Are we alone in the universe?
September 6, 2017; traveling towards earth from the direction of the star Vega... 25 light-years away...some weird object intercepts the orbital plane within which planets in our solar system revolve around the Sun. Its extreme hyperbolic trajectory guarantees it'd only visit and not stay. September, 9th, 2017; the object reaches the point at which its trajectory takes it closest to the Sun.
It speeds away, more than ensures its escape from the Sun’s gravity. Unlike asteroids and comets, observed before, the object isn’t bound by the Sun’s gravity. September 29, 2017; it passes through Venus's orbital distance from the Sun around. And, October 7, 2017; it passes through the earth moving swiftly toward the constellation, Pegasus, and the blackness beyond. The Hawaiian word Oumuamua, a messenger from afar arriving first, is the name given to the object. It’s dubbed as weird, mysterious, and strange. Unlike comets, Oumuamaua doesn’t have the outgassing cometary tail of dust and water vapors.
Interstellar visitors are far rarer than asteroids or comets. In fact, at the time of Oumuamua, no single object has ever been seen that (originates outside of our solar system) passes through it. The vision of visiting ‘another star’ within our lifetimes, captivates the public’s imagination ditto the Apollo-11, moon-landing. Following Oumuamua pass-overhead, it’s now believed that a quarter of stars host habitable earth-scale planets. Even if only a small fraction of all habitable earths led to technological civilizations, like our own, during the lifetime of their stars, there might be plenty of relics out there in the milky-way for us to explore. A quarter of stars host a planet, the size and surface temperature of the earth.
September 14, 2020; potential evidence of extraterrestrial life is discovered right next to earth. Phosphine (PH3) is tentatively discovered in the clouds of Venus at an elevation of 56 Kms above the planet’s surface. The surface of Venus is too hot for liquid water to exist. Its rocky terrain is inhospitable to life. At such a height the temperature and pressure resemble the conditions in earth’s lower atmosphere………raising the distinct possibility that microbes could live inside liquid droplets suspended in the atmosphere of Venus. On earth, phosphine is a product of life. This potential discovery galvanizes the astronomers/scientists to test the reported detection, & send a probe that physically visits Venus, snoops the material from its clouds, and searches for microbes in those samples.
No terrestrial life has ever been discovered to exist without liquid water. Identifying planets at the Goldilocks distance from a star, that zone in which water neither freezes nor evaporates, is the Astro-archeologist’s starting point in the hunt for an alien civilization. With the discovery of thousands of exoplanets that reside outside the solar system, a quarter of all stars are orbited by planets of earth’s size and surface temperature, planets that might have liquid water on their surfaces. Telescopes and observational instruments are seeking evidence of life on rocky planets with features that are consistent with the earth.
There’ve been myths, beliefs, and legends about strange aliens. People report the presence of UFOs from outer space. Science fiction authors make these aliens look like humans with bigger heads, extra eyes, or maybe wings. Even when they’re not humanoid, most fictional aliens are modified versions of octopuses, spiders, or mushrooms. Perhaps there’s really a good reason to suppose that aliens, if there are any, might not look too unfamiliar to us. Convergent evolution suggests similarity in convergence/ancestry terms. Fermi’s paradox states that if the universe is so big then why haven’t we encountered any other intelligent life. Over the vastness of the universe, the probability of extraterrestrial life seems high, yet there’s no certain evidence for anything but terrestrial life.
Any planet that’s life on it, is pretty much bound to be in the vicinity of a star because the star is the obvious source of the energy that all life needs. So the chances are good that light will be available wherever life is present, and where light is present it’s very likely that eyes will evolve because they’re so useful. Eyes, there in the galaxies, can see us only in our past, as we see when we look at a distant galaxy, for the light takes billions of years to reach us. The inhabitants of a world, 100 million light-years distant, might at that moment, see if they could see anything at all, on our planet, dinosaurs lunging over the rose-tinted plains.
Zoo-hypothesis suggests that aliens are just watching over us and letting us be for now, presumably until we reach their level of sophistication; and something like its inverse--- that we’ve not heard from aliens because they’re the ones sleeping, in a civilization-scale system of extended-sleep pods, like the ones we know from science suitable to their needs. Without being overly anthropocentric, while searching for advanced life if we discover an extraterrestrial civilization, it’s likely to already have gone superintelligent. The history of human technological civilization is measured in a few centuries. When you imagine aliens, don't think of little green fellows with two arms and two legs but think of the superintelligent spacefaring life we explored earlier.
Science fiction narratives have prepared us to expect no certain evidence for life outside earth. In effect, we’re woefully ill-prepared for an encounter with an extraterrestrial counterpart. Above us, we see seemingly empty space. The question arises: are we the only intelligent life in the universe? What if we find extraterrestrial life or the latter found us? Astronomers may assume if we found it both of us would welcome each other. When we discover two relatively intelligent species like chimpanzees, we simply shoot them, cut them off for trophies, put them on exhibit in cages, kill them for medical experiments and destroy or take over their habitats. Humans did it with their fellow technically less advanced humans when they explored them. An advanced extraterrestrial who discovered us would surely treat us in the same way. If there really are any radio civilizations within listening distance of us, then for heaven's sake, let’s turn off our transmitters and try to escape detection or we’re doomed.
Fortunately for us silence from outer space is deafening. Probably there are no others in our galaxy and within hundreds of light-years of us. Had there been planets with suitable conditions for life, flying saucers and intelligent beings should be visiting us or at least directing radio signals at us. We’re unlikely ever to see flying saucers. For practical purposes, we’re unique and alone in a crowded universe.