Interstellar travel is one of the most frustrating topics in all of astrophysics. Despite hundreds of articles, movies and TV shows devoted to the subject, in most professional astronomical circles the issue seems about as welcome as the Grinch at Christmas.
It’s a fascinating topic. But no one can say with certainty that humans will ever be able to send robotic probes to visit another star system, much less colonize an extrasolar earthlike planet.
And, sadly, none of the major space agencies seem to have a long-term itch to send spacecraft on dedicated interstellar precursor missions.
Sending a 500 kg – 1000 kg robotic spacecraft to another star with a realistic travel time of a few hundred years will not likely be technologically feasible for another 75 – 150 years, Les Johnson, author of “A Traveler’s Guide to the Stars,” and a propulsion technologist at NASA Marshall Space Flight Center, told me via email. But he admits that if in 1990 someone had asked him how long it would take for Earth to have its current system of global telephony, he would have said far longer than it’s taken.
Even though Johnson is a longtime advocate of interstellar propulsion research, he is emphatic to note that his views on the subject are not NASA’s but rather very much his own. All of which begs the question: Why do mainstream rocket scientists and theoretical physicists appear to be so reluctant to discuss interstellar propulsion?
The distances are vast, and the energies required are almost unimaginably large, says Johnson. Thus, the steps we must take between today’s state of the art and the propulsion systems required are so numerous that they consider it to be science fiction, he says. Traveling to the stars is important, but we will likely not seriously begin considering them until we are masters of our own solar system, says Johnson.
What should we be doing to make interstellar travel possible?
“We need to bring back funding for basic research and development and run away from the notion that all R&D must have a near-term return on investment,” said Johnson.
Some form of warp drive is likely the most feasible way to enable realistic Star Trek-styled travel since each warp factor is a multiple of the speed of light cubed. As Johnson explains in “A Traveler’s Guide to the Stars,” Warp drive “uses tremendous energies to change the shape of space-time, allowing the ship to cross normal, albeit warped/compressed/expanded space very quickly.”
In a now-famous 1994 refereed paper, Mexican theoretical physicist Miguel Alcubierre describes a warp drive that “works mathematically and would allow a starship to appear to be traveling faster than light, while not really doing so,” Johnson notes in his book.
Can Alcubierre’s warp drive work?
The Alcubierre Drive postulates that a spaceship might appear to move faster-than-light by contracting space in front of it and expanding space behind it, thereby riding spacetime like a surfer rides a wave, says Johnson.
“After the ship crosses the contracted space-time, it expands back to normal size behind the ship, leaving nature beautifully intact and space-time undisturbed, with the ship appearing to move much faster than light,” Johnson notes in his book.
The mathematics is “elegant,” but to achieve the energies necessary to make the Alcubierre Drive a reality would require the existence of negative mass (where 1 kg would be -1kg), says Johnson. No one has ever detected negative mass and there is no evidence that it exists, he says. And until we find some, the Alcubierre Drive will remain speculative physics, says Johnson.
So, when can we expect human astronauts to touch down on an Earth 2.0?
The likelihood of finding an Earth 2.0 anywhere in the galaxy is very small, but probably not zero, says Johnson. However, the chances of finding it relatively close to Earth are so small as to be rounded to zero, he says. That does not mean we will not take such voyages; it does mean that we will likely need to not only learn how to travel to distant stars, but also how to terraform distant planets to make them truly habitable, Johnson says.
Does technology that could take us to the stars already exist in someone’s lab here on Earth?
It’s possible that the big new idea that brings interstellar travel closer to reality has already been envisioned by someone, somewhere in the world, says Johnson. But to meet the challenges of interstellar travel, we will need many big, new ideas and approaches, he says.
To that end, this coming July in Montreal, Johnson and colleagues are taking part in The 8th Interstellar Symposium, an interdisciplinary, global meeting of researchers working to one day make interstellar travel possible.