It is unlikely that any extraterrestrials have ever visited earth.

Thanks for the challenge, likespeace. Good luck!In addition to what Con has already laid out, I add the following: I will leave my last post empty so that we will both have an equal number of posts.I'm just cutting and pasting this opening from my last debate on this same topic.This is my argument in a nutshell:1. If any extraterrestrials have ever visited earth, then they probably live within 50 light years of earth.2. It is unlikely that any extraterrestrials capable of traveling to earth live within 50 light of earth.3. Therefore, it is unlikely that any extraterrestrials have ever visited earth.This argument is logically valid, so the only question is whether the premises are true. Let's discuss them one at a time.1. If any extraterrestrials have ever visited earth, then they probably live within 50 light years of earth.Not even considering the size of the whole universe, our galaxy is very large. It is about 100,000 light years in diameter, and there are anywhere from 200 to 400 billion stars in our galaxy.[1] Roughly half of the stars are in binary systems where two stars rotate around each other in close proximity.[2] The closest star to earth is about 4.2 light years away.[3] Since these stars and systems are spaced so far apart, it would be quite the undertaking for anybody to travel even to one nearby.The only reason anybody would come to earth is either if they already thought there was something very unique about earth or if they just happened upon earth while exploring the galaxy. Given that there are hundreds of billions of stars in the galaxy, the odds are against anybody just luckily running into the earth. It is far more likely that if anybody comes to the earth, it is because they already know the earth is has intelligent life on it. That's really the only thing that would single us out and make such a major undertaking worth it.Earth produced the first radio communication in the 1890's.[4] That means the farthest any intelligent signal could've traveled from earth so far is only 110 light years away. Supposing some civilization 110 light years away is just now recieving those signals and discovering that there's life in this part of the galaxy, it would take them another 110 years to get here if they travel at the speed of light. Assuming our earliest radio waves could be detected in other places in the galaxy, and assuming light speed travel is possible, and assuming the aliens left immediately upon receiving the signals, the farthest anybody could be from us in order to get here today is 55 light years away. That would allow 55 years for our earliest signals to get to them and another 55 years for them to arrive here.According to Einstein's special theory of relativity, no matter can travel at the speed of light.[5] It is doubtful anybody could even come close. It is also doubtful that the earliest signals produced on earth would be strong enough to be detected 50 light years away. That means if any aliens have ever visited earth, they would have to live well within 50 light years of us.2. It is unlikely that any extraterrestrials capable of traveling to earth live within 50 light of earth.Any civilization advanced enough to undertake a trip to earth would have to be vastly more technologically advanced than we are since we are incapable of making such a trip. That means they probably invented radio technology long before we did. But if there were any such civilizations within 50 light years of us, we would already know about it. SETI has been searching the skies for the last 40 years or so for signs of extraterrestrial life.[6] So far, they have turned up nothing. But if there were civilizations within 50 light years who had radiotechnology long before us, then SETI would've found them. Since SETI hasn't found them, they likely aren't out there.ConclusionIn summary, any aliens that have visited earth would have to live within 50 light years of us because (1) the trip would be a major undertaking and would require quite a bit of motivation to undertake, (2) the discovery of intelligent life is about the only thing interesting enough to warrant a trip to earth as opposed to any of the other billions of solar systems in the galaxy, and (3) even traveling at the speed of light, which is not feasible, ET's that discovered our existence and left immediately could only have been traveling for half the time our earliest radio signals left earth.But any civilization capable of such travel would be far more adanvced than us, and it is unlikely there are any civilizations more advanced than us within 50 light years because if there were, we'd know it. It follows that it's unlikely any extraterrestrials have ever visited earth.[1] http://en.wikipedia.org......[2] http://www.astro.cornell.edu......[3] http://www.astro.wisc.edu......[4] http://www.clemson.edu......[5] http://curious.astro.cornell.edu......[6] http://www.seti.org......