Consider this. The Universe is enormous.
There are as many as four-hundred billion stars in our galaxy: the Milky Way. And there are more than one-hundred-and-seventy billion galaxies in the observable Universe. Most of those stars have planets, and many of those planets have got to contain useful minerals and fall within their star’s habitable zone where liquid water is present.
The conditions for life are probably everywhere.
But where are all the aliens?
Comment by Oliviero Mannucci: Where are all the aliens??! Under our noses every day. But many men do not want to accept their existence just as in the past it was considered crazy who wanted to go beyond the Pillars of Hercules, because the "science" then stated that beyond this boundary could not be other forms of life, because the Earth was flat and then fell below. Fortunately, not all scientists are deaf to this topic. In September 2008, at the UNESCO Palace in Paris, during the course of an international conference SETI, astrophysicist at the University of Orsay dr.Labèque, remembered a famous UFO sighting made by six officers of the USAF in 1957. They were doing a routine flight over the U.S. aboard a RB47. Suddenly, a UFO appeared near them and followed the plane for 700 miles. The six soldiers, using the systems for electronic countermeasures which had on board, got a signal on a frequency of 3 GHz from the UFO, which was communicating with someone, maybe his mother ship. After the story of this qualified witness said: Dear colleagues go ahead and look for extraterrestrial life with radio telescopes, but be careful because something is here!
And think about this.
The Universe has been around for 13.8 billion years. Human beings originated 200,000 years ago, so we’ve only been around for 0.01% of the age of the Universe. An intelligent species could arise on any one of those countless worlds, and broadcast their existence to the entire galaxy.
Once a species developed interstellar travel, they could completely colonize our galaxy within a few tens of millions of years; just a heartbeat in the age of the Universe.
So where are they?
As far as we know, Earth is the only place in the Universe where life has arisen, let alone developed an intelligent civilization.
This baffling contradiction is known as the Fermi Paradox, first described in 1950 by the physicist Enrico Fermi.
Comment by Oliviero Mannucci: When quoting the Fermi Paradox, we must remember in what context it was said. In 1950 in the U.S. and worldwide occurred thousands of UFO sightings every day. Fermi when he said these words, he did not say this in a negative sense, but in a good way. His calculations showed that millions of intelligent alien civilization had to be present in space, and therefore must have come on Earth. This happens every day, but man pretends not to see this. Someone said: The brain is like a parachute, it only works when it is open.
Scientists have been trying to resolve this mystery for decades, listening for radio signals from other worlds. We’ve only sampled a fraction of the radio spectrum, and so far, we haven’t detected anything that could be a signal from an intelligent species.
How can we explain this?
Maybe we really are the only planet in the entire Universe to develop life. Maybe we’re the first civilization to reach this level of advancement in the entire galaxy. But with so many worlds out there, that really seems unlikely.
Maybe civilizations destroy themselves when they reach a certain point. Nuclear weapons, global warming, killer epidemics, and overpopulation could all end humanity. Asteroids could strike the planet and wipe us out. But would this happen to every single civilization? one-hundred-percent of them? Even if ninety-nine-percent of civilizations destroy themselves, we’d still have a couple that made it through and fully colonized the galaxy. Maybe they’re just too far away, and our signals can’t reach each other. But then, self-replicating probes could traverse those distances and leave a local artifact in every single star system.
Maybe we can’t understand their signals or recognize their artifacts. Maybe, but if aliens constructed a series of artifacts on Earth, I think we’d notice them. The aliens would have experience creating obvious structures.
Comment by Oliviero Mannucci: The problem are not them, are us. Most scientists believe that is not possible to travel through the universe quickly. The scientists still believe they can find extraterrestrial civilizations with the primitive radio waves. Scientists believe that we are the only technological civilization of the universe. Most scientists do not believe in UFO sightings. Yet UFOs were spotted by a lot of people also prepared, such as fighter pilots, civilian pilots, astronauts and military. Not only by ordinary people who exchanges Venus for a UFO. As I said before, someone said, the brain is like a parachute, it only works when it is open. Scientists skeptical need only open their brains, this is the real problem.
Maybe they’re just too alien and we just can’t understand them. Maybe we’re too insignificant, and they don’t think we’re even worth talking to. We don’t need to talk to them to know they exist. If they flew through our Solar System, ignoring us, we’d still know they’re around.
Maybe they’re not talking to us on purpose, and we’re really in some kind of galactic zoo. Or aliens have a Prime Directive, and they’re not allowed to talk to us. Again, all the aliens? Not a single one has gotten through and snuck us some evidence?
There are many other potential solutions to the Fermi Paradox, but I personally find them all insufficient. The Universe is big, and old, and if extraterrestrial life is anything like us, it wants to multiply and spread out. Perhaps the most unsettling thought is that something happens to 100% of intelligent civilizations that prevents them from exploring and settling the galaxy. Maybe something good, like the discovery of a transportation system to another Universe. Or maybe something bad, like a destructive technology that has destroyed every single civilization before us.
How do you feel about the Fermi Paradox? How do you resolve the contradictions? Whatever the solution, it’s really fun to think about.
We’ve recorded a couple of episodes of Astronomy Cast about the Drake Equation and the Fermi Paradox, and we did a sequel episode called, Solutions to the Fermi Paradox.
Comment by Oliviero Mannucci: The only real solution to the Fermi Paradox is : open your mind. There is no other solution. The science challenges to religion to base their beliefs on dogmas, but then the science behaves in the same way. The dogmas do not serve the progress of humanity. I still remember what the doctor said about the Labèque ET: Something is here! This is the only true fact.
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