The Hawking Paradox suggests that during their disappearance, black holes erase all information about their origins, contradicting the laws of quantum physics. This paradox has now been resolved.
According to theoretical physicist Stephen Hawking, black holes gradually dissipate as they leak a type of radiation known as “Hawking radiation,” but in the form of thermal energy. While the radiation can carry information about its source, thermal energy does not. Thus, as black holes slowly evaporate, all information about the stars that created them also disappears.
Information about the formation of black holes may be found in the radiation they emit, according to new research explaining the Hawking paradox. (Image: NASA).
This contradicts the laws of quantum mechanics, which state that information cannot be destroyed and that the final state of an object can reveal clues about its initial state. This is known as the “Hawking Information Paradox.”
The Hawking Paradox
Black holes are objects so massive that nothing can escape their gravitational pull, not even light. They form when massive stars collapse under their own gravity.
In classical physics, black holes are considered very simple objects, characterized by three numbers: mass, angular momentum, and charge, explains Xavier Calmet, a physics professor at the University of Sussex. However, the original star that generates a black hole is a complex astronomical object, consisting of protons, electrons, and neutrons that combine to form the chemical elements of that star, Calmet notes.
The first image captured of a black hole, located at the center of the M87 galaxy, nearly 54 million light-years from Earth. (Image: EHT Collaboration).
Although black holes do not carry traces of these complex chemical elements, the rules of quantum physics indicate that information cannot be erased from the universe. Therefore, theoretically, it is possible to recover information about the original complex star from the radiation emitted by the black hole.
In 1976, Stephen Hawking “broke” this rule by suggesting that black holes continuously emit a type of radiation. This radiation leak causes black holes to gradually evaporate and ultimately disappear completely. However, this radiation is emitted in the form of heat, meaning that all information about the star that created the black hole has also disappeared.
“This contradicts the rules of quantum physics, suggesting that the ‘lifetime’ of a black hole can be reversed, and through the radiation, one can reconstruct the black hole and the star that created it,” Calmet said.
Decoding the Black Hole Paradox
Calmet spent nearly three years decoding the Hawking paradox. In his new research, he reassessed Hawking’s calculations from 1976 but this time took into account the effects of “quantum gravity” —which describes gravity according to the principles of quantum mechanics—a consideration that Hawking did not include.
“Although these quantum gravitational corrections are very small, they are crucial for the evaporation of black holes. We were able to show that these effects make Hawking radiation no longer just thermal energy, but it can contain information,” Calmet stated.
Calmet’s research team also identified the physical phenomenon through which information escapes from black holes via Hawking radiation, and how an outside observer can retrieve this information to reconstruct the black hole and the original star. However, this process is not yet feasible in practice, as it requires a sufficiently sensitive device to detect Hawking radiation, which currently does not exist.
