ORIGINALLY PUBLISHED ON 10/16/09
We may be alone.
I have been thinking about alien life of late. More specifically: why we have not found any indication of intelligent life in the universe. The search for life - let alone intelligent life - has found nothing in the last fifty years of actively looking. You could say that the searches of the past were not advanced enough, or we have not looked in all the right places; but the fact remains that our assumption that life is common (and intelligent life should be too) could be flawed. I know a negative result does not mean that life does not exist but we expected to find life and we have not.
The idea that intelligent life is out there is based on the ‘mediocrity principle,’ which states in its basic form that there is nothing special about the Earth or humans. Link to a fuller explanation:
This idea was what helped spark the scientific age, and led to our modern world. It is also the basis of the idea that life - and intelligent life - must be common in the universe, because we are not special. The only problem with that is that it is not true. The Earth is a unique planet and maybe extremely rare.
One of the obvious oddities is that the Earth has a large moon; it is so large that if it orbited the sun under the old definition of a planet it would be called a planet (it only misses the size requirement of the new by 300km). The existence of the earth’s moon and how it was formed is what makes the Earth unique in the solar system.
The latest theory on our moons’ formation is that a Mars-sized object hit the newly-formed earth at an angle. This caused a large amount of the Earth’s light surface material to be ejected into space. Most of the mass thrown into space fell back, but some went into orbit and over time formed the moon. The majority of the mass from the impacting object itself became part of the earth with the heavy elements increasing the density of the earth’s core. http://en.wikipedia.org/wiki/Giant_impact_hypothesis
This denser core had two major effects: it caused the Earth to produce a stronger-than-usual magnetic field, which protects us from most solar and some cosmic radiation. Venus, our sister planet in size and composition, has almost no magnetic field and its atmosphere is bombarded with the solar wind. This has caused water in the atmosphere to dissociate and the hydrogen to be lost to space, making Venus a dry planet.
The other effect of a dense core is that the Earth still has active plate tectonics. The core is still hot, unlike the other terrestrial planets (Mercury, Venus, and Mars); a hot core is what has kept it producing its magnetic field. The hot core is why the Earth still has active volcanoes which might have helped produce life on the early earth.
When the moon formed, it was many times closer than it is now. This made the moon a good shield protecting the earth from a large percentage of objects that might have hit it. As the moon has spiraled out it has slowed the earth’s rotation from a 4 hour day to our present 24 hour day. The moon also stabilized the earth’s axis. If it wasn’t there, the axis would vary over time by as much as 90 degrees, and the climate on earth would be far different than it is today. Life might not have formed, or if it did it might not have gotten passed the single cell stage.
The last thing that is unique is that the Earth is in the sweet spot of the “Liquid Water” range of the Sun. Venus is about the closest to the sun that life as we understand it can form. Mars is at the farthest point. The Earth is in the exact point were life would be easiest to form. This has to do with the need for liquid water to support life. Any closer than Venus, and water can only exist as a vapor, any further than Mars, and water can only exist as a solid.
Since the Earth is such a unique planet, it calls into question the whole idea that intelligent life or any life is common in the universe. We may have to rethink our ideas about the origins of life and whether or not we are one of many intelligent species or if we are alone in the universe.