If you look at probability distributions rather than single estimates for every term in the Drake Equation then the absence of visible aliens isn't so unlikely.

If you look at probability distributions rather than single estimates for every term in the Drake Equation then the absence of visible aliens isn't so unlikely. http://www.jodrellbank.manchester.ac.uk/media/eps/jodrell-bank-centre-for-astrophysics/news-and-events/2017/uksrn-slides/Anders-Sandberg---Dissolving-Fermi-Paradox-UKSRN.pdf http://www.jodrellbank.manchester.ac.uk/media/eps/jodrell-ba... And just the existence of life doesn't mean there's complex life. We don't have a firm lower bound on how long life took to arise on Earth after we got liquid water on the surface but it can't have been more than 120 million years. Photosynthesis, mitochondria, and other innovations allowing for complex life like you and me took way, way longer. I made a diagram for a blog post here: http://hopefullyintersting.blogspot.com/2018/03/the-drake-equation-again.html http://hopefullyintersting.blogspot.com/2018/03/the-drake-eq...