In the Milky Way alone:
The researchers confined their search to exoplanets between 0.5 and 1.5 times the mass of Earth and stars between 4,800 and 6,300 Kelvin (4,530 to 6,025 degrees Celsius; 8,180 and 10,880 degrees Fahrenheit) in effective temperature (the Sun has an effective temperature of 5,780 Kelvin).
The team found that around half these stars, based on their calculations, should have rocky, Goldilocks-zone exoplanets. That’s roughly 300 million stars in the Milky Way, based on our current counts.
Michelle Starr, “There Could Be at Least 300 Million Potentially Habitable Worlds in The Milky Way” at ScienceAlert
And yet we never hear from anyone living there. Here’s a list, just for fun, of eight possible reasons:
1.Are the Aliens We Never Find Obeying Star Trek’s Prime Directive? The Directive is, don’t interfere in the evolution of alien societies, even if you have good intentions. Assuming the aliens exist, perhaps it’s just as well, on the whole, if they do want to leave us alone. They could want to “fix” us instead…
2.How can we be sure we are not just an ET’s simulation? A number of books and films are based on the idea. Should we believe it? We make a faith-based decision that logic and evidence together are reasonable guides to what is true. Logical possibility alone does not make an idea true.
3.Did the smart machines destroy the aliens who invented them? That’s the Berserker hypothesis. A smart deadly weapon could well decide to do without its inventor and, lacking moral guidance, destroy everything in sight. Extinction of a highly advanced civilization by its own lethal technology may be more likely than extinction by natural disaster. They could control nature.
4.Researchers: The aliens exist but they are sleeping… And we wake them at our peril. The Aestivation hypothesis is that immensely powerful aliens are waiting in a digitized form for the universe to cool down from the heat their computers emit.
5.Maybe there are just very few aliens out there… The Rare Earth hypothesis offers science-based reasons that life in the universe is rare. Even if life is rare in the universe, Earth may be uniquely suited to space exploration, as the Privileged Planet hypothesis suggests.
6.Does science fiction hint that we are actually doomed? That’s the implication of an influential theory as to why we never see extraterrestrials. Depending how we read the Kardashev scale, civilizations disappear somewhere between where we are now and the advanced state needed for intergalactic travel.
7.Space aliens could in fact be watching us. Using the methods we use to spot exoplanets. But if they are technologically advanced, wouldn’t they be here by now? The Hart-Tipler conjecture (they don’t exist) is, of course, very unpopular in sci-fi. But let’s confront it, if only to move on to more promising speculations.
- Is the brief window for finding ET closing? According to some scenarios, we could be past our best-before date for contacting aliens. Of course, here we are assuming a law of nature as to how long civilizations last. Can someone state that law? How is it derived?