The possibility of extraterrestrial life has always fascinated me. Looking out at all the stars in the night sky, these are all suns like our own. It seemed that the galaxy and universe is teeming with life. Well, that is probably true. But what about technological civilizations like our own? They may not be as common as I once thought.
Most astronomer believe that most, if not all stars have planets. Many agree that planets are by-products of star formation. According to the Drake model, many of these planets in the habitable zone may contain some sort of life. This life may be simple, such as microbes. Plant life may less common, but still pretty abundant. There would be fewer worlds with animal life. Primitive civilizations, such as Earth’s Stone Age, would be a rarity. although more common than technological worlds. Technological civilizations capable of sending signals or traveling in space is about 350 in the Milky Way Galaxy, according to the Drake model. This is based on that a civilization lasts 1000 years.
Another model is the Astrobiological Copernican Principle, which calculates fewer civilizations. This model has criteria that many more factors need to exist for technological civilizations to exist. For instance, its based on the number of stars in the galaxy, rather than the star formation rate used in Drake. The Astrobiological Copernican Principle also takes into account the age of the star and the amount of metals available. This leaves 36 technological civilizations at 60, although this can vary between 30 and 900 depending on the numbers used.
Although these numbers appear incredibly few, considering all the stars in the Milky Way Galaxy, which ranges anywhere from 100 billion to 250 billion. Based on the models, the criteria for a n advanced civilization are quite strict. A long way from Star War’s far far away galaxy where it seems every planet is inhabited. These numbers don’t take into account worlds that have been colonized by very advanced societies.
One factor that severely limits the number of civilizations is the lifetime of signals sent into space. This ranges from 100 years in the Astrobiological Copernican Principle to 1000 years in the Drake model. This appears that an advanced civilization is short lived. This indicates that an advanced civilizations self-destruct at some point. Certainly, the potential for self-destruction is present on earth, it does not have to happen. There is also the potential for the opposite. Perhaps a society can evolve to a point where it passes this danger zone. On the flip side, others may not be so lucky.
Supposing the numbers in these models are true, we are only looking at the Milky Way. What about the rest of the universe? There is an estimated 125 billion galaxies in the observable universe. This is not including what we can’t see. For instance, the galaxies blocked by the Milky way itself. Even if there were only one technological society per galaxy, there would be hundreds of billions or trillions of such civilizations. It would seem like the universe is teeming with life.