![]() ![]() It is a solution for a distribution of mass and energy.īut. So this is what physicists usually mean by a solution of General Relativity. Then you can calculate what the curvature is at that initial time, and you can calculate how the energies and masses will move around and how the curvature changes with that. The way you normally solve these equations is to use a distribution of energies and masses at some initial time. Einstein’s equations then tell you that the distribution of different types of energy determines the curvature, and the curvature in return determines the how the distribution of the stress-energy changes. That includes pressure and momentum flux and so on. T is called the stress-energy tensor and it collects all kinds of energy densities and mass densities. The R’s quantify the curvature of space-time.Īnd on the right side you have T. More important is that on the left side you have these R’s. It helps if you try to ignore all these small Greek indices, because they really just say that there is an equation for each combination of directions in space-time. I know this looks somewhat intimidating, but the overall structure is fairly easy to understand. General Relativity works by solving Einstein’s field equations. To understand my problem with the Alcubierre Drive, I have to tell you briefly how General Relativity works. So how does it work? A few weeks ago, someone sent me a paper that beautifully sorts out the confusion surrounding warp drives. And even if you had this negative energy that would not explain how you break the speed of light barrier. It’s bad because, well, there isn’t any such thing as negative energy. Instead, his equations say that this warp drive requires large amounts of negative energy. Because why would this allow you to break the speed of light barrier? Indeed, if you look at Alcubierre’s mathematics, it does not explain how this is supposed to work. That didn’t make sense to you? Just among us, it never made sense to me either. The explanation that you usually get for how the Alcubierre Drive works, is that you contract space-time in front of you and expand it behind you, which moves you forward. His idea is now called the Alcubierre Drive. Warp drives were a fairly vague idea until in 1994, Miguel Alcubierre found a way to make them work in General Relativity. I know that sounds somewhat disappointing, but I think it would be pretty cool to move around by warping spacetime at any speed. You can also have slower-than-light warp drives. The second point I want to emphasize is that the term “warp drive” refers to a propulsion system that relies on the warping of space-time, but just because you are using a warp drive does not mean you have to go faster than light. So the problem is really crossing the speed of light barrier, not being above it. Instead, the problem is that, according to Einstein, you cannot accelerate from below to above the speed of light. Neither does this faster-than light travel necessarily lead to causality paradoxes. You can very well have objects in these theories that move faster than the speed of light. There are two points I want to highlight here: First, it is a really common misunderstanding, but Einstein’s theories of special and general relativity do NOT forbid faster-than-light motion. Indeed, physicists think that the universe expanded faster than the speed of light in its very early phase. Space-time can bend, expand, or warp at any speed. However, this restriction applies to objects in space-time, not to space-time itself. This is not entirely crazy, for the following reason.Įinstein’s theory of general relativity says you cannot accelerate objects from below to above the speed of light because that would take an infinite amount of energy. The idea is that by warping space-time, you can beat the speed of light barrier. And just a few weeks ago, a new paper appeared about warp drives that puts the idea on a much more solid basis.īut first of all, what is a warp drive? In the science fiction literature, a warp drive is a technology that allows you to travel faster than the speed of light or “superluminally” by “warping” or deforming space-time. Today I want to talk about warp drives because I think on the spectrum from fiction to science, warp drives are on the more scientific end. So, to some extent, I became a physicist to find out which science fiction technologies have a chance to one day become real technologies. But of course the depressing part of science fiction is that you know it’s not real. Teleportation, levitation, wormholes, time-travel, warp drives, and all that, I thought was super-fascinating. As many others, I became interested in physics by reading too much science fiction. ![]()
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