Most inquiring minds wonder whether there are any other intelligent civilizations somewhere in the vast starry expanse of the Milky Way. Maybe the question should be whether there were any.
Bad news if you want to believe. It isn’t impossible for aliens at least as (and possibly more) intelligent as we are to have existed at some point. The problem is, Caltech physicists found results that were not so favorable when they created a galactic simulation to measure whether extraterrestrial intelligence exists within the Milky Way by using criteria that included how life could have spawned in the beginning and self-annihilated in the end. They are now suggesting that if any alien civilizations with sizeable brains lived on some exoplanet in the Milky Way, they are probably alien fossils by now.
The Milky Way has been around for billions of years. In that time, life has not only had had plenty of time to evolve to an advanced level and achieve heights of technology even our wildest sci-fi dreams couldn't fathom, but also to destroy itself.
“We found [self-annihilation of complex life] to be the most influential parameter determining the quantity and age of galactic intelligent life,” the physicists said in a study recently published in Astrophysics of Galaxies.
There were three types of limitations for the existence of aliens that the team studied. They considered the possibilities of abiogenesis, how long it might have taken (or be taking) for an intelligent civilization to evolve, and chances of such a civilization crushing itself. Abiogenesis is the idea of life spawning from things that are definitely not alive. If you rewind 4 billion years, Earth was a primordial ooze of organic and inorganic substances, both of which were inanimate. Some believe that these substances came together in a certain way to produce the first life-forms on the planet. These supposed microbes are thought to have then evolved into more and more complex organisms.
Then the Fermi paradox just has to come in and ruin everything. This argument, which is the paradox between our belief in the high probability for life with hardly any evidence for it, was started by Enrico Fermi when he asked his fellow scientists where exactly all the aliens were.
Here is the issue with life having had enough time to evolve. The Milky Way is around 13.6 billion years old, though updated estimates of the age of its disc have put that part of the galaxy at around 10 billion years. Humans have just barely come into existence compared to that. Even just a few billion years would be more than enough for a civilization to advance so far ahead of us that they would have tech able to scour the entire galaxy for other intelligent civilizations. But what if alien tech is nothing like we can imagine or have even though to yet? Maybe there is a hypothetical civilization using a star-powered Dyson sphere as a spaceship, or some other spacecraft with the entire galaxy as its power source, but it doesn't seem that any signals are coming through. Maybe we just haven’t learned how to detect them yet.
For now, it seems that all the weird signals are coming from fast radio bursts (FRBs) and weird wavelengths being produced by neutron stars and other objects that make the SETI institute want to party for a few seconds until the real source of the signals is revealed.
Maybe it is a galactic graveyard out there. So many human civilizations have risen to unbelievable heights only to be torn down in just a few hundred or thousand years. Because these civilizations rose and fell within our own species, this technically does count as self-annihilation. We just happened to have enough of us spread far enough apart to keep homo sapiens going until now. It sounds grim. However, the CalTech physicists do offer a glimpse of hope for anyone who wishes they could live out The X-Files. There is a chance that humans might be the most advanced intelligent life-forms in this galaxy, and that other civilizations are where life on Earth was when microbes were just crawling out of the ooze.
“The simulated age distributions also suggest that most of the intelligent life in our galaxy are young, thus making observation or detection difficult,” they said. If you really want to believe, maybe you shouldn’t give up just yet.