who wants to build a warp drive anyway?
Usually, when I post about a scientific paper, the focus is on its methodology and interpreting its conclusions into real world applications. This time, we’re going to do something a little different and use an oft cited paper on the plausibility of warp drive propulsion to build a theoretical model of our own. You see, when physicists Richard Obousy and Gerald Cleaver put together the energy requirements for a warp drive, they noted that a sufficiently advanced civilization could one day build it. And we’re going to use those requirements to find out whether a civilization like that could conceivably exist and what would happen to their solar system if they ever tried to create a device that warps space and time by locally boosting the ongoing expansion of the universe.
So how much energy does it take to get a warp drive revving? A jaw dropping 1042 J / m3 which is like taking a planet a bit more massive than Saturn, crushing it into a cube about the size of a nightstand and turning all of that into raw, pure energy. Do that, say Obousy and Cleaver, and you effectively start changing the value of the cosmological constant, the Λ in Einstein’s general relativity equations. Each time you do that, you’ll get a cubic meter of warped space-time which will propel your ship forward at the speed of light. This is the kind of energy output that our hypothetical alien race interested in superluminal travel would have to meet to get then within a whisker of their goal. We’ll have to assume that they’re tens of thousands of years ahead of us in science and technology, and have an industrial capacity we could only dream of for the foreseeable future. Otherwise, any chance of them building any kind of warp device would be nil.
For the sake of argument, let’s get our aliens started with a more or less conventional approach. To pinch the fabric of space and time, they’re going to have to build an enormous bomb that will essentially implode into a cubic meter of warped space-time. Why a bomb? Because this energy would have to be delivered in a burst, or it will simply dissipate. Even though it sounds like a lot, the energy requirement we’re dealing with isn’t that much on a cosmic scales. Supernova explosions give off far more energy which simply spreads through their galaxy in a bubble measuring light years across. We want to take all those Joules and focus them on the area of space-time we want to manipulate. So how big would the bomb have to be when we use a technology that both we and our advanced aliens would know very well?
One of the most powerful explosive designs we’ve created was the Tsar Bomba which was initially built with a stunning 100 megaton yield that was later reduced due to concerns over widespread fallout. But let’s say that our aliens build an explosive sphere of staged thermonuclear devices with the full intended yield and with the same size and density. If we run through a quick blizzard of math, we’ll come up with a device that should be the stuff of nightmares for just about any intelligent species. It would be 7.5 billion km across and tip whatever monster scales you’d use to measure it at 50 quintillion metric tons. In other words, it would be roughly as big as a solar system and have a mass comparable to Mars. Clearly that’s not a very practical project since even at a rate of a million bombs a year, the giant device would take some 2.3 quintillion years to complete and the result wouldn’t be a reusable method of propulsion for a fleet of spacraft. Oh and by the way, those quintillions of years are longer than the lifetime of our current phase of the universe. The very last star would’ve died eons before the bomb is built and ready to go. Clearly, we’re not off to a good start here.
Luckily for us and our hypothetical aliens, Obousy and Cleaver provide an alternative in the form of 1028 kg of antimatter which could be used to generate more than enough power for a warp bubble accommodating one spacecraft with a volume of a cubic kilometer. Unfortunately that’s not a great alternative either. If we take half of that antimatter and come up with a chunk of matter just as huge, then collide them, we’ve effectively made a doomsday machine that would wipe out our hypothetical alien species. When matter and antimatter collide in an explosive reaction, they emit a flood of gamma rays. The ionizing radiation from the equivalent of blowing up Jupiter could easily decimate life in the solar system where the device is being built by triggering horrifying mass extinctions and changing the chemical structure of previously habitable atmospheres. It would be like a gamma ray burst from a hypernova and it doesn’t seem very likely that any civilization could survive triggering one in their own backyard. Besides, the sheer mechanics of assembling this much matter would be easily on par with the bomb scenario and whatever species started the project would be extinct long before completing it. Even boosting production rates by thousands of times wouldn’t help.
Finally, let’s go back to the initial requirements and consider what a density of 1042 J / m3 actually means. By converting this energy to mass, we’ll see that it far exceeds the density of the core of a neutron star. And since neutron stars are as dense as matter can get until it collapses into a black hole, anything that would create a similar energy density could essentially create a black hole about 33 meters across with an expected lifetime of 3.6 × 1060 years if it recreated the conditions needed for Obousy and Cleaver’s theoretical spacecraft to hit the speed of light. To escape the shockwave and be able to aim the GRB far enough away, the civilization that created this black hole machine would have to build it hundreds of millions of miles away from the planet it would occupy. Though, as we saw already, any civilization capable of building a black hole machine would be living in a cold, dark universe lit by embers of old, dead stars slowly simmering away into dense, solid matter, even if it started working on the project now. And in my humble opinion, such an advanced species would find other things to do with its time or just opt to make the best out of relativistic rocketry to get around.
See: Richard Obousy, Gerald Cleaver (2008). Warp Drive: A New Approach JBIS arXiv: 0712.1649v6