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Warp drives: physicists boost faster-than-light space travel
Travel faster than light is the only way humans can reach other stars in a reasonable amount of time. The Bossinas / NASA / Wikimedia Commons The closest star to Earth is Proxima Centauri. It is about 4.25 light years away, or about 40 trillion kilometers. The fastest spacecraft of all time, the Parker solar probe now in space will reach a top speed of 450,000 mph. It would only take 20 seconds to get from Los Angeles to New York at this speed, but it would take about 6,633 years for the solar probe to reach Earth’s closest neighboring solar system. If humanity wants to travel easily between the stars, people will have to go faster than light. But so far, traveling faster than light is only possible in science fiction. In Issac Asimov’s Foundation series, humanity can travel from planet to planet, star to star, or across the universe using jump commands. As a kid, I read as many of these stories as I could get my hands on. I am now a theoretical physicist and I study nanotechnology, but I am still fascinated by the ways in which humanity might one day travel in space. Some characters – like the astronauts in the “Interstellar” and “Thor” movies – use wormholes to travel between solar systems in seconds. Another approach – familiar to “Star Trek” fans – is warp drive technology. Warp training is theoretically possible if it is still a far-fetched technology. Two recent articles made headlines in March when researchers claimed to have overcome one of the many challenges that stand between warp drive theory and reality. But how do these theoretical distortion training really work? And will humans jump to warp speed anytime soon? This two-dimensional representation shows the flat, undeformed space-time bubble in the center where a distortion drive would be surrounded by compressed space-time to the right (curve down) and extended space-time to the left. (curve upwards). AllenMcC / Wikimedia Commons Compression and Expansion The current understanding of space-time by physicists comes from Albert Einstein’s theory of general relativity. General relativity states that space and time are merged and that nothing can travel faster than the speed of light. General relativity also describes how mass and energy warp space-time – heavy objects like stars and black holes bend space-time around them. This curvature is what you experience as gravity and why many space heroes worry about “getting stuck” or “falling into” a gravity pit. Early science fiction writers John Campbell and Asimov saw this distortion as a way to get around the speed limit. What if a ship could compress the space in front of it while expanding the space-time behind it? “Star Trek” took this idea and named it the Warp Drive. In 1994, Miguel Alcubierre, a Mexican theoretical physicist, showed that compressing space-time in front of the spacecraft while expanding behind it was mathematically possible under the laws of general relativity. So what does this mean? Imagine that the distance between two points is 10 meters (33 feet). If you stand at point A and can travel a meter per second, it would take 10 seconds to get to point B. However, let’s say you could somehow compress the space between you and the point B so that the interval is no more than one meter. Then, by moving through space-time at your maximum speed of one meter per second, you would be able to reach point B in about a second. In theory, this approach does not contradict the laws of relativity since you are not moving faster than light in the space around you. Alcubierre has shown that “Star Trek” distortion training is in fact theoretically possible. Proxima Centauri here we are, right? Unfortunately, Alcubierre’s space-time compression method had a problem: it requires negative energy or negative mass. This two-dimensional representation shows how the positive mass curves space-time (left side, blue earth) and the negative mass curves space-time in an opposite direction (right side, red earth). Tokamac / Wikimedia Commons, CC BY-SA A negative energy problem Alcubierre’s distortion training would work by creating a flat space-time bubble around the spacecraft and curving the space-time around that bubble to reduce distances. The chain drive would require either negative mass – a theorized type of matter – or a negative energy density ring to function. Physicists have never observed negative mass, which leaves negative energy as the only option. To create negative energy, a chain drive would use an enormous amount of mass to create an imbalance between particles and antiparticles. For example, if an electron and an anti-electron appear near the chain reader, one of the particles would be trapped by the mass and this would cause an imbalance. This imbalance results in negative energy density. Alcubierre’s warp training would use this negative energy to create the space-time bubble. But in order for a warp drive to generate enough negative energy, you would need a lot of material. Alcubierre estimated that a warp drive with a 100-meter bubble would require the mass of the entire visible universe. In 1999, physicist Chris Van Den Broeck showed that increasing the volume inside the bubble while keeping the surface constant would significantly reduce energy requirements, roughly to the mass of the sun. A significant improvement, but still far beyond all practical possibilities. A science fiction future? Two recent articles – one by Alexey Bobrick and Gianni Martire and another by Erik Lentz – provide solutions that seem to bring distortion training closer to reality. Bobrick and Martire realized that by changing the spacetime in the bubble in some way, they could remove the need to use negative energy. This solution, however, does not produce a distortion drive that can go faster than light. [Over 100,000 readers rely on The Conversation’s newsletter to understand the world. Sign up today.] Independently, Lentz also came up with a solution that does not require negative energy. He used a different geometric approach to solve the equations of general relativity, and in doing so, he discovered that a distortion reader would not need to use negative energy. Lentz’s solution would allow the bubble to travel faster than the speed of light. It is essential to stress that these exciting developments are mathematical models. As a physicist, I won’t fully trust models until we have experimental evidence. Yet the science of warp training is emerging. As a science fiction fan, I applaud all of this innovative thinking. According to Captain Picard, things are only impossible until they are. This article is republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Mario Borunda, Oklahoma State University. Read More: Scariest Things In The Universe Are Black Holes – And Here Are 3 Reasons If Earth Falls, Will Interstellar Space Travel Be Our Salvation? Mario Borunda does not work, consult, own stock or receive funding from any company or organization that would benefit from this article, and has not disclosed any relevant affiliation beyond his academic appointment.