Physicist Marcelo Gleiser, author of The Island of Knowledge (2014), points out that the fact that there are trillions and trillions of worlds in our universe does not mean that anything we imagine can somehow exist:
While the laws of physics and chemistry allow for similar processes to unfold across the Universe, they also act to limit what is possible or viable. Even if science doesn’t allow us to completely rule out what cannot exist, we can use the laws of physics and chemistry to infer what might.Marcelo Gleiser, “What is life like elsewhere in the Universe?” at Big Think (December 22, 2021)
There is limit to diversity. While it may be possible for life to be based on something other than carbon (silicon?) or water (ammonia?), they are impractical by comparison.
But here’s the catch:
Combined, the staggering planetary diversity and the historic contingencies for life’s evolution have an amazing consequence: there cannot be two planets with identical life forms. Furthermore, the more complex the life form, the lower the odds it will be replicated — even approximately — in another world.
It follows that we are the only humans in the Universe. Yes, there could (at least in principle) be other biped intelligent species with left-right symmetry out there, but they will not be like us.Marcelo Gleiser, “What is life like elsewhere in the Universe?” at Big Think (December 22, 2021)
Star Trek featured many extraterrestrial beings who are really just dress-up humans — and was all the better a series for that. If the extraterrestrials were completely different from humans, mentally and emotionally, because of different planetary developments, the story might fall apart. In science fiction, we need the extraterrestrials to be enough like us that the interactions make sense. That’s just good storytelling:
You may also wish to read: Physicist: Science, by nature, can’t have a theory of everything Such a theory is a sort of religious quest that has united philosophers, theologians, and scientists, But is it possible? As Marcelo Gleiser puts it, “The very process of discovery leads to more unknowns.” And they may be smaller or larger than our current knowns.