The Physics of Fiction: How Art and Science Inspire Each Other
Paul Halpern on Literary Representations of Black Holes, Wormholes, and Multiple Dimensions
While much science fiction is based on theoretical physics, occasionally literature returns the favor and inspires scientific ideas. A perfect symbiosis between the two came about in the early 1980s, when astronomer-turned-novelist Carl Sagan was researching his fictional work Contact and turned to his friend physicist Kip Thorne for advice.
Sagan wished to devise a way the main character of his novel could journey quickly to a remote civilization in space. He knew that there had been considerable discussion of how Schwarzschild black holes might be able to connect with other objects: additional black holes, or perhaps even their hypothetical opposites that spew energy rather than absorbing it, dubbed “white holes.” Those connected bodies could potentially be very distant from each other in ordinary space—perhaps even in another part of our galaxy, or other galaxies altogether.
Such a mechanism could be a conceivable shortcut to a faraway, inhabited world, Sagan pondered, at least in speculative fiction. However, he read that astronauts attempting to travel through such links could possibly end up in danger. He asked Thorne to clarify.
Thorne’s extensive knowledge of the wildest solutions in general relativity, from black holes to gravitational waves, made him exactly the right person to ask. He had been fascinated by astronomy since a young age, while growing up in Logan, Utah. Logan lies in a valley that gets a lot of snow in the winter, so as a boy Thorne wanted to be a snowplow driver.
At the age of eight, however, his mother brought him to a talk about the solar system. Five years later, reading a popular book by physicist George Gamow, who helped develop the Big Bang theory, sealed the deal; Thorne wanted to be an astronomer.
After undergraduate work at Caltech, Thorne began a PhD program in physics at Princeton. There, his mentor, John Wheeler, introduced him to wondrous objects in general relativity, such as black holes, geons, wormholes, and so forth. Later Misner, Thorne, and Wheeler jointly authored an innovative textbook, Gravitation, that remains a classic.
Thorne’s subsequent work in gravitational wave detection, along with Rainer Weiss and others, culminated in the successful LIGO (Laser Interferometer Gravitational-Wave Observatory) detectors, and Nobel Prizes for both of them in 2017, along with former LIGO director Barry Barish, for discovering the first gravitational wave signals.
In responding to Sagan, Thorne pointed out that venturing into a black hole, with the hope of finding a spatial shortcut to elsewhere, would not be a good idea. Astronauts would be stretched like taffy due to its intense gravitational field, bombarded by lethal energy released by infalling matter, and accelerated to a dangerous level like the most unsafe thrill ride imaginable.
Moreover, even if they could somehow survive those perils and find a wormhole connection to another part of the galaxy, its throat would be unstable, and shut off immediately upon entrance. There would be no way of making it through. In short, the mission would be doomed to failure, and almost certainly to death.
That dialogue motivated Thorne to think of a solution to Sagan’s query. He assigned Michael Morris, one of his graduate students at Caltech—where he had become a professor—the task of designing a safe, traversable wormhole, if that were at all possible. Morris took on the task with great enthusiasm, and worked with Thorne to find a general relativistic solution with stable wormhole throats, swift, secure, and comfortable passage through them, and minimal risk when entering and exiting. Indeed, they found a traversable wormhole that would meet those specifications.
There was one catch, though: the wormhole would have to be built with enormous quantities of matter—perhaps comparable to the heft of galaxies—and, at least partly, with an unknown antigravity material with negative mass, dubbed “exotic matter.” No known astronomical or terrestrial objects have masses less than zero. There are ways, however, in quantum field theory to construct states with negative overall energy, and hence negative mass.
Conceivably, a highly advanced civilization could thereby mine the quantum vacuum in negative energy regions to collect exotic matter for wormhole construction. Then it would be faced with the additional challenges of finding the gargantuan amount of ordinary masses needed and building the wormhole according to safe and speedy specifications.
In 1987, Morris and Thorne published a paper with their findings in a pedagogical physics journal, American Journal of Physics. Their work inspired other physicists to try their hand in developing wormhole models. In particular, New Zealand physicist Matt Visser soon found alternative solutions, which he determined to require a smaller percentage of exotic matter. Though constructing traversable wormholes remains far beyond our capabilities, and may ultimately prove to be impossible, Visser’s results offered a welcome step forward.
In the 2014 movie Interstellar, Thorne, as co-producer and scientific consultant, explored the idea of traversable wormholes in fiction in far greater detail than Sagan had attempted. The film uses them as a plot device for astronauts to explore other worlds in our universe to assess their habitability.
Yet if traversable wormholes are feasible, they could well link to other universes—that is, otherwise-disconnected parts of space—instead of our own universe. Conceivably, therefore, by offering passageways between disparate cosmic enclaves, such a wormhole network would represent yet another kind of multiverse. Note though that the theory of wormholes is not yet developed enough to determine which spatial regions they’d connect. One might only speculate.
Excerpted from The Allure of the Multiverse: Extra Dimensions, Other Worlds, and Parallel Universes by Paul Halpern. Copyright © 2024. Available from Basic Books, an imprint of Hachette Book Group, Inc.