Interstellar's Black Hole Once Seen As Pure Speculation
***SPOILER ALERT: This article contains plot spoilers for the movie "Interstellar." If you would like to avoid the spoilers, skip the THREE paragraphs that are italicized. ***
(Inside Science) -- Gargantua is the star of the new movie "Interstellar." Sure, the human cast includes Anne Hathaway, Matthew McConaughey, Jessica Chastain and other notable actors. But Gargantua, a huge, rapidly spinning black hole, is the astronomical centerpiece of the movie. In a movie that features plausible but fantastic ideas from modern physics, including wormholes, time travel, and extra dimensions, a spinning black hole is perhaps the easiest-to-accept cosmological element in the entire film.
In the movie, astronauts attempt to save humans on an increasingly uninhabitable Earth by attempting to find another planet with livable conditions. With the assistance of what seems to be an advanced life form, they travel through an exotic tunnel known as a wormhole, to a planet-containing star system containing Gargantua.
Black holes such as Gargantua are widely accepted as objects in our cosmos. But scarcely more than half a century ago, many physicists bitterly rejected the very existence of black holes. What helped turn the tide was a pivotal science meeting in Dallas in December, 1963, held despite the traumatic aftermath of the Kennedy assassination, according to Charles Misner, an emeritus professor of physics at the University of Maryland, in College Park, who was also my guest at a preview screening of "Interstellar."
The architect of the physics in "Interstellar" is one of Misner's long-time colleagues, theoretical physicist Kip Thorne. Thorne was the movie's science consultant and is credited as one of the film's executive producers. His book, "The Science of Interstellar," comes out on Friday, along with the wide theatrical release of the film. But Thorne has been a physicist since the 1960s, before black holes went Hollywood. Thorne and Misner co-authored the 1973 textbook "Gravitation,” with famous physicist John Wheeler, their former graduate school advisor, who is credited with popularizing the term "black hole."
Their textbook presented the physics of black holes, even though, at the time of its writing, their actual existence had not yet been confirmed with strong astronomical observations, said Misner. But the trio didn't think they were imaginary.
"We were all true believers," Misner said.
The film's science takes a lead role in the story, and the filmmakers clearly considered many aspects of cutting-edge theoretical and observational cosmology in crafting the narrative.
The modern idea of black holes emerged in 1915 from Einstein's theory of general relativity, which describes how gravity acts on large scales such as galaxies, clusters of galaxies, and the entire universe. In the following year, physicist Karl Schwarzschild found a solution to Einstein's equations that suggested the existence of black holes. As scientists came to understand in subsequent decades, black holes are objects in which gravity is so strong that even light cannot escape from them. However, black holes remained a theoretical curiosity, with physicists debating whether they were just a strange mathematical artifact or if they actually existed.
In the late 1950s, Misner recalls, other physicists told some of his colleagues to stay away from studying black holes and the other strange consequences of the mathematics from Einstein's general theory of relativity.
Famous physicists argued over whether black holes really existed, including Nobel laureate Richard Feynman.
At a June 1963 meeting at Cornell University in Ithaca, New York, "Feynman came to my defense and said they were possible," Misner recounted. On the other hand, Philip Morrison, an MIT physicist who, like Feynman, had worked on the Manhattan project, was staunchly opposed to the idea of black holes, which seem to require a region of infinite density in their center known as a singularity.
Indeed, what happens inside black holes is still not completely known or understood.
"Interstellar" takes advantage of this mystery. In the movie, the inside of Gargantua holds the key for an astronaut to travel through space and time in an attempt to save the people on Earth.
Attitudes towards the actual existence of black holes began to shift in the early 1960s. Astrophysicists were observing strange phenomena such as quasars, pointlike objects that radiate radio waves that can be more intense than those from entire galaxies. What could be causing these objects to appear? Could black holes be pulling in disks of matter in the center of galaxies and causing them to radiate huge amounts of electromagnetic radiation?
Misner remembers that the first Texas Symposium on Relativistic Astrophysics in Dallas, organized by University of Texas physicists in the summer of 1963, researchers discussed quasars and became "willing to think about gravity" and black holes as a main factor in powering these objects, Misner said. The conference occurred in December 1963, shortly after the assassination of President John F. Kennedy. As the Dallas Morning News has recounted, Mayor Earle Cabell urged the organizers to carry on with the meeting, despite their doubts on its timing after the historic tragedy. According to Wolfgang Rindler, a University of Texas at Dallas physicist who participated in the meeting, the organizers reflected on Kennedy's support of science and felt it would help everyone move ahead to the future.
Recollections of the Relativistic Astrophysics Revolution at the University of Texas at Dallas on December 11, 2013
Shortly thereafter, astronomers detected neutron stars, compact objects that could be as small as Manhattan but have the mass of the sun. As scientists came to realize, neutron stars formed when a dying star collapsed under the weight of its own gravity.
Later in the 1960s, Misner, Thorne and Wheeler decided they wanted to write a textbook that applied the latest mathematics to Einstein's theory of gravitation. They spent three years on it, meeting in all sorts of places to work on it, including spending a summer on High Island off of Maine.
Published in 1973, "Gravitation" is still being used today. "It's never been out of print, and never been revised," Misner said. Though published before many developments in the study of black holes, including some of the major ones from physicist Stephen Hawking, "its mathematics remains solid," he said.
Sales of the book spiked in the 1990s, as observational astronomy advanced and scientists began to observe evidence for more and more black holes. But, Misner emphasized, physicists can't rely on the equations alone in order to fully understand the physics of black holes. They needed an additional element. They needed to make pictures to show what was happening.
"No one could understand what the equations were saying unless they looked at the visualizations,” Misner said. Nowadays, a visualization specialist is often a member of the research team.
Forty years later, Thorne, the sci-fi buff in the textbook trio, has applied this practice to cinema through "Interstellar." As reported in Wired, he worked with computer-graphics expert Paul Franklin to convert the equations of black holes into vivid, detailed simulations of black holes. They show dramatic strands of light appearing above, below, and around the disk of matter surrounding the black hole. Thorne has indicated that the insights from these visualizations will be the basis of at least a couple of upcoming research papers.
Amidst these realistic simulations, Misner said, the movie has "glimmers of real physics wildly exaggerated." For example, physicists have established that wormholes, tunnels to different parts of space and time, are possible, but they usually imagine their openings to be very small, around the size of the elementary particles that make up protons and neutrons.
In the movie, a wormhole, found just outside of Saturn, is large enough for a spaceship to pass through, and Misner wondered how the opening of the wormhole could be big enough without the presence of a huge black hole that would surely disrupt the orbit of Saturn, and much of the solar system with it. Indeed, present-day physics can’t explain how such a wormhole could occur, so, in the movie, its details are left to the alien civilization that put it there. However, Misner appreciated accurate touches in the movie such as the Penrose process, in which space travelers could harvest useful energy from a black hole.
Misner said we are living in an era where the study of gravitation is "getting better all the time," with work on black holes, neutron stars, and the cosmic microwave background explained with the help of mathematical equations that were once purely theoretical.
"Science provides a stepping stone into a universe that it would be exciting in which to live, and which we can enjoy as fiction," he added in an email to Inside Science.
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