University of Sussex duo solve Stephen Hawking teaser

Professor Xavier Calmet and research student Folkert Kuipers have changed the way we perceive black holes to act, and proven they are more complex than previously thought.

Black holes are areas of spacetime, where gravity is so strong that nothing can escape its pull. It was previously thought that their only observational features were mass, spin, and charge – until now.

The pair from the University of Sussex, along with two international physicists, have shown that when matter collapses on entering a black hole, it leaves an imprint in the hole’s gravitational field.

Professor Xavier Calmet of the University of Sussex

It resolves Hawking's Black Hole Information Paradox, which has challenged physicists and pitted quantum mechanics and Einstein’s theory of general relativity against one another for 46 years.

Prof Calmet said: "It was generally assumed within the scientific community that resolving this paradox would require a huge paradigm shift in physics, forcing the potential reformulation of either quantum mechanics or general relativity.

“What we found – and I think is particularly exciting – is that this isn’t necessary. Our solution doesn’t require any speculative idea. Instead, our research demonstrates that the two theories can be used to make consistent calculations for black holes and explain how information is stored without the need for radical new physics.

Professor Stephen Hawking

“It turns out that black holes are in fact good children, holding onto the memory of the stars that gave birth to them.”

The imprint is what the four scientists are referring to as a 'quantum hair', with the findings published in two co-authored papers.

Black Hole NGC 1850

Explaining the discovery of the quantum hair, Roberto Casadio, professor of theoretical physics from the University of Bologna, said: “A crucial aspect is that black holes are formed by the collapse of compact objects and then, according to the quantum theory, there is no absolute separation between the interior and the exterior of the black hole.

“In the classical theory, the horizon of a black hole acts as a perfect one-way membrane which does not let anything out, and the exterior is therefore the same for all black holes of a given mass. This is the classical no-hair theorem.

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“However, in the quantum theory, the state of the matter that collapses and forms the black hole continues to affect the state of the exterior, albeit in a way that is compatible with present experimental bounds. This is what is known as quantum hair.”