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Can We Make Warp Drives Happen?

Being able to travel long distances at high speeds is something that we only see in sci-fi movies. It's just impossible to have something that could surpass the speed of light. But a scientist has thought of a way to get around the limitations.

This not-entirely-impossible warp drive is the brainchild of Miguel Alcubierre, a theoretical physicist at the National Autonomous University of Mexico.
According to Einstein’s special theory of relativity, nothing can go faster than light. Given the vast distances between stars, even the fastest possible vessel would still take way too long to get anywhere useful to humans.
But Alcubierre found a catch: nothing in relativity suggests that spacetime cannot contract or stretch faster than light. If spacetime around the ship bends in a certain way, the craft can be swiftly propelled and, in theory, travel a vast distance in little time.

(Image credit: Wikimedia Commons)


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Maintaining acceleration for a long enough time to travel galactic distances would be impractical as far as we currently know, as the Tsiolkovsky rocket equation is quite harsh.

If you accelerated at 1g for about 3.5 years of ship time, that would be enough to get to Alpha Centauri, including coming to a stop there. Alternatively, if you didn't try stopping and accelerated in the same direction for 3.5 years, you could reach 96% of c. At 96% c though, distances to destinations would shrink only by about 70% in the ship's frame compared to measurements on Earth. So in a 80 year human lifetime within the ship's time coasting at 96% c, you would get about ~270 light years (as originally measured from Earth).

Now to maintain that 1 g for 3.5 years, assuming you had an ideal rocket with an exhaust velocity of c, the rocket equation tells you your ship needs to start as 97% fuel by mass, and only allows 3% of the mass to go toward engine, fuel containment, and payload (all of which needs to be strong enough to hold up to 1g, i.e. built like a building and storage vessel on Earth, not paper thin). The rocket equation is exponential, so any variation from this can get even worse with small changes. For example, an antimatter rocket with generously estimated exhaust velocity of c/3, would drop your nonfuel fraction for a 3.5 year trip from 3% down to 0.002% of your total ship starting mass. A longer acceleration is likewise bad, so like say 20 years, which would get you to the center of the galaxy at constant 1 g, requires your starting ship to only be one part per billion not-fuel.

The only way to get away from the rocket equation is to not carry your fuel. However something like a laser propelled light sail would become extremely difficult over light years of distance or at relativistic speeds. And fuel collection en route like the Bussard ramjet idea tends to have speed limits way below relativistic speeds due to drag from the collected fuel.

For now, it seems really hard scifi would be limited to generational ships for travel to the stars.

(All numbers in this post should be relativistic if I did things correctly...)
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Onboard time dilation due to special relativity means a ship travelling close to the speed of light could get anywhere in our galaxy in a few years of ship time. This effect is a common theme in "hard" science fiction, as opposed to popular science fiction.

So no need for warp drives. Unless you want that when you return, the people you left behind should still be alive.
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I wouldn't go as far as saying it is impossible, because who knows what will be discovered or thought up in the future, but I would be willing to make a decent bet that it won't happen. There is a list of problems with it that need to be overcome beyond just the need for a large amount of some exotic form of matter that might not exist. Two of the simpler ones: the inside of the bubble might be full of radiation that quickly increases as the bubble's speed approaches the speed of light and the inside of the bubble cannot influence the outside world. The latter means it can't steer or possibly even create the bubble itself, making it more like a railroad than what people picture of a scifi spaceship. How to stop it at the destination is also a mess, and may make it more of a weapon than mode of transportation.
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