The essential reason why so many scientists are confident that life exists elsewhere is the regularity of the laws of physics and chemistry across the cosmos. The same laws of nature that apply in our solar system apply to galaxies billions of light-years away. They move in similar ways and shine in similar ways to galaxies nearby, allowing us to identify their distance and chemical composition with near certainty. If the same laws apply everywhere and at (mostly) every moment of the universe’s history, and if the same chemical elements are found in distant stellar systems, it’s fair to assume that the same chemical processes that led to life here on Earth some 3.5 billion years ago will reoccur in other planetary platforms. This is what could be called the argument from regularity.
But is it enough?