Stephen Hawking now thinks "there are no black holes"

The physicist, whose pioneering work on black holes in the 1970s made him a household name, has proposed a radical fudge to try and resolve a baffling paradox.

For a scientist whose career was made by his work on black holes, it might seem a little confusing to read that Stephen Hawking now thinks that they don’t exist. But that’s what “Information Preservation and Weather Forecasting for Black Holes”, the study Hawking published last week on arXiv, says: “there are no black holes”.

While this might seem surprising - after all, there’s a huge amount of (indirect) evidence that black holes exist, including a massive one several million times the mass of our Sun at the centre of the Milky Way - it’s really not. It’s Hawking’s latest attempt to solve a paradox that he, and other astrophysicists, have been grappling with for a couple of years.

So what’s he talking about? Here’s the background: black holes are objects which are so massive, with such strong gravity, that even light can’t escape. The distance from the black hole, beyond which nothing gets out, is the event horizon. However, Hawking made his name in the 1970s when he published a paper showing that black holes don’t just suck stuff up, endlessly - they spew out a beam of so-called “Hawking radiation” as they absorb other matter. That means black holes actually lose mass over time, eventually whittling away to nothing.

Black holes are frustrating, though, because their extreme gravity exposes the major inadequacy in our current scientific understanding of the universe - we don’t know how to reconcile quantum mechanics and general relativity. With general relativity, we can make accurate predictions about objects with certainty, but on the tiny scale of quantum mechanics it’s only possible to talk about the behaviour of objects in terms of probability. When we do the maths on what happens to things that fall into black holes, using relativity gives results that break quantum mechanics; the same goes vice versa.

One of the key things about quantum mechanics is that it tells us information can’t be destroyed - that is, if you measure the radiation given off by a black hole, you should be able to build up a picture of what matter fell into the hole to create it. However, if general relativity holds, and nothing can escape from inside the event horizon, then that should apply to that quantum information - any radiation that’s coming out is, Hawking showed, random. It’s the black hole “information paradox”. Either give up quantum mechanics, or accept that information can die.

Hawking was in the “information can die” camp, until 2004, when it became clear - thanks to string theory - that quantum mechanics held up (and there’s an excellent in-depth explanation of this in Nature that explores this story more fully if interested). There was just one problem - nobody could work out *how* information was getting out of black holes, even if it was happening mathematically.

And, just in case this wasn’t all entirely confusing, it turns out that our best post-2004 theory about what’s been going on gives rise to an entirely new paradox - the “firewall”.

It’s to do with quantum entanglement, where two particles are created that are identical on the quantum level. The way it works isn’t exactly clear yet - it could be something to do with string theory and wormholes - but it means that measuring the properties of one particle will give readings that mirror those found on its entangled particle. It might lead to teleportation technology, but scientists aren’t sure yet.

Joseph Polchinski from the Kavli Institute for Theoretical Physics in Santa Barbara, California published a paper in 2012 that worked out the information paradox could be solved if Hawking radiation was quantum entangled with the stuff falling in. But, due to the limitations of entanglement, if this is true, that would mean that at the event horizon a massive amount of energy was given off by particles entering and leaving.

Hence “firewall” - anything crossing the event horizon would be burnt to a crisp. And even though most scientists, including Polchinski, thought this couldn’t possibly be right - it completely contradicts a lot of the stuff underlying general relativity, for example - nobody’s yet managed to disprove it.

The choice for physicists, once again, was to: a) accept the firewall, and throw out general relativity, or b) accept that information dies in black holes, and quantum mechanics is wrong.

Still with me? Here’s where Hawking’s latest paper comes in.

(That title - “Information Preservation and Weather Forecasting for Black Holes” - might make some more sense too, hopefully.)

Hawking’s proposed solution, building on an idea first floated in 2005, is that the event horizon isn’t as defined as we’ve come to imagine it. He instead proposes something called an “apparent horizon”, which light and other stuff can escape from:

"The absence of event horizons mean that there are no black holes - in the sense of regimes from which light can't escape to infinnity. There are however apparent horizons which persist for a period of time."

Black holes should be treated more like massive galactic washing machines. Stuff falls in and starts getting tossed around, mixed up with other stuff in there, and only eventually is allowed to escape out again when ready. This happens because the quantum effects around a black hole, like weather on Earth, churn so violently and unpredictably that it’s just impossible to either predict the position of an event horizon or expect uniform effects for stuff crossing it. While the theoretical basis, that information is preserved, remains, in practice it's so difficult as to be impractical.

It’s a fudge of an idea, which tries to have its general relativity and quantum mechanics cakes, and eat them, too. Possible weaknesses, as Nature points out, are that it could imply that escaping from black holes is easier than it is in reality. It could also be the apparent horizons are just as much of a firewall as the traditional conception of an event horizon. Hawking's peers have yet to have a go at assessing his idea, so we'll have to wait to see whether the idea has merit - or whether it merely gives rise to yet more paradoxes.

Hawking in Cambridge, September 2013. (Photo: Getty)

Ian Steadman is a staff science and technology writer at the New Statesman. He is on Twitter as @iansteadman.

John Moore
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The man who created the fake Tube sign explains why he did it

"We need to consider the fact that fake news isn't always fake news at the source," says John Moore.

"I wrote that at 8 o'clock on the evening and before midday the next day it had been read out in the Houses of Parliament."

John Moore, a 44-year-old doctor from Windsor, is describing the whirlwind process by which his social media response to Wednesday's Westminster attack became national news.

Moore used a Tube-sign generator on the evening after the attack to create a sign on a TfL Service Announcement board that read: "All terrorists are politely reminded that THIS IS LONDON and whatever you do to us we will drink tea and jolly well carry on thank you." Within three hours, it had just fifty shares. By the morning, it had accumulated 200. Yet by the afternoon, over 30,000 people had shared Moore's post, which was then read aloud on BBC Radio 4 and called a "wonderful tribute" by prime minister Theresa May, who at the time believed it was a genuine Underground sign. 

"I think you have to be very mindful of how powerful the internet is," says Moore, whose viral post was quickly debunked by social media users and then national newspapers such as the Guardian and the Sun. On Thursday, the online world split into two camps: those spreading the word that the sign was "fake news" and urging people not to share it, and those who said that it didn't matter that it was fake - the sentiment was what was important. 

Moore agrees with the latter camp. "I never claimed it was a real tube sign, I never claimed that at all," he says. "In my opinion the only fake news about that sign is that it has been reported as fake news. It was literally just how I was feeling at the time."

Moore was motivated to create and post the sign when he was struck by the "very British response" to the Westminster attack. "There was no sort of knee-jerk Islamaphobia, there was no dramatisation, it was all pretty much, I thought, very calm reporting," he says. "So my initial thought at the time was just a bit of pride in how London had reacted really." Though he saw other, real Tube signs online, he wanted to create his own in order to create a tribute that specifically epitomised the "very London" response. 

Yet though Moore insists he never claimed the sign was real, his caption on the image - which now has 100,800 shares - is arguably misleading. "Quintessentially British..." Moore wrote on his Facebook post, and agrees now that this was ambiguous. "It was meant to relate to the reaction that I saw in London in that day which I just thought was very calm and measured. What the sign was trying to do was capture the spirit I'd seen, so that's what I was actually talking about."

Not only did Moore not mean to mislead, he is actually shocked that anyone thought the sign was real. 

"I'm reasonably digitally savvy and I was extremely shocked that anyone thought it was real," he says, explaining that he thought everyone would be able to spot a fake after a "You ain't no muslim bruv" sign went viral after the Leytonstone Tube attack in 2015. "I thought this is an internet meme that people know isn't true and it's fine to do because this is a digital thing in a digital world."

Yet despite his intentions, Moore's sign has become the centre of debate about whether "nice" fake news is as problematic as that which was notoriously spread during the 2016 United States Presidential elections. Though Moore can understand this perspective, he ultimately feels as though the sentiment behind the sign makes it acceptable. 

"I use the word fake in inverted commas because I think fake implies the intention to deceive and there wasn't [any]... I think if the sentiment is ok then I think it is ok. I think if you were trying to be divisive and you were trying to stir up controversy or influence people's behaviour then perhaps I wouldn't have chosen that forum but I think when you're only expressing your own emotion, I think it's ok.

"The fact that it became so-called fake news was down to other people's interpretation and not down to the actual intention... So in many interesting ways you can see that fake news doesn't even have to originate from the source of the news."

Though Moore was initially "extremely shocked" at the reponse to his post, he says that on reflection he is "pretty proud". 

"I'm glad that other people, even the powers that be, found it an appropriate phrase to use," he says. "I also think social media is often denigrated as a source of evil and bad things in the world, but on occasion I think it can be used for very positive things. I think the vast majority of people who shared my post and liked my post have actually found the phrase and the sentiment useful to them, so I think we have to give social media a fair judgement at times and respect the fact it can be a source for good."

Amelia Tait is a technology and digital culture writer at the New Statesman.