Fig. 1: Image Showing the Alcubierre Warp Drive
Our theoretical description of space is the entire observable universe which extends to 13.8 Billion Lightyears (because the universe is 13.8 Billion Years old) through whichever direction we look at it (and is the same from any point of observation in the universe, since the universe is infinite). But, how much have we explored? The furthest distance reached by a machine, the voyager I, is the outskirts of our solar which is a few light hours from earth which it took 35 years to sail in empty space going at an astonishing speed of 1100 Km/sec. Humans, on the other hand have not gone further than the moon (360,000 km away from earth) and are soon planning a trip to mars. The closest star to our solar system is the Proxima Centauri System which is about 4.2 light years away which would essentially take the fastest machine ever built (The Voyager Satellite) about 76,000 years which is not an inspiring number given that the average life expectancy of a human being is around 60 to 70 years (as of now).
The human species might have originated on earth but to ensure the survival of our race we may have to venture out search the stars for a new home or to comb the universe to find other life forms or to gain a deeper understanding on the origins and the dynamics of the universe. To accomplish either one or all of these tasks we would require a means of transportation which travel at a speed which would be a significant fraction of the speed of light or even more for greater distances. But, is the light speed barrier breakable? If not, then why?
The Speed of Light and Einstein’s Theory of Relativity
The speed of light is around 300,000 km/sec and is the speed at which light (which is an electromagnetic wave) travels through vacuum. Albert Einstein posed a thought experiment which led to him postulating the theory of general and special relativity. He questioned whether a person holding a mirror at arm’s length and is travelling on a ship moving at light speed, could see his own reflection. If he is travelling at the speed of light, the light leaving his face wouldn’t have time to cover the additional distance between him and the mirror and back to his eyes making him invisible to the mirror. This led him to a breakthrough figuring out that the speed of light is the true constant of the universe and cannot be broken by any mass containing body. Instead, time lengthens to slow down a body approaching light speed. This could be understood by the famous equation of Einstein (which he formulated from this idea), E=mc2, which actually means that mass is just energy which has been compressed by a large value (the magnitude of square of the light speed) and therefore meaning that mass cannot cross the light speed barrier since it cannot go faster than itself (Since Mass is Energy). Therefore making the speed of light the true constant of the universe as opposed to the length of time being constant (making it possible for time travel).
Fig. 2: Figure Showing Space-Time Continuum with Gravitational Stretching Effect
The three dimensional space and time is theorized to be an interwoven mathematical model called Space-Time. It is a continuum (homogenous throughout the universe) and is required to better understand many important physical properties which happen in the universe such as gravity. The three dimensions of space and one dimension of time (past, present and future dimension) therefore construct a four dimensional space-time model. Every single thing that has happened, is happening and will happen is located along the space-time continuum consisting of its spatial location located along a strand of the past-future line.
The space-time is referred to as the space-time fabric due to its elastic nature, meaning that it can be stretched by certain physical phenomena. Gravity is one such property which causes a stretch in the fabric of space-time which explains why smaller physical bodies revolve around larger bodies in space like the earth goes around the sun because the sun, being more massive, stretches the space-time fabric to a greater extent than the earth which makes the earth go around the sun to avoid falling into it. This could be understood by placing a football on a stretched cloth and making a small marble go around the football. If the marble doesn’t revolve around the football it will fall into it.
3.The Alcubierre Drive
Fig. 3: Graphical Presentational of Space-Time Warping
The Alcubierre drive, proposed by Mexican Physicist Miguel Alcubierre in 1994 and derived from the Einstein’s equation describing space and time formulation of the 4 dimensional space-time fabric in the general theory of relativity. It utilizes the fact that space-time can be stretched to bypass the speed limit of the universe. By stretching the space-time fabric such that it compresses in front of a spacecraft and expands behind it creating a gravity wave which the spacecraft can ride on which would appear it to be travelling faster than light from a frame of reference taken outside the gravity wave. This gravity bubble in essence would not be violating the speed of light but would be tweaking space-time continuum so that the space and time would compress in front of the space craft which would relatively increase the light speed in that frame of reference and also the spacecraft would ride this wave like a surfboard riding on a tide. In effect the spaceship would traverse the distance at superluminal speeds which would help us greatly in achieving interstellar travel.
Fig. 4: Graphical Image Showing a Ship Riding the Alcubierre Warp Drive
One question which would arise is what effect will be there inside the bubble where the spaceship and crew be present? If there is a stretch in space-time, would the crew have endure the elongation of space-time? This is not true particularly because the warp bubble would have normal space zone between the expansion and compression wavefronts which would be free of any tidal forces which would be present. Due to the presence of the warped fields, a gravitational effect on the spaceship exists causing it to be in a continuous free fall but the crew would not experience any inertial effect such as g-forces. The wave would require a negative energy density to be produced behind it which would call for an exotic matter energy source. The warp drive space-time field is described by what is called the Alcubierre Metric which is defined in the General Relativistic context.
Fig. 5: Continuum Stretching Effect on Movement of a Subject
Fig.6: Gravitational Bubble
Fig. 7: Graphical Presentation of Modified Torus shaped Bubble
Although it sounds reasonable, the elasticity of space-time is quite less which would mean that it would require lots of energy. Early calculations for the creation of a warp bubble resulted in quite a grim figure equivalent to the energy equivalent to the mass of the planet Jupiter (1.9 x 1027 Kg). Therefore the idea of warp drive was initially scrapped by scientists. But, in 2012, NASA physicist Harold White and his team have started working on the Alcubierre warp drive engine which took the aeronautics world by surprise. He proposed a design which would alter the geometry of the warp bubble which might lower the energy requirements of warp bubble generation. The initially ring shaped warp bubble in which the spaceship would be placed, if replaced by a thicker and curvier Alcubierre’s ring (like a donut or torus shape) would possible reduce the energy consumption by a great amount according to White which has reignited the interest in considering it as a contender for powering interstellar travel. Currently they are conducting tests on a modified Michelson – Morley Inferometer which has two legs out of which a minor bubble would tried to be induced on one of the legs which would cause it to stretch. So the concept would be proved if there is change in the lengths of the test leg with respect to the other.
Fig.8: Picture of Michelson-Morley Infero Testing Device
There would also be certain problems which will be associated with the development of the AD engine, one of which would be that it would be out of communication with any source outside the bubble since the local light speed change would cause an interference. The spaceship cannot be maneuvered as it has to travel only along the bubble trajectory like a train on a track. The energy fields required for the Alcubierre warp drive is primarily required for creating the space-time warp but not in accelerating the space vessel and to create those energy fields, would require a significant amount of exotic matter elements like Tachyons. Another recently discovered problem is that the mass gathered along the path of the warp bubble would accumulate and shoot out at hyper velocities when the vessel stops (similar to a shockwave) and could destroy any physical object located directly in front of the ship.
Warp drive technology is decades or even centuries away from complete development and comes out into usage but not something that would likely come out during our lifetime. Development of energy technologies, sub – atomic particle research, superluminal space dynamics, and many other advanced focuses need to be reinforced before going into its research. Although, it is at its very initial stage right now, the very thought of it is mind boggling thinking about interstellar travel. This could give the human race, its mark on a galactic scale and could possibly introduce us to a new planet or an entire new alien civilization (good or bad is another issue). With the Alcubierre warp, the nearest star Proxima Centauri which is 4.2 Lightyears away, can be reached in a mere 2 weeks. Those numbers should certainly encourage scientists to work on the warp drive project.
Fig. 9: Picture Showing Enterprise Starship Concept intended for Warp Drive Application