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The Daily Galaxy

http://www.dailygalaxy.com/my_weblog/2014/11/the-physics-behind-interstellars-stunning-wormhole-images.html

November 22, 2014

The Science Behind “Interstellar’s” Stunning Wormhole Voyage (Weekend Feature)

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Similar in premise to many other science fiction films, something sets Interstellar apart:  Many of the images are–for the most part–scientifically accurate, based on lensing calculations produced by Cornell University and California Institute of Technology scientists that show what black holes or wormholes look like.  At this point, the blockbuster movie has created such a stir that one would almost have to be inside a black hole not to know about it.  And while the science fiction thriller may have taken some liberties with science to make its Hollywood plot work, the imagery comes straight from science–National Science Foundation (NSF)-funded science, in fact.

“Gravity bends the path that light follows in space,” said Pedro Marronetti, an National Science Foundation program director for gravitational physics and Google Scholar.  “The stronger the gravitation, the more dramatic its effect.”In the plot of Interstellar, Earth is dying; to save the human race, astronauts and scientists search for a new planet via a wormhole, essentially a shortcut through space to find a giant black hole at the other end.  Interstellar producers sought to make visual representations of the wormhole as accurate as possible.  They worked closely with Kip Thorne, a theoretical physicist at Caltech and the film’s executive producer, who gave the special effects team the scientific equations to create a reasonable facsimile of a wormhole.  Thorne’s involvement in this gravitational lensing project led him to talk with the three Cornell grad students and their Caltech collaborators.  The research of Bohn, Hébert and Throwe “on visualizing colliding black holes by gravitational lensing is very interesting and important,” Thorne said.Interstellar-film-physik-540x304

Wormholes do not actually exist in space, but black holes do, Throwe said, so the students created two short videos for Thorne, which showed what moving by a black hole in space would look like.  It would be impossible to move through an actual black hole, they said, because the pull of gravity would tear a person apart.

Astronomers haven’t been able to visually observe black holes because nothing can escape from them, not even light or radiation.  They can only be studied by noting their effects on nearby objects.  That’s what makes this recent research so important–because it creates a new visualization.

The four graduate students who work in NSF-funded, Cornell astronomy professor Saul Teukolsky’s group–Andy Bohn, François Hébert, William Throwe and Katherine Henriksson–as well as NSF-funded Caltech researchers Mark A. Scheel, Nicholas W. Taylor and undergraduate Darius Bunandar–have been doing related research and recently published their work about binary black holes on an online repository for scientific papers called ArXiv.  The paper, “What Would a Binary Black Hole Merger Look Like?” immediately garnered media attention, including in Nature.

“We know [interstellar travel through wormholes is] kind of crazy, but it makes a good story,” Throwe said.  Thorne used the students’ videos to help explain to the special effects team what kinds of information would be needed to make the visualizations believable.

While much is known about what a single black hole would look like in space, little was known about what two merging black holes would look like.  New technology allowed the students to do that for their paper.

“The idea that you’re going to be one of the first people to look at what a merging pair of black holes would look like is a good incentive to keep going,” Hébert said.

One of the best descriptions of wormholes in science fiction was the movie Contact, based on a novel by Carl Sagan.  While Sagan was writing the novel, he also consulted an expert in General Relativity, Kip Thorne,  to make sure that the way wormholes were treated in Contact was actually as close to being scientifically correct as possible.  Ellie, played by Jodie Foster, travels through a series of wormholes to a place near the center of the Milky Way galaxy, where the crew meets the senders of a message to Earth guised as persons significant in the lives of the travelers.

Studies from French and German physicists suggest that some unexplained objects in the universe might actually be “wormholes” -portals to other universes.  Thibault Damour and Sergey Solodukhin of the International University Bremen, believe that wormholes mimic black holes so closely that it might be impossible to distinguish.

Black holes and wormholes each distort the space and around them in a similar way, but though topically similar, they are, pardon the pun, universally different:

Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the sun.  When a star of that proportion undergoes a supernova explosion, it may leave behind a burned out stellar remnant.  With no outward forces to oppose gravitational forces, the remnant will collapse in on itself.  In other words, all of its mass is squeezed into a single point where time and space stop.  The point at the center of this black hole is called a singularity.  Within a certain distance of the singularity, the gravitational pull is so strong that nothing – not even light – can escape.

Wormholes, on the other hand, are theoretical warps in the fabric of space-time.  If wormholes could exist, they could potentially function as time machines.  (They also provide the fodder for many science fiction novels…)  According to Einstein’s theory of relativity, time passes more slowly for a highly accelerated body.  If one end of a wormhole were accelerated to close to the speed of light while another were stationary, a traveler entering into the stationary hole would emerge in the past from the accelerated hole.

Physicists like Stephen Hawking, however, aren’t convinced that wormholes even exist, arguing that properties of wormholes would be physically forbidden by basic universal laws.  If time travel existed, it would cause irresolvable paradoxes: it would be impossible, for example, to travel back in time and kill your former self.

Ironically, Damour and Solodukhin theoretically differentiate the two by using “Hawking Radiation,” the existence for which Hawking himself argued in 1974.  Hawking radiation is an emission of particles and light which should only come from black holes and would have a characteristic energy spectrum.  Both Damour and Solodukhin found this radiation to be so weak, however, that it would be completely swamped by other sources, such as the background glow of microwaves left over from the big bang.

Unfortunately, it seems the only way to definitively resolve the question is to make the plunge inside one of these massive holes – but considering that doing so would cause the instantaneous explosion of every atom of anyone or anything daring enough to try, our closest experience is still a visit to the science fiction section of local bookstores.

The Daily Galaxy via Anna Carmichael, Cornell University cunews@cornell.edu

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