Warp drives: Physicists give likelihood of faster-than-light space travel a boost

The closest star to Earth is Proxima Centauri. It really is about 4.25 light-years away, or about 25 trillion miles (40 trillion km). The fastest ever spacecraft, the now- in-space Parker Solar Probe will reach a top speed of 450,000 mph. It could take just 20 seconds to go from Los Angeles to New York City at that speed, nonetheless it would take the solar probe about 6,633 years to attain Earth’s nearest neighboring solar system.

If humanity ever really wants to travel easily between stars, persons should go faster than light. But so far, faster-than-light travel is possible only in science fiction.

In Issac Asimov’s Foundation series, humanity can travel from planet to planet, star to star or over the universe using jump drives. As a youngster, I read as much of those stories as I possibly could get my practical. I am now a theoretical physicist and study nanotechnology, but I am still fascinated with the ways humanity could one day travel in space.

Some characters - just like the astronauts in the films “Interstellar” and “Thor” - use wormholes to travel between solar systems in seconds. Another approach - familiar to “Star Trek” fans - is warp drive technology. Warp drives are theoretically possible if still far-fetched technology. Two recent papers made headlines in March when researchers claimed to have overcome among the many challenges that stand between the theory of warp drives and reality.

But just how do these theoretical warp drives really work? And can humans be making the jump to warp speed anytime soon?

Compression and expansion

Physicists’ current understanding of spacetime originates from Albert Einstein’s theory of General Relativity. General Relativity states that space and time are fused and that nothing can travel faster compared to the speed of light. General relativity also describes how mass and energy warp spacetime - hefty objects like stars and black holes curve spacetime around them. This curvature is everything you feel as gravity and why many spacefaring heroes worry about “getting stuck in” or “falling into” a gravity well. Early science fiction writers John Campbell and Asimov saw this warping in an effort to skirt the speed limit.

Imagine if a starship could compress space before it while expanding spacetime behind it? “Star Trek” took this notion and named it the warp drive.

In 1994, Miguel Alcubierre, a Mexican theoretical physicist, showed that compressing spacetime in front of the spaceship while expanding it behind was mathematically possible within the laws of General Relativity. So, what does which means that? Imagine the distance between two points is 10 meters. For anyone who is standing at point A and can travel one meter per second, it could take 10 seconds to access point B. However, let’s say you could somehow compress the area between you and point B to ensure that the interval is now just one meter. Then, moving through spacetime at your maximum speed of 1 meter per second, you would be in a position to reach point B in about one second. In theory, this approach does not contradict the laws of relativity because you are not moving faster than light in the area around you. Alcubierre showed that the warp drive from “Star Trek” was in fact theoretically possible.

Proxima Centauri here we come, right? Unfortunately, Alcubierre’s approach to compressing spacetime had one problem: it needs negative energy or negative mass.

A poor energy problem

Alcubierre’s warp drive works by creating a bubble of flat spacetime around the spaceship and curving spacetime around that bubble to lessen distances. The warp drive would require either negative mass - a theorized type of matter - or a ring of negative energy density to work. Physicists haven't observed negative mass, in order that leaves negative energy as the only choice.

To create negative energy, a warp drive would use a huge amount of mass to create an imbalance between particles and antiparticles. For instance, if an electron and an antielectron appear near to the warp drive, among the particles would get trapped by the mass and this results within an imbalance. This imbalance results in negative energy density. Alcubierre’s warp drive would utilize this negative energy to create the spacetime bubble.

But for a warp drive to create enough negative energy, you'll need a large amount of matter. Alcubierre estimated a warp drive with a 100-meter bubble would require the mass of the whole visible universe.

In 1999, physicist Chris Van Den Broeck showed that expanding the quantity inside bubble but keeping the surface area frequent would reduced the energy requirements significantly, to nearly the mass of sunlight. A significant improvement, but nonetheless far beyond all practical possibilities.

A sci-fi future?

Two recent papers - one by Alexey Bobrick and Gianni Martire and another by Erik Lentz - provide solutions that seem to be to bring warp drives closer to reality.

Bobrick and Martire realized that by modifying spacetime within the bubble in a certain way, they could take away the have to use negative energy. This solution, though, will not create a warp drive that can go faster than light.

Independently, Lentz also proposed a remedy that does not require negative energy. He used a different geometric method of fix the equations of General Relativity, and in so doing, he found that a warp drive wouldn’t have to use negative energy. Lentz’s solution allows the bubble to visit faster than the speed of light.

It is essential to point out these exciting developments are mathematical models. As a physicist, I won’t fully trust models until we've experimental proof. Yet, the science of warp drives is getting into view. As a science fiction fan, I welcome all of this innovative thinking. In what of Captain Picard, things are just impossible until they aren't.