There is a standard answer for this. Once life appeared on earth, it pretty much immediately changed conditions so that life could no longer spontaneously arise; it created a barrier to entry. Basically, gen 1 life lives off readily-available chemical energy in the environment. Gen 2 life takes advantage of extra complexity available to feed on either gen 1 life or on pre-cursors of the “readily-available” chemical energy that are both more abundant and harder to use. gen 1 life quickly dies out. Thereafter, gen 2 life or later is the only thing that you can find.
Another answer for this is that we don’t really know if viruses, in general, have a common ancestry with other life or with each other (if viruses are even really alive). So viruses could be life with no common ancestors.
There’s also the possibility of panspermia, that life originated somewhere and hitchhiked (metaphorically) on a meteor to spread to Earth. But if you take that idea, speculating about how it came to be or if it spread somewhere else is pointless, since that’s like saying we know nothing about how it works and we’re blindly guessing.
It’s difficult (impossible except in a place like Lake Vostok) to search for the precursors of new life here because all the vestiges of current life would drown out the signal.
Also, it would be difficult to have a “built from scratch” entity, when everything around you wants to gobble your bits. ie. evolution has already worked this out. Based on the resources and conditions on planet earth, we have filled the niches that life can accommodate, and any new life would have to compete against existing. That is extraordinarily difficult considered everything else has had a 3.5 billion year head start.
@vinraith, where do most people sit on the Danish claims that the first gravitation wave detection was false?
It seems like there is sufficient proof that it was a good finding although it appears that the LIGO people haven’t exactly been as transparent as they could be.
Good question. It’s a little hard to pin down, honestly - there’s at least a large minority that think there’s something questionable about that first detection. In short, though, it probably doesn’t matter - most of the subsequent detections seem irrefutably solid.
It has to be understood just how incredibly hard it is to distinguish a gravitational wave from background “noise.” Any little perturbation nearby is going to be so much larger, this is like looking for a needle in a bale of hay the size of the solar system. I’m continually amazed it can be done at all, honestly.
It’s pure conjecture, but this feels about right to me. I suspect the “great filter” is somewhere between simple life and complex life, and the probability of anything we’d recognize as intelligent arising is so vanishingly small that any such intelligence sits outside our particle horizon (i.e. is so far away that any sign of its existence wouldn’t remotely have reached us yet).
With the tremendous variety of life on Earth I just find it difficult to believe that complex life doesn’t evolve from simple life in every system given time. Why would it do so on Earth but not on other planets (especially Earth-like planets)?
Or in other words, in our single example that we have to draw from, complex life is very common, so why would we assume that’s not the case universally? What’s the reasoning? Similarly, in our only example, intelligent life evolved as well, and depending on your definition of intelligence, it has evolved in a multitude of species across the animal kingdom. Why would it only do so here?
It just seems to contradict everything we know about the history of biology and evolution on this planet. I could more easily accept that simple life arising spontaneously in the first place is the exceedingly rare phenomenon. We still have no idea how or why that happened.
But when it does, I’m inclined to believe that it proliferates and evolves into the kind of managerie we see here on Earth, given the adequate environment and timescale.
The operational definition of “extra-terrestrial intelligence” involves the ability to do things that can be detected from another solar system, like manipulate radio waves or travel beyond a home planet. These are all things that only one species on in this planet can do, and therefore I think it’s exceedingly unlikely we will find another life form with similar capabilities.
But of the one planet we have found with life on it, it does have such a species. That’s 100% of planets we know of. Why would you then assume the odds are closer to 0% than 100% for other planets? Beyond that, our planet could have potentially had multiple species with such intelligence, but the competition was wiped out / bred out. Maybe it’s a natural tendency for ecosystems to only support one highly intelligent race. When you think about it, unless the two species are very closely related (like Neanderthal and Homo sapiens for example), the odds of two totally different species developing high intelligence during the exact same time frame have to be extremely unlikely.
So for two to exist at the same time on the same planet, one would have to evolve while the other was already in existence. And because such evolution takes such a tremendous amount of time, the intelligent species already there would likely have advanced technologically far beyond even where human beings are today. It would certainly be to the point where that new species would never, ever be able to threaten them (if they were even allowed to live to begin with). In other words, if kangaroos started talking and building crossbows, I’m pretty sure we’d put a stop to it before it got to the point where they were assembling ICBMs.
I don’t necessarily think intelligent life has to be “exceedingly rare”, but I do think having multiple instances of it on the same planet at the same time probably would be. Hell, just look at how we’ve affected our ecosystem just in the last couple hundred years. Chimpanzees and Cetaceans are pretty smart, but we’re more likely to drive them to extinction than allow them to evolve any further.
100% of planets we know of has a species that can easily develop a fatal addiction to C21H23NO5. How likely do you think we are to find an extraterrestrial species with opiate receptors that work the same way? My best guess is zero. We are more likely to find a species that independently invented Rolex watches.
It’s hard to make any reasonable inference with a sample size of one planet. But there are millions of species, and only one is intelligent enough to synthesize heroin. That’s a denominator you can work with.
If intelligent species tend to wipe each other out, then that’s even more reason to believe that they are exceedingly rare on other planets.
It is impossible for me to imagine we won’t get to step one (finding life outside of earth) in the next 30 years.
Step two? Fermi paradox v Drake.
Step two we may find some mobile life or a fish or something on some planet in 500 years or so. I bet it’s a big deal in 2543.
Step 3? After a few thousand years of searching we find intelligent life. I can only hope we will get along because they could be a billion years ahead of us.
Let’s just find life somewhere else. Europa, Mars (maybe more water there than it seems), Titan… then let’s get to step two.
Finally until space can get commercialized step one and step two are gonna be a long ways off…
