No Object Can Travel Faster Than Light, So Why Doesn’t That Apply To Warp Drives?

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The universe has a maximum speed limit, which is the vacuum speed of light. Any object with mass finds that it has much more of it as it accelerates toward it; thus, it requires increasing amounts of energy until it hits infinity to approach it.

It’s depressing. There is a vast universe waiting to be explored, and it would be helpful if we could have access to a fraction of it without building generational spacecraft or waiting to receive signals from human explorers or probes for hundreds of years. Enter the warp drive now. Regions of space can move apart faster than the speed of light, however masscontaining things are not allowed to travel faster than the speed of light (for more detail, see the expansion of the universe). Warp engines, made famous by the science fiction series Star Trek, are an ideal tool to avoid the speed limit by light-miles by encasing a ship in a bubble of spacetime. One theoretical scientist working with this concept is Miguel Alcubierre of Mexico. The spacecraft would remain stationary inside the bubble, but its outside could then conceivably travel at superluminal speeds.

“By a purely local expansion of spacetime behind the spaceship and an opposite contraction in front of it, motion faster than the speed of light as seen by observers outside the disturbed region is possible,” Alcubierre writes in a paper. The distortion that results is similar to science fiction’s “warp drive.” But, exotic stuff will be required to produce a spacetime distortion, just as it does with wormholes.

Efforts have been made to reduce the amount of exotic matter needed or even to question whether exotic matter is required at all.

“Even if one believes that exotic matter is forbidden classically, it is well known that quantum field theory permits the existence of regions with negative energy densities in some special circumstances (as, for example, in the Casimir effect, Alcubierre says. “The need of exotic matter therefore doesn’t necessarily eliminate the possibility of using a spacetime distortion like the one described above for hyper-fast interstellar travel.”

It may be possible, according to some teams that have tried to model what would be possible in the absence of exotic matter, to make a warp bubble inside the bounds of known physics using “traditional and novel gravitational techniques”. This would be extremely difficult to do, consume vast amounts of energy, and would almost certainly travel at slower than light speeds.

That’s it then: some exotic matter and a few technical revolutions, or some less exotic matter and a few technological revolutions, will surely get the warp drive going. Time to launch a Star Trek game. Right? Well, probably not after all. The problems with warp drives may well imply that those objectionable rules of the universe disallow them.

Another possibility is that as you move through the universe, you collect matter, and when you slow down, this matter expels itself.

Which means you’ll have reached your destination, only to find that it had been completely obliterated. However, even if you’re angling a bit left of your target and don’t care much that you are demolishing a whole lot of things in some far-off part of space, traveling faster than light speed still presents other problems that might eventually break causality. More simply, observers in different frames of reference begin arguing about when the events occur if the travel is faster-than-light. More simply, imagine a warp ship coming your way at twice the speed of light from your perspective. Because the light from the ship’s originating point has not reached you yet, the first you would see of it was when it got there.

However, that light would come to you; it would first come to you from points in the journey which were closer to you, and then backwards till the journey started. This would make a ship begin appearing out of nothing and shoot away from you at the speed of light. This is a problem because there is no frame that is inherently more fundamental than the others. When you consider many observers, and communication is faster than the speed of light, things get not only worse but also strictly break reality. We probably shall find ourselves restricted by the speed of causality, and something will most likely prevent us from shattering the cosmos. At least for now though, we should hope that somebody will make it happen.

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