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To travel from star to star, ships could surf a wave in space-time itself. Since the 1990s, theories of interstellar flight have focused as much on gravity, electromagnetism, and the properties of space-time as on propulsion systems. (Paul DiMare)

Mars, and Step on It

When it’s not the journey but the destination that counts.

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Few stories distill the question of human destiny as neatly as the 2000 movie Cast Away. In it, Chuck Noland (Tom Hanks), the sole survivor of an airplane crash in the South Pacific, ends up on an uncharted island. As days become weeks, he slides into despair, realizing that no one is coming for him. The years pass, and the permanence of his isolation sinks in, continually pounded home by the muffled roar of the surf breaking on the island’s encircling reef.

Noland can be thought to represent humanity on planet Earth. Will we ever get off the island? We swam out to the reef a handful of times during the Apollo program, arguably our greatest technical achievement as a species. But ever since, we’ve been back on the beach. Can we build the craft we need to break out?

Voyager 1, launched on an outer planet tour in 1977, is now the most distant object humans have sent into space, having left the solar system after 32 years of voyaging at a little better than 38,000 mph. At this rate, Voyager could get from New York to San Francisco in three minutes and 55 seconds, but wouldn’t reach the nearest star, Proxima Centauri, for 73,000 years. (It’s not headed there; it’s instead wandering toward the constellation Camelopardalis, where it will drift past its first star in about 300,000 years.) But if Voyager were traveling at the speed of light, a little more than 670 million mph, it would take only 4.2 years, a journey almost imaginable.

“We can see the theoretical possibilities of these things happening, but we just can’t get the engineering there,” says Bob Frisbee, an engineer at NASA’s Jet Propulsion Laboratory in California. Frisbee is one of dozens of U.S. scientists and engineers who are studying how humans could cross the vast gulfs of interstellar space in some meaningful time frame. Frisbee is known for his work on a propulsion system that uses the energy released from collisions of matter and anti-matter. His design uses a superconducting magnet as a nozzle to direct charged particles—produced by annihilating protons and anti-protons—to produce thrust.

“Philosophically, this is the kind of brainstorming stuff that people were doing about how to get to the moon,” says Frisbee. “What velocity? What kind of engine? What do we need to bring? And golly, they did it.”

Frisbee, who, in his day job studies how electric propulsion could be used for future robotic missions, is also a member of the Tau Zero Foundation, a group of scientists, engineers, and laypeople who stroll the distant shoals of theoretical spaceflight. Marc Millis, a physicist at NASA’s Glenn Research Center in Cleveland, Ohio, created the foundation and maintains a Web site (www.tauzero.aero) for the members, who have agreed to work together toward practical interstellar flight and to use this quest to teach people about science, technology, and our place in the universe. From 1996 to 2002, Millis ran what was, for NASA, an unusually future-oriented program called the Breakthrough Propulsion Physics Project. The program acknowledged the limitations of rocketry as we know it and encouraged studies of faster-than-light travel using the properties of matter—gravity and electromagnetism, for example—and of space and time. “All in all, we’re getting smart enough to ask the right questions,” says Millis.

The field gained momentum in the 1990s, shortly after the publication of three papers, all analyzing geometrical properties of space-time, the coordinate system containing both spatial and time dimensions rooted in Albert Einstein’s general theory of relativity. The papers proposed that through the manipulation of space-time, objects could get around the universe’s speed limit—the speed of light. The first two papers offered mathematical equations describing shortcuts for getting from one place in the universe to another: so-called wormholes. The third transformed the concept of warp drive from an element of science fiction, made famous by the TV series “Star Trek,” into a serious topic among theoretical physicists.

In that 1994 paper, Mexican physicist Miguel Alcubierre offered a mathematical proof that faster-than-light travel is possible within the constraints imposed by Einstein’s general theory of relativity. A spacecraft, Alcubierre theorized, would not dart across interstellar space; instead, it would ride a wave in the fabric of space-time, traveling inside a “warp bubble” like a person standing on a moving sidewalk. Some not-yet-defined force would work to condense the space-time ahead of the spacecraft and stretch out the space-time behind.

Millis has compiled the results of the Breakthrough Propulsion Physics Project and related work into a book of technical articles, The Frontiers of Propulsion Science, and members of the Tau Zero Foundation continue to exchange ideas and debate strategies, though a program no longer exists to fund experiments and observation. “We talk among ourselves and encourage each other to launch into projects,” says Millis, “and we’ve been very successful with that, even without money.” One member, for example, is revisiting the British Interplanetary Society’s Daedalus program. Daedalus is a 1970s effort to invent a practical starship powered by nuclear fusion, the process in which extreme pressures and temperatures cause the nuclei of atoms to join, releasing energy. The society is holding a symposium this month to reconsider the idea in light of the advances in relevant technologies made over the past 30 years.

“I think back to the era of Dirac and Schrödinger and Einstein,” says Millis of the great theoretical physicists of the early 20th century, Paul Dirac and Erwin Schrödinger, who shared a Nobel Prize in 1933 for groundbreaking work in quantum mechanics. “When they were having their pivotal meetings and sometimes heated debates, they weren’t being funded for that work. They were just doing it because that’s what they did. And they made significant advances.

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