As I've written in previous posts, I travel a bunch for business which often has me eating dinner alone in different cities. During one of those instances a little while back, I overheard a family at a table next to me having a discussion about the nonexistence of aliens or extraterrestrial life. I was alone and had nothing in particular that I was focused on at the time so I listened. It was a family of 4. Mom, dad and two young boys (probably 9 to 11ish in age). Mom and dad explained that there is "No such thing as aliens" and that it was make believe for stories and movies. I sat there eavesdropping on their conversation and could barely keep from interjecting. As with many things in life I have an opinion and sometimes it's ok to share it with others but most times it is not. This was definitely one of those times where it was best for me to keep my mouth shut.
What I would have said to them if I could have, would have gone something like this:
Hi. I couldn't help but overhear your conversation about extraterrestrial life being make believe. I'm not an science geek or anything like that but I would ask that you consider this… What many people believe to be truth is often rooted in a fixed perspective such as what we can see, taste, touch, smell or hear however real truth is inherently perspective-independent. The fact that we can or cannot perceive a thing has no bearing on whether it is real or not. Having said that, the statistical probability of extraterrestrial life is not only likely, it is as close to certainty as possible despite not having physical proof.
Let me explain. The observable universe (just what we can see) is estimated to contain more than 100 billion galaxies. We also know that our own galaxy, (the Milky Way) is home to roughly 300 billion stars. Which gives the observable universe a total stellar population at roughly 70 billion trillion stars. Now, in astronomy and astrobiology there is something called the circumstellar habitable zone (CHZ), or simply the habitable zone. It's the range of orbits around a star within which a planetary surface can support liquid water. We also know that liquid water is the basis of all life as we know it.
The characteristics of the CHZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun. That's our baseline. Out of the 300 billion stars in our galaxy, the number of planets that exist within the CHZ of a star in the Milky Way is estimated to be 40 billion. Remember, that's just within the Milky Way. When you add in the number of planets that exist within a CHZ of a star in the entire observable universe the number is staggering. Additionally, scientists believe that the universe was born roughly 13.8 billion years ago which also needs to be considered. That's a heck of a lot of time for things to develop.
So when you put it all together, if you pessimistically assume that the probability of life and an evolving civilization on a habitable planet were, say, one in a trillion, it implies that what has happened here on Earth with humanity has in fact happened about 10 billion other times over the course of cosmic history!
Sooooo to say that alien life is "make believe" is a tough argument when in fact it's statistically improbable for there NOT to be life on other planets.
Enjoy the rest of your dinner.