14 DAY TRIAL // Ever wondered why we haven't been visited by aliens yet? Common sense and scientific evidence suggest that our universe is just right for our existence, and for the existence of other possible species and civilizations. However, if this presumption were to be false, that would mean that the cosmic constants that describe the universe would need to be slightly different, and thus, we would not exist.
A second property of the universe is that it has evolved in such a way that it keeps everyone isolated, and we have found out about these properties of the universe recently in our history. It was first observed in 1838, when an astronomer, named Friedrich Bessel, measured for the first time the distance between two stars, the Sun and the binary star 61 Cygni respectively, and found out that they were placed at a distance of 11 light years away. To give you an idea of the distance between the two stars, compared to their size, think of the Sun as a body of the size of a ping-ball somewhere in the New York Central Park. The binary star would be a slightly smaller sphere somewhere near Denver.
Considering the distances between us and the stars in our close proximity, the distance between us and the closest planet bearing life, assuming there is any in the relative close vicinity, would be somewhere about hundreds of light years away; this would represent some kind of an average distance between adjacent civilizations, and would remain constant whether there are two or five million galactic societies.
If the constants describing our universe had been slightly different, such as a smaller gravitational constant, the stars would have been closer to each other, enabling trips between then, the same way as riding the train. To make a trip with the current vehicles provided by technology would take somewhere about 100,000 years.
Alien civilizations might have managed to manipulate high amounts of energy and radiation shielding for relativistic spaceflight, and they might have populated the vicinity of the universe, to create some kind of a galactic empire similar to the empires that existed throughout our history, which conquered vast stretches of land. But even for them, some trips would still take several years.
However, even if it may be possible to travel at the speed of light, it would still not be fast enough to effectively intervene outside the radius of control, even for distances less than one light year, which is considered a small distance on the large scale of the universe. The same principle can be applied for communication.
These implications have severe effects on the Search for Extraterrestrial Intelligence or SETI program. A signal would have to be sent hundreds of thousands of years before it would reach its destination, which implies that the possible existing aliens have longer lives, or are of non-biological origin, or we cannot yet comprehend the real properties of the universe which permit the travel at super-luminal speeds.
Most of us prefer to take into consideration the second option. Anyway, the technology and the time scale do not yet permit us to think about interacting with any alien civilization, at least for a century or so.