The Warped Universe of Kip Thorne A concept such as a traversable wormhole is not a terribly difficult idea for theoretical physicists. After all, engaging in theory is their purpose. Creating a mathematically sound set of principles in which a traversable wormhole could exist, though, is something far more innovative. Kip Thorne was able to create such a list of properties in his 1988 paper, Wormholes in spacetime and their use for interstellar travel: A tool for teaching general relativity. The basis for the idea rested in earlier concepts brought forth by other scientists like Karl Schwarzschild and Albert Einstein, but Thorne’s path to publishing his 1988 paper on wormholes stemmed from more than other scientists’ ideas. Thorne would eventually come to realize that travel to distant parts of the universe through a wormhole could not only be theoretically possible, but so could time travel.
Starting Out To understand how a traversable wormhole might exist, Thorne had to understand how other, similar concepts—such as black holes—functioned. Before he could ask even these questions, however, he had to first become a scientist. His interest in physics came at an early age, from reading scientific books and magazines. A significant factor in developing his interest in science came from reading the book One, Two, Three… Infinity by George Gamow, a Russian-born physicist. In Gamow’s book was a diagram of a tesseract, a four-dimensional model of a cube. “It look[ed] like two cubes, one inside another, and I spent hours staring at that, trying to come to grips with it,” Thorne told science writer Daniel Clery. “I found it so fascinating that it was one of the more significant influences on me to become a theoretical physicist.” Thorne went on to study at the California Institute of Technology for his B.S. degree, and his Ph.D. from Princeton University. He returned to Caltech to teach, and from the university’s campus in Pasadena, California, he spent most of his career coming up with theories and educating new generations of physicists. His ideas have often been characterized as radical and unusual, but Thorne’s outside the box thinking has produced remarkable theories.
Foundations of Discovery Thorne’s work in theoretical physics spans a wide variety of subjects, from gravity and spacetime in general relativity, to black holes and wormholes. In 1973, Thorne co-authored Gravitation with Charles Misner and John Wheeler. The text is now widely considered a classical instruction tool on general relativity. It was used by a generation of students studying physics because of its nature as a “breezier” read that still included complex physics knowledge. In 1983, he cofounded one of his more influential and foundational projects: the Laser Interferometer Gravitational Wave Observatory, called LIGO, along with fellow Caltech physicist Ronald Drever and Rainer Weiss, a physicist at MIT. The three scientists founded LIGO to study gravitational waves, the curvatures of spacetime from sources such as black holes or neutron stars, which form waves. LIGO’s purpose is to study different sources of these waves and determine their signatures. For example, a black hole would emit a gravitational wave signature that would identify its placement in the universe, as well as giving physicists data to help understand nonlinear systems—systems where output is not directly proportional to input. Gravitational waves had never been directly measured before, and LIGO was the answer. It was an ambitious project, but one that Thorne believed in strongly. As renowned physicist and personal friend Stephen Hawking once said of Thorne’s involvement in the project, “I don’t think [LIGO] would have happened if he hadn’t pushed it so hard.” Construction on LIGO facilities in Louisiana and Washington began in 1992. The first phase of foundational observation began in August 2002 and ran up to October 2010. Unfortunately no gravitational waves were detected during this period. However, a new phase of the system called Advanced LIGO opened on May 19, 2015. Instrument sensitivity was increased by a factor of ten, which provides a thousand-fold increase in the number of signals that can be detected by the system. Thorne remains optimistic that Advanced LIGO will be able to detect gravitational waves. The new phase began full operation in September 2015, following calibration work.
The Universe in View Through his studies, Thorne came to see the Universe from the perspective of a physicist. To him, space is not an empty void as most people consider it, but a fabric of the Universe that stretches, squeezes, bends, and even folds. This folding occurs when something as extreme as a black hole disturbs the fabric of space, causing it to fold in on itself, like a heavy rock sinking into a rubber sheet. In a 2007 interview with Discover magazine, Thorne explains how a black hole is actually formed: “A big misconception is that a black hole is made of matter that has just been compacted to a very small size. That’s not true. A black hole is made from warped space and time. It may have been created by an imploding star [where the gravity becomes so concentrated that nothing, not even light, can escape]. But the star’s matter is destroyed at the hole’s center, where space-time is infinitely warped. There’s nothing left anywhere but warped space-time… Its warped space whirls around the central singularity like air in a tornado. It has time slowing as you approach the hole’s edge, the so-called horizon, and then inside the horizon, time flows toward and into the singularity, dragging everything that’s inside the horizon forward in time to its destruction.”
Most observational evidence of black holes follow what Thorne describes, but some black holes do not rotate. These are called Schwarzschild black holes, named for Karl Schwarzschild. He created the metric, or solution, to part of Einstein’s field equations, the ten equations in his theory of relativity. The original concept of a wormhole is not traversable, because it behaves in the same fashion as a Schwarzschild black hole. Specifically, the stresses of gravity would tear apart any traveler before they could pass through the ‘throat’ of the wormhole, or the tunnel that connects the two ends. Thorne’s idea that formed his 1988 paper on traversable wormholes occurred during the phase when he was working to get LIGO off the ground. Most notably, he raised $365 million dollars for the program. By applying his knowledge of Schwarzschild wormholes, gravity, and black holes, Thorne and his graduate student Michael Morris theorized that a wormhole could be held open by using exotic matter. While exotic matter can refer to a number of things, in this case it referred to matter with a negative mass. Negative mass would be capable of acting as a counterbalance against normal matter, like opposing magnets repelling each other. Thorne and Morris created nine properties in which a traversable wormhole could exist. This theory later formed the scientific and mathematical base for wormhole travel in the 2014 film Interstellar.
The Thorne-Morris Properties of a Traversable Wormhole: 1. The metric should be spherically symmetric and static, independent of time. 2. The solution must everywhere obey the Einstein field equations. 3. To be a wormhole, the solution must have a throat that connects two asymptomatically flat regions of space-time. 4. There should be no horizon, since a horizon, if present, would prevent two-way travel through the wormhole. 5. The tidal gravitational forces experienced by a traveler must be bearably small. 6. A traveler must be able to cross through the wormhole in a finite and reasonably small proper time (e.g. less than a year) as measured by herself, but also by observers who remain behind or who await her outside the wormhole. 7. The matter and fields that generate the wormhole’s spacetime curvature must have a physically reasonable stress-energy tensor. 8. The solution should be perturbatively stable (especially as a spaceship passes through). 9. It should be possible to assemble the wormhole.
Interstellar’s wormhole in full view, 2 kilometers in diameter
Traveling into the wormhole in Interstellar
Traveling through a wormhole was one of Thorne’s more radical theories. Those nine properties would not only allow for the creation of a wormhole that could allow two-way travel for an adventurer, but would also allow for the possibility of time travel by an advanced civilization. Thorne’s theory was also influenced by one of his many illustrious scientific friends and colleagues, Carl Sagan. Before Sagan’s novel Contact was released in 1985, Sagan sought Thorne’s help, and at that point Thorne began to think about wormholes and time travel. “In Carl Sagan’s original version of his novel Contact, he had his heroine traveling through a black hole to a distant part of the universe, and he asked me for advice. I immediately told him, ‘You can’t do that. Black holes can’t be used in that way,’ and I suggested he use a wormhole instead. That got me interested in the issue of whether or not there really could be wormholes that you could travel through, and quite quickly I came to realize that if they did exist, it would not be hard for a very advanced civilization to use a traversable wormhole to make a time machine.” - Kip Thorne
Thinking Outside the Box Such unusual and groundbreaking theories earned Thorne an esteemed place among his peers. When he created the theory of traversable wormholes, some of his fellows thought him mad. However, he convinced them that his ideas were sound, as well as acceptable under Einstein’s theory of relativity. “I had friends who worried about whether I’d gone off the deep end when they first heard about [my wormhole theory], but most became enthusiastic after they learned the details.” Thorne’s work has proven that he has the creativity and the genius to come up with some of the most innovative theories in physics for the last fifty years. His uncommon positions have earned him a reputation of sorts, though. He was once described by Caltech president David Baltimore as “Caltech’s number-one strange scientist, the prince of counterintuitive science.”
A Modest Genius It takes a brilliant innovator to be able to soundly theorize that wormholes and time travel could be possible. It requires a mind capable of incredibly complex, original, and inventive thought. To make difficult subjects understandable and relatable to those without the complex knowledge of physics takes a gift of a different kind entirely. Kip Thorne has all of these traits. Despite possessing a singular mind, he remains a humble man. When asked about the highlights of his career, Thorne will often list the achievements of his former students rather than his own. Around 50 students have earned their Ph.D. under his tutelage at Caltech. In his own words, “I’m not a poor scientist, but if I have achieved some measure of greatness, it is through my students.”