There are calculations that give us a percentage. However, what I think is more fascinating than aliens is the thought that our universe is changing in cycles of expansion and compression, each time creating a new universe in which the natural laws that we consider "unchangeable" change. The universe is so fascinating as it makes everything and yet also takes everything. It is the foundation of all that exists, at least as far as we know and we do not know very much. I am excited about what we will figure out in the future. Cheers!