On the afternoon of September 23, 2014, a few minutes before his lecture at the Magma auditorium in Los Pueblos in Tenerife, Stephen William Hawking was rewriting parts of his speech. Hawking, who is unusual in being both a theoretical physicist working on some of the most fundamental problems in physics (his most recent paper, in January 2014, was titled "Information preservation and weather forecasting for black holes") and being very famous, is a slow writer.

He operates his computer by moving his right cheek muscle. The movements are detected by an infrared sensor attached to his spectacles allowing him to move a cursor on a computer screen attached to his wheelchair. He painstakingly builds sentences at a rate of a few words per minute, a speed that might be slowly decreasing as his muscle control deteriorates. His condition is a consequence of amyotrophic lateral sclerosis (aka motor neurone disease), an illness from which he has suffered since the age of 21 (he took part in the ALS Ice Bucket Challenge in August by volunteering his children: "Because I had pneumonia last year it would not be wise for me to have a bucket of cold water poured over me"). His Tenerife lecture was titled "The Quantum Creation of the Universe." The 1,500-capacity auditorium was packed.

"He was changing the content at the very last minute so we panicked a bit," says Jonathan Wood, Hawking's graduate assistant, a position which involves a variety of responsibilities, from technical assistance to managing social media. "He always does that. I produce the PowerPoint slides because he can't. I'm not a physicist, so often he will be talking about things that I don't understand and he'll have to explain what slides he wants." The lecture was part of the second edition of Starmus, a six-day science festival that gathered a group of eminent scientists, including physics Nobel laureate John Mather, biologist Richard Dawkins and Queen guitarist Brian May, who is an expert in three-dimensional astronomy. But the star turn was Hawking.

As he made his way to the stage, helped by his entourage of nurses and assistants, a giant screen showed a video montage which included visualisations of black-hole collisions and footage shot from Hawking's point-of-view in his wheelchair, with "Hole in the Sky," by the doom-metal band AtomA, blaring throughout the hall.

Marco Grob/WIRED UK

Hawking always starts his lectures with the same quip: "Can you hear me?" Hawking managed to be characteristically funny while guiding the audience through the bold ideas he has developed about the origins of the universe over the past decades. This delivery, a blend of humor and complicated theoretical physics, is the kind of performance that Hawking, 72, is now well known for, even as he has become a celebrity ambassador for science, a physicist whose office is adorned with portraits taken with Barack Obama, Bill Clinton and Steven Spielberg (twice) as well as stills from his many appearances in Star Trek and The Simpsons.

"I attended his famous inaugural lecture 'Is the End In Sight for Theoretical Physics?'" says physicist Neil Turok, a longtime friend and collaborator. "The whole lecture was given in a very amusing tone, really nothing more to it than a series of jokes. He was bold and naïve and stuck his neck out and said he thought within 20 years it would all be wrapped up. Twenty years later, he gave another lecture, titled 'Is the End of Theoretical Physics Finally In Sight?' He conceded he probably had to wait another 20 years."

Hawking's public persona manages to combine Carl Sagan's popular appeal with Richard Feynman's maverick brilliance for theoretical insight. He has deftly packaged his theories and thoughts (he is known to be able to reflect deeply about physics even when engaged in social events) in popular books, from A Brief History of Time – a bestseller which almost single-handedly launched the popular-science publishing industry – to The Grand Design, co-written with physicist Leonard Mlodinow in 2010. These books more than anything demonstrate Hawking's propensity for concise and bold statements laced with an unconventional humour. Here, for example, is Hawking deliberating on the idea of the multiverse, the notion that the Universe doesn't have a unique history, but rather that there exists a collection of all possible histories of the Universe, all equally real and with their own set of physical laws: "There might be one history in which the Moon is made of Roquefort cheese," he writes. "But we have observed that the Moon is not made of cheese, which is bad news for mice."

Hawking's public role doesn't detract from the fact that, over the past five decades, he has been one the boldest explorers of the cosmos, at least in the realms of thought – his mind roams in theoretical dimensions that, for the most part, remain inaccessible to experiment and direct observation. Through necessity (he's no longer able to write equations), Hawking has developed an original way of thinking about the mysteries of the cosmos, not relying so much on equations as most physicists do, but preferring to think in terms of pictures and geometries. Such tools are allied to an approach that aims to make big, intuitive breakthroughs, rather than incremental contributions, in our understanding of the cosmos.

"He has pioneered completely new areas in physics," says Kip Thorne, a physicist at Caltech and one of the world's foremost experts in general relativity. "There were several key junctures in his career when he'd make a huge breakthrough and everybody else was struggling to catch up or struggling to understand."

Stephen Hawking on October 10, 1979 in Princeton, New Jersey. Santi Visalli/Getty Images

The manner in which he blazed from breakthrough to breakthrough, particularly in his most prolific period in the 1970s and '80s, was unorthodox, as Hawking not only regularly demonstrated a far-reaching insight, but also a penchant for dramatic about-turns. Here is a theoretician who first proved that the universe starts with a singularity—an event in space and time where all the laws of physics break down—and then, with collaborator James Hartle, developed his "no boundary" proposal, which suggests that time didn't exist before the Big Bang and, therefore, the universe doesn't have a beginning. ("It makes no sense to talk of a time before the universe began. It would be like asking for a point south of the South Pole.")

He was also one of the first physicists to put forward a set of laws for the dynamics of black holes, including one that stated that black holes can never get smaller, but later discovered that they can indeed get smaller—in fact, they could evaporate through radiation (known today as Hawking radiation). That result was very contentious, generating a debate that lasted decades, as evidenced by the title of a book published by the physicist Leonard Susskind, The Black Hole War: My Battle With Stephen Hawking to Make the World Safe for Quantum Mechanics.

WIRED met Stephen Hawking the day after his lecture; his nurse, Patricia Dowdy, held his hand, to enable a light handshake, while Jeanna York, his personal assistant, made the introductions. His team has developed an idiosyncratic way of communicating with him, asking mostly questions that require only a yes or no answer and closely watching his facial expressions to interpret his thoughts and feelings. Hawking travelled to Tenerife by boat (his doctor forbade him from flying because of his health), a journey that took six days.

He was in good spirits, frequently flashing a smile that defies the stillness of his body. Exhaustion is probably the condition he is most familiar with, but that has never stopped him from extensive travelling, both physically and mentally. And that is what perhaps defines him the most: his unbreakable persistence. "I am just a child who has never grown up," he writes in his autobiography, My Brief History. "I keep asking 'how' and 'why' questions. Occasionally, I find answers."

Stephen Hawking floats on a zero-gravity jet, April 26, 2007. Zero Gravity Corp/AP

WIRED: What lessons in cosmology do you think the WIRED reader needs to understand if they are to keep up with current thinking?

Stephen Hawking: They need to understand that the universe began with a period of inflation in which it expanded at an ever-increasing rate. Quantum fluctuations would have caused some regions to have expanded slower than the rest of the universe. These regions would eventually stop expanding and collapse to form galaxies, stars and all the structure in the universe. Quantum fluctuations during inflation would also generate primordial gravitational waves.

WIRED: [The mathematician] Roger Penrose has mentioned that you always ask awkward questions. What questions are you asking right now?

Hawking: I'm working on how to reconcile the apparent loss of information when a black hole evaporates with our understanding of physics that information is never lost. I raised the question 40 years ago and, despite a large number of papers since, no satisfactory resolution of the paradox has been proposed. Indeed, it has been shown that there is a contradiction between information not being lost and the usual assumption that physics is local. It has been suggested that the resolution is that there is a firewall just outside a black hole that would burn up anything falling in, but I don't believe in firewalls. Instead I think space-time is warped.

WIRED: You also believe that the universe doesn't have a single past but various possible histories. What kind of experimental evidence would be needed to prove this theory?

__Hawking: __Feynman's idea of a sum over histories is that a system evolves by every path of history. This can be demonstrated by directing a stream of particles at a sheet with two slits in it. The number of particles arriving at a subsequent screen will form fringes, as if they were light rays. The interpretation is that each particle has two alternative histories, one going through one slit, and the other through the other slit, and they interfere like light rays.

WIRED: In your book The Grand Design, you write that M-theory is the theory that Einstein was hoping to find, one that predicts and describes the universe, and that physicists were led to it by abstract considerations of logic. However, the theory hasn't been confirmed by observations. If experimental physics weren't limited by current technology and financial budgets, what predictions from your theories would you love to confirm empirically? And if you could devise an experiment without such constraints, what would that experiment be?

__Hawking: __I'm beginning to have doubts about M-theory, but there seems no viable alternative. M-theory presumes supersymmetry is a symmetry between matter particles, like the electron, with force-carrying particles, like the photon. Supersymmetry would imply that all the particles we know have superpartners, but none have been found. The experiment I would like performed is to detect Hawking radiation from a black hole, because then I would win the Nobel Prize.

Hawking radiation is very difficult to detect, because the radiation from a black hole with mass a few times that of the sun would have a temperature of only a millionth of a degree above absolute zero. Smaller primordial black holes would have a higher temperature but there don't seem to be any around.

WIRED: Your longtime friend, physicist Kip Thorne, has described how, as you lost the use of your hands, you developed a powerful set of tools that no one else has, including an unusual ability to manipulate mental images of objects, curves, surfaces, shapes, not merely in three dimensions but in the four dimensions of space and time. Can you describe that mental process? Do you think you managed to solve problems that others couldn't because of that special set of mental tools?

Eddie Redmayne as Stephen Hawking and Felicity Jones as Jane Wilde in The Theory of Everything. Liam Daniel/Focus Features

Hawking: No one can visualise four dimensions. Three dimensions are hard enough. What I do is visualise two-dimensional sections, remembering they are part of a four-dimensional whole. This geometric visualisation I used in proving singularity theorems and my work on black holes, including black-hole radiation. My disability makes it difficult to write down complicated equations so I prefer problems with a geometric interpretation.

WIRED: You said that there's nothing like the eureka moment of discovering something new. Can you describe your favourite eureka moment?

Hawking: I was getting into bed shortly after the birth of my daughter, Lucy. My disability made this slow, so I had time to think about black holes. Suddenly I realised that if two black holes collided and merged, the area of the horizon of the final black hole would be greater than the sum of the areas of the original black holes. I was so excited I didn't get my sleep that night.

WIRED: There was a point in your life where you lost the ability to speak and, in effect, to communicate. Later, you wrote A Brief History of Time, which reshaped the science publishing landscape and opened up the market for popular-science books. Where does your desire to communicate science come from?

Hawking: I was able to speak with a speech synthesiser, though it gave me an American accent. I have kept that voice, because it's now my trademark. Before I lost my voice, it was slurred, so only those close to me could understand, but with the computer voice, I found I could give popular lectures. I enjoy communicating science. It is important that the public understands basic science, if they are not to leave vital decisions to others.

WIRED: You have long defended the view that we should colonise other worlds. How would humanity achieve this?

__Hawking: __I believe that the human race will not survive indefinitely on Earth without some disaster. I would like us therefore to spread out into space, so humanity doesn't have all its eggs in one basket, or on one planet.

WIRED: Can you tell us more about the work you're developing with Intel to develop technology that would improve the speed at which you can communicate, such as text-prediction engines, brain interfaces, facial recognition and other sensors?

Lisa, Marge, Stephen Hawking, and Homer on the "They Saved Lisa's Brain" episode of The Simpsons. FOX

Hawking: Intel has created a writing program for me using predictive text which allows me to write faster. The program is activated by a small sensor on my glasses. I'm writing these answers using it. Intel is going to open source it, to make it available to other disabled people. Intel has also tried facial recognition, though the range of messages that can be conveyed is limited. I have not had much success with brain-computer interfaces. My carers say it's because I have no brainwaves.

WIRED: You've been on The Simpsons, you took part in a documentary directed by Errol Morris and produced by Steven Spielberg, and acted on Star Trek. What would be your ideal movie role? Also, what are your views on current pop culture?

Hawking: My ideal role would be a baddie in a James Bond film. I think the wheelchair and the computer voice would fit the part. I know little of popular culture, having spent my time on science.

This story was first published in WIRED UK issue 01.15