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Researchers Say The Aliens Are Silent Because They Are Extinct (theconversation.com)
HughPickens.com writes: The Conversation reports that according to research by Dr. Charles Lineweaver and Dr. Aditya Chopra, a plausible solution to Fermi's paradox is near universal early extinction of life on exoplanets, which they have named the Gaian Bottleneck. "The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens," says Chopra. "The mystery of why we haven't yet found signs of aliens may have less to do with the likelihood of the origin of life or intelligence and have more to do with the rarity of the rapid emergence of biological regulation of feedback cycles on planetary surfaces." According to the researchers, most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable. About four billion years ago, Earth, Venus and Mars may have all been habitable. However, a billion years or so after formation, Venus turned into a hothouse and Mars froze into an icebox. Even if wet rocky Earth-like planets are in the "Goldilocks Zone" of their host stars, it seems that runaway freezing or heating may be their default fate. Large impactors and huge variation in the amounts of water and greenhouse gases can also induce positive feedback cycles that push planets away from habitable conditions. The difference on Earth may be that as soon as life became widespread on our planet, the earliest metabolisms began to modulate the greenhouse gas composition of the atmosphere. "The emergence of life's ability to regulate initially non-biological feedback mechanisms could be the most significant factor responsible for life's persistence on Earth, conclude Lineweaver and Chopra. "Even if life does emerge on a planet, it rarely evolves quickly enough to regulate greenhouse gases, and thereby keep surface temperatures compatible with liquid water and habitability."
Just some of the things that had to happen for us to be where we are now:
1) Life had to evolve
2) Multicelluar life had to evolve (this took a billion years after life itself arose so is probably not a forgone conclusion)
3) Life had to climb out of the oceans (dolphins might be smart but they won't be building any rockets with their flippers anytime soon)
4) Suitable intelligence had to evolve. Had it not been for the asteroid the dinosaurs would still be in charge.
5) Humans had to survive numerous climate changes and if the genetics is to be believed we almost died out and everyone today comes from a very small population who made it.
6) Farming had to be created to allow people to do something other than hunting and gathering.
7) For the industrial revolution plenty of freely available energy had to be lying around near the surface - ie coal. You can't melt iron with wood fires.
8) Someone had to invent radio.
I'm sure there are dozens of other things that could fit inbetween those points but my basic point is that a technological civilisation than can broadcast information out from his own planey is very VERY unlikely. IMO we could well be the only one surrounded by planets full of the equivalents of bacteria and jellyfish but little more.
For four billion years, life on Earth was microscopic blobs of goo.
Then 600 million years ago - BAM - complex life emerged pretty much in the blink of an eye.
We have no idea how likely that transition to complex life 600 million years ago was - we have a sample size of ONE.
Now go back an read my first sentence: For four billion years, life on Earth was microscopic blobs of goo.
That four billion years was about half the expected lifetime of the Earth. The probability that complex life evolves may very well be infinitesimally small. WE DON'T KNOW.
Believing the universe must be teeming with intelligence is based on nothing more than faith.