So I was intrigued when I saw this space related programme on television - not your usual Discovery channel rubbish - this was a Channel 4 programme and I loved it - addressing a number of key questions......

If I mention the word 'alien' I do promise not to go on about HG Well's 'The war of the worlds' or the  x–files. The most compelling evidence for the existence of other life must be the shear expanse of space, not just in our own galaxy or our own universe....but should they exist, then in other universes too. There are 10,000 billion billion stars visible from earths telescopes alone, and a conservative estimate places orbiting planets around one in ten of them. Would it not be very strange if earth were to be the only planet out of potentially so many billions to have been a cradle for life?? If there are 400 billion stars in our galaxy alone, and there are billions of galaxies, surely somewhere, somehow, there must be other forms of life.

If there is life out there then how do we know what to look for? Is it a given constant that all living things must crawl over the surface of their home planets. I feel that we need to drop our parochial notions and imagine underground biospheres or living beings that float in the fogs of dense atmospheres. Even in our own solar system there are moons which contain surface water, look at Europa and the possibility that there may be oceans under the surface ice, and potentially life. One of the undeniable specialties of the earth that makes it a good home for life is that it has liquid water on its surface. Life is inconceivable without it. The chemical reactions that are believed to have originally sparked the evolution of life couldn't have happened without liquid water, and no life form that we know of can live and reproduce if devoid of water. But.. a planet can only retain liquid water if it is just the right distance from its heater, the sun. If it is too close then the water will boil off as it did on Venus, and if it too far away it is locked up in ice, as it is on Europa.

There are thought to be one million million planets that possess the necessary criteria for having liquid water...endless potential for life.

All living things on earth are built from the same ingredients, but why shouldn't life elsewhere in the cosmos be built from somewhere else. However over time this idea has lost ground, and scientists now suspect that life on other planets would have started from the very same chemicals as life on earth did. Indeed there is evidence to suggest that life once existed, or still exists on Mars, with gases indicating the presence of living things have turned up in the Martian atmosphere. Methane found on Mars indicates that underneath that sterile surface there maybe some bacteria living there, telling us right away that another planet had biology.

There is an argument that if evolution were to be run again from scratch, it would throw up a completely different set of life forms. Indeed it could be said that the process of evolution is a lawless, chancy business that's impossible to predict on this or any other planet. However there are some who argue against this belief, stating that some underlying patterns to the evolutionary process which begins to suggest rules of engagement, which allow us to predict what evolution will throw up almost anywhere. This latter point is an important shift in thinking. Biology is littered with examples of this so called 'convergent evolution' – sex, photosynthesis, flight, crawling on land, all have evolved several times over. If life on other planets is made of the same stuff as us, and there is reason to believe that this is the case, then it will follow the same patterns. We could be surprised to discover alien worlds that are not that dissimilar to our own.

'No one would have believed in the last years of the 19th century that this world was being watched keenly and closely by intelligence greater than mans and yet as mortal as his own.' HG Wells – War of the worlds.....In more recent decades a conviction that alien life is inevitable has bubbled into scientific consciousness. If the conviction is right then there is reason to believe that life might have evolved in one or more of the solar systems that are much older than our own. These biospheres could have had well over a one billion or two billion year head start over us in terms of evolution.

Furthermore if complexity and intelligence are the products of natural universal laws then at least some of the beings on planets older than our own will have superseded our intelligence. If they have done that, then you'd have thought that they'd know about us. And if so why cant we find them? Why are they not here? Indeed this was a question posed by the Italian physicist Enrico Fermi in 1950. For many if we solve such a question it will terrify us because what will be out there will be so different, and we will not be a race that is the centre of the universe and the only form of life created in 'gods' image. Either we are completely lonely, which is somewhat dispiriting, and if we are surrounded by higher levels of intelligent life, then for me that is just as dispiriting as we still don't know!!

Which would you rather?????