Conceptual computer artwork of multiple universes: Some physicists believe that there are an infinite number of parallel universes, created for each possible quantum mechanical outcome. The collective name for these universes is the multiverse.

Credit: Mehau Kulyk/SPL

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Because the distances between stars are so vast, and the number of unsuitable, lifeless solar systems so large, a Type III civilisation would be faced with the next question: what is the most efficient way of exploring the hundreds of billions of stars in the galaxy?

In TV science fiction, the search for inhabitable worlds is shown as the exclusive dominion of heroic captains boldly commanding a single starship, or as the murderous Borg society of Star Trek – a Type III civilisation which absorbs lower Type II civilisations (such as Star Trek's United Federation of Planets). However, the most mathematically efficient method to explore space is far less glamorous: to send fleets of 'von Neumann probes' throughout the galaxy. These are named after John von Neumann, the Hungarian-born mathematician who defined the mathematical laws of self-replicating systems.

A von Neumann probe is a robot designed to reach distant star systems and create factories that will reproduce copies of themselves by the thousands. For von Neumann probes, a planet is a less ideal destination than a dead moon; these have no atmosphere and no erosion, which means the probes can easily land and take off and can 'live off the land', using naturally occurring deposits of iron, nickel and other minerals to build replicants for dispersal in search for other star systems.

Similar to a virus colonising a body many times its size, eventually ever-increasing numbers of von Neumann probes would expand in all directions, at a fraction of the speed of light. So in this fashion, even a galaxy 100,000 light years across may be fully explored within, say, a half million years.

If a von Neumann probe only finds evidence of primitive life – such as an unstable, warlike and savage Type 0 civilisation – it might simply lie dormant on the moon, silently waiting for the Type 0 civilisation to evolve into a stable Type I civilisation. After waiting quietly for several millennia, it may be activated when the emerging Type I civilisation is advanced enough to set up a lunar colony. Physicist Paul Davies of the Australian Centre for Astrobiology in Sydney, has even raised the possibility that a von Neumann probe could be resting on our own Moon, left over from a previous visitation in our system aeons ago.

If that sounds familiar, that's because it was the basis of the film, 2001: A Space Odyssey. Originally, Stanley Kubrick began the film with a series of scientists explaining how probes like these would be the most efficient method of exploring space. Unfortunately, at the last minute, Kubrick cut the opening segment from his film, and the famous monoliths – von Neumann probes – became almost mystical entities.

This raises the question asked by Italian physicist Enrico Fermi: if von Neumann probes exist, where are they? If such advanced civilisations exist, they would have already visited us years ago. Yet we see no evidence for them. But by analogy, think of walking down a country road and encountering an anthill. Do we bend down to the ants and say to them, "I bring you trinkets and beads. I bring you nuclear energy and space travel. Take me to your leader"? Or, are you perhaps tempted to step on a few of them? Or ignore them altogether?

It's humbling to realise that the developmental gulf between a miniscule ant colony and our modern human civilisation is only a tiny fraction of the distance between a Type 0 and a Type III civilisation – a factor of 100 billion billion, in fact. Yet we have such a highly regarded view of ourselves, we believe a Type III civilisation would find us irresistible and would rush to make contact with us. The truth is, however, they may be as interested in communicating with humans as we are keen to communicate with ants.

Of course, such an encounter with a Type III civilisation has its perils. The danger is not that its citizens would want to eat us or steal our resources – themes that have propelled many a plot in science fiction films. Their DNA, if they have any, would be incompatible with ours, and hence our proteins would be indigestible to them; furthermore, there are plenty of uninhabited planets in the galaxy with more natural resources than Earth, so why would they need to plunder inhabited real estate?

The main danger we face is the same as that faced by our ant colony: the danger of being paved over. Many lifeforms are being imperilled on Earth not because humans want to conquer and plunder them, but because they get in the way of what humans want to do. No ant would understand the construction of a highway or the flooding of a dam, but they would be its victims.

Furthermore, citizens of a Type III civilisation probably wouldn't resemble anything we'd be able to recognise immediately. Humanity's pathway to intelligence required only three basic elements: eyes, hands, and language. Beyond those requirements, almost anything goes. There is nothing sacrosanct about the human shape or form. One can, for example, imagine that it's possible to breed a race of intelligent octopods if we had a few million years to play with. Lastly, if we ever encounter a vessel from outer space, chances are it will be a von Neumann robotic probe of some sort, rather than a transport ship occupied by the aliens themselves.

But by the time a civilisation reaches Type I stage of development stage, it will probably have discovered biotechnology and computers. Hence, there's a likelihood they would gradually abandon the inherited shape and form from evolution and adopt more radical designs. It is well within the laws of biology and computing to imagine a civilisation that creates bodies which are immortal, possess great strength, or have other key attributes.

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