We live on a planet, which is in orbit around a star, which is in orbit around a galactic centre on a circular journey that takes around 220 million years. The galactic centre is seen in the constellation Sagittarius from our point of view. It appears to have a supermassive black hole at the centre. The galaxy contains between 200-400 billion stars. We are not certain of their number, but the total mass of the galaxy is known to be around a thousand billion times the mass of the Sun. The oldest known star is about 13.6 billion years old. The distance from our Sun from the galactic centre is about 27,000 light years. Even light, which nothing can overtake, travelling at around 300 kilometres per second, takes27,000 years to reach the centre of the galaxy from our solar system. The thickness of our galaxy is around 2,000 light years at its widest.
The diameter of the Milky Way is approximately 100,000 light years. This means that even if you could travel at the speed of light, it would take you 100,000 years to go from one side of the galaxy to the other. But lets us examine that in its proper context. Let us assume that our Sun is a typical star in the galaxy, at around 5 billion years old, and is only half way through its life cycle. How many galactic crossings could you perform travelling at the speed of light within the half age of a star like our Sun? That would be simply 5 billion years divided by 100,000 years, which is 50,000 times. So if we could only travel at, say, ten percent of light speed, perhaps with a fusion powered starship, the time for one crossing would be around one million years, and this would permit 5,000 crossings of the galaxy in only half the age of the Sun. And what if we could travel at only one percent of the speed of light, the sort of speed we might expect for a world ship carrying many succeeding generations of humans to some distant star for colonization purposes? The time for one crossing would then be 10 million years, and this would permit 100 crossings of the galaxy within the half age of a Sun like star. With each of these crossings a starship is coming close to 100-400 billion stars. It is virtually certain, given our recent discoveries of exoplanets, that most of these stars will have planetary systems.
This leads to some stark conclusions. Consider the scale of the galaxy, its distribution and type and age of stars, and the likely myriad worlds. If you have the technology to build starships, with on board telemetry, long distance communications, observational capability, then, if there are civilizations out there in the void, there is a good chance you are going to encounter them. This leads us naturally to the “Fermi Paradox”, the apparent contradiction between our theoretical expectations for intelligent life in the universe and our observations that we do not see any.
Some "chauvinist" arguments prevailing in the scientific community were described by Martin & Bond . Drake-Sagan chauvinism suggests a crowded galaxy [2, 3]. Arguably, the extreme version of this includes an acceptance of alien abduction as a serious possibility. Hart-Viewing chauvinism suggests that our species is probably the first intelligent life to arise in the galaxy [4, 5, 6], and, arguably, the extreme version of this implies a belief in a deity (religious) who created only ourselves and no others – thus humanity is unique.
There are many other potential solutions to the Fermi paradox. Perhaps the galaxy is too big to allow interaction within our civilization time, or that we are being deliberately quarantined from other more peaceful species, the so-called Zoo hypothesis. It may also be the case that advanced intelligent probes are or have been here but our limited technology is not capable of detecting them. Another favourite is that civilizations reach a critical point in their technological development where they either flourish or destroy themselves in a nuclear war or other self-inflicted catastrophe. Large scale natural catastrophes will also affect the number of long-lasting civilizations in the galaxy and thereby the probability of interaction.
It is very difficult to achieve resolution of this without further information. We lack sufficient information upon which to base our hypotheses. Our assumptions may contain biases about how the universe does or does not work. How do we define life and is it only defined by carbon based chemistry? What is the nature of intelligence? is it possible that the answers are staring us straight in the face every time we look up at the night sky, but that our own blinkered point of view prevents us from reaching the most obvious and awesome conclusions. What is clear is that we do need more information. We will gain much more information from our deep space telescopes as they improve. But let’s get out there and do some reconnaissance. Let us send the next generation of Voyager successors beyond the boundary of our knowledge, and let these important and profound insights into the universe be informed by scientific discoveries - not by merely our hopes and fears.
Executive Director, i4iS
 Martin, A.R & A. Bond, “Is Mankind Unique? – The Lack of Evidence For Extraterrestrial Intelligence”, JBIS, 36, pp.223-225, 1983.
 Shklovskii, I.S & C. Sagan, “Intelligent Life in the Universe”, Holden Day, 1966.
 Sagan, C & F. Drake, “The Search for Extraterrestrial Intelligence”, Sci.Am.,232,80, May 1975.
 Viewing, D, “Directly Interacting Extraterrestrial Technological Communities”, JBIS, 28, 735, 1975.
 Hart, M, “An Explanation for the Absence of Extraterrestrials on Earth”, QJRAS, 16, 128, 1975.
 Tipler, F.J, “Extraterrestrial Intelligent Beings Do Not Exist”, QJRAS, 21, 267, 1980.