Stephen Hawking Fell Short in His Prediction: The Universe Is Doomed To Evaporate

Even stars that are too small to become black holes will gradually fade away.

una galaxia en el universo
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Pablo Martínez-Juarez

The end of the universe is a question that has occupied the minds of scientists for many decades. Recent research on black holes serves as a reminder of how most physicists believe it will happen: Not with a bang, but rather, just fading away. The key lies in Hawking radiation, developed by the famous physicist of the same name, Stephen Hawking.

From black holes to the entire universe. Black holes are not objects that are doomed to grow forever by absorbing matter; they can shrink, too. This happens because they give off energy in the form of radiation–which is known as Hawking radiation–and, as we can deduce from the best-known equivalence in physics, this translates into a loss of mass.

Last year, a study carried out by experts at Radboud University in Nijmegen in the Netherlands expanded this phenomenon from just black holes to all objects with a certain amount of mass.

Hawking radiation. So, how is this possible? Hawking radiation is one of the most astonishing phenomena in the universe, not only because of its involvement in making the most gluttonous objects in our universe thinner, but also because it combines knowledge from quantum field theory with that provided by the theory of gravity.

Out of nowhere. Under normal conditions, particles and antiparticles can appear out of nowhere. These events last for infinitesimal fractions of time, where particles and antiparticles annihilate each other. However, there is a context in which this does not happen, and that is around the event horizon of a black hole. In this case, particles and antiparticles can end up on opposite paths, unable to annihilate each other.

This generates radiation that escapes from the black hole, which in turn implies a loss of mass.

Erring on the side of caution. The recent study, which was published in the journal Physical Review Letters, challenges the notion that only the presence of a black hole event horizon is capable of generating enough space-time curvature to avoid particle and antiparticle annihilation.

This, in turn, implies that this particular radiative decay can appear in objects that, despite having large masses capable of bending the space-time fabric, do not have an event horizon because they do not generate enough gravitational attraction to absorb light. As such, even stars that are not massive enough to result in a black hole might fade away when they reach their end.

Falling short. “We show that far beyond a black hole the curvature of space-time plays a big role in creating radiation. The particles are already separated there by the tidal forces of the gravitational field,” Wanter van Suijlekom, one of the authors of the study, explained. We could say that even though Hawking was right in his theory about the fading of black holes, he could have fallen short by having based his analysis on the existence of singularities associated with black holes.

The ever-expanding universe. No one knows for sure what the end of the universe will be like, but astrophysicists have a well-established hypothesis (and several, less accepted alternatives). The idea of an evaporating universe is precisely in line with the most widespread hypothesis. In this scenario, the cosmos and everything in it will expand at increasingly greater speeds, which will cause matter to move further and further away in an increasingly colder, less dense universe.

Everything that inhabits it could have vanished by then.

Image | Unsplash

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