Is The Alcubierre Warp Drive Possible Space Time PBS Digital Studios


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Rumor has it NASA is actually working on a real faster than light warp drive. So when do we get our first starship? Faster than light travel is a staple of science fiction. Star Trek warp drives zip around the galaxy at hundreds of times the speed of light. But traveling at the real cosmic speed limit of 1 times the speed of light would make for some pretty dull sci-fi. It would have taken Han Solo 40 years to make the Kessel Run in 12 parsecs, traveling at only light speed. It's understandable that both physicists and sci-fi fans dream of cracking FTL travel. Spanish physicist and sci-fi fan Miguel Alcubierre was so inspired by the idea that he decided that the Star Trek warp drive should become a reality. In fact, he was inspired by Gene Roddenberry's choice of the word "warp." Alcubierre constructed a warp field in the mathematical language of Einstein's theory of general relativity, a real solution to the equations of GR that would actually allow faster than light travel. Yep, pretty much the ultimate in fan fiction. But is it actually fiction? NASA doesn't seem to think so. It's Eagleworks Laboratories is actually trying to produce and detect warp fields. More on that later. But if NASA's researching it, it must be legit, right? So when are we going to be warping around the galaxy? Let's break this idea apart. First, it's important to note that this idea does not contradict the principle of a cosmic speed limit. That limit, the speed of light, refers to things-- mass, energy, information-- traveling through space. However, according to general relativity, there's no limit on the relative speeds of two separate patches of spacetime. For example, as we talk about in this episode, the expansion of the universe means that very distant galaxies are moving apart from each other faster than light, even if the galaxies are relatively still in their local frames of reference. Also, below the event horizon of a black hole, spacetime cascades towards the central singularity faster than light, carrying light, matter, monkeys, and everything else with it. Now, the spacetime around and within a black hole is predicted by solving Einstein's field equations around a point of extreme positive energy density. Basically, mass and energy tell us how space should warp. But if you're cheeky, you can actually just make up a solution to the equations of GR without starting with a real mass/energy distribution. That's what Alcubierre did. He developed a spacetime description, a metric tensor, that describes a volume of nice, flat spacetime enclosed in a bubble of extreme curvature, a pinching or warping of spacetime in the surrounding shell that causes space to expand behind and contract in front of the bubble. As a result, the bubble is pushed and pulled by spacetime itself, moving at speeds only limited by the intensity of the warp. A starship inside the bubble is carried along for the ride while feeling no acceleration at all. It's sort of like building a conveyor belt out of spacetime. You stand still with respect to the conveyor belt, but the belt itself moves faster than light. But is this even valid? Can you just make up a spacetime description and then essentially solve the Einstein equations backwards to figure out what arrangement of matter and energy would be needed to create it? It's sort of like giving the answer before you have the question. So, 42. Yeah, sure you can do this. There's just no guarantee that the resulting mass/energy distribution would be physically meaningful. In fact, when you try to do this for the warp field, you find that you need to produce a ring of negative energy density in a band around the ship to produce the right warp bubble. That means our ship looks something like this in order to produce a spacetime curvature like this. Unfortunately, it may not even be possible to make negative energy densities on large enough scales. We can create something like it, a negative pressure, on quantum scales via Casimir effect. But on macroscopic scales, you'd probably need some sort of exotic negative mass matter, like element zero, which is tricky, because there may be no such thing. There are other minor issues. Any FTL device can, in principle, be used to make a time machine. Excellent! Except Stephen Hawking chronology protection conjecture states that quantum mechanics will always stop causality-breaking actions. It suggests that there's something in the deeper union of GR and quantum mechanics, the theory of everything, that prohibits the warp drive. One possible quantum disaster is that the extreme spacetime curvature of the warp bubble walls would roast the interior with crazy Hawking radiation. Does anyone else get the idea that Stephen Hawking really doesn't want us to build time machines? Suspicious. Here's another challenge. Assuming that you can even make negative mass matter, to make a warp field, some of it would need to go outside the warp bubble, which means it gets left behind when you go to warp speed. There are some proposed solutions, one of which is to lay down the external negative energy conditions along the path before you leave, sort of like a warp highway. The first trip has to be made at sub light speed. But I'm personally cool with the awesomeness of warp highways. Last tricky thing-- as Alcubierre devised the warp bubble, he figured it would take a lot of negative energy. In fact, it would take significantly more negative energy than there is positive mass/energy in the entire observable universe. Later refinements brought this down to the mass equivalent of Jupiter. Either way, not practical. Happily, recent reworkings of the bubble geometry have cut this down further. Thicken the walls of the warp field, and you get the negative mass/energy requirement down to the equivalent of maybe the moon or even an asteroid. Rapidly oscillate the warp field, and you hypothetically soften the fabric of space via higher dimensional effects-- literally, a hyper space warp drive. And this brings mass needed down to kilograms. Given that we're just making up solutions to the Einstein equations, we could even shrink down the warp bubble while expanding the internal volume, Tardis style, which could get us down to needing only milligrams of negative mass. If the bubble is small enough, then we may not even need actual exotic matter. Quantum scale manipulation of the vacuum energy a la the Casimir effect may be enough. Check the description for the sources of all of these ideas. Now, this sort of wild optimism has inspired NASA's Eagleworks Laboratory to try an experiment to create and detect a warp field. Now, this would be a field created by positive, not negative, energy density. But baby steps, right? It uses a Michelson interferometer, like a mini version of the one being used to detect gravitational waves, To measure the tiny changes in path length created by a warp field. Now, some intriguing results have been detected. But interpretation is very, very challenging. So when are we going to be warping around the galaxy? If it's even possible, it'll take several centuries at a minimum. As I've argued before, we'll reach the stars by sub light speed starships long before that. Even the Kugelblitz engine, the black hole drive, has fewer physics hurdles than the warp drive. Honestly, I think it's going to take an actively interstellar, or at least interplanetary, human race to motivate the monumental advancements needed to build the first warp drive. The good news is we're going to need a ton of physicists to get to that point. Let's make it so on the next episode of "Space Time." Last week, we talked about gravitational waves, and whether the advanced LIGO Observatory has maybe seen them. You guys had lots of amazing questions, so let's get to them. Renato Grigoli and others asked, what about the LISA Mission? LISA is amazing, although now it's ELISA, the Evolved Laser Interferometer Space Antenna. It'll be an orbiting gravitational wave observatory designed to detect much higher frequency gravitational waves than advanced LIGO. And this should actually allow it to detect binary star systems in our galaxy. The program is being developed by the European Space Agency. NASA was originally a part of it, but had to drop out due to funding cuts. And so now, the original plan is scaled back significantly. Now, that seems a shame, doesn't it? The scheduled launch date is 2034. psantochi asks if we have any comments on the BICEP 2 experiment. OK. So this was the much hyped gravitational wave detection based on polarization anisotropies in the cosmic microwave background radiation that came out earlier this year. Yeah. So now, the money is on the signal actually being due to dust, not G waves. The lesson-- quadruple check your quadrupole. This is why LIGO won't say anything until at least the end of the year. Now, MrSh1pman wants to know, if we find these G waves, will it change anything? Can we build something cool with them? Well, maybe. Quantum mechanics began as an abstract musing on the nature of reality. And I doubt that Max Planck and Schrodinger and Bohr imagined that this crazy theory would lead to the invention of the transistor, a quantum mechanical device, let alone the computer, the smartphone, the Apple Watch. Tenebrae wants our thoughts on that amazing new Kepler Space Telescope result that the media is hyping that there's an alien megastructure eclipsing a distance star. Now, this is a stunning result. But as we say on "Space Time," it's never aliens. Check out the actual signal that reveals this eclipsing material. Those dips are the drops in the star's brightness from some stuff moving in front of the star. It's dimmed by a crazy 20% at some points. Now, this is definitely not a clean geometric structure. It looks like it has to be some fragmented clumpy material, like the proposed swarm of comets. That suggests a natural origin. Although I imagine it could possibly be insanely vast ragtag colony of space structures surrounding a parent planet== except it's never aliens. Radio telescopes are now pointed at it. So perhaps we'll know pretty soon. To Un Disclosed, I say, you laugh, but the first evidence of alien life may be the spectroscopic signature of biogenetic atmospheric methane on another world. To Simon Martin, don't worry. They're holding me very gently.