Any science topic that divides left and right isn't science it is opinion.
Nonsense. Global warming is an indisputable empirical scientific fact. The propaganda unleashed by corporate interests that profit from the destruction of the ecosphere is irrelevant - none of it changes the hard scientific data which shows dramatically rising CO2 levels, dramatically rising global temperatures, and dramatically rising sea levels - none of these empirical facts are "opinion."
The problem with ETH is lack of hard evidence.
I don't know what "hard evidence" you're talking about - there's a mountain of hard evidence in support of the ETH, across a wide variety of scientific disciplines. If you mean "hard evidence that AAVs are interplanetary," then that's a red herring - there's no such thing as "hard evidence of origin." At best we could attempt to determine that a device does not originate on the Earth, but even that's tricky because we can never know the full capabilities of secret military aerospace research projects.
My computations based on the fact we haven't found an earthlike world (and the more we learn about earth's history the stranger it is) is that intelligent life is about one planet in a 300-500 light year radius and there are about 500 of them.
Your base assumption is grossly inaccurate because it's virtually impossible to detect an Earth-like planet in the habitable zone of a Sun-like star using our best contemporary instruments. But this can be addressed through proper analysis of the data. I know of two such analyses to date, and here's what it boils down to:
- There are roughly 200 billion stars in the Milky Way galaxy alone.
- Roughly 40 billion of those stars are Sun-like.
- Roughly 20% of those Sun-like stars are orbited by an Earth-like planet in the habitable Zone.
- So various estimates show that there are between 2 billion to 11 billion Earth-like planets in our galaxy (8 billion is probably the right approximate answer).
- All of the factors that we can detect point to a relatively high prevalence for life: water is ubiquitous, amino acids are ubiquitous, and recent work by a Harvard-Smithsonian collaboration found that Earth-like planets will have very similar composition and magnetic fields to our Earth. So the main area of uncertainty now is the prevalence of intelligent life, which is debatable. I favor the view that our planet is probably relatively ordinary in the scheme of things, and that since intelligence is the greatest survival advantage, it probably happens on a reasonable share of living worlds.
- Interestingly, research has also found that the average age of habitable Earth-like worlds is between 2-3 billion years older than our Earth. This provides ample opportunity for intelligent life to arise on such worlds, and to have vastly exceeded our present technological capabilities.
- As far as detection of technological civilizations goes, we don't have the technology to pick up the kinds of radio transmissions that our civilization has been generating for the last century at significant interstellar distances, so the non-detection of SETI is meaningless. And we're already moving beyond the high-power-transmission era of radio and television broadcasting, favoring cable connectivity and comparatively lower-power directed satellites transmissions instead - this is a sensible move toward greater efficiency, which is likely with any technological civilization. So the chances of detecting the roughly one-century era of radio broadcasting in the billions of years of planetary development, are essentially nil. In my view technological civilizations are likely quite common throughout the universe, and they simply don't use radio signals to communicate at interstellar distances because their technological progress moved beyond that phase billions of years ago, on average.
If we are getting visited it isn't happening often or by many different ones.
All of the data that we have refutes both components of that statement.
(assuming that is even possible) would appear to be about as likely, or perhaps some Eemian civilization achieved space travel (the previous interglacial) and is playing hide and seek with us.
Apples and oranges. I can't even fathom how any rational mind could liken the possibility of interstellar visitation to the wildly speculative notion of interdimensional travel. There's a wealth of supporting data favoring the ETH, and zero supporting evidence for the interdimensional idea (if other universes even exist at all).
