Still another reason? From Leah Crane at New Scientist:
Grimaldi assumed that signals from an extraterrestrial emitter might get weaker or be blocked as they travel, so they would only cover a certain volume of space. It’s relatively simple to calculate the probability that Earth is within that space and so able to detect the signal. “Not all signals can be visible at the same time – only those that intersect with the Earth,” says Grimaldi.
He found that even if half of our galaxy was full of alien noise, the average number of signals that we would be able to detect from Earth is less than one (Scientific Reports, doi.org/b562).
This implies that, even if there are lots of aliens out there, we might never be able to hear from them. More.
Colleagues, of course, disagree. They carry the torch for those aliens who never write, never phone, never visit. There’s something noble about it all if we have a great deal of time on our hands. 😉
Anyway, here are some other theories:
More often we are just told that we lack imagination, we have searched too narrowly: Moonless planets have been unfairly dismissed and sunless ones could maybe ferry life around the galaxy. Some argue that hardy Earth life forms could have made it to one of Jupiter’s moons and survived there. Jupiter’s moon Europa looks promising to many. NASA has talked of a “flying-saucer-shaped space boat” to Saturn’s moon Titan, some day. And the excitable word about another Saturn moon is, “Enceladus Now Looks Wet, So It May Be ALIVE!”
Exoplanets orbiting red dwarfs at a distance, it is said, may counterintuitively support life. So might exoplanets’ moons. Every month, we hear of a planet or moon capable of supporting hype.
More exotically, some seek life around failed or dying stars. If that doesn’t work, dark matter could make planets habitable (though we don’t yet know what dark matter is). And, should the laws of physics vary from place to place, life elsewhere might follow different laws. In that case, should the physics term “constant” be changed to “local variant”?
Lastly, encountering hard, doubting hearts, alien life proponents resort to moralizing: An editorial preaches “Uniqueness seems rather too presumptuous a claim for one small planet in an undistinguished corner of a vast cosmos.” Our vaunted respect for evidence is a mere cloak for pride and presumption!
See also: How do we grapple with the idea that ET might not be out there?
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