Despite being extremely unlikely, is there a possibility that Earth is the only planet in the universe with life? originally appeared on Quora: the knowledge sharing network where compelling questions are answered by people with unique insights.
Expressing my personal opinion here on whether or not Earth is the only planet in the universe with life, yes, it is a huge universe, but it is also a young universe. This means that life on Earth appeared pretty much the instant conditions became favorable to life. Yes, this is a sample of one, but it nonetheless leads me to suspect that primitive life may be common in the universe. In fact, I would not be surprised if within the next decade, we found direct evidence of life on Mars or life on an exoplanet.
But complex life? On Earth, it took nearly two billion years for eukaryotic cells to emerge, and (as far as I know) there may be a common ancestor to all eukaryotes; which means that this incredible accident only happened once in all those billions of years.
As I mentioned, the universe is young. Only 13.8 billion years old. For much of that time, it was too “metal poor”, as astronomers call it, namely it had too little of the elements heavier than hydrogen and helium. So it’s really unlikely that there were solar systems much older than our own with the right ingredients for life. How many of them had that lucky accident already? How many had it sufficiently long ago for those eukaryotes to grow up and start building airplanes and computers and discuss the possibility of life elsewhere? How many are planets on which the right conditions persisted for billions of years, not interrupted by some calamity?
Another point to consider: if our civilization survives, very soon it will become a civilization, at least in part, of machines. Machines that are not limited by human biology. Machines that can survive centuries in space or accelerate to near the speed of light. This suggests to me that in a few million years (an eye blink compared to geological/astronomical time scales), the products of our civilization will have spread throughout the Milky Way. Conversely, had there been another advanced technological civilization around already a few hundred thousand years ago, its artifacts likely would have reached us by now. In fact, we might never have had a chance to evolve. But, evolve we did, and for all I know, we are the first.
So yes, unlikely, but I don’t consider it impossible that if not in the whole (possibly infinite) universe, but at least in a large slice of it, we are the only kids in town.
Of course if tomorrow a UFO lands on the White House lawn, all my nice reasoning based on a sample of one goes out the window, and then there might be “life” completely unrelated to the carbon-based chemistry that is the basis of our own, and who knows what that means.