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.

Show Hide image

With everything from iPhones to clothing turning monochrome, is the West afraid of colour?

If modern design appears particularly achromatic, it only reflects the "chromophobia" which courses through the history of Western thought.

To many English observers, 1666 – the year that the poet John Dryden christened the annus mirabilis, or “year of miracles” – wasn’t especially miraculous. The country was gripped by plague and, after a hot, dry summer, the Great Fire cut a swath through London. But for Isaac Newton, then still a student, it did prove illuminating. It was in 1666 that he first used prisms to prove that white light was not a pure, indissoluble substance but was made up of different coloured rays. This was such a profound challenge to the prevailing world-view that even Newton was shaken. “I perswade my self,” he wrote, “that this Assertion above the rest appears Paradoxical, & is with most difficulty admitted.”

The belief that colours are inferior and therefore naturally subordinate, rather than fundamental, was not new in Newton’s day, nor did it end with his discovery of spectral colour. A pattern of chromophobia – an aversion to colours – courses through Western thought.

Writing in the fourth century BC, Aristotle argued: “The most attractive colours would never yield as much pleasure as a definite image without colour.” For Renaissance artists, this idea was defined by the division between disegno, drawing or design, and colore. Disegno was the foundation of any serious artistic endeavour. The preference for achromatic, “intellectual” form is also evident in architecture. Despite rock-solid evidence from the 19th century proving that Greek marble buildings and statues were once brightly painted, the classical ideal has remained anachronistically bleached. And while modernist and postmodern architects have made some use of colour, the primacy of form is unmistakable in the work of everyone from John Pawson to Zaha Hadid and Toyo Ito.

A broad cultural dislike of colour is curious because, speaking in evolutionary terms, our ability to see it has been crucial to our success. Colour vision in primates developed between 38 and 65 million years ago and makes us better able to find ripening red and yellow fruits amid green foliage. Neurons devoted to visual processing occupy much more of our neocortex real estate than those devoted to hearing or touch. Estimates vary but the Optical Society of America has suggested that it may be possible for humans to distinguish between up to ten million different shades.

And we have put this skill to good use. Bold colours have been used by many cultures to mark temporal and spiritual power. Tyrian purple, a rich, reddish dye said to resemble clotted blood, was made using an extract from two different kinds of Mediterranean shellfish and was beloved by emperors in the ancient world. A single pound of dyed cloth would cost a skilled craftsman three years’ wages and became steadily more expensive as the shellfish became rarer.

But even as such saturated colours were coveted, they also elicited disgust. The manufacture of many, including Tyrian purple, involved ingredients such as stale urine and dung. Dye and paintworks were relegated to the urban fringes. Increasingly, the wearing of bright colours was seen as vainglorious and ungodly. Protestants indicated their humility by whitewashing over jewel-coloured murals and smashing stained-glass windows in churches, and by restricting their sartorial palette predominantly to black. An echo prevails today in men’s suits: colours are largely confined to small accessories such as ties and white shirts are held up as the ne plus ultra of refined sophistication. (The late Apple co-founder Steve Jobs went one better, opting for a uniform of identical black turtlenecks.)

One reason for this distrust is that colours are difficult to conceptualise. Do they exist physically, or only in our brains? Does everyone see them the same way? Colours have been maligned as chaotic, fickle, irrational and female. The early Christian thinker St Augustine of Hippo accused them of “a seductive and dangerous sweetness”.

Our ambivalence to colour, however, has profited white. Like black, white has not been classed as a real colour since Newton. It has almost become an anti-colour. Take Apple, for example. Although Sir Jony Ive is usually credited with the company’s love for monochrome products (it was certainly Ive who brought this to its apogee), the trend predates his arrival. It can be traced back to the “Snow White” design language developed in the 1980s. Today, as consumer neophilia demands that technology be continually refreshed, Apple’s higher-end products are available in the smallest range of colours – usually just white, black and, for the Asian market, gold – while those lower down come in a slew of fruity brights.

White is not only big business for Apple. In 2014, a Californian man named Walter Liew was found guilty of 20 counts of economic espionage and sentenced to 15 years in jail for selling the secret to a very special shade of titanium-oxide white, used in everything from luxury cars to tennis courts, to Chinese firms for $28m.

Perhaps the final word on the matter should go to Le Corbusier. In 1925, the great modernist recommended that all interior walls should be whitewashed, to act as a moral and spiritual restorative. But he wasn’t just advocating white for white’s sake: although he continued to dabble with colour, he disapproved of it, too. “Let us leave to the clothes-dyers,” he wrote, “the sensory jubilations of the paint tube.”

“The Secret Lives of Colour” (John Murray) by Kassia St Clair will be published on 20 October

This article first appeared in the 26 May 2016 issue of the New Statesman, The Brexit odd squad