Interstellar: Uniting time, gravity, and love


The 2014 epic brought astrophysics to the big screen in a way that physicists can respect.

Article Image

Image by Paramount Pictures

By Ethan Attwood

CHRISTOPHER NOLAN'S 2014 space epic Interstellar has become somewhat divisive. Lauded for the scale, creativity and beauty of its visuals and score, some find the attempt to balance an electrifying tale of conquering distant worlds to save humanity with a far smaller-scale drama of love, hope and sacrifice to fall short of fulfilling either’s promise. Regardless of the film’s quality, it made a novel attempt to visualise astrophysical wonders for a billion-dollar audience. Luckily, there was a narrative theme available to the filmmakers that unites spacefaring, astrophysics, and the love, hope and destiny of Interstellar’s characters: time. Next, they needed a physics consultant.

Kip Thorne was trained at CalTech and Princeton. His trophy cabinet contains a litany of physics’ most prestigious awards, culminating in a 2017 Nobel Prize. A close friend of Stephen Hawking and Carl Sagan, they shared a passion for scientific communication. Hawking’s book A Brief History of Time has topped international bestseller lists. Sagan narrated the 1980 television series Cosmos: A Personal Voyage, a documentary which remains one of the most-watched programmes in American history. Kip Thorne instead set his sights on the big screen and became a consultant for the film industry.

Working closely with director Christopher Nolan and his screenwriting brother Jonathan, Thorne described the principles behind several plot devices used in the film. He also detailed mathematical relationships used by the visual effects designers to create some of the most realistic depictions of black holes ever to appear on film. Various psychedelic-yet-real astrophysical structures play a central role, and have profound consequences for the characters. Minor spoilers will follow.

Black holes were once found only in theory, but have since been confirmed and even photographed. The latter is especially impressive considering how they affect light, which has profoundly altered our understanding of gravity. Not only useful for dropping apples on famous scientists’ heads, the mysteries of gravity continue to wreak havoc with physical models. The scientists in Interstellar grapple with its effects as a central plot point, but why is it such a problem when its actions can be seen so clearly in the macroscopic world?

Firstly, gravity is weak. Compared to the other fundamental forces of nature, such as those governing electricity, temperature and atoms, it is so weak that its mechanism can’t be explained with the same physics. This has led to theories that gravity leaks energy into other dimensions (something alluded to by Matthew McConaughey’s Cooper). Secondly, stars and planets have been observed to bend light, an effect named the gravitational lens. Light, aptly named as it is, has no mass, so under Newton’s classical theory it shouldn’t be affected by gravity. Albert Einstein eventually explained this by suggesting that massive objects actually bend the fabric of space around them, and what we observe as gravity is really just objects or light taking the shortest path along this distorted surface. This can be thought of like a bowling ball sitting on a bed sheet – anything placed near it will roll toward the heavy ball.

Black holes are regions of space where gravity is so strong that not even light can escape their pull. A boundary called the event horizon marks the point past which nothing can escape. Any mass approaching it will be torn to shreds by massive gravitational forces in a process known as “spaghettification” or the “noodle effect”. Black holes are visible only by the eerie glowing halos of orbiting light and gases which have not yet passed the event horizon.

Gravity has one final perplexing effect. The protagonists in Interstellar are forced to view time as a finite resource because their experience of it is running faster than their families back on Earth, an effect known as relativistic time dilation.

When gravity distorts space, it’s really distorting spacetime, a term made necessary by the discovery that time, as the nominal fourth dimension, is inseparable from the three dimensions of space in which we move. For fundamental physical laws to remain consistent when space distorts, time must distort as well. So if you enter a very high gravitational field (or move at very high speed), time passes slower for you than someone stationary on Earth. Hypothetically then, a parent could end up younger than their children.

Interstellar is a celebration of how the selfless pursuit of science and exploration can save the world. It’s also a commentary on how impossible selflessness can be in the face of love, and how that motivation may be exactly what saviours need to do something incredible.