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The Science Of Interstellar

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Roger Highfield, Director of External Affairs at the Science Museum, explores the physics of Hollywood blockbuster Interstellar. Book tickets here to see Interstellar in full 70mm IMAX quality.

Black holes are thought to lie at the heart of most, possibly all, galaxies. So it should come as no surprise that a particularly striking black hole lurks at the heart of the galaxy of Hollywood stars—Matthew McConaughey, Anne Hathaway, Jessica Chastain, Michael Caine, Bill Irwin, Casey Affleck and John Lithgow— in the blockbuster Interstellar.

What is truly remarkable is that Christopher Nolan’s sci-fi epic spins around Gargantua, the most accurate black hole ever simulated, the fruits of a remarkable collaboration between a leading scientist, Kip Thorne, and a team led by Oscar winning visual effects wizard, Paul Franklin, who will help present the film with me in the Science Museum’s IMAX Theatre on Saturday (8 Nov 2014).

Interstellar’s plot, which started out being developed by Nolan’s brother Jonathan, relies on the monster black hole to explore the theme of time dilation, through which clocks can tick at different rates for different characters.

This is an idea that appeals deeply to Nolan. He used it in his mind-bending hit Inception, in which time moved at different speeds depending on the dream state of his characters. The extraordinary computer generated visions of Nolan’s dream worlds would win Franklin an Oscar.


Black holes are so dense that their gravitational pull prevents anything from ever escaping their grasp. At their heart is what physicists call a singularity, a point of effectively infinite density where the existing laws of physics break down (the laws of quantum gravity are thought to take hold in its core but we don’t understand them at all well). Around the black hole space-time itself bends to the point where even light can’t escape.

This extreme bending of space-time means that as you approach a black hole time will slow down noticeably for you relative to the outside world. An astronaut who managed to navigate into the closest orbit around a rapidly-spinning black hole – without falling in – could, in a subjectively short period, view an immensely long time span unfold.

Nolan was adamant that for Interstellar he wanted to explore ‘real possibilities’, not pure fantasy. Enter Kip Thorne, the 74-year-old Feynman Professor of Theoretical Physics Emeritus at Caltech, who was the inspiration for the character played in the movie by Michael Caine.

Thorne is one of the world’s leading experts on general relativity, the theory of gravity that Albert Einstein unveiled almost a century ago, and he once helped Carl Sagan with interstellar travel in his novel and movie Contact. Nolan brought Thorne together with Paul Franklin, along with his 30 strong team at the British visual effects company, Double Negative.

To make Gargantua scientifically plausible, Franklin asked Thorne to provide him with equations that would guide their visual effects software in precisely the way that Einstein’s physics models the real world.‘This is the first time that a movie’s black-hole visualisation started with Einstein’s general relativity equations,’ says Thorne.

Franklin and the Double Negative team, notably Eugénie Von Tunzelmann (CG Supervisor) and Oliver James (Chief Scientist), used a “render farm”, consisting of thousands of computers running in parallel, to trace light beams around the black hole. Some individual frames for the movie took up to 100 hours to create this way and, in all, the movie manipulated an eye-watering 800 terabytes of data.

Christopher Nolan filming on the set of Interstellar. © 2014 Warner Bros. Entertainment. All rights reserved

Christopher Nolan filming on the set of Interstellar. © 2014 Warner Bros. Entertainment. All rights reserved

The resulting Gargantua black hole looks like “a great lens in the sky with a dark heart,” says Franklin. And there is no way better to enjoy this, the most accurate depiction of a black hole created to date, than on one of the handful of 70 millimetre IMAX cinemas in the UK, notably at the Science Museum in London and the National Media Museum in Bradford.

Physics modelled by the film includes one of Einstein’s most famous predictions: that the path of a light beam can be warped by the gravity of a massive object, such as a star. When light from distant bodies passes through the gravitational field of much nearer massive objects, it bends by an effect known as “gravitational lensing,” providing extra magnification akin to a natural telescope and, as Thorne puts it, “image distortion akin to a fun-house warped mirror.”

This modelling of warped space around Gargantua creates a curious, compelling and surprising feature of the gravitational lensing of the star-studded sky along with the simulated accretion disc, the matter swirling into the hole at speeds approaching in the speed of light, which glows brightly.

‘This is the first time that a movie’s black-hole visualisation started with Einstein’s general relativity equations.’

At first they thought that there was a bug in their programming but when it persisted in the Double Negative simulations Thorne became convinced that the unexpectedly complex halo near Gargantua’s shadow was real and not an artefact. He expects at least two papers to emerge from the new details they found lurking in Einstein’s equations: one in the British journal Classical and Quantum Gravity for astrophysicists and one for the computer graphics community.

Thorne’s long term scientific collaborator and friend, Stephen Hawking, has argued that the long-term survival of our species depends on us developing interstellar travel. This is the central theme explored in Interstellar but, of course, to visit another star without spending thousands of years on the journey is not easy.

As one example of the distances involved, it takes light itself some 25,000 years to reach Earth from the gaping maw of the black hole that sits at the heart of our own galaxy, one with a mass of around three or four million times that of the Sun but 30 times smaller than Gargantua.

Physics forbids travel that is faster than the speed of light but might possibly allow for radical shortcuts: wormholes – hypothetical tunnels through space-time – predicted by Einstein’s general theory of relativity that can connect remote parts of the universe.

Their inception dates back decades to 1916 work by Ludwig Flamm at the University of Vienna, and later work in the 1930s by Einstein himself and Nathan Rosen in Princeton. Flamm, Einstein and Rosen discovered a solution of Einstein’s general relativity equations that describes a bridge between two places/times (regions of what scientists call space-time). This so called ‘Einstein-Rosen bridge’ – what we now call a wormhole – could pave the way to the possibility of moving colossal distances across the universe, even time travel.

It turned out that an Einstein-Rosen wormhole could not exist for long enough for light to cross from one part of the universe to the other. In effect, gravity slams this interstellar portal shut. This was a headache when the late astronomer Carl Sagan decided to write a science fiction novel, Contact, to travel from Earth to a point near the star Vega.

In 1985, when the book was in page proof form and Sagan’s attempt at interstellar travel relied on a black hole, he approached Thorne at Caltech, whom he had known since 1970. Indeed, Sagan had even set up Thorne on a blind date with Lynda Obst, who later became the producer of the film Contact (and of Interstellar). Thorne said a wormhole, not a black hole, was what was needed and enlisted the help of his students to work out what flavours of matter and energy would be needed to enable this feat of interstellar travel.

Thorne, Michael Morris and Ulvi Yurtsever speculated that with the help of fluctuations in quantum theory – one aspect of the bizarre theory that governs the subatomic world in terms of probabilities, not certainties – it might be possible to travel between different places and times.

In 1987, they reported that, for a wormhole to be held open, its throat would have to be threaded by some form of exotic matter, or some form of field that, because of quantum fluctuations, could exert negative pressure or negative energy and thus have antigravity associated with it. Thorne suggested that only an advanced civilization could make and maintain a traversable wormhole, “if it is even allowed by the laws of physics.”

At Hawking’s 60th birthday celebrations in Cambridge in 2002, Thorne told me that the laws of physics probably forbid ever collecting enough of exotic matter inside a human-sized wormhole to hold it open, but the final story was not in. There were still researchers studying whether it is possible to stuff enough exotic matter into the maw of a wormhole to maintain its gape – and there still are today.

So wormholes, while likely forbidden by physical laws, are still the subject of serious and respectable scientific study, and hence also of serious science fiction. Thorne has now written a book to accompany Nolan’s movie, The Science of Interstellar, in which he tackles wormholes, black holes and much more. With Interstellar we have another remarkable example, along with Contact and Gravity, of where the dreams and imagination of Hollywood thrive on real science.

See Interstellar in the Science Museum’s IMAX Theatre from 8 November 2014.Book tickets here.

Written by Roger Highfield

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