[Sicon]

I wasn't assuming the same developmental timelines. Of course it's possible that other civilizations have come and gone, or come and advanced far beyond anything we can imagine, in the 15 billion or so years of the universe's existence. Advanced enough to have figured out how to travel faster than light? Maybe, maybe not.

Nevertheless, there are still two things that stand out in my mind on the subject:
First, that the odds of actually being found by another civilization, no matter how advanced, are incredibly remote. Again, WE have only been producing signals that could be detected from a distance for 107 years. And again I assert that a sphere 107 light-years across is very, very small on a cosmic scale. The odds of an advanced species happening to be in the neighborhood to see/hear us are minimal. And I think you overestimate the detectibility of things like the Trinity test or any other nuclear explosion on earth, and like the radio signals, whatever aftereffects might have reached space can only have gone 63 light-years from here by now. It would be like sitting in a raft in the middle of the Pacific ocean, and just happening to be in the precise spot that a single grain of sand falling randomly from orbit struck the water. Even that analogy probably overstates the probability considerably.

Second, as someone else has pointed out, there are now thousands and thousands of cameras, many that take relatively good quality images, all over the planet. And yet, we still don't have much in the way of proof of any alien visitations.

I am not saying alien civilizations don't exist - given the size of the universe and the number of galaxies, solar systems, and planets, it seems far too likely that they do exist somewhere. All I am saying is that I do not believe for one second that any have ever visited, or are currently visiting, earth. And without solid, scientific, verifiable proof, I see no reason to believe those who insist that they are or have, particularly the "I was abducted by aliens" crowd.

[MHGinTN]

You have made a common error, in taking the 4.5 billion years our planet has been existing and dividing it into the approx. 15 billion years since the Big Bang, and found we are in the last one third so why not life evolving during the previous approx. eleven billion?... The quiet state of our neck of this spiral galaxy is as important to the possibility of life catching hold and evolving as the big bnag as step one. The violent nature of galaxies and stars interacting is the usual state of the universe of galaxies. Our position and the state of our spiral galaxy is dependent upon the rest of the galaxy and the other galaxies! A delicate balance has only been possible in our galaxy for a window in which life on earth has been possible and a period long enough for the life to rise to the level of complexity we see.

Rememeber, the first stars did not have planets with heavy elements circling them. All the heavier elements than helium and lithium were generated by the life cycle and death of stars. Followed by the dispersion of these elements to be gathered into clouds then galaxies that eventually generated stars and planets as we have now. In short, we may be at the leading edge of the process which can allow for the formation of conditions absolutely necessary for the rise of life and continued development thereof. How long does it take to destroy the first stars, collect the dust in clouds then generate galaxies? How long must the process run to reach a quiet enough state such as our planet has arisen in?

If you would like to read and listen to more along this line of reasoning, try linking to reasons.org an astrophysicists explains the notion much better than simple ol' me.