apart, new stars will stop forming, old stars will burn out, and the universe will grow cold, dark, and inactive. Over time, all heat and light will fade away, leading to a final, motionless state known as the Big Freeze, or heat death.