In a previous post, I discussed why life in the universe should be incredibly common. The only problem is that it isn’t. Or at least, it doesn’t seem to be. So maybe we got something wrong?
Who is to say the Earth is typical? Or that life tends to appear on planets like Earth? Maybe we are a cosmic accident in an otherwise desolate and lifeless universe?
The problem is, it’s not a good idea to imagine we’re special.
Cosmology — the study of the universe itself — is specifically built on us not taking a privileged vantage point. For us to apply our laws of physics to the whole of reality, we rely on the fact that whatever happens here applies, broadly speaking, everywhere else too.
It’s a somewhat philosophical argument, because we cannot empirically verify that some distant region of space has slightly different physics. Equally, it’s difficult for us to imagine a scenario where life is unique and we have instead assumed one of the majority vantage points of, well, not being alive. Hence, whilst this law of mediocrity is a helpful scientific tool, it’s not foolproof.
Nevertheless, let’s take a fine tooth comb to the process by which a lump of rock turns into a lump of rock with creatures that like ice cream and blog posts, to see if there are any problems with our conclusion that aliens should be everywhere.
Firstly, in our original argument we stated there are lots of planets out there. Is that really true?
Yes. Yes it is.
As of the start of this year, there have been almost 5000 confirmed exoplanet discoveries. This number seems small, but it represents the number we have discovered in the last thirty years. Remember, planets don’t tend to emit light like stars. They’re both far away and very difficult to spot.
According to NASA, since the 1990s the number of known exoplanets has doubled approximately every 27 months. In some cases, multiple planets have been found orbiting a star.
In fact, we can be more specific about our planetary estimate. It’s believed that one in five sun-like stars have an Earth-sized planet, leading us to think there could be 11 billion habitable Earth sized planets in the Milky Way alone.