Originally posted by maritimer Being a hardcore astronomy buff I find it pathetic that people actually believe we are the only intelligent life in the universe. I could put up some ( very factual btw ) numbers that almost proves we can't be the only things out there. [...] 150 BILLION stars [...] I firmly believe it is straight up arrogance that makes people believe we ARE the only things out there.
Originally posted by rparmar But the same mathematical logic that can be used (pace Carl Sagan) to show the likelihood of life throughout the universe can also be used to show that such life could have evolved and died millions of times without it ever happening near enough to other lifeforms (in time and distance) for contact to ever occur.
Originally posted by KrisK10D Each blink represented the beginning, and end, of a civilisation on some planet, at some point in time, from the beginning of time. 2 never lit up at the same time.
Both arguments (the space is too big to have only one civilization; and no two civilizations ever exist at the same moment) are arguments which have been typical of the 50s. The third such argument is that extraterrestrial life may be so alien we may not even recognize it when we see it.
However, 50 years later, none of the three arguments represents anymore what is current science. Rather, things now look like this:
- A civilization, once it reaches a state about ours in 100 years, will start to hop to the next habitable planet (~30 lightyears away). Either by using generation space vessels. Or cybernetic organisms. This mechanism is called colonization wavefront. Otherwise speaking: Once a single planet in a galaxy reaches this critical state we are so close at, intelligent life will spread throughout the galaxy and will never disappear again. You would see it everywhere. That we don't is called Fermi's paradox. We don't see it everywhere. The galaxy appears to be sterile.
- The fundamental laws of physics seem to be fine-tuned (for a yet unknown reason) to allow for biological, carbon-based life. There is little chance that there can be other forms of life, if not created by carbon-based intelligence.
- For carbon-based intelligence, we can compute vague probabilities that it is created by a process of chemical, biological and social evolution. As it turns out, it is quite likely that biological life exists but very unlikely that it evolves into a technological civilization.
- A galaxy may have 3 * 10^11 stars, the universe may have 10^24 planets within our light cone, but is is relatively easy to "eat up" a dozen of factors of ten by requiring unlikely, still necessary events, like:
+ planet crash creating a moon so big that it stabilizes the axis of rotation, but not too big that it stops rotation over billion of years.
+ the right frequency of big meteor incidences to fuel evolution
+ a planet staying in the habitable ring despite the fact that this ring moves outward when the star gets hotter. Which means too that the star must be of the right size.
+ the human race emerged after 4700 million years and only about 100 million years before the earth will have become too hot. This shows that the entire process was unlikely in the first place. One can compute, how unlikely. If conditions are stable as they are.
+ no near-by supernova or gamma ray burst event (the sun is a relatively empty region of the galaxy, and was most of the time. Of course, most stars are in the crowded region).
+ a star created in a region with the right mix of heavier elements (only relatively few stars are -- the sun is an exception in that for its age, it is far away from the crowded center for its mix of elements).
+ a planet not been thrown out of the solar system and keeping a near-circle orbit (the sun seems to have had more planets in the past).
+ a planet keeping its vulcanism over billion of years.
+ ... I could go on forever
Did you know that the human race was once near extinct with only a couple of thousand individuums left?
We cannot yet compute the exact expectation value for number of civilizations in a galaxy after 13.7 billion years. Too many factors are not known exactly enough. But I wouldn't be too surprised if it is below 1.
Some physicists now believe that there are zillions of (disconnected) universes out there, differing in their laws of physics, most of them empty (read: unobservable), and of the non-empty, only populated by a single observer (read: civilization). If this is so, then most likely, we are alone in our universe and our universe is special because we are in it. I don't say that this is a fact. I only say that this is a more serious argument than the nice but naive idea that we "cannot" be alone.
Personally, this recent scientific progress has made me appreciate the importance of the human race. We are the gem on this planet, if not in this galaxy. I don't believe in god, so I don't say it is a wonder. But our mere existance is the closest thing to it. Hiding alien space crafts in our atmosphere would be the second closest thing.
But how do people say: When it rains wonders, it pours wonders