What would mankind do if we suddenly discovered that extra-terrestrial life existed?
This kind of communication, though, is likely to be extremely difficult and not very productive. We have to consider distance. Our galaxy, the Milky Way, is about 100,000 light years across. We are about 28,000 light years from the centre. That means if life exists elsewhere in our galaxy, it could be on a world up to 78,000 light years distant. Even the nearest star to us (other than our Sun) is over 4 light years away, and there are only about a dozen or so within ten light years.
Any signal we send out to an alien civilisation will be limited by the speed of light, so even if we got lucky and found life existing on a near neighbour we would still be waiting years to get a reply to each communication. Each answer would be received by the next generation from the one asking the question (or maybe several generations further down the line).
Faster Than Light?
How could we speed this up a bit? And could we even make the trip there to meet them? To make interstellar communications and travel possible we need to be able to send messages (or ourselves) across these vast distances in considerably less time that it takes for light or conventional radio waves to make the journey.
When Einstein published his theory of Special Relativity in 1905, contrary to a popular misconception about his theory, he did not state that travel faster than light is impossible. However, his theory included the following equation:
(E is energy, m is mass, v is velocity and c stands for the speed of light. This is the equation more commonly represented as E=mc2, simplified for objects at rest, velocity being zero.)
As velocity approaches the speed of light the lower half of this equation tends to zero, and the energy requirement tends towards infinity. This means that accelerating to speeds greater than light using conventional means would require more than infinite energy, and hence it is not possible to accelerate from less than to greater than light speed.
Hence, we would need to find a mechanism to allow the distances to be covered in less time than light would travel in a direct line between the two points without actually exceeding the speed of light locally to the traveller, or the message.
Science Fiction has two popular ways of achieving this - Warp Drive and Wormholes. But are these methods actually feasible?
In 1994 Mexican theoretical physicist Miguel Alcubierre decided to investigate if a Star Trek type Warp Drive could be created, achieving superluminal speeds (faster than light) without breaking the rules of relativity. His starting point was the curving of space caused by gravity. He postulated that if you distort spacetime by greatly extending it behind the spacecraft whilst simultaneously contracting it in front of the craft, then the craft itself could travel inside this region of distorted space at sub-light speeds whilst achieving superluminal speeds when compared to objects in normal space.
This warp "bubble" would shield the craft and its occupants from the effects of the massive acceleration and deceleration of the journey, and would mean that the travellers would not experience time dilation effects. The downside of this method is it requires the use of Exotic Matter – matter with a negative energy density. Physicists are not convinced this matter even exists – the laws of quantum physics suggest it might, but no proof has yet been found. Even if it does exist, it might not be possible to collect enough to build a working Warp Drive.
Wormholes are a well-known and frequently proposed mechanism for achieving FTL travel. Albert Einstein and Nathan Rosen were the first to describe wormholes in 1935 (they were originally known as Einstein-Rosen bridges). Physicist John Wheeler would coin the term "wormhole" in 1955 (and would also invent the terms "black hole" and "quantum foam").
The concept can be described simply. If you imagine the universe as the skin of an apple, then to get from a point on the surface to a second point on the far side we would have to travel around the edge. However, if we were to burrow through the apple just like a worm might, then we get there much more quickly.
If we could burrow in this way through the spacetime of the universe then we could move at sub-light speeds directly through the tunnel crossing the distance in a far shorter time than light travelling in regular space could manage.
We would have achieved our objective without having to break that pesky light-speed barrier. But exactly how could a wormhole be opened?
Michael Morris, Kip Thorne, and Uri Yertsever working at the California Institute of Technology published a paper in 1987 describing Traversable Wormholes.
Space has an underlying energy, known as Vacuum Energy, even when it appears totally empty of matter: the empty space of a vacuum is not actually empty if you look at it at the quantum level. Even in a total vacuum, Virtual Particles are continually being created, always as particle/antiparticle pairs, living brief lives and then mutually annihilating each other. These Virtual Particles are also known as Vacuum Fluctuations in the Vacuum Energy.
As well as these Virtual Particles a vacuum is teeming with violent but incredibly small-scale fluctuations in space-time itself, ultra-small wormholes that are continually being created and destroyed in an instant.
However these wormholes could be kept stabilised by using exotic matter to keep their entrances open. Exotic matter exerts a negative pressure – if you were to attempt to inflate a balloon using exotic matter you would find that the more you pumped into the balloon the less inflated it would become. If you were to thread the entrance of a wormhole with such material, then this negative pressure would prevent the mouth's collapse.
Once stabilised it may be possible to move these entrances across vast areas whilst maintaining their link. The initial trip would, by necessity, need to be made at normal velocities, but once the entrances were installed at their respective destinationis we could then have FTL communication and possibly travel through this wormhole. The theory does allow for the entrances to be expanded to the macroscopic by adding energy.
However there is a hurdle to overcome with this method, aside from discovering these tiny wormhole entrances. The force required to keep the entrance open is huge. So great, in fact, that it may well tear apart anything trying to pass through the wormhole.
But they may provide a useful means of communicating with a ship moving at Subluminal speeds (slower than light) away from Earth.
Is the Speed of Light Constant?
There are other possibilities that might help us. We could make light travel faster, and so be able to achieve greater velocities without having to travel FTL. This sounds a little like Scotty's famous line on Star Trek about the laws of physics, but it could be possible.
Vacuum Fluctuations fill (in a virtual sense) a vacuum, with particle/anti-particle pairs continuously being created and annihilated. If a photon strikes these pairs it is absorbed, to be re-emitted when the pair self-destructs. This slows down the photon.
In 1990 Klaus Scharnhorst of the Humboldt-Universität zu Berlin in East Germany and Gabriel Barton of the University of Sussex, working independently, explored what would happen to photons travelling perpendicularly to two parallel plates placed extremely close together (roughly one micrometer of separation) in a vacuum.
This degree of separation is less than the wavelengths of some of the Virtual Particles and so lowers the density of the Virtual Particles in the vacuum. This lowering of Vacuum Energy results in the photon being less likely to encounter Virtual Particles and therefore being able to travel faster than our accepted speed of light. This phenomenon has been called the Scharnhorst Effect.
This is on an incredibly small scale, but if we could expand the range and effect of this we could be able to travel faster than light outside the local area of effect whilst not actually breaking the restrictions imposed by relativity.
Quantum Theory allows for two particles to interact, such that the quantum states of the particles are joined forming a single entangled state. This results in the two particles being not completely independent of the other, so that affecting one of the entangled pair would produce a result in the other. This would occur irrespective of the extent of spatial separation between the two particles.
So could these entangled particles be used for superluminal communications? To achieve this we would need to create two or more identical (or cloned) particles and then separate them physically from each other. Then if we were to act on one of the particles, an observer of the second should be able to detect an effect. Then introducing a code (such as Morse Code) would mean we should be able to communicate at greater than the speed of light.
Such a thing is unfortunately impossible. In 1982 physicists Bill Wootters, Wojciech H. Zurek and Dennis Dieks introduced the No Cloning Theorem. This theorem states that it is impossible to create an identical copy of an arbitrary unknown quantum state. As cloning is a requirement of using these entangled particles for superluminal communication, we have to rule this method out.
Relativity might state that we cannot accelerate from sub-light speeds to super-light speeds, but it does not explicitly forbid the existence of particles travelling faster than light. Tachyons are theoretical particles that travel at speeds greater than light, but are not capable of slowing to below light-speed (the barrier operates in both directions).
If such particles exist (and there is some doubt amongst physicists) then could they be used to transmit messages? The problem would be how to detect them, and how then to affect them in such a way as to send our message.
In 1934 Pavel Cherenkov was investigating the effects of radiation in liquids. Light travels through water at a speed far less than it does in a vacuum. This means that it is possible for a particle to travel through water at speeds greater than that of light in the same medium. Cherenkov noticed that when a charged particle does exceed the speed of light in this medium, the water glowed blue. This effect is known as Cherenkov Radiation.
If there are charged Tachyons moving through the vacuum we should be able to detect this Cherenkov Radiation. So far no such Tachyons have been discovered, and many physicists doubt their existence.
From the subluminal perspective, fast moving charged particles interacting with other particles would lose energy and slow down. For charged Tachyons these interactions would also cause them to lose energy. The problem for charges Tachyons is that relativity states that moving closer to the speed of light requires more and more energy.
Hence, if tachyons move faster than the speed of light, losing energy would cause them to accelerate, resulting in more and more collisions and a runaway reaction of speed increase and energy loss until the Tachyon would have infinite velocity. So we must assume that if Tachyons exist then they cannot be electrically charged.
If we assume Tachyons do exist and that we can control them, could we use them to transmit messages faster than light? To do this we would need to encode the message on a localised Tachyon field, one confined to a definable region of spacetime. Once encoded we can then transmit this field to its intended recipient. However, there is a problem with this.
Relativistic quantum mechanics examines the wave properties of Tachyons by means of the Klein-Gordon equation, a relativistic method of describing particles. There are two possible solutions to this equation for Tachyon disturbances.
The first has the particles' momentum being lower than their energy. This solution states that the disturbances are localised, but also that they are propagated at speeds less than that of light. The second solution, with energy exceeding momentum, does indeed produce waves at superluminal velocities. The problem however is that we cannot localise the wave, which would mean we cannot use the wave to transmit a message.
So, even if Tachyons do exist, they do not seem to present us with a method of faster-than-light communication.
Unfortunately, with our current knowledge of physics, if we want to get to another solar system it will take a long, long time. On January 23rd 2006 NASA's New Horizons Space Mission was launched. This is speeding towards Pluto at 58,000 kilometres per hour. Even using a slingshot from Jupiter to gain more speed this probe will not arrive at Pluto until 2015.
Pluto is about 4.28 billion kilometres form Earth at its closest. The nearest star other then our Sun is Proxima Centauri at over 40 trillion kilometres. It takes light 4.2 years to cross the distance between the solar systems. If New Horizons had been aimed at Proxima Centauri it would not arrive for thousands of years.
But science has been advancing at ever increasing rates. It's only just over a hundred years since the Wright Brothers built the first craft capable of flight, and we have already landed men on the moon and sent probes to the other seven planets in our Solar System. Another hundred years might see such advances that could see mankind leave this solar system.
Article Copyright © 2007 by I. E. Lester. All rights reserved.
About the author
I.E. Lester is a lifelong fan of science fiction, having acquired the bug whilst on a washed-out family holiday as a child when, sheltering from the rain in a seafront kiosk store, the cover on a collection of Isaac Asimov short stories attracted a nine year old eye.
Having worked through all the fiction of Asimov (as well as Heinlein, Clarke, Moorcock, and many others) he moved onto Asimov's non-fiction, encouraging a love of science.
He studied Mathematics and Astrophysics whilst at University and works as a software designer. When not reading sf or factual science, he can often be found watching cricket or rugby, or wandering medieval streets in France or Italy.
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