So, one of the things I have been doing with my spare time is thinking about how evolution and the history of life can be used to inform issues that I (and we) think about. One issue that has been around longer than I have is interstellar space travel. Interestingly, evolution has something to say on the topic: Nope, we can’t do it. My reasoning basically comes down to the fact that there is no evidence that anybody or anything has ever done any interstellar travel. Of course, it is hard to prove a negative, and I, not surprisingly, won’t succeed. Nevertheless, I think I can make a strong argument that interstellar space travel won’t happen.
The first thing to point out is that earth is certainly not unique, and that there must be uncountably many planets with life on them. Even if only a tiny subset of those planets have life technologically advanced enough to make space ships, there will still be a huge number of such planets
The second observation is that life, and especially technological life always leaves a trace. There are billion year old fossils, although some are iffy. Importantly, some of our best fossils are waste products. How do we know when photosynthesis evolved? It left behind waste products (oxygen). Caproliths (fossil poop) provide evidence of what animals used to be here, and we have fossil castings of ancient burrowing mammals, not to mention tracks of everything from sea creatures to dinosaurs. Technology only produces more artifacts. My home is stuffed with everything from native American arrow heads and pre-Columbian artifacts (don’t hate me, my father collected most of them in the 1940s, I collected others in the 1960s). Evidence of human activity on earth abounds, most recently being found as patterns that show up on photos taken from space. Importantly, one of the major traces of life is garbage. Thus, there will be evidence that humans went to the moon in the form of footprints, and the base of the lunar lander. It is likely that these traces of space travel will be present for thousands of years at a minimum. The point is that life, and especially technological life leaves traces.
Life Leaves Evidence. (https://geochristian.com/2008/10/28/dinosaur-footprints-part-3/)
The reason that this is relevant is that we have been looking at the heavens for a long time, and around earth even longer. Nevertheless, we have yet to see any evidence of interstellar travel. Some have argued that things like the Nazca lines suggest space travel. I won’t argue that that could be an explanation, only that human ingenuity is at least as plausible and that as a consequence it can’t be used as proof of alien visitors. More importantly, we have never found a piece of broken alien technology, the alien equivalent of the lunar lander base, or anything similar to the middens and garbage dumps that typify human societies.
One mitigating factor is that you could argue that aliens had not visited for a long time (I would argue at least 500 million years) and that the garbage had rusted away. While you would still expect a discarded ray gun or something to appear, maybe we have missed it. However, this brings me to the next point: There is no evidence of space travel.
Consider human travel on earth and in our solar system. We have left a lot of evidence of our travels. First there is the garbage. Our ocean bottoms are littered with ship wrecks, there are airplane and car wrecks everywhere. (I stumbled on one in the Amazon for example). We have left part of the lunar lander on the moon, and various vehicles on Mars and other planets throughout the solar system. Nevertheless, we have never seen an alien space ship or evidence of past space travel by non-humans.
This can be explained because wrecks don’t emit energy and are hard to detect as a result. After all it’s a big deal when a Spanish galleon is found, and because the have gold bullion people are looking for them. What is a problem, however, is that our ports and airports are very easy to detect. Ports have always been harked by sight houses and flags (not to mention flotsam). More importantly, airports are purposely very easy to find. In the western part of the country you will find cement markers pointing towards airports, and airports emit radiation in every part of the spectrum, from long waves to microwaves. Importantly, this is not an accident. This radiation is important for communication (radio), navigation (e.g. Loran), and monitoring air traffic (radar). Of course, airplanes and ships all have transponders and other devices (EPIRBS) that make them easy to detects. The point is that the transportation on earth generally leaves a big signal both historically and in the form of released energy. There is no reason to believe that space travel would be any different, and in fact we would expect it to produce more signals since getting lost in space would be, if anything, more serious than being lost on earth. That said, there is no evidence of any form of radio communication or interstellar navigation aids.
No wonder they were lost in space: They didn’t have navigation aids. (http://www.peoplequiz.com/trivia-quizzes-1459-Lost_in_Space_60s_Space_Adventure.html)
Putting this all together, I see no evidence that extraterrestrials have ever visited us, or that there is and evidence that there is interstellar space travel in our region of the universe, even though such evidence should exist if space travel did occur. Perhaps I am overlooking something. Perhaps pulsars are navigation aids. Perhaps the Nazca lines were put there by aliens. Perhaps aliens directed human evolution. All that is, of course, possible, but that would require that alien life was entirely different than terrestrial life in that it always cleaned up after itself, and navigated without using energy. A much simpler explanation is that interstellar travel doesn’t happen, and mysteries such as the Nazca line have a mundane explanation instead of being evidence of aliens.