For years, people have dreamed about travelling to distant stars and galaxies. Best-selling science fiction stories and blockbuster movies take this capability for granted, with notions of wormholes, warp drives and time dilations. You might easily get the impression that the opportunity of deep space travel was just around the corner. However, to date, nobody has gone to the closest star - our Sun, and there is currently not much likelihood that this will happen anytime in the near future.
Why is this?
First of all, we are talking about really huge distances here. Really, really huge. The closest star to us, Proxima Centauri, is 40,000,000,000,000km away (24 trillion miles, or 4.2 light years). And that's close, even by distances in the Milky Way, our home galaxy, which is 40,000 times bigger than this again. So, travelling to the stars is a bit of a chore, distance wise.
Secondly, even our fastest spacecraft haven't a hope of getting to the nearest star in any reasonable time. The fastest speed recorded for any existing spacecraft is 241,000km per hour. At this speed it would still take almost 19,000 years to reach Proxima Centauri. Put in perspective - 19,000 years ago we lived in caves. What we will be doing in 19,000 years time is anyone's guess.
Thirdly, the effort, cost and resources needed to go to the stars is impossible to imagine by our standards. To travel to the nearest star would require almost three million loaves of bread for one person alone; not to mention water, vegetables, minerals, oxygen to breathe, rocket fuel and other things necessary to make the trip as pleasant as possible for the would-be traveller.
Finally, technologically we are just not there yet. We have only just started to explore the moon, and there are now plans to put men on Mars in the next 20 years. The Mars trip alone will tax and stretch human capability (and money reserves) further than ever before, and all to go to a place which is, astronomically speaking, in our back yard.
So How Could We Get to the Stars?
There are a number of approaches which get serious consideration. These can be put in the broad categories of meddling with the spacecraft, meddling with the passengers, or meddling with time and space itself.
Meddling with Spacecraft
The idea here is to build faster craft so we can bring the travel time down to a manageable few years. Most scientists now realise that conventional fuels, hydrogen and oxygen, will be a non-runner for long-distance space travel because of the sheer cost and volume of fuel required, and the speed at which they are burned up. However, new technologies, which include ion drives, solar sails and space tethers are being seriously considered. Other technologies such as fusion drives, antimatter drives and warp drives are also mentioned here.
Ion drives involve taking advantage of the small forces present when electrons are separated from atoms using a strong magnetic field. This small force, working over days or weeks, could propel a spacecraft to speeds far in excess of current speeds because it works over a much longer time than current fuels. Already, successful tests have been carried out, and the possibilities for ion drives is enormous.
Solar sails involve assembling gigantic carbon fibre sails in space, which will take advantage of the solar wind - tiny charged particles blowing away from the sun. This force is strong enough to propel a craft to enormous speeds, with no need for us to bring fuels on board. This approach is getting serious attention at the moment with the first tests in space to take place in the next few years.
Tethers involves creating massive 'slingshots' in the Earth's orbit which take advantage of gravity to propel spacecraft away from the planet at speed. These will probably have greater applicability for smaller distances (the moon and the solar system's planets) than they might have for travel to the stars.
Fusion drives would, in theory, provide massive propulsion power to spacecraft. Fusion drives work by harnessing the energy released when simple atoms are forced together to form more complex atoms - this process powers the sun and all the stars in the sky. However, it is difficult in practice to make this happen without causing a thermonuclear explosion, so the scientists still have a long way to go before fusion drives become a reality.
Antimatter Drives would be far more powerful even than fusion drives. Antimatter is the opposite to matter, and when it comes in contact with matter, a massive explosive reaction takes place, destroying both matter and antimatter in the process. However, because it is so reactive, it is very, very rare, extremely shortlived, and present in such small quantities as to be useless for practical purposes. Nevertheless, only quite small quantities of antimatter are all that is required to produce boundless energy, so maybe in the future this may become possible. Then, all you have to do is contain it! Scientists have a long way to go yet.
All of the above technologies could either practically or theoretically accelerate spacecraft to enormous speeds. However a constraint exists. Nothing can travel faster than light in a vacuum. Even if it was possible to travel at the speed of light, it could still take hundreds of years to reach even relatively close stars. We might also start to travel backwards in time. A scary prospect for some. For the time being, faster-than-light travel remains in the realms of fiction.
Making craft go faster will reduce the time required greatly, but the risks will increase. You don't even want to hit a tiny, microscopic particle of dust when travelling at a few million kilometres per hour, not to mention an asteroid. Particle detection mechanisms will have to be very sophisticated indeed.
Meddling with Passengers
Even if we can speed our spacecraft up, chances are the passengers will be on board for a very long time - possibly a few generations will pass by on Earth before our intrepid pioneers reach the stars. Options include freezing people down, genetically modifying people, creating space habitats, or transporting genetic material.
This idea, so often seen in science fiction movies, involves freezing the passengers to very low temperatures. In this state, the passengers could be preserved for millennia, as the spacecraft courses through the cosmos. However, because of the ethical issues it poses (eg who would be the first live person to do it?), and the dangers inherent in freezing live people, it could yet be a while before it becomes a reality for space travel. However, the technology is there, and people already pay good money to be frozen as soon as they die, in the hope that they can be resuscitated by future doctors, so who knows?
Another possibility is to start modifying the human gene sequence of would-be stellar travellers, so they can live much longer, consume much less resources, and go into stasis for long periods so that the time spent onboard is as comfortable as possible. Pure speculation of course, but now that we have made massive advances in understanding the human gene, who can say?
Humans have a short life in this universe — 70 – 80 years or so if we are lucky. So instead of putting people into stasis, why not let nature take its course and allow generations of people to be born while on your journey. Although the original passengers would not make it to the destination their distant great-children might do it instead. This is a bit disappointing and tough on your progeny if nothing valuable is there when you get to your destination. Also, as we know, a lot can happen with humans over a thousand years, so strict control of families and people may not be possible. Even at relatively reasonable birthrates, a starting crew of four astronauts could generate a final complement of two million passengers by the time the spacecraft reaches its destination.
Transporting Genetic Material
But why send living people at all? Why not just freeze human embryos instead? When the fertilized eggs reach their destination they are spurred into development within an artificial womb, then reared and educated with the help of automated servants and multimedia recordings from the home planet. Although this is again pure science fiction, and again raises many ethical issues, it might offer the most effective way of sending humans to the stars in some distant future setting.
Meddling with Time and Space
Even the closest star system to us is a long way away. So it comes as no surprise then that people would search for a short cut to get to the stars, in effect, to leap huge distances in the twinkle of an eye. Options here are completely theoretical, and include Black Holes, Wormholes, Warp Drives and Teleportation.
Black Holes and Wormholes
Albert Einstein was among the first people to postulate that space-time is curved. In other words, light does not travel in straight lines - it follows a curved path which, given enough time, would possibly find its way back to the source of the light in the first place. This begs a question; if it is curved, what is it curved around? Maybe, just like a physical landscape on Earth, space contains contours, valleys, mountains, and perhaps even caves or wormholes - hidden ways of getting to distant stars without having to travel the colossal distances which Earth observations would suggest.
Black holes are a phenomenon which could indicate that such 'caves' exist. A black hole is a collapsed star. In a black hole, the force of gravity is so high, that not even light is allowed to escape. Theoretically, if one were to be sucked into one, it might be possible to reappear in some other part of the universe instantaneously. The problem unfortunately is that no one gives us human beings a serious chance of surviving such an episode, and there are no known black holes even moderately close to us to test the theory.
Warp Drives and Negative Energy
Science fiction programmes such as Star Trek indicate that if you were able to warp the space around you, you could cover vast distances in space almost instantaneously. Scientists have even postulated that it might be possible to travel to distant stars if one were able to harness negative energy, the direct opposite to Energy. Unfortunately, negative energy is a rare commodity in the universe, and current calculations suggest that the amount of negative energy required to transport a spacecraft would eclipse the energy of thousands of suns, so science has a bit more work to do!
Light travels pretty fast, and light is capable of carrying information, so if you could transform all of the information that makes up a person or an object into light signals, maybe you could cover vast tracts of space in a relatively short time. All you need is a decoder at the other end to transform the signals back into real matter. The problems are, how do you do this, and once you construct the encoder, how to you construct a decoder in the target star system? Over shorter distances it might have an application. Don't wait up, though. And, don't allow any flies to be around when you are doing your final tests...
So, the prospect of travelling to the stars is still beyond our capabilities here on Earth. Some progress is being made to speed up our spacecraft, and ethical reasons will probably prevent us modifying humans in the short term. As for time and space modifications, it's only a figment of theoretical imaginings for the present.
To say that we will be travelling to the stars in the next 10 years would seem foolish, however to say that we will never travel to the stars would seem equally foolish, given where we have come from as a species even in the last 100 years. We should continue to speculate, imagine and experiment, because the prize of unparalleled discovery is out there just waiting to be claimed.