The Hubble Space Telescope has made it possible for humanity to look further into the past through time and space than a lot of other tools, and it's just recently been used to determine that the observable universe contains just ten percent of all the galaxies that exist1. More than this, recent studies have shown that the early observable universe itself contains ten times the number of galaxies than previously estimated. Considering the sheer size of the cosmos, these numbers are absolutely mind blowing. With roughly 2-trillion galaxies to explore, each with millions or billions of stars of their own, we will likely have enough new places to study and explore until the last starts in the universe grow cold and dark.
When I think about the numbers involved in space exploration, I can't help but feel that humanity is a small and insignificant accident in the grand scheme of things. This single planet has been home to billions of different forms of life, and quadrillions of individual lives if not more. Given the richness of life on this world, it only makes sense that life must exist in other forms on other celestial objects. If we were to assume that two trillion galaxies each contained a quarter-billion stars and each star had an average of 3 planets orbiting them, we'd be looking at around 1,500,000,000,000,000,000 planets. That's 1.5-sextillion worlds. Could life have evolved on just this one? I'd like to hope not.
But I have had conversations with people who steadfastly believe that life only exists on the Earth and that we are special because God chose to create us and only us. So far as I know, there are no religious texts that explicitly talk about life on other worlds. What if we are the only sentient beings in the universe? What if this planet is the sole home to all life in the universe? What would this ultimately mean when humanity begins to expand into the universe? Would it mean anything at all?
If it's determined after an indeterminate number of eons that humans are the only sentient forms of life in the universe, we will likely be at a point technologically and societally that it will no longer matter. Colonies would have existed on various worlds for an incredible amount of time, and the people from those colonies would have their own unique languages, customs, traditions, and genetic differences. Given enough time, there would be various branches of humanity as a result of cosmic radiation or intentional eugenics programs making changes to our DNA. We'll begin to see different types of human. Going further still, there will be communities of people who have completely separated from existing societies to create their own worlds. These people, over time, would evolve in various ways to become completely alien to other groups of future humans.
Ultimately, if it's proven that there is no other life to be discovered in the universe, our descendants will become that life for other descendants to learn about. The universe is a vast, vast place. So large that our minds will likely never truly understand or appreciate its scale and complexity. And that's completely okay. It's there for us to explore. I just hope that, when we do find new life and new civilizations out there — human or otherwise — we greet them with open arms and open minds.
To the best of our knowledge, anyway.