Think that everything in a black hole gets swallowed up, never to be seen again? Well, you're half right

What happens to the information in a black hole once it disappears? Stephen Hawking thought he knew, betted on it, and lost.

Young people? Nothing but trouble. If you don’t believe the politicians, just look at physicists’ current anguish over the question of what is lost when stuff falls into a black hole. We are now in the middle of a huge crisis of confidence, just because the kids couldn’t keep their ideas to themselves.
 
If you think that stuff in a black hole just gets swallowed up, never to be seen again, you’re half right. The stuff is indeed gone. Yet the information about the stuff can’t be. In the 1970s, a young Stephen Hawking showed that, due to a quirk of quantum theory, black holes don’t just swallow; they also spit. A trail of particles is emitted from a black hole over its lifetime. As a result, the black hole eventually loses so much energy that it evaporates and disappears from the universe. According to Hawking’s theory, those particles contain no information of any kind, so the original information is lost once the black hole disappears.
 
However, a fundamental law of physics states that information can’t be destroyed. In 1997, John Preskill of the California Institute of Technology was so confident that Hawking must be wrong that the pair entered into a bet. That year, a young theorist called Juan Maldacena showed that, as stuff fell in, the information could be caught on the “event horizon”, the spherical surface of a black hole. With the information residing on the event horizon, it isn’t erased from the universe and might eventually leak back out.
 
Maldacena’s work was convincing enough for Hawking to concede. In 2004, he bought Preskill a baseball encyclopaedia (for reasons we won’t go into here) and the bet was considered settled.
 
Then, in 2010, along came the vibrant young mind of Mark Van Raamsdonk. His work has led to the new debate over the “cosmic firewall”. For information on the event horizon to leak back into the universe, there has to be a layer of ultra-high-energy particles – a firewall – just inside the event horizon. Each particle taking information from the event horizon has what Albert Einstein once termed a “spooky” link with a particle in the firewall. The link is called “entanglement” and it means that you can’t fully describe one of the particles unless you have information that resides in the other.
 
The problem is, the nature of Hawking’s original result shows that the particle on the outside of the event horizon also has to be entangled with another particle, one that carried away a little information from the black hole some time in the past. And a single particle can’t share that kind of entanglement with two others. So Maldacena’s idea doesn’t work. The best solution anyone can come up with involves another entanglement, this time between the particle inside the firewall and the particle that left the black hole all that time ago. That particular spooky link resolves the problem because those two entangled particles are actually one and the same.
 
It’s a classic Shakespearean twist. The whole problem has been a case of mistaken identity: the cosmic firewall story is the Twelfth Night of cosmology. However, most physicists don’t like this ending. Resolving all these entanglements stretches credulity too far, they say. The resolution they prefer is to acknowledge that this whole shebang exposes a gaping hole in our understanding of the universe. Maybe, they say, we need to start again.
 
While they scratch their heads and wonder what to do, Hawking could justifiably ask for his encyclopaedia back. If Preskill has any sense of how to play the foiled schemer, he’ll reluctantly hand it over while muttering something about those pesky kids. 
 
Michael Brooks’s “The Secret Anarchy of Science” is published by Profile Books (£7.99) 
In 1997 Hakwing made a bet with John Preskill of the California Institute of Technology - and lost. Photograph: Andrew Burman/Evevine/Contrasto.

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article first appeared in the 02 September 2013 issue of the New Statesman, Syria: The west humiliated

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The moonwalkers: what it's like to belong to the world's most exclusive club

"The blue and the white and the brown just hung in the blackness of space."

It’s been almost 50 years since man first walked on the moon – and there were only a grand total of six missions.

From 1969 until 1972, as humanity reached out into space, these men – and they were all men – were at the forefront of scientific research and discovery.

But in 2017, the six survivors – now with a combined age of 505 – are the rare members of an exclusive club. The other six moonwalkers have already passed away.

Astronaut Buzz Aldrin was on Apollo 11, Charlie Duke was on Apollo 16 and Harrison "Jack" Schmitt was an Apollo 17 moonwalker. For the first time, at the Starmus festival in Trondheim, Norway, the three have come together to discuss their experience.

The three share “a special relationship, no question about it”, according to Duke. He tells me: “Our experiences are different but they’re the same in so many respects.”

Aldrin – unable to appear in person due to doctor’s orders – quips on camera from his home in Florida that President Dwight Eisenhower was advised that they should send a philosopher or maybe a poet up. His response, possibly apocryphal, came: “No, no - I want success."

As a result, it is up to these scientists to find the words to describe the off-Earth adventure which is the defining event of a moonwalker's life. 

A poetic description comes from Texan resident Duke. First and foremost a test pilot, his interest in space was piqued by the launch of Sputnik, the first artificial satellite, in 1957. He joined Nasa in 1966.

Now 81, Duke served as mission control support throughout many Apollo missions, most notably as the voice of Capsule Communicator when Neil Armstrong and Aldrin landed on the Moon in 1969.

He tells me: “Once we left Earth’s orbit, we turned our spaceship around and there was the whole Earth 40,000km away.

“The blue and the white and the brown just hung in the blackness of space. That contrast between the vivid blackness and the bright Earth – this jewel of Earth I like to call it - was right there.”

Aldrin started his career as a mechanical engineer, before joining up as a jet fighter in the US Air Force during the Korean War.

His gung-ho spirit and enthusiasm for space have not deserted him even at the age of 87 – he appears onscreen at the festival wearing a "Get your ass to Mars" T-shirt.

The most memorable experience for him came when he congratulated Neil Armstrong, the first of the team to walk on the moon (he died in 2012). But in the lunarscape, memories get confused – the men remember the moment differently.

“After the landing, I looked over at Neil, and we smiled. I remember patting him on the back and he remembers shaking hands. So here were two first-hand witnesses and we couldn’t agree on what actually happened when we got there.”

For Aldrin, the significance of the moonwalk was looking at the moon’s surface from close-up – the lunar soil, or regolith – and what happened when an astronaut's boot stepped onto it. 

“It was so remarkable, the way that it retained its exact form,” he marvels, 48 years on.

Aldrin's fascination with the moon's surface was shared by Schmitt, the 12th, and so far, last, man to walk on the Moon. A trained geologist, he was also the first scientist to do so.

In Schmitt's case, the rocky surface of the moon was enough to draw him into lunar research, which he still conducts at the age of 81.

“The commander told me as soon as I got out I had to look up and see the Earth," he recalls. "I said ‘Well, chief, you’ve seen one Earth, you’ve seen them all’."

In truth, having spent three days looking at the Earth from his craft, Schmitt’s priority was in looking down at the new surface under his feet.

After landing in a valley deeper than the Grand Canyon, his chief concern was just getting to work collecting samples in a lifesize laboratory.

While the moment on the moon may be the initiation into an elevated celebrity, it is followed quite literally a fall back to earth. 

In his post-Moon life, Duke found God.

“A lot of us have a letdown [afterwards]," he admits. Duke was 36 when he landed on the moon in April 1972. By December, the Apollo programme was over. "In January ’73, the thought occurred to me, ‘what am I going to do now?’"

Achieving his life's ambition before hitting middle age turned out not to be as satisfying as he expected. "Because you’d climbed the top, you got to the ultimate high when you were still a young man - and the drive that took you to the ultimate high was still there," he says. "That was a struggle."

In the years since, Duke has looked at his experience as a religious one. Yet he insists God wasn’t present for him when he touched down on the lunar body.

“The Moon flight was not a spiritual experience," he says. "I didn’t understand the wonder of God’s universe. I was enjoying the beauty and the excitement of this mission.”

The three men agree that Mars is the next step for the future of humanity, but there are safety and speed concerns.

“There is potential important work to be done in better physiological understanding of human exposure to long duration space flight which is going to happen whenever we go to Mars,” says Schmitt.

“Anything we do as human beings that’s productive and worthwhile carries risk, either physical of psychological. Radiation, physiological exposure to weightlessness for long durations, and the danger of landing on a distant planet where the atmosphere is not going to be much help - but you do accept the risk that it might end up as a one-way trip.”

But after all of that - the life, the death, the heartache - Duke says he would go back up there if he could.

“At my age now I wouldn’t volunteer to go to Mars - but I would volunteer for a round-trip to the Moon again.”

Starmus Festival runs in Trondheim until Friday June 23. For more information, visit Starmus.

Kirstie McCrum is a freelance journalist. Follow her @kirstiemccrum.

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