While much science fiction is based on theoretical physics, occasionally literature returns the favor and inspires scientific ideas. A perfect symbiosis between the two emerged in the early 1980s, when astronomer-turned-novelist Carl Sagan was researching his fictional work. Contact and asked his physicist friend Kip Thorne for advice.
Sagan wished to discover a way in which his novel’s main character could quickly travel to a remote civilization in space. He knew there had been considerable discussion about how Schwarzschild black holes might be able to attach themselves to other objects: additional black holes, or perhaps even their hypothetical opposites that expel energy rather than absorb it, dubbed “white holes.” ”. These connected bodies could potentially be very far from each other in ordinary space – perhaps even in another part of our galaxy, or in other galaxies.
Such a mechanism could be a conceivable shortcut to a distant, inhabited world, Sagan reasoned, at least in speculative fiction. However, he read that astronauts who attempted to travel through such links could end up in danger. He asked Thorne to clarify.
Thorne’s extensive knowledge of general relativity’s wildest solutions, from black holes to gravitational waves, made him the right person to ask. He was fascinated by astronomy from a young age while growing up in Logan, Utah. Logan is 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 took him to a lecture on 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.
If traversable wormholes are viable, they could very well connect to other universes – that is, parts of space that would otherwise be disconnected – rather than to our own universe.
After graduating from Caltech, Thorne began a doctoral program in physics at Princeton. There, his mentor, John Wheeler, introduced him to wonderful objects of general relativity, such as black holes, geons, wormholes, and so on. Later, Misner, Thorne, and Wheeler jointly wrote a groundbreaking book, Gravitationthis remains a classic.
Thorne’s subsequent work on detecting gravitational waves, together with Rainer Weiss and others, culminated in the successful LIGO (Laser Interferometer Gravitational-Wave Observatory) detectors and the Nobel Prize for both in 2017, together with former LIGO director Barry Barish, for discovering the first signs of gravitational waves.
In responding to Sagan, Thorne pointed out that venturing into a black hole, with the hope of finding a spatial shortcut to somewhere else, would not be a good idea. The astronauts would be stretched like taffy by their intense gravitational field, bombarded by the lethal energy released by falling matter, and accelerated to a dangerous level, like the most unsafe thrill ride imaginable.
Furthermore, even if they somehow managed to survive these dangers and find a wormhole connection to another part of the galaxy, their throat would be unstable and close immediately upon entry. There would be no way to get through this. In short, the mission would be doomed to failure and almost certainly to death.
This dialogue motivated Thorne to think of a solution to Sagan’s doubt. 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 possible. Morris took on the task with great enthusiasm and worked with Thorne to find a general relativistic solution with stable wormhole throats, quick, safe and comfortable passage through them, and minimal risk when entering and exiting. In fact, they found a traversable wormhole that would meet these specifications.
However, there was a problem: the wormhole would have to be constructed from enormous amounts of matter – perhaps comparable to the weight of galaxies – and at least partially from an unknown anti-gravitational material with negative mass, dubbed “exotic matter”. . No known astronomical or terrestrial object has a mass less than zero. There are ways, however, in quantum field theory to construct states with negative overall energy and thus negative mass.
It is conceivable that a highly advanced civilization could explore the quantum vacuum in regions of negative energy to collect exotic matter for the construction of wormholes. It would then be faced with the additional challenges of finding the gigantic amount of common masses needed and building the wormhole to specifications safely and quickly.
In 1987, Morris and Thorne published an article with their findings in a pedagogical physics journal, American Journal of Physics. His work inspired other physicists to try to develop models of wormholes. In particular, New Zealand physicist Matt Visser soon found alternative solutions, which he determined required a lower percentage of exotic matter. While constructing traversable wormholes remains far beyond our capabilities and may ultimately prove impossible, Visser’s results offered a welcome step forward.
In the 2014 film Interstellar, Thorne, as co-producer and scientific consultant, explored the idea of traversable wormholes in fiction in much greater detail than Sagan had attempted. The film uses them as a plot for astronauts to explore other worlds in our universe to assess their habitability.
However, if traversable wormholes are viable, they could very well connect to other universes – that is, parts of space that would otherwise be disconnected – rather than to our own universe. It is conceivable, therefore, that by offering gateways between disparate cosmic enclaves, such a network of wormholes would represent yet another type of multiverse. Note, however, that wormhole theory is not yet developed enough to determine which spatial regions they would connect. We could only speculate.
Extracted in O Fascination of Multiverse: Extra dimensions, other worlds and parallel universes by Paul Halpern. Copyright © 2024. Available in Basic Books, an imprint of Hachette Book Group, Inc.