The other day I was Wiki Walking and ended up reading about the Rare Earth Hypothesis in reference to the Fermi Paradox and the Drake Equation. We’ve discovered that most stars in our galaxy appear to have planets of some kind, although ones with human-friendly environments may be quite rare. The presence of a plethora of planets presumably provides a potentially large factor for at least one part of the professor’s pretty problem.
But it’s possible that some of its other factors are extremely small. They may be much smaller than anyone had imagined. They may be so small as to ensure that we are alone in the galaxy.
It’s even possible we are alone — or nearly alone — in the universe!