How long the universe lasts is not a question with practical consequences, but it is one physicists can now answer better than they could last year, and the new answer is shorter. A team at Radboud University in the Netherlands calculates that the last objects in the cosmos will decay in roughly 10⁷⁸ years — a one with 78 zeros — rather than the 10¹¹⁰⁰ years assumed before. The universe is about 1.4 × 10¹⁰ years old, so neither number is a worry. The interesting part is the reasoning.
What Hawking radiation is
In 1974 Stephen Hawking argued that black holes are not perfectly black. At the event horizon, quantum fluctuations constantly create pairs of particles; occasionally one falls in and the other escapes, carrying away a little energy. Over enormous time this leaks away the black hole’s mass until it vanishes. The radiation is far too faint to have been observed, but it is one of the most trusted predictions in theoretical physics.
The new idea
Heino Falcke, Michael Wondrak and Walter van Suijlekom asked whether the effect requires an event horizon at all. Their earlier work suggested it does not — that any sufficiently dense object with a strong gravitational field produces a similar radiation. In the new paper, published in the Journal of Cosmology and Astroparticle Physics, they apply that to neutron stars and white dwarfs, the dense remnants left when ordinary stars die. White dwarfs were previously the longest-lived things in the universe, expected to survive for 10¹¹⁰⁰ years; if they evaporate by a Hawking-like process, they are gone in 10⁷⁸. Everything else decays sooner. That sets the new end date.
Why it matters more than the number
“It is a beautiful combination of astrophysics, quantum physics and mathematics,” van Suijlekom said. The importance is not the date but the claim underneath it: that Hawking radiation is a general feature of gravity, not a special property of black holes. If that holds, it changes how physicists think about the fate of all matter, and it gives them a new set of extreme objects to test the theory on. “We want to unravel the mystery of Hawking radiation one day,” he added. There is still much to learn about how the universe ends — but the list of things that eventually dissolve into radiation just got longer, and it now includes the Sun’s own remains.
Source: NDTV, via Prothom Alo.
