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The science of warp drives

Warp drives, negative mass, exotic matter - these all sound like the stuff of science fiction. But MIT explains how our stranger-than-fiction universe could be explained by real science!

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Video transcript

ISAAC: Suppose you wanted to take a trip to the North Star, like, actually go there. (I hear it's lovely this time of the century.) Well, the North Star is 4 million billion miles away, and there's a universal speed limit-- the speed of light. Now we don't have any ships that can go even nearly that fast. But even if we did, it would take over 400 years to get there. But what if instead of traveling through space, we move space around us in order to get to our final destination. And what if instead of taking 400 years, it took more like four months. Now this sounds like science fiction. But NASA is actually funding some really, really early research related to the Alcubierre Warp Drive, which would allow us to appear to be breaking the universe's speed limit by bending space itself around us. If you take a slinky and stretch it out like this, it represents the space between Earth and the North Star, quite a ways to travel. But if we can somehow find a way to expand the space behind us and contract the space in front of us, then we've made it most of the way to the North Star without having moved hardly at all. And that is exactly how the Alcubierre Warp Drive works. You would contract space far enough in front of you, and expand space far enough behind you, leaving you with a stable bubble to ride in your ship. The space in this bubble hasn't been warped, so you still experience time the same way you normally would. That's different from if your ship itself was traveling close to the speed of light, where time would pass more slowly. The idea of space contracting or expanding sounds weird, but the universe has been expanding since the Big Bang, and has been doing so faster than the speed of light. So the universe started 14 billion years ago from a single point with a Big Bang. If we assume that it started expanding in every direction at the speed of light, then today it would be 14 billion light years wide. But astronomers have calculated that it's actually over three times that size. So this means that it must be expanding faster than the speed of light. It turns out that the universe's speed limit only applies to objects moving through space. Space itself can expand and contract at any speed whatsoever. So if we can squish and stretch space really fast, we can make it seem like we travel faster than the speed of light. So how would we work space like this? With mass. You may be familiar with Einstein's famous equation-- energy is equal to mass times the speed of light, squared. In other words, mass is just another form of energy. Einstein also noticed that a lot of energy or mass does something funny to space-- it contracts it. But in order to get enough contraction to build a warp drive, you need a lot of mass, bare minimum, something as massive as Jupiter. And that's the easy part. The hard part is figuring out how to expand space behind us. It turns out that you need negative mass, which is a very weird thing. An apple of negative mass is lighter than nothing it's repelled by gravity, and falls away from the Earth instead of towards Isaac Newton's head. When you push it away, it accelerates towards you. I mean, warping space is weird enough, but negative mass? That just crosses a line, right? Turns out that negative mass is also technically possible. In the field known to physicists as quantum field theory, and to the rest of the world as basically magic, you can get negative mass by holding two conducting metal plates extremely close to each other in a closed, empty space. In the universe, virtual particles spontaneously and constantly appear, bump into each other, and disappear. The total number of particles appearing and disappearing is the same throughout space. So the overall energy or mass throughout space is also the same. But if we bring our plates together, then they act as a filter for particles of certain energy, so fewer particles can appear and disappear in the space between them. The overall energy or mass in the space between our plates is less than that in normal space. Effectively, it's negative mass. But it's not like a chunk of negative mass that you could just throw behind your ship. Plus, the positive mass of the plates is huge in comparison to the negative mass. So any useful effects would be totally canceled out. It's possible the chunks of negative mass do exist, they'd be called exotic matter. But even if exotic matter is floating around in the universe, it would be nearly impossible to find, because it's repelled by gravity and nowhere near us. And there are some other reasons we're not all hopping on warp drives and heading off to the North Star right now. Even if you did manage to collect enough positive and negative mass to get the warp going, the ship would be basically unsteerable once you did, because it is impossible to communicate with the outside of the bubble. And even if you did manage to make it to the North Star, your warp bubble would pick up a bunch of dust and light on the way there. And all this space junk would build up a ton of energy at the edge of the warp bubble. So when you go to return space to its normal shape in order to land, all that high energy space stuff would basically blast every living thing in your destination into oblivion. So all NASA is doing now is trying to create teeny, tiny warp fields in order to see if this sort of thing is even possible. And if it is, we're still probably a millennium away from actually using it. If you want to learn more, you should check out some of the links below. And until then, if you want to get to the North Star, guess you're better off just hitchhiking.