Have we reached the point when it is kooky to not believe in massive amounts of intelligent life having evolved throughout the universe?

Great Debates
747

First of all, cite that our solar system is somehow atypical? What does that even mean?

Second, if just one in a thousand planetary systems have a planet in the habitable zone, that gives you around 200 million candidate planets. Quite a respectable number.

ETA: Depending on the criteria you apply, we currently know of either 37 or at least 12 exoplanets in the habitable zone that are suitable for life as we know it. And that’s within the very, very limited range of our instruments.

That’s possible but extremely unlikely, and I’ve already addressed that. It’s just one of the far-out premises of the Great Filter hypothesis.

748

The problem with this, is that the Fermi paradox does not only concern why we haven’t had aliens land on our doorstep, but also why we cannot see any evidence of life anywhere.
Humans are already quite close to technology that would be detectable on interstellar scales. Remember that centuries, even millennia, are a blink of an eye in this context.

Now, it could be that the millions of life-bearing worlds that you allude to, includes few to zero technological civilizations. In which case, that’s still the primary filters being behind us. Anything up to human levels of progress that gets us down to a handful or less civilizations is a great filter we’ve passed.

There’s a vast number of required events between the organic materials required for a protocell (which is the limit of what we can see forms spontaneously) and even a modern cell, let alone a technological civilization.
We have no idea of the probability of the majority of these events, let alone their probability in total. We don’t need to suggest that there’s anything different about all the other billions of planets in our galaxy. We simply have no basis yet to assume that there should be some minimum number of worlds that reached our level or above. The only data we have for sure is: we don’t see any yet.

749

You raise some good points but I take issue with this part. The term “interstellar scale” spans quite a large range in a galaxy that’s between 100,000 to about 150,000 light-years in diameter.

Suppose that the nearest alien civilization with approximately our level of technological capability was – very optimistically – 100 light-years away. What would you expect to see in order to detect them? What could they see if they happened to be looking in precisely our direction?

I would suggest that the answer is “absolutely nothing” to both questions, and this would still be true 100 years from now when they observed today’s radio emissions from Earth. Such signals would all just be lost in galactic noise, the CMB, and intrinsic quantum mechanical limits, even assuming the aliens knew what to look for and exactly where to look for it. We have the same problem, and the farther away such technological civilizations might be, the more intractable the problem of detecting them.

I think the old adage that “absence of evidence is not evidence of absence” is especially applicable here.

750

I was thinking of scales up to a few thousand light years. On first draft I considered saying “galactic scales” but that might have implied being able to see across the zone of avoidance, or even into other galaxies.

A couple of things on that.

Firstly, it’s not so much expectation, as what could potentially be visible. I think an (incorrect) assumption sometimes made in this context, is that the Fermi paradox only concerns technology that we can envision aliens having. But of course it’s possible, indeed I would think likely, that we wouldn’t understand many of their grand projects.

Anyway, in answer to the question; anything that blocks, emits or refracts large amounts of EM radiation (as, for example, a Dyson swarm would).

In terms of what aliens looking towards earth would see, it’s unlikely that any of our 1926 technology would be detectable, so they wouldn’t know there was intelligent life here. But our atmosphere, if they could detect it, has various indicators of biological life.

Even if it is true that modern signals would be undetectable at that range, why are we talking about human levels of technological progress?
In the context of the Fermi paradox, and if we’re not positing any prior great filters, it’s necessary to explain why the signs of species millions, perhaps billions, of years of technological progress ahead of us cannot be seen. This is why the apparent lack of Dyson swarms is a meaningful observation.

751

Yes, they’re consistent with life but they’re also consistent with, um, not life. Their presence doesn’t really say anything one way or the other about there being life. Venus and Mars have carbon dioxide in their atmospheres, Venus far more than Earth, and they’re both dead worlds. In fact, Venus is positively hostile to life in spite of having an atmosphere lousy with carbon dioxide and water. Titan, Saturn’s largest moon, has more methane in it’s atmosphere than Earth does and it’s likewise dead. Dimethyl sulfide has been detected in comets which, again, are dead.

As far as the Miller-Urey experiment, well, it’s irrelevant because a few amino acids and all nucleotides have been detected in interstellar clouds or comets and asteroids.

You’re framing these things in too positive way, I think. The fact is that we’ve found few planets that are about the same mass of Earth and orbit in their star’s habitable zone. You compare that number to the all the planets we haven’t found. Like, why? Why not compare that number to the total number of planets we’ve detected? It’s, as you said, at most 37 out of more than 6,300 that meet the bare minimum conditions that would allow life like our own to develop.

You’re indulging in a bit of motte-and-bailey fallacy. You lay out a case for why simple life might be extremely common even in our galaxy then pivot to that being a case for the existence of technological life. Those are different things. It took more than 3 billion years for life on Earth to become technological life. You say that it’s inconceivable that a planet that’s like our own wouldn’t develop life but ignore that it took until three-fourths into it’s habitable period for technological life to appear. If it takes billions of years for potentially starfaring life to appear once any life appears, then it’s not really that weird that any one point in time there would only be a few in a galaxy the size of ours or indeed that we are among the first or very first in the Milky Way.

It’s also possible that we are the only potentially starfaring life-form that the Solar System will produce. We are the only human species left. The animals most closely related to us are dying out. There’s only about another billion years for a new potentially starfaring species to evolve if we die out before we become one. It’s definitely within the realm of possibility that if we don’t travel the stars, then no being from this system will.

752

And if Earth’s history is any example, maybe life almost always gets snuffed out (at least back to the microbe level) by repeated catastrophes. Humanity having arisen only because our ancestors managed to drunkenly teeter on the brink of extinction all the way back to the Snowball Earth.

753

There’s been some speculation that intelligent technological dinos could have arisen at some point, but other pundits have indicated that they may have fundamental biological constraints preventing such. Their environment was radically different than the one which gave rise to us as well (you may not have the luxury to develop a large brain when T-Rex’es and Velociraptors are constantly hunting you).

The thing that is striking about our now-extinct Homo cousins is that none of them ever apparently developed bows and arrows on their own, or even used captured ones from sapiens sapiens. It may be that we were a truly improbable species indeed, and that if we hadn’t come along, today if you were an alien looking down, you would yeah see a bunch of upright hominids walking around, but with cultures as such that have been minimal and static for hundreds of thousands of years.

754

Avi Loeb is an interesting figure - an actual Harvard theoretical physicist, yet kooky enough to be a little problematic. I tried listening to him on a podcast once and couldn’t get past the first ten minutes which was him bragging about all his military experience and other stuff.

My sense is that he does understand the counter arguments to some of his more peculiar proclamations, but he’s become very invested in getting attention by saying things that excite the media and general public.

755

Because they are harder to detect.
The fact that most of the exoplanets we’ve detected have been jupiter-sized worlds orbiting very closely to relatively dim stars is due to the difficulty of detecting exoplanets rather than that being a representative sample (for all we know).
The picture will likely change a lot with the launch of the habitable worlds observatory, but that’s more than a decade away.

In the meantime, it doesn’t seem very plausible that in itself this is going to be a significant filter. Right now even the most pessimistic estimates for earthlike planets in the milky way is in the hundreds of millions.

We don’t know that. There doesn’t appear to be multicellular life on the surface, that’s all we can say.

A billion years is a long time though. If we are representative, then there’s plenty of time for a species to evolve around a G type star and have colonized the whole galaxy.

To be clear: I think we’re likely alone but I base that only on the lack of observation and that this is a situation where the absence of evidence *is* significant. I think arguments of why we should expect few other sentient species / why there hasn’t been enough time, are not very compelling.

756

Because Titan has a reducing atmosphere it is often touted as analogous to pre-biotic Earth. But given how cold it is and therefore the necessity of postulating substitutes for liquid water, with all the dubiousness that implies, I doubt we’ll find anything we would call life on Titan. It’s just possible that we’ll find some fascinating organic chemistry there that will offer important clues to the riddle of abiogenesis, but I think that’s about it.

757

Theres about 10^24 planets in the observable universe. When you apply all the different factors in the drake equation, the number that can support intelligent life shrinks pretty dramatically.

Like phosphorus. The vast majority of planets supposedly do not have usable phosphorus, as a result life can’t really evolve without this.

Or the water level on a planet. There is a very narrow range of how much water there can be on a planet’s surface. Too much and the entire planet is an ocean. too little and the planet is a desert.

Theres endless other bottlenecks. An intelligent civilization could evolve but if it doesn’t have a geothermically active core, then the crust may not have pockets of elements that can be easily mined to create technology. Or it could have no fossil fuels, which would make it far harder to have an industrial revolution.

Or take humans. We and chimps separated from a common ancestor about 6 million years ago. For the first 3 million years of our divergence, our brains didn’t grow and were stable at about 450cc. However about 3 million years ago, a land bridge in Panama formed between central America and South America. This land bridge changed global climate and weather patterns. This caused far less rainfall in Africa and caused a lot of the forests to fail and become replaced by grasslands. Our ancestors developed bigger brains to cope with this new environment, and over the course of the last 3 million years our brains grew from 450cc to 1400cc. Had there never been a land bridge in panama connecting north America and South America, maybe the climate never would’ve changed in Africa and we’d still be as intelligent as chimpanzees.

10^24 is a big number, but if one filter only has a 10% chance of passing, and another filter only has a 1% chance of passing, etc etc then the more filters you add the more narrow the number of planets that can harbor intelligent life that can create advanced technology. There’s probably lots of other filters we don’t even know about yet or we just take them for granted. Like how our atmosphere has a negative feedback mechanism instead of a positive feedback mechanism like venus and mars had which destroyed the atmosphere capable of supporting life.

The point is that if you have 24 different bottlenecks, and only 10% of planets pass each bottleneck, and those numbers aren’t dependent on each other, that would theoretically mean only 1 planet in the universe is capable of harboring intelligent life.

However another thing to keep in mind is how young the universe is. 13.8 billion years sounds old, but the universe will have stars for 100 trillion years. the universe won’t reach peak life formation years until 1 trillion years from now, when metal rich planets orbiting stable stars are far more common. Also supposedly gamma rays sterilized the universe constantly until 5 billion years ago.

So the fact that intelligent life has evolved so early in the universe could imply that intelligent life will be very common in the universe, its just that the universe is very young and we are among the first ones. Maybe that is the true great filter, how young the universe is.

However even if humans never master FTL travel, we will have probably settled the entire galaxy within a few million years.

758

But we may never know that we did so.
We send a ship out to colonize another planet, but they cannot reasonably communicate with us that they reached their destination, so we have no idea if they were successful. How many times can we do this before the people rise up and say “I am not getting within a mile of your ship until there is some evidence that this isn’t a suicide mission!”?

759

Even if we did spread that far, those people wouldn’t be us any longer.

Several million years and tens of thousands of light years of separation? Not only would our descendants be in no way the same culture, they wouldn’t be the same species. Or the same cultures and species as each other.

760

No, but they would all be intelligent civilizations. Also evolution by natural selection wouldn’t apply at that point, it would be engineering ourselves to achieve various goals since survival and reproduction would be all but guaranteed with things like artificial wombs.

761

Maybe.

Natural selection’s still going to get in there. Whatever a species is trying to accomplish by engineering, actual survival is going to sometimes depend on something unexpected, and there would still undoubtedly be unintended consequences of the engineering.

Even presuming that the rest of your scenario happens.

762

Offspring thread this morning about the Drake Equation:

763

I’m sure we can go faster than the Voyager. I used it as an example because we know it’s fast, and it’s a good thing to understand how far away everything is. I think a lot of people don’t understand how much empty space there is in space.

764

Oops, that was supposed to be a reply

766

FWIW: a recent paper on the abiogenesis riddle suggesting that while all life (that we know of) shares a common genetic code, apparently bacteria and archaea have fundamentally different enzymic processes to achieve the same metabolic goals. Meaning that they may have split as far back as the not-quite-alive proto-cell stage.