The Halo Drive

when I was a boy I remember lying out in the grass on a warm summer evening looking up at the night sky in the Stars and dreaming of ways to reach them I remember the feeling of disappointment I felt when I learned that the nearest star Proxima Centauri is 25 trillion miles away a distance so vast that our fastest Rockets would take tens of thousands of years to reach them the dream seemed lost do civilizations ever find a way to travel between the stars at faster speeds even just a few percent the speed of light could potentially allow a star hopping species to colonize the galaxy over a few million years perhaps even trade goods between systems and engage in cultural interchange but that's a speed increase of 10,000 times versus current spacecraft or more importantly 100 million times more kinetic energy when we speak of energy scales like this we are usually talking about the engines of the cosmos itself such as the power of a star these Astrophysical objects have plenty of energy to spare enough after all to be seen across the void and even warp the fabric of space and now got me thinking if we can't build engines with the power levels that we need maybe we could borrow it from the universe maybe we could steal it from a star or more specifically a dead star today I want to tell you about a new paper which I've written which introduces a new interstellar propulsion system which I called the halo drive [Music] let's begin by the fact that we already know are the proven technique to steal energy from a massive body it's called a gravitational slingshot or gravity assist we've actually already used this method many times in a solar system with our spacecraft for example Voyager 1 did a slingshot around Jupiter and Saturn imagine a spacecraft approaching a planet but not quite head-on as it approaches it feels a gravitational pull towards the direction of the planet bending its path now the mass of the planet is much greater than that of the spacecraft and so it barely reacts to the presence of this intruder and thus the system simply conserves momentum causing the spacecraft to move along at the same speed as before but bent round in a new direction now subtly you might notice that we assumed here the planet is not moving it is completely at rest planets don't really do this they orbit the Sun and thus are in continuous motion and so this picture that I just painted you was technically the picture as seen from the planets perspective only the planets rest frame of reference if you were watching this encounter play out in the rest frame of the solar system you'd see something quite different the spacecraft would appear to have sped up after the encounter that's because in the rest frame of the planet the spacecraft speed is unchanged but when we move back to the observers frame we have to add the planet's velocity back in and this leads to an overall increase in speed I think the best intuitive explanation is to understand what's happening here to imagine that the gravitational field of the planet is a solid object against which this spacecraft scatters or bounces off now if you throw a ping-pong ball against a moving wall a wall that's moving towards you the ping-pong ball will not come back with the same speed that it left your hand it will come back faster it will steal some of the kinetic energy off that wall and the same thing happens with gravitational slingshots the spacecraft bounces off the gravitational field and thus picks up some extra speed from the fact that the gravitational field itself the wall in our earlier analogy is moving gravity assists our free energy for the spacecraft which is great but they have a major problem and that's that you can only accelerate at best up to twice the speed of the planet and playas don't move at relativistic speeds in fact the planets our own solar system move at around 1% of 1% of the speed of light that's far too slow to be useful for travelling between the stars on timescales of say a century or so what we need is a planet or a massive object that is moving much much faster in 1963 the Princeton physicist Freeman Dyson speculated that advanced civilizations might consider binary stars to be the solution the via Kepler's the law we know that the velocity of an orbiting star or planet depends on how close to the center of mass that it is the closer you get the faster the orbital speed so Dyson imagined two stars that orbited extremely close to one another in fact to get the stars close enough he shrunk them down by imagining that they were in fact dead stars neutron stars with sizes of just 20 kilometers across the compact binary like this could accelerate spacecraft up to 20 sent the speed of light for free almost like a giant cosmic particle accelerator except the particles that are being accelerated a spacecraft it's a beautiful idea and is sometimes called the Dyson slingshot in honor of the Princeton physicists now binary systems like this are rare but we know that they certainly exist thanks to LIGO Dyson even speculated that civilizations might construct such binary systems for the purposes of interstellar travel but the Dyson slingshot comes with a problem because to utilize it you have to hurtle your spacecraft straight down towards a pair of binary stars which are orbiting one another at blistering speeds you have to somehow time your slingshot at just the right moment to avoid hitting one of them or getting caught up in the gravitational Maelstrom caused by the complex warping of space-time not only that but you have to somehow survive the extreme tidal forces acting upon your body trying to spaghettify it as you approach the two stars as well as the radiation environment of the binary itself in short the Dyson slingshot is not for the faint of heart it is a decidedly risky and gut-wrenching maneuver to attempt there's a small community of us who are interested in ideas like this and last year I was invited to attend a meeting about interstellar travel focused on the breakthrough starshot programme the idea here is to use lasers to push propel tiny spacecraft via light pressure up to 20% the speed of light and of course this is something we've discussed on this channel before there's certainly a lot of interest and excitement about the idea of using lasers to propel spacecraft between the stars it comes with a lot of advantages for example it's a very efficient means of transferring energy however it doesn't really get a fundamental problem that faces almost all forms of interstellar travel and that's just the huge energy cost involved you somehow have to generate a vast amount of energy and then transfer it via the lasers to the spacecraft for example even accelerating a single gram mass object something the size of a microchip to 20% the speed of light would require a kinetic energy of 2 trillion joules which is the cumulative energy output of a nuclear power plant operating continuously for 20 days and of course remember that that is assuming just a single tiny gram mass spacecraft as well as assuming that there are absolutely no energy losses from generating the energy to dumping it into the spacecraft so on the one hand you have this ultra efficient laser sailing concept that would work great if only you had the vast amounts of energy necessary to accelerate your spacecraft and on the other hand you have the Dyson slingshot idea where here you have huge amounts of energy at your disposal but the environment in which you have to siphon that energy is extremely hazardous to attempt to approach in a new paper which I've just put online I have fused these two ideas together essentially imagine you are in a spaceship near a binary star system where both stars have died and collapsed into black holes the black hole's orbit very close together whizzing around at relativistic speeds it's an ideal environment to perform a Dyson slingshot but you know that it's simply too dangerous to attempt but your ship does have a laser onboard you monitor the orbiting black holes closely and then at just the right moment you fire your laser straight down at one of the black holes more specifically you fire it at the black hole that's moving towards you the beam traveling of course at the speed of light almost instantly reaches the black hole the directory you chose was such that the beam just misses the event horizon that's the distance where even light would fall in so rather than falling in the beam skims the event horizon and the black hole's gravity bends the path of light so much so that the light loops around and actually comes back to you the black hole has now become a mirror causing the beam of light to follow what is known as a boomerang geodesic first discovered by William Stokoe in 1993 the light now returns to your spacecraft and you can harvest the energy back once again [Music] so that's the picture that I want you to keep in your mind but now let's break down all of those steps and think about physically what actually happened first off you fired a photon or really a bunch of photons and when you did that actually gave you a little push back in the opposite direction that's because even light even though it has no mass has momentum and thus by Newton's third law every action has an equal and opposite reaction there by pushing you in the other direction next the light then whips around this black hole which remember is moving towards you at extreme speed the beam of light has conducted a gravitational slingshot which really by conventional wisdom should cause it to speed up but light can't speed up it has to travel at the same speed all over the universe and so instead of gaining energy through kinetic energy as a spacecraft word it gains energy by changing frequency it becomes blue shifted and so this beam of light not only returns back to the spacecraft but it returns back to you with more energy than it started out with next this beam of light comes back to you strikes your spacecraft and you absorb it you get another push you actually light sail off your own laser beam and so you accelerate further not only that but you actually got back all of the energy the fuel that you expended to create that laser beam in the first place in fact that's not quite true because the laser beam comes back blue shifted unless you actually get more energy out than you put in unless you could charge up the batteries of your spacecraft during this process onboard the spacecraft of course you would feel and notice the acceleration of your spaceship but also as you look out of the window you would see this beam of light suspended in a loop around the black hole a halo of light and that's why I call it the halo Drive you can keep accelerating in this way but to the point where your speed now is equal to that of the black hole after that point the laser beam no longer comes back blue shifted in fact it starts to come back with less energy than you put in and this is redshifted beyond that point but that's ok because by this point you have been charging up your battery for quite a while now and thus you have a lot of energy to spare and so you can actually expend that gained extra energy to continue to use the halo drive to continue to accelerate until eventually you come back to the same amount of energy on board that you started out with at that point I calculate that your speed would be 33% faster than that of the black hole and thus if the binary black hole is compact enough to have relativistic speeds much as how Freeman Dyson imagined then you would have accelerated your spacecraft for free with no fuel expended and now you can cruise between the stars that pretty much describes the halo drive and I think it has some nice advantages for space travel first unlike the Dyson slingshot you do this slingshot essentially remotely thereby avoiding the need to plunge your spaceship into the maelstrom of this binary second as stated earlier you actually expend no energy or fuel at all in order to accelerate up to this speed and you can accelerate in pretty much any direction you want the only direction you won't be able to accelerate up to is orthogonal directions to the plane of the binary orbit third because you expended no fuel in the act of a accelerating you can essentially accelerate any mass object you want so long as the mass of that object is much lower than that of the black hole so yes that means in principle you could accelerate a planet-sized spacecraft to relativistic speeds for free finally you can use the halo drive to also decelerate as well as accelerate it's the same strategy just in Reverse so that's when you arrive at your destination if it has a black hole as well you can turn on the halo drive and brake against that black hole to come to a stop I think the most obvious drawback of the halo drivers that you require a binary black hole to get things going however there's an estimated ten million such systems in the Milky Way galaxy and each one is a potential starship accelerator one might even imagine that an advanced civilization would use these special systems as waypoints an interstellar highway system for rapid and free transit across the galaxy to access this interstellar highway system you just have to pay the one-time fee of the cost to reach the nearest binary black hole system I'm certainly excited to think about other tricks in nature that we might be able to use to accomplish that goal - sadly I know that I will very likely not live long enough to fulfill this dream I had as a boy to one day reach the Stars to visit another planet and maybe even meet the people that live there but that's okay sometimes the dream is enough the dream can be enough to keep us inspired to keep us working towards ideas that might one day realize that dream maybe one day humanity can touch the Stars and with that thought stay thoughtful and stay curious you [Music]

Channel: Cool Worlds

Views: 498,088

Keywords: halo drive, interstellar spaceship, interstellar propulsion, spaceship propulsion, traveling between the stars, new space technology, futuristic space technology, speed of light travel, black hole starship, black hole technology, interstellar technology, ways to travel to other stars, methods to travel to other stars, interstellar ideas, david kipping, cool worlds, interstellar physics, new technology space, halo technology, halo interstellar

Id: rFqL9CkNxXw

Length: 17min 33sec (1053 seconds)

Published: Fri Mar 01 2019