Stephen Hawking’s famous black hole paradox may finally have a solution

Published

2 years ago

March 31, 2023

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One of physicist Stephen Hawking’s most famous paradoxes may finally be solved: Black holes may in fact hang onto information about the massive stars that created them, new research indicates.

This information may lurk in the radiation around black holes – colloquially known as “quantum hair” – and could, in theory, be retrieved to retell the origins of those black holes, the research suggests.

These findings, published March 6 in the journal Physics Letters B. (opens in new tab) , may finally resolve a thorny problem that Hawking was working on in his last years.

Related: Stephen Hawking’s final book says there’s ‘no possibility’ of God in our universe

According to Hawking’s work, radiation slowly “leaks” out of black holes in the form of thermal energy, which has come to be known as “Hawking radiation.” But because of its thermal nature, this radiation can’t carry information. That means that as black holes evaporate, they methodically destroy all information about the stars that created them. This is contrary to the laws of quantum mechanics, which say that information cannot be destroyed and that an object’s final state can reveal clues about its initial state. This problem has troubled cosmologists for decades and is known as the “Hawking information paradox.”

“[This research] is the final nail in the coffin for the paradox because we now understand the exact physical phenomenon by which information escapes a decaying black hole,” lead study author Xavier Calmet (opens in new tab) , a professor of physics at the University of Sussex, told Live Science via email. He suggests a modification to Hawking radiation that makes it “non-thermal” and thus capable of carrying information with it away from the final fate of the black hole.

Physicist Stephen Hawking in his office in 1989. (Image credit: Jean-Regis Rouston/Roger Viollet via Getty Images) The black hole problem

Black holes are objects so massive that nothing can escape the pull of their gravity, not even light. They form when enormous stars run out of fuel and collapse in on themselves.

In classical physics, black holes are “very simple objects,” Calmet said. “So simple that they can be characterized by three numbers: their mass, angular momentum, and electric charge.”

Famous physicist John Wheeler described this lack of distinguishing characteristics by saying “black holes have no hair.” But, Calmet explained, while the final black hole is very simple, the original star that birthed it is a complex astrophysical object, consisting of a complicated amalgam of protons, electrons, and neutrons which come together to form the elements that build the chemical composition of that star.

While black holes carry no “memory” of the stars they once were, the rules of quantum physics say that information can’t simply be erased from the universe. In 1976, Hawking introduced a fly to this cosmic ointment by showing this information couldn’t dwell indefinitely within black holes sealed away from the outside universe either. Applying the rules of quantum mechanics to black holes, Hawking suggested they emit a type of thermal radiation, later called Hawking radiation. Over immense periods of time, the leaking of this radiation causes black holes to completely evaporate, leaving only a vacuum behind. In this way, information is irretrievably lost.

“This is however not allowed by quantum physics, which posits that the movie of this black hole’s ‘life’ could be rewound,” Calmet said. “Starting from the radiation we should be able to rebuild the original black hole and then eventually the star.”Finding the black hole’s ‘hair’

Along with his colleague Steve Hsu (opens in new tab) , a professor of theoretical physics at Michigan State University, Calmet has been working since 2021 to crack Hawking’s paradox. In a previous study, published in March 2022, the team argued that black holes do indeed have “quantum hair,” in the form of a unique quantum imprint in the gravitational fields that surround them

In their new research, the team reassessed Hawking’s 1976 calculations, but this time accounted for the effects of “quantum gravity” — the description of gravity according to the principles of quantum mechanics — something Hawking hadn’t done. Related stories— The 12 Strangest Objects in the Universe

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“While these quantum gravitational corrections are minuscule, they are crucial for black hole evaporation,” Calmet said. “We were able to show that these effects modify Hawking radiation in such a way that this radiation becomes non-thermal. In other words, factoring in quantum gravity the radiation can contain information.”

While the quantum hair suggested in Calmetand Hsu’s previous work was an abstract mathematical concept, the team has now identified the exact physical phenomenon by which information escapes the black hole via Hawking radiation, and how it could be retrieved by an outside observer. This is currently not possible, as it would require an instrument sensitive enough to measure Hawking radiation, which currently is purely theoretical.

Currently there is no real way for astrophysicists to measure the effect the researchers propose, as it is minuscule, Calmet acknowledged. Instead, he suggests one way to progress this theory would be by studying simulations of black holes in labs on Earth. The team’s mathematical modeling of Hawking radiation and black holes could prove invaluable in these simulations.

World

Trump warns Hamas – and claims Israel has agreed to 60-day ceasefire in Gaza

Published

43 mins ago

July 2, 2025

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Trump warns Hamas - and claims Israel has agreed to 60-day ceasefire in Gaza

Analysis: Many unanswered questions remain

In the long Gaza war, this is a significant moment.

For the people of Gaza, for the hostages and their families – this could be the moment it ends. But we have been here before, so many times.

The key question – will Hamas accept what Israel has agreed to: a 60-day ceasefire?

At the weekend, a source at the heart of the negotiations told me: “Both Hamas and Israel are refusing to budge from their position – Hamas wants the ceasefire to last until a permanent agreement is reached. Israel is opposed to this. At this point only President Trump can break this deadlock.”

The source added: “Unless Trump pushes, we are in a stalemate.”

The problem is that the announcement made now by Donald Trump – which is his social-media-summarised version of whatever Israel has actually agreed to – may just amount to Israel’s already-established position.

We don’t know the details and conditions attached to Israel’s proposals.

Would Israeli troops withdraw from Gaza? Totally? Or partially? How many Palestinian prisoners would they agree to release from Israel’s jails? And why only 60 days? Why not a total ceasefire? What are they asking of Hamas in return? We just don’t know the answers to any of these questions, except one.

We do know why Israel wants a 60-day ceasefire, not a permanent one. It’s all about domestic politics.

If Israeli Prime Minister Benjamin Netanyahu was to agree now to a permanent ceasefire, the extreme right-wingers in his coalition would collapse his government.

Itamar Ben-Gvir and Bezalel Smotrich have both been clear about their desire for the war to continue. They hold the balance of power in Mr Netanyahu’s coalition.

If Mr Netanyahu instead agrees to just 60 days – which domestically he can sell as just a pause – then that may placate the extreme right-wingers for a few weeks until the Israeli parliament, the Knesset, is adjourned for the summer.

It is also no coincidence that the US president has called for Mr Netanyahu’s corruption trial to be scrapped.

Without the prospect of jail, Mr Netanyahu might be more willing to quit the war safe in the knowledge that focus will not shift immediately to his own political and legal vulnerability.

UK

The PM faced down his party on welfare and lost. I suspect things may only get worse

Published

44 mins ago

July 2, 2025

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The PM faced down his party on welfare and lost. I suspect things may only get worse

So much for an end to chaos and sticking plaster politics.

Yesterday, Sir Keir Starmer abandoned his flagship welfare reforms at the eleventh hour – hectic scenes in the House of Commons that left onlookers aghast.

Facing possible defeat on his welfare bill, the PM folded in a last-minute climbdown to save his skin.

The decision was so rushed that some government insiders didn’t even know it was coming – as the deputy PM, deployed as a negotiator, scrambled to save the bill or how much it would cost.

“Too early to answer, it’s moved at a really fast pace,” said one.

The changes were enough to whittle back the rebellion to 49 MPs as the prime minister prevailed, but this was a pyrrhic victory.

Sir Keir lost the argument with his own backbenchers over his flagship welfare reforms, as they roundly rejected his proposed cuts to disability benefits for existing claimants or future ones, without a proper review of the entire personal independence payment (PIP) system first.

PM wins key welfare vote – follow latest

That in turn has blown a hole in the public finances, as billions of planned welfare savings are shelved.

Chancellor Rachel Reeves now faces the prospect of having to find £5bn.

As for the politics, the prime minister has – to use a war analogy – spilled an awful lot of blood for little reward.

He has faced down his MPs and he has lost.

They will be emboldened from this and – as some of those close to him admit – will find it even harder to govern.

After the vote, in central lobby, MPs were already saying that the government should regard this as a reset moment for relations between No 10 and the party.

The prime minister always said during the election that he would put country first and party second – and yet, less than a year into office, he finds himself pinned back by his party and blocked from making what he sees are necessary reforms.

I suspect it will only get worse. When I asked two of the rebel MPs how they expected the government to cover off the losses in welfare savings, Rachael Maskell, a leading rebel, suggested the government introduce welfare taxes.

Meanwhile, Work and Pensions Select Committee chair Debbie Abrahams told me “fiscal rules are not natural laws” – suggesting the chancellor could perhaps borrow more to fund public spending.

These of course are both things that Ms Reeves has ruled out.

But the lesson MPs will take from this climbdown is that – if they push hard in enough and in big enough numbers – the government will give ground.

The fallout for now is that any serious cuts to welfare – something the PM says is absolutely necessary – are stalled for the time being, with the Stephen Timms review into PIP not reporting back until November 2026.

Had the government done this differently and reviewed the system before trying to impose the cuts – a process only done ahead of the Spring Statement in order to help the chancellor fix her fiscal black hole – they may have had more success.

Those close to the PM say he wants to deliver on the mandate the country gave him in last year’s election, and point out that Sir Keir Starmer is often underestimated – first as party leader and now as prime minister.

But on this occasion, he underestimated his own MPs.

His job was already difficult enough – and after this it will be even harder still.

If he can’t govern his party, he can’t deliver change he promised.