The Sci-fi industry is massive with nearly every conceivable genre being developed at a frightening pace. A few decades ago wobbly plastic aliens terrorised mainstream viewers while Kirk shagged his way through the ones with mystical powers of soft focus. Thankfully those days are largely dead - or are they?

First off, it is important to define what is meant by 'believable'? There are many levels of believability, which are largely defined by the level of intelligence, and/or knowledge of the audience.

Take for example the film Pitch Black. If you can suspend your disbelief enough to allow for interstellar flight, then surely it is only a small step to believe that there are huge nocturnal carnivorous creatures that dwell underground just waiting for an eclipse in order to terrorise the surface. The basic premise is that they use infrared so cannot come out in daylight. This is enough to satisfy most of the audience, but for the more discerning viewer this is mostly tosh!

These carnivores dwelt in unnatural underground tunnels with chimneys but built by what and when - they only come out every for a couple of days every few decades? They are top of the food chain - feeding on what? Where is the rest of the food chain? They can fly, why, if they live underground. They have developed IR - as believable as creatures in a vacuum developing sonar - it could happen, couldn't it?

At the end of the day however, was it watchable? Yes, unrealistic, but believable to a larger degree.

On of a more classic line, there is the standard Startrek alien species - suprisingly human with a little bit of plastic stuck on the head and some jangly jewellery hanging of one appendage (always one, has to be asymmetrical - obviously alien). Seems reasonable, two arms, two legs, both manipulation and motivation allowed for. Nature on the other hand tends to promote evolution into forms adapted to a specific role. These rarely have anything to do with aesthetics. A quick glance at the most intelligent species on Earth testifies to this (humans, octupi, whales and their ilk). Again, it is possible to suspend disbelief for the universe created by the Startrek phenomena however implausible it is.

This is the first standard. Believable and realistic need not be the same. It is a matter of creating an environment that however unlikely will take a few knocks, i.e. it is easier to believe in a world containing dragons than one where it rains donuts!

As writers of a purely text-based medium, there is the advantage of not being limited to either scale or prosthetics. Aliens can be as weird and wonderful as desired as long as simple guidelines concerning the rudiments of biology and technology are followed.

Nature never evolves useless attributes. There may be vestigial remains or a prior evolution. A heavily armoured creature with no natural enemies, for example, is only likely where the environment itself is hostile. Alternatively, a set of gills for a species on a desert world is highly implausible at face value, but had most of the seas boiled of as the star entered red giant phase, it is possible. It is always best to keep these things in mind when designing aliens.

Culture of cause can act as an evolutionary process. This can be subtle such as a cultural preference for taller people, these achieving higher social statuses and thereby allowing them to support greater numbers of offspring. Higher technologies use controlled eugenics, selective DNA replication of certain genes, which can promote or prevent certain traits being passed on to children. Then there are much more brutal form of evolution such as pogroms and genocide.

This is the second standard. The weird and the wonderful should serve a purpose or have been derived from believable origins. It is not always necessary to inform the audience of the reasoning immediately. If the creator cannot justify it then it is unlikely to stand the test of time.

This creation process also serves another very important function for the creation of believable sci-fi; this defines both the surroundings and the history. By having these things to mind at the outset it becomes merely a process of expansion to generate the world supporting the object. This can even be used as a hook by which the audience is drawn in. This is especially important where the audience can participate. It allows the story to flow in the direction desired, even if the book in which the events are being written is still largely blank.

PBM takes the unique angle, allowing audience participation in the generation of history and in many cases, dictating the fleshing out of an aspect of the universe setting. This requires considerable amounts of thought if the whole thing is not to fall over in a short period of time. Films and even books have the luxury of having everything sewn up. Once written, they have their course laid out for them. For PBM, the captains of the ship are the players; the GM's are merely the navigators. Any GM that thinks differently will ultimately become a tyrant and the game will run aground. Continuing on in this nautical analogy, it is the role of the GM to produce the chart that will be used by the captains to take them to where they wish to go. Giving enough options for creative interpretation by the player generally does this. This binary relationship can and should be used to further the believability of the universe.

This is the third standard. A good writer draws from whatever sources are available. A good GM uses the feedback from his players to make the game universe real, which is one reason why computer games despite stunning graphics will never compete with human moderation for longevity.

From time to time as the universe develops and ages, it will become even more necessary to fill in the history. It is the natural way of things. Aspects that are accepted at face value when shown along with many others will eventually be individually scrutinised. Depending on the size of the universe, certain defining 'facts' may well prove to be false. It is even possible to allow two or more mutually exclusive facts to be presented and still remain believable. This is because history is still alive and is nearly as dynamic as the future. Scientists are constantly dismissing old 'truths' about the Earth history. It is important however that it is the audience participation that draws out these facts. Their very investigation changed the universe; all the GM did was allow the possibility of change!

This is the fourth standard. The ultimate test of believability is when the audience can predict the universe to the point that they are no longer the audience but part of the universe. This does not preclude surprises but these are believable surprises - moons are not made of cheese, but may have an alien automated defence platform protecting it!

There are more standards concerning technology (Humm, if we realign the emitter to produce an inverse tachyon pulse, it just may work - well it did in the last dozen episodes); planetary ecology and geology (wow, isn't amazing that all these natural caverns have flat floors); and cultural development (After two hundred years of study by tens of thousands of archaeologists it is finally realised that the extinct aliens that built cities half way up cliffs with no means of access must have been able to fly).

Mica Goldstone has been GMing Beyond the Stellar Empire (BSE) for seven years. While he admits that BSE is a little spurious in places, he adds that these locations generally originate with earlier less fastidious GM's - there was no excuse for hurricanes on airless moons. Since the recent launch of the new generation Phoenix: Beyond the Stellar Empire, these have been largely removed to make a coherent universe

He hates the bit with the giant asteroid monster in Star Wars and feels that it was quite frankly crap, not even up to the standard of B-movie. He used to gnash his teeth when reading Terry Prat(chett) although the cure was surprisingly simple and can be taken every 5th November if necessary.

His favourite sci-fi author is Greg Bear (Eon sagas) followed by Julian May (Orion Arm Series - not the dull Torc stuff). Asimov and Clarke are excellent authors but their stories often lack character interplay.

In the field of fantasy, it has to be George Martin (Game of Thrones) and Tolkien. Both have produced works giving glimpses of a much vaster history that not only lends credence to the current events but also makes the world feel alive.