Other theoretical universes, and other different laws of physics, exist outside our cosmic bubble, beyond our ability to look.
Here, let us add another qualification to our discussion: by life, we mean any self-sustaining network of chemical reactions that metabolizes energy from the environment and reproduces according to Darwin’s rules of natural selection. Therefore, there is no more advanced mind machine in the universe than us; no strange intelligent nebula that breeds stars, nor nanorobots that inhabit wormholes and are endowed with some kind of collective self-awareness. “It makes more sense (see below).
The foundation shared by the entire universe
Based on these realizations, now we can actually start the discussion. Perhaps one of the most striking results of modern science is the realization that the same laws of physics and chemistry apply to the vastness of space and time. We can now observe stars and small galaxies billions of light-years away, and they are also billions of years old. When we look at and analyze their properties, they have the same chemical elements (albeit in different proportions) and their evolution follows the same dynamics as the Sun. The laws of physics and chemistry are the same wherever and whenever. This allows us living creatures to also expand the horizons of exploration to the entire universe.
We also know another surprising finding of modern astronomy, that most stars have multiple planets, and these planets often have many moons of their own. Each planet or moon is a world of its own, with unique physical properties and chemical composition. Planets are large and small, rocky and gaseous; some have many moons, some have one or two, or none. The planets spin like tops, with greater or lesser inclinations (Earth’s axis is about 23.5 degrees, and Uranus is a staggering 97.7 degrees). The atmospheres of planets can be thick or thin, and the gas composition they contain varies. The list goes on.
Flying face god
In round numbers, our galaxy alone is home to about a trillion worlds, each of which is a unique entity with its own history.
If we add in the hundreds of billions of other galaxies in the cosmic bubble, we can calculate that there are about 1 trillion trillion worlds in the universe, with an error of about 100 times (someone commented that this value is similar to Avogadro’s The constant is too close, it’s a dimensionless number, about 6 x 10^23 per mole, originally defined as the number of atoms contained in 1 gram of atomic hydrogen, and later redefined as the number of atoms contained in 12 grams of carbon-12 number).
From this perspective, you might take it for granted that in a universe with such an astonishing variety of worlds, almost anything is possible. At first glance it seems so, but this huge amount is not as “free” as it might seem. The unification of the laws of physics and chemistry is an extremely powerful constraint on what can and cannot exist.
In science, we can’t really rule out the possibility of something as long as it satisfies the laws of physics as we know it. But we can infer what might be there through the laws of physics and chemistry. For example, the existence of “Flying Mian God” makes scientific sense. We can imagine that billions of years ago, an octopus-like creature ventured out of the water on the planet MumbaXX; millions of years later, the creature grew feathers on its tentacles and began to fly. Or, instead of feathers, they may have developed some mechanism for using hot air—from their digestive tract or the hydrothermal vents they feed on—to fly like a balloon.
So what can we expect to find when we search for life in the universe’s many worlds? No one can answer this question yet, but we can make some basic rules.
Rule 1: Life will be based on carbon. Why? Because carbon is a very easy-going atom, it has a chemical diversity unmatched by other elements. Carbon has 4 unpaired outer electrons that can form tight chemical bonds by sharing these electrons with other chemical elements. Another potential replacement element is silicon, but its biochemical composition would be severely limited compared to carbon, forming bonds about half as strong as carbon. Life requires pluripotency to thrive.
Rule 2: Life needs liquid water. Of course, we do find frozen bacteria in permafrost, but they are not alive. In essence, life is a complex network of biochemical reactions that move compounds in this direction or that direction all the time. It needs a solvent, a medium in which the reaction can unfold. Water consists of oxygen and hydrogen, two of the most abundant chemical elements in the universe, with distinct advantages. In addition, water has a very unique property: solid water (ice) is less dense than liquid water and can float.
Ammonia is sometimes cited as another possibility, but it is a gas at room temperature and only becomes a liquid at atmospheric pressure below minus 28 degrees. A planet with a cold, thick atmosphere might have liquid ammonia, but that would be too demanding for life. In fact, the metabolism of any life form would be very slow under such conditions. Water is an amazing substance, it is transparent, colorless, odorless, and expands when it freezes (a very critical property for water-based life in cold climates, as there can be liquid). Water is also the main ingredient of our body.
Are there other humans in the universe?
With these two constraints, the essence of life is very simple, it will include carbon, water and some other substances (at least nitrogen).
However, if you continue to dig deeper, the situation is not so simple. Every planet that could potentially contain life has its own history. Therefore, life there will also have a history of their own, and their history will depend on the history of the host planet. The properties of the planets determine the form of life. In turn, any life that lives on a planet shapes the properties of that planet. In every world, natural selection is an existential pressure under historical conditions. As planetary conditions change—many times due to the presence of life—life adapts in unique ways. In different worlds, life will take on completely different appearances.
So, despite the common carbon-water nature of life, different life forms arise on different planets. The more complex a life form is, the less likely it is to be replicated elsewhere, even if it is approximated.
If the “Flying Mian God” really exists, it should only exist in a certain world in the universe. Likewise, we can only exist in the world of Earth. We are the only humans in the universe. If we look back at the history of life on Earth, we will find that intelligent life is likely to be extremely rare. Although intelligence is an obvious advantage in the struggle for survival among species, it is not the purpose of evolution; evolution has no purpose.
Before intelligence, life was just happily replicating; with intelligence, their reproduction process may appear less happy. In short, this is the essential state of human beings.
Taken together, it can be argued that humans are indeed chemically linked to the rest of the universe – we have the same life base as any other hypothetical alien beings. At the same time, humans are unique, as are all other creatures. Life is a magical force. Starting with a carbon-based code and a common genetic ancestor, it can create amazing wonders of diversity in this world, and possibly others.