Aliens - Are they out there? Have they visited us? And related questions

[Anomalocaris]

That much is apparent from looking at systems such as 55 Cancri, but that's not the point I was making. The point was, where there are also terrestrial planets in addition to gas giant whose mass acts like a gravity well that offers some means of protection from the onslaught of celestial bodies with rogue orbits, now currently only four planetary systems including Cancri and our Solar System are known to consist of at least five planets..

Most of our planetary discoveries have been made by finding cyclic doppler shifts in star light. It can be deduced even a priori that a major sampling biase in favor of finding solar system dissimilar in configuration to our own would result from the choice of method:

1. Planets close to its star are easier to detect because of faster and stronger doppler cycles they induce in the light from their star as observed from earth.
2. Big Planets are easier to detect because of faster and stronger doppler cycles they induce in the light from their star as observed from earth.
3. Therefore most of the planetary system we have detected contained big planets orbiting very closer to their primary stars.

So it is not surprising that even if planetary systems with configuration similar to our own is common, they would not be common in the result of our initial search for extra-solar planets.

That's because we don't know if such life-forms can actually exist, asserting anything else at this point is pure speculation. I've heard all sorts of pseudo-science-fiction hypotheses that life may thrive inside stars! I can't really dismiss it as 'utter nonsense', as tempting as that is, since its plausible the cosmos may harbour extraterrestrial life in ways and forms which we've not yet observed or anticipated, but until we do discover them, we've no reason to believe otherwise. What we do know to a fairly high degree of certainty is that life can come from non-life on terrestrial planets such as Earth. The whole goal of proposed projects such as the Terrestrial Planet Finder is to try and find extrasolar planets like Earth that are more likely to harbour alien life-forms, than say a black hole, or a hypergiant star without a planetary system even, or a runaway planet and so on and so on...

We don't need black holes or inside of stars. Even life evolved on earth will likely be able to tolerate conditions outside the goldilock zone. For example, the subsurface ocean of Europa probably contain all that is necessary to replicate conditions near hydrothermal vents on earth's ocean floor, where life on earth likely first originated on earth. In our own solar system, there are probably many more moons outside the goldilock zone that could either support life currently found earth than there are planets in the goldilock zone. One could debate whether life arising there or planted there has good chance of evolving towards high complexity, but I am unwilling to venture a strong opinion on that.

I think you'll agree we've very nearly destroyed ourselves quite a few times (and still might do so in the near-future when overpopulation takes hold and our resources start to run out); bearing in mind internal threats such as war and conflict were being used as just an example....

No, I don't agree. Human can cause massive depopulation, civilizational regression, and loss of learning and science. We've not come close to pulling ourselves up by the roots or had our roots pulled out by femine, over population, etc. I also think we are unlikely to be able to actually either completely exterminate ourselves or arrange things for survivors so that no advanced civilization will be reborn in the geologically relative near future. Genetic studies suggests ancesters of native Americans who came to America numbered no more than a few hundred. Yet in 10,000 years they populated 2 continents and developed cultural sophistication perhaps only a millenium or two behind the old world. I think it will take a very large natural catastrophic event like an asteroid collision coinciding with a period of very deep civilizational decline to bring about human extinction.

Given the current age of the universe, our existence as a species and current progress at space exploration, the answer is obvious, they would have to evolve and develop the interstellar travel technology at an exponential rate than our own. .

A reasonable view, but not the only one.