Candy wrote: "Hey They have found a Planet like Earth but I do not know how far away.
Perhaps the Planet is younger than ours..Don't know."
This statement points out another profound problem with accepting the actuality of interstellar travel. Time. Human technology has only been practiced,even in it's crudest,rock shaping form,for about 2 million years. Since our solar system is 4.7 billion years old,we have been making things (tools,fire,rocket ships) less than 1/2 of 1/10th of 1% of our planet's existence.That's an awful tiny time span to be thinking of building anything that moves on it's own.We only learned of the existence of interstellar space a few hundred years ago.So why did the "aliens" start showing up now? What are the odds they started travelling to the stars just when we became aware of the stars' existence?
One may conjecture that "they" were coming here before but we couldn't conceive of interstellar travelers so we perceived them as "gods".Well,if they were coming here before and are still coming here now,where is the evidence Tyler asked about? "They" have been visiting Earth for hundreds,possibly thousands,of years but NOT ONE artifact has been found made of any material not traceable to a source right here on Earth? We have added several new elements to the periodic table,but there is no trace of these elements having been here before.Are we to believe that these "super-advanced" races couldn't produce what we produce in our labs every day?
Evolutionary processes are being understood more completely every year and we know that protein molecules wrap themselves up into complex shapes that foster replication.It is a chemical process that needs no gods.In my humble opinion,intelligent life elsewhere in the vast universe is inevitable.
But a society that A: Conquered the speed of light, B: Travels here, and C: Leaves no mark, is,I can comfortably say, an impossibility.