Proxima Centauri is the nearest star to Earth and is about 4.25 light-years away, or approximately 25 trillion miles away. The Parker Solar Probe, considered the fast-ever spacecraft that is now in space, according to NASA, will have a top speed of 450,000 miles per hour. At that speed, traveling from New York to Los Angeles would take just around 20 seconds. But to reach Proxima Centauri, the probe would take 6,633 years.
As such, if humans indeed want to have inter-star travel possible, they need to go faster than the speed of light. But currently, such as travel only remains in science fiction.
Warp Drives Abound in Science Fiction
In the fictional tales of Isaac Asimov, humans are depicted to travel planet to planet, star to star, and between universes through what he calls a jump drive.
Films like "Interstellar" or "Thor", "wormholes" are used to go around solar systems in mere seconds, For "Star Trek" fans this approach is through a "warp drive", which is theoretically possible yet far-fetched. Two recent studies caused a stir in March after researchers said they have overcome the difficulties associated with warp drives and reality.
How do warp drives theoretically work and will humans achieve it in the foreseeable future?
Theory of General Relativity as Basis for Spacetime
Scientists' present understanding of spacetime emanates from Albert Einstein's theory of General Relativity, which states that space and time are fused and that nothing moves faster than the speed of light.
It also describes how energy and mass could warp spacetime, with immense objects such as stars and black holes curving spacetime around them. Such curvature is what we sense as gravity, which makes fictional space-traveling heroes worry about getting trapped or collapsing into a gravity well. Such writers as Asimov and John Campbell consider this warping as a method to go beyond the speed limit.
But what if a spacecraft could compress space at its front while stretching spacetime at its back? This is the idea behind Star Trek's "warp drive."
Making Warp Drive Possible
Mexican theoretical physicist Miguel Alcubierre presented that spacetime compression at the front of a spaceship while stretching it from behind provide it was actually mathematically possible using the Laws of General Relativity, as we read in this Phys.Org feature.
This means if the distance between two points is compressed, it would take a much shorter time traveling between two points. This does not theoretically contradict the laws of relativity since you don't move faster than the speed of light. Alcubierre had shown that Star Trek's warp drive was definitely possible.
Would this mean Proxima Centauri is within reach? Alcubierre's approach of spacetime compression, however, had one flaw: it needs negative mass or negative energy.
This warp drive posited by Alcubierre would work by having a bubble of flat spacetime around the spacecraft and curving spacetime surrounding that bubble to cut distances. This would mean having negative mass or an amount of negative energy to make a warp drive actually work. Scientists have yet to observe negative mass, and because of this, negative energy is the only alternative.
Negative Energy Needed for Spacetime Bubble
To make negative energy, a warp drive would need an immense amount of mass to push an imbalance between particles and antiparticles. If such particles appear in close proximity to the warp drive, the mass would trap the particles, causing an imbalance. And this results in negative energy density. The warp drive of Alcubierre would utilize this negative energy to make the spacetime bubble.
However, for a warp drive to produce the needed negative energy, a lot of matter is needed. Alcubierre sees that a warp drive having a 100-meter bubble would need the mass of the entire visible universe.
Physicist Chris Van Broeck demonstrated that expanding the volume within the bubble while keeping the surface area constant would decrease energy requirements to about the mass of the Sun.
Eliminating the Need for Negative Energy
Two recent studies showed solutions about warp drives. A study, "Introducing physical warp drives," by Alexey Bobrick and Gianni Martire showed that modifying spacetime inside the bubble could eliminate the need for negative energy. This however would not produce a warp drive that could go faster than light.
Another separate study by Erik Lentz, "Breaking the Warp Barrier: Hyper-Fast Solitons in Einstein-Maxwell-Plasma Theory," proposed a warp drive that does not need negative energy. Lentz utilized a different geometric method to solve the General Relativity equations and thus finding out that a warp drive would not require negative energy. Lentz, thus, came up with a solution that would allow the bubble to go faster than the speed of light.
These exciting developments, however, a mere mathematical models. No such models could be fully trusted until it is actually experimented. However, warp drives and the science behind it are becoming quite evident.
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