Feature: The Physics of Star Trek: Are warp drive and space travel achievable?

Dr Elisabetta Canetta, BSc Applied Physics Lecturer at St Mary’s University, Twickenham explores the world of space travel. Who has not dreamt to travel between galaxies, to go from one corner of the universe to the other, to explore deep space? We are constantly exposed to sci-fi movies and TV series where heroes travel on hyper-technological spaceships and fight against aliens arriving from the farthest corner of the universe to conquer Earth, the magnificent “Blue planet”. In addition, virtual reality (e.g. 3D video games) allows us to travel in space and experience any sort of adventure we can think of. But how far we are scientifically and technologically from all these marvels? Will we soon be able to emulate Captain Kirk (Star Trek) or Captain Picard (Star Trek: Next generation) and travel on a sort of USS Enterprise “to boldly go where no man has gone before” as Captain Kirk used to say in the introductory sequence of the original Star Trek science fiction TV series created by Gene Rodenberry in the 1960s? To answer this question, we need to answer two further questions: 1) is space travel achievable? and 2) will warp drive ever be a reality? Most people know what “space travel” is about, but what about “warp drive”? Warp drive is a hypothetical faster-than-light propulsion system that allows humans to travel in space at a speed faster than the speed of light (~300,000 Km/sec) without breaking the laws of physics. But let us start from the first question: Is space travel achievable? It could be. In fact, NASA (National Aeronautic and Space Administration) has developed a new propulsion device that could produce a thrust (i.e. a reaction force as described by the second and third Newton’s laws) of about 30-50 microNewtons (i.e. 0.00003 – 0.00005 Newtons where Newton is the unit used to measure a force) by pushing against particles and anti-particles that continuously come “in” and “out” of existence (they are called “virtual particles” and belong to the weirdest universe you can think of and where also the “impossible” can become possible because everything is uncertain: the quantum universe!). To make an analogy with something familiar, this “thrust propulsion device” moves by pushing back virtual particles in space as an airplane moves by pushing back air in the sky. So, although the development of an engine that could allow a spaceship to travel in space and reach the Andromeda galaxy (the closest – only 2.9 million light years! – major galaxy to the Milky Way, which is our own galaxy) in just a few weeks or even days rather than the billions of years that it would take now, is possible, its concrete realisation is still a chimera. Let us now go to the second question. Will warp drive ever be a reality? First of all, let us see in more detail what a “warp drive” is. According to Einstein’s theory of gravity (general relativity) it would be possible to “warp” space, i.e. to make it move faster than light. This means that it could be possible to “squeeze” the space in front of a spaceship and to “stretch” the space behind the spaceship. This is a pretty nice and fascinating concept but could it be possible in our “real world”? According to theoretical physicist Dr Miguel Alcubierre it could. In fact, he developed an idea known as “Alcubierre drive”, which shifts space around an object (for example a spaceship). It uses space and time as propellant by pulling a spaceship through the “warp bubble” created by squeezing and stretching the space itself. Hence, using the “Alcubierre drive” a spaceship could hypothetically travel faster than light and so cover extremely large distances (for example millions of light years) in a very short period of time. The idea of the “Alcubierre drive” is good but is it also feasible? Could we build an “Alcubierre drive” and install it on a spaceship? The answer is still uncertain even if it is becoming clear that too many practical difficulties could make the realisation of an “Alcubierre drive” highly improbable. One of the main problems seems to be that this drive would need “negative energy”. But what is it? It is a region of space that contains “less than nothing”, which means that its energy per unit volume is less than zero, which means that it is negative. This sounds weird! However, the laws of physics and nature do not deny the existence of negative energy (also called “exotic matter” because of its far from normal properties) and so they do not deny the possibility to “warp” space and to build an “Alcubierre warp drive”. What is making its realisation highly improbable is the incredibly high amount of negative energy needed and also the too complex and currently “out-of-our-reach” technology. However, we should not despair. In fact, some physicists at NASA have slightly revisited Alcubierre warp theory to make it more feasible although the practical realisation of a warp drive is something that only the future generations will see. Let us now go back to the initial question. How far we are scientifically and technologically from space travel and warp drives? We are very far although not hopelessly far. Technology and theoretical physics keep advancing and the conquest of space will sooner or later become a reality.