Also, the article seems to use "our galaxy" and "the universe" as interchangeable terms, which of course they are not.

I don’t see how the Fermi paradox is a paradox: given the distances involved and what we know about the speed of light, an alien civilization would have had to develop a very long time ago in order to send signals that we would be able to detect today. Just because, maybe, no civilization was able to do that a billion years ago doesn’t mean nothing happened since (as you say, at least we happened).

We just don’t know.

It is simply asking basically "if the universe is teeming with life, where is it?" and by that raising both the question of whether or not the universe actually is teeming with life, and if it is, why aren't they here? It reduces to an actual paradox only if you assume an answer to one part (the amount of life) that isn't reasonably compatible with the second part (why we haven't seen evidence of it) without a reasonable explanation.

That it simply on average takes too long for us to have seen evidence yet is in fact one of the many suggested solutions.

But overall the point of the Fermi paradox is that the problem if why we don't see aliens is two-pronged: They might never develop, or just not have developed yet, to a sufficient stage. But it's also possible they do, but that something else prevents them from contacting us.

Thus the idea of "great filters" for example. E.g. maybe the universe is full of life, but it's exceedingly rare for it to survive long enough to be able to make contact without being destroyed. Maybe the odds of getting killed off by asteroids is too high. Maybe war takes out most that get to a certain level. Maybe someone out there takes pot-shots at anyone sticking their head out? Maybe some galactic events sterilises large swathes of space too often? (intense gamma bursts have been raised as one possibility)

As well as many other options. E.g. maybe we're quarantined? Maybe we're in a simulation, and simulating aliens just isn't part of the program?

I think this is a misunderstanding of the use of the word "paradox". Informally, people use "paradox" like it means "contradiction" when in actuality it means "APPARENT contradiction". See, e.g., https://en.wikipedia.org/wiki/Paradox

> A paradox is a statement that, despite apparently sound reasoning from true premises, leads to an apparently self-contradictory or logically unacceptable conclusion.

The Fermi paradox is indeed an apparent contradiction, whether or not it is an actual contradiction.

The same holds for many, if not almost all uses of the word "paradox" in standard literature. For example, Zeno's Paradox is not a contradiction, we've resolved it (an infinite sum of decreasing values can add up to a finite number), and yet it is still a paradox.

(For a more precise classification, see e.g. Quine's classification of Paradoxes)

One of the crazier things I've heard recently is that the time between the present and the Tyrannosaurus Rex [1] (68-66 million years) is less than the time between the T-Rex and the Brontosaurus [2] (156-147 million years ago, or 79 million years before the T-Rex).

[1] https://en.wikipedia.org/wiki/Tyrannosaurus

[2] https://en.wikipedia.org/wiki/Brontosaurus

Really on it's own intelligence does not change much. You need both long term food storage and fire to really advance.

But no other (non-extinct) species can start a fire.

1. https://srfoundation.blogspot.com/2009/01/other-animals-with...

In particular it’s accepted in the field (I believe) that animal languages are not generative, which is to say they do not provide for production of new forms over time. Anything an animal speakes has already been spoken before because the possible set of valid sentences is strangled by lack of variability in the syntax. Intuitively, and this is where I’m going off the rails, I feel that generativity and Turing-completeness are near the same thing - they can describe something that is yet to be. Non generative language can only describe what has already been. That is constructing a new world requires description of the machinery operating that new world, whereas describing an old world you can lean on prior knowledge of the speaker and make do with a much poorer descriptive facility.

https://hubpages.com/education/Language-A-Brief-Treatment

There was a linguist who brought up those five key attributes of human language as being crucial, I can’t find his name right now :(

And I did not say that animals don’t use language. Or did I?

What I mean to say is that there is a dramatic difference in expressive power, in particular in being able to convey a plan of action. Animal language can convey “there is a tiger south-south-west 15 meters, run for your life”. But it can’t express “if there is a tiger run left, if there are two tigers run to the right” unless the animals have previously encountered that situation and survived unwittingly executing this plan of action.

To me this is akin to the difference between Turing complete and subturing languages, in that the expresssive power is so very different.

Do the skills get more advanced with each generation?

Note it's not unique to dolphin as some cat species for example are known to bring back wounded prey for their young to practice with.

What would be interesting is if we found intelligent (or any!) life that evolved completely independently from our own origins.

Are you sure?I seem to recall watching random youtube videos a few weeks / months back and saw something on octopi I vaguely recall it saying they developed intelligence differently. Although probably I have got it muddled with something else :)

- Presume that even with something like travel at 1% o speed of light, the Milky Way is colonizable in a couple of million years.

- Presume that we are not special at all and there exist more technological advanced civilizations that predate us by at least a couple million years

- Presume such a large scale colonization would be easy to observe

If you accept the 3 presuppositions, the only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely).

Or you can choose to attack any of the presuppositions, but that's also very hard in my humble oppinion.

You're not assuming that it is, you're assuming that if it can be, it must be.

Which assumes that every part of the milky way is equally amenable to colonization, as if the galaxy were merely points laid out on a Cartesian grid, and that any species capable of colonizing one star must continue to colonize them all.

You must consider the case of technologically advanced species incapable of colonizing other stars, and technologically advanced species capable of colonizing other stars, but unwilling to do so on a large scale, or attempts at large scale colonization which fail across a scale of millions of years or even attempts to hide the obvious presence of such colonization from observers.

>Presume that we are not special at all and there exist more technological advanced civilizations that predate us by at least a couple million years

Ok.

>Presume such a large scale colonization would be easy to observe

By humans, given that we only recently became aware that extrasolar planets are even a thing, and have only been studying the universe with anything but optical telescopes for less than a century, and don't even know what the signs of "large scale colonization" would look like. No. Why?

>Or you can choose to attack any of the presuppositions, but that's also very hard in my humble oppinion.

Any argument can seem airtight when you refuse to consider more than a single case to be valid.

1. We're really not.

2. Solar panels obey the inverse square law. Right now, we can't even use solar panels to power probes beyond the orbit of Jupiter - let alone drive an energy-hungry ion engine.

3. Even with an ion engine, you need fuel to thrust.

4. Even if we could send them, they'd need incredibly power-hungry antennas to transmit any useful data back. See 2.

People say things like 'only 1% of c' as if it's trivial. It's only 1%! It's also 3,000 km/s. No man-made machine has ever gone faster then 16 km/s. If we tried really hard, we might hit 1% of 1% of C.

And then it would still take that probe 400 years to visit our nearest star. 10 million years to cross the galaxy.

We can't, though.

We literally have no idea what a >10^6 more advanced civ would look like.

There’s a kind of parochialism about these arguments. They seem to assume that aliens will be flying around the galaxy communicating by radio in big metal boxes or giant rocket powered rocks looking for planets to xenoform.

But in the same way that ants can’t see a human city around them, it’s possible humans will see no evidence of an advanced civ that isn’t doing any of the things we expect technology to do.

Yep. We don't even have much of a clue about what our own civilization will look like a few hundred years from now, it seems insane to pretend we would know what a far more advanced alien civilization would look like. Imagine showing someone from a thousand years ago a picture of suburbia and them saying, "Nope, this place must be abandoned...no one is growing crops on the land, there are no wells around, deer and other wildlife are walking around houses without being hunted. Must be no humans there." Even just a few decades ago a lot of people thought we would be building cities under the seas by now (hey, maybe not everyone would do it - but with billions of humans, it would only take a few splinter groups).

It's also worth pointing out that even a civilization at our level existing at the nearest star would be undetectable to us in most circumstances (even in the extremely unlikely event that the timing matched up).

Meaning: likes to explore, accumulate knowledge/understanding, harness the laws of physics for its own betterment/pleasure.

I have two takes on it:

1) We don't know the possible implication of new discoveries. Well, actually we get some glimpse of it, for example with nuclear or biological weapons around, it is fairly easy to wipe out a large part of the population. The more advanced the technology becomes it seems there is a higher chance of it blowing up in our faces and us destroying ourselves. So the galaxy could be colonizable in a few million years, but any civilization headed closer to that ability, gets closer (and faster) to its own destruction as well.

> The only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely).

Given my other pessimistic take on it (1), I would say it likely there were (are) quite a few technologically advanced species, but they've wiped themselves out or will do so before the reach the ability to colonize planets in other galaxies.

2) Another take on it is these civilization have to share the same physics and chemistry that we do. And maybe there is just a limit that gets achieved and long term colonization or fast travel is just no possible. That is there are no shortcuts like wormholes, Alcubierre drives, antigravity and other such things. We've been used to seeing huge leaps in technology and science in the last 1000 years, so it's tempting to extrapolate and but maybe we are close to reaching a wall. So there are quite a few civilizations out there but they've flown probes in their own start system, now developed internet and are sharing pictures of alien cats, hanging out on their version of Facebook and watching their alien Netflix, and of course discussing their equivalent of Fermi's Paradox on online forums. All without a chance of ever leaving their neighborhood.

2) 1% of the speed of light is very achievable even with today's technology, it's just the(irrational) fear of nuclear reactors in space and lack of political will that keeps us from exploring interstellar travel.

Why? See my other post. You provide no evidence for this claim. We currently have no plans to colonize the galaxy so why would other "advanced" civilization get this crazy idea? Birth control was invented in the 60s already.

I'm not so sure. The only difference between a colony ship and a kinetic world destroyer is that the colony ship slows down before it reaches its destination

2. On straight lines perhaps with ages long acceleration. Planning such a course might well take more than nuclear reactor, no?

There are other proposed schemes to travel at ~light speeds - light sails, nuclear fragment rockets, but I'd bet on nuclear fusion in the not so distant future.

Faster than light travel may be off the table, but I see no reason why nuclear energy alone could not get us "close" to the speed of light in the next centuries or so.

- Cyclical cultures, filters, and large time frames are not properly taken into account. If you take them into account, colonization of the whole Milky Way seems unlikely.

- Life could occur only very rarely.

So basically, the missing premise is that if all of your conditions are fulfilled, then a civilization will colonize the Milky Way and has done so far enough in the past that we can easily observe it. There is no reason to think that.

Now here is the bad news: Even if we accept your original line of thought, that would still be entirely compatible with the view that some intelligent species is just about to colonize the Milky Way and just in front of our doorstep...

I'm just kidding, of course. Like others have pointed out, this "research" is almost entirely based on speculation. We don't even know how likely life would arise if all conditions for life are fulfilled, let alone whether that also means that intelligent life will arise or with which likelihood. We know nothing.

The only thing that we can say with relative certainty according to our current knowledge is that if intelligent life develops with high probability whenever the conditions for life are met, then it is a bit harder to detect then we thought or Xenoarchaeology will be booming some day in the future.

This just isn't true. There are current value and belief systems, even ones held by people with a relative large amount of political and economic power, that do in fact recommend such an expansion (someday).

https://d33wubrfki0l68.cloudfront.net/0784d9d63336606d4ca025...

This may be at least in part due to the shifting of energy-intensive industries to countries like China, but it does show that countries can continue to grow their GDP (per capita) while dropping their energy usage per capita, which bodes well for the future.

There are definitely reasons to believe that.

You certainly don't want to be in a galaxy where someone else does it first: if you can't coëxist with them, you're probably going to be wiped out.

Large-scale projects like Dyson spheres would, I imagine, require vast resources taken from multiple solar systems. So even if you're not colonizing every star, you're probably mining from many of them.

Anyway, just a couple of reasons that spring to mind. Given our data set is exactly one intelligent civilization it's hard to draw conclusions, but expansionist pressure seems to be the safe assumption.

Well, since the problem of even figuring out if you are alone is nontrivial why would you opt to do such a astronomical operation because of a hypothetical? We most certainly would not.

Why the pessimism? We do know that we currently do not have any plans for massive expansion through the whole Milky Way, and even if we made such plans, we would definitely include safe zones and ample space for other species we might encounter. If we are that good, maybe other species are no less good? That's not an unreasonable assumption, though ultimately anthropocentric, of course.

But the point I was trying to make was different. I should have said "There is not enough reason". There are just as many hypothetical reasons for as there are against. We really don't know.

>expansionist pressure seems to be the safe assumption.

Then again, the universe is very, very large...

We haven't really done such a great job on or own planet. What makes you think would do any better in the stars?

Possibility (b) seems at least somewhat unlikely, given that we (at least) evolved over millions of years to the very particular conditions of Earth 0. So finding somewhere 'better' would likely involve some gene-gineering to adapt, and maybe involve a shallower gravity well than we currently inhabit.

Possibility (a) is a really good reason to spread out a bit, but you likely don't need more than a few insurance policies... Certainly there's no need to aggressively conquer the entire galaxy: Given difficulties of communication and transport over long distances, there's likely some real question of what 'conquer' would even mean...

It occurs to me that it would be interesting to look into how much stars drift apart from one another over the course of time involved in getting from one to another. Consider that the launch window for mars comes up once every two years; what are the launch windows like for stars, where travel might take hundreds or thousands of years? Maybe it takes a thousand years to get a scouting run done, and then it's infeasible to follow up with an actual colony ship...

Pretty much every star system becomes habitable if you don't have to care about whether or not it has a planet that meets your species's environmental needs.

This is mainly because humans are adapted to live standing upright in gravitational conditions, with a pressure gradient across their body. If you take animals which are not adapted for this (e.g. large invertebrates from the sea) they're crushed by their own weight when taken out of a buoyant environment.

Even so, that doesn't make it infeasible to live in space for long periods of time. Artificial gravity can be generated with a centrifuge.

However, I would say it's likely that gravity is necessary for life similar to what we are familiar with to form in the first place. Earth's gravity facilitates the existence of dense fluids, allowing for the complex reactions of primordial life.

A WW1 wireless operator of only 100 years ago wouldn't be able to detect modern spread-spectrum military radios, let alone separate encrypted signals from the noise.

Why should we suppose we could detect a civilisation two million years more advanced?

Maybe every advanced civilisation ends up turning inwards to simulations rather than outwards. Maybe there are aliens all around us, but we can't notice them, because we're living in someones phone, in the latest top-hit: SimHumans5000.

There's quite literally an infinite number of possibilities where we're not alone after all, and part of the problem is that we don't just not know the values to plug into the relevant probability calculations, but we don't even know all the variables.

For a civilization living for trillions upon trilions of years inside a simulation, intergalactic latancy is just a blink of an eye -- they have no reason not to distribute their simulation across the galaxy.

All of the burning stars would be just lost time for such a civilization

Not saying I believe this, but are we sure they haven’t? There’s a bunch of fringe people who believe it did happen.

Or they have a culture/value system that doesn't care about sprawling out to occupy as much space as possible. Why is it presumed that advanced alien civilizations would use their technology to maximize, rather than minimize their ecological footprint?

It stands to reason that environmental degradation could be one of the major filtering mechanisms for advanced life and any civilization that clears the filter will need to have fostered sustainable, symbiotic production systems rather than extractive ones.

Unless we're talking about hive-minds I don't think this premise holds at all.

Civilizations that culturally value domination and expansion can dominate within their own civilization much more easily than casting out into space to find alien ones. They're more likely to destroy themselves than others.

Why is this unlikely? The likelihood of intelligent life emerging that gets far enough in their development to try to colonize a galaxy might be so low that it could easily only be once per galaxy or even rarer than that.

Think about how long multicellular life has existed on this planet and yet a very narrow band ended up 'becoming intelligent' and even then it took a long time before industrialization that finally propelled us forward.

> Presume such a large scale colonization would be easy to observe

There is no reason why this should be true.

Or even further where they can effectively gather all the energy from their star?

The only reasons to branch out is because your own star is dying or your population (demand for energy) is growing too fast.

Essentially I think that population control is a big hurdle for any advanced species. Which would be the main drive for colonizing space. But at what rate does it grow? After their first star, how long does it take for the next one to be used fully.

The whole Fermi Paradox reasoning is flawed, because the assumptions are flawed.

We will observe ourselves, no matter how it is unlikely for us to exist. We may not be special, but highly improbable and therefore the first and the only.

But such explanation isn't that interesting.

Imagine you're sitting in a prison cell, and you've been told you're going to be executed by a firing squad of a dozen expert marksmen, who will shoot you from a distance of only a few feet away.

You're led out of your cell, tied to a stake, the marksmen line up, they raise their rifles and aim at you, and you hear the mass bang of their simultaneous firing. And... you discover you are unharmed. All twelve expert marksmen completely missed you, at close range!

The anthropic argument says you should be completely unsurprised; after all, the only way for you to be observing the marksmen now is if they all missed, so the probability of them having missed, given that you are observing them, is 1. We should not be surprised by something which has probability 1.

While this is trivially true, it is also utterly unconvincing and utterly pointless. You are perfectly justified in being surprised that all the marksmen missed, and here is the equivocation: the anthropic argument tells you not to be surprised, but the thing it tells you not to be surprised at is not the thing that was actually surprising. Your prior for all the marksmen missing and leaving you completely unharmed should have been very, very low, and no amount of ex-post-facto wrangling can change that.

Or, put more simply, anthropic arguments can be used to launder any past event to a probability of 1; after all, the probability of event X having happened, given that you observed event X, is always trivially 1. But it tells you nothing useful whatsoever.

It's completely convincing to me. If you are unharmed, no single bullet hit you. Even if you've had the "prior" information like that they are "a firing squad of a dozen expert marksmen" if you are "utterly surprised" by the result it probably means that your priors simply miss something, not that it couldn't have happened at all. E.g. maybe that dozen of experts had some additional decision you didn't know about, e.g. they want to influence a regime change and agreed before that it would start with you not being harmed.

Such kind of information turns very improbable event to very probable.

More than that, even improbable events do happen all the time. It is very improbable that I personally will never win a huge prize on the lottery ticket, but the lotteries are intentionally made that somebody from time to time wins it. If we are a "lottery winner" and don't know anything about the rules of the lottery and the number of the participants, we just can't conclude anything else about the lottery probabilities than that we got what we got. As long as more different universes are possible, no matter how we think our is improbable, as long as we have information only about our state we don't have to be able to conclude more than that we have what we have.

So there's no value is empty talk, we know more only by moving the boundaries of what we can measure. We have actually have learned amazingly much about the Universe, but there's no "guaranteed first prize win" ("learning everything") in these endeavors.

The issue is, as I pointed out, that it works for anything and produces the same result. Anthropic arguments literally consist of stating that "P(A|A) = 1". Which of course is true, but what does that actually tell you?

If you find it used "for anything" you can point to such cases where it is improperly used. When it is used for the case where we genuinely don't have enough information to claim any "probability" then it is simply a more colorful statement of that fact: that there is really nothing actually measured and known based on which any other statement than "we know exactly one example that such outcome is possible because we live in this outcome" is honestly impossible.

You may psychologically not like that fact, but when there is no more data, it has to be admitted that there is no more data to claim anything else than that. Maybe the following can help you: Imagine you find yourself in the middle of the desert, in all directions you see only sand. People today know that every desert ends somewhere, but that's based on the fact that enough people don't live in the middle of the desert, so you must imagine that you are the very first person that ever existed and that you find yourself in the middle of the desert. While moving around the place, looking for any signs, you may or may not find the proofs about something else in the distance. But you can genuinely be in the phase where you see only sand and can't conclude anything about the existence of, for example, the rivers or the sees.

The way I see it, the message is not "give up any attempt to learn more about the Universe you are in" the message should be "sitting around and inventing stories doesn't help: you have to move and actively search to find out more." The humanity was for a while good in inventing stories that sounded comforting but were completely unsupported, but we have actually in the last 100 years found the exact and provable signs about much more of our Universe than ever in our history: think about it: 100 years ago nobody knew that there exists anything more than one galaxy: ours. Today we can actually claim that there are one hundred billion galaxies in our Universe. And that most of them move away from ours. And we can calculate very precisely when all of them were on "one place": around 13.8 billion years ago. I'm always so glad that I live in this point of history to be even able to learn about that.(1)

If you want more answers, support the science which looks for the answers -- there have to be serious investments in the real experiments for finding out more because easily reachable information is already found. And the humanity sadly invests more in military equipment than in science. And a lot of what we've learned we have learned from the projects that are less "sexy": you don't have to have many humans walking on the moon to learn more about the moon, for example: using robotic probes is all that we need today.

But you should also not realistically expect the answers that are behind the limits of what's reachable for us. In the example of the first human in the desert, he can reach some land behind the desert, but being just a first human, walking there, he surely won't walk on the moon. He can however look at the moon and the changes in the shades from the sun on different places on the Earth and develop the idea that the Earth is also round. And that's how scientific discovery works: carefully doing enough experiments to be able to conclude something that was before unknown.

1) to reestablish the perspective for the day-to-day events, search for "Everything Is Amazing And Nobody Is Happy"

I should mention at this point that my degree is in philosophy, and my thesis was on the argument from design post-Darwin. Much of it consisted of exploring how various people -- not at all religious people! -- have been struck by the seeming improbability of our universe full of complex structured arrangements of matter and energy (including us) and sought explanations beyond "God must have done it". I had to read Barrow and Tipler's door-stopper of a book on the anthropic principle as part of that, along with criticisms of anthropic arguments, and came away convinced that the anthropic principle is at best a tautology possessing no explanatory power.

That explains, thank you.

> Anthropic "answers" are used precisely to tell people they should "give up any attempt to learn more".

I don’t see any support for that claim and I claim the opposite and I’ve already elaborated my claim.

We know of nothing -- yet -- to suggest those particular values were necessary. We know that even tiny changes to those values produce a very different universe in which significant accumulations of matter and energy don't occur.

So the particular universe we observe around us appears to be staggeringly improbable.

The anthropic argument says "well, we observe it, therefore it happened, therefore don't bother digging any more because that explains that". And it's incredibly unsatisfying.

(I should note Barrow and Tipler did go further and proposed a variety of anthropic principles, some of which border on religious, but I'm talking here mainly about the base anthropic argument, as trotted out way back at the start of this comment chain)

There are people who look for deeper theories in which the particular conditions we observe do fall out as necessary. There are people who work on multiverse theories where it's inevitable that at least some universes will have conditions amenable to complex accumulations of matter (and thus to conscious observers). There are even people who've gone way out there proposing theories of natural selection applied at the level of whole universes, where arrangements of the constants that help a universe "reproduce" more (usually through forming singularities) are also coincidentally ones which require complex accumulations of matter.

There's a whole wealth of things out there to think about and explore. But anthropic arguments tell us to just shrug our shoulders, say it's totally unsurprising that a seemingly-so-unlikely thing happened, and stop trying to explore.

(and, of course, they do it in a away that's suspect from both a logical and a probability standpoint)

Says who? Anybody who knows what he really talks about will tell you that there aren’t any real physical data to claim any “probability” at all to the physical constants we observe. Let me repeat: you can’t use “probability” for that in mathematical or physical sense. That’s all.

Also please quote who actually says that doing experiments to learn more should not be done. If somebody just says that some philosophers talk about something they don’t undestand, and that there isn’t enough data from the experiments we’ve already done to say more, that’s what I can imagine.

Ah, you've got me. Literally no-one in the history of humanity has ever suggested that the particular configuration of our universe, suitable for the formation of complex accumulations of matter, is surprising, improbable or unlikely. I completely fabricated that notion, which had never before been expressed by any person, from whole cloth.

Or, you know... https://en.wikipedia.org/wiki/Fine-tuned_Universe for an introduction and some bibliography. If and when you eventually come round to the idea that perhaps this is something people have thought, talked, and argued about, we can continue from there, but I'm having an extremely difficult time assuming good faith on your part right now.

Incidentally, some of your other questions about whether anyone has ever at any point in history said or done something with respect to anthropic arguments will be touched on even in that introductory Wikipedia article.

“Fine tuned” claimed by some people is currently only a metaphysical claim: “IF we believe that the physical constants can take any value, then only some exact constants define the Universe with the characteristics like ours.” Note if. There’s no real evidence for that belief, that all the values are/were actually possible. We don’t know if there’s something outside of the results of our current experiments that can support such claim, but given what we exactly know, there’s also no real reason to believe that the other constants were possible.

Note: we also have absolutely zero of exact evidence that multiverses exist. So what we actually have is only this Universe of ours, with only the constants that we observe.

To paraphrase one joke, if you only saw only one sheep, looking black, through you window in your whole life, moving from left to right, the only valid mathematical and physical claim you can make is "there exists at least one sheep there, whose one side is black." Nothing more unless you make more observations. It's basic scientific literacy.

Or to paraphrase another example: you've just went to your search machine and typed "seinfeld license plate picture." You've received the image of the plate on which is "new york assman." Then you go around saying "imagine, from all combinations that I can imagine that the license plates can have, I've got exactly this one. It's so improbable." No, it isn't. Sorry to burst your bubble. Now imagine a relaxed experiment: You live in New York, go outside your door, wait for the first car to pass by. You never saw any license plate in your life, or got any information how they are issued. Then you go out and see the license plate "BGY 3891." You say again "oh look, from all the license plates in New York, if I assume they can have 7 letters and digits, how 'improbable' it is for me to see exactly BGY 3891." Again, in that experiment, there's no mathematical probability involved. You simply observed one license plate. You can invent "fine tuning" story about it, of course: imagine, if the Earth wouldn't exist, there would be no humans, there would be no cars, there would be no license plates, there would be no me making the experiment. Yes. But given all that actually exists, and that you actually went and observed one plate, it's simply the first (the only) license plate you saw.

I've also generated a number of random bytes, hex encoded, which can be observed as one big number:

4ad41f5650977f991bb1b1a12a29f1cefe1e6ffede 8bb7d71ab0199832ca60345236ca343a0e3aff02fc 8b8a6d24aef012b3b15e688f3bcd7d82a77e3f0e35 6745b1a6d4bcd1fc90ff4e3ee273cb1f0989fa140a b0a932252e9bf2ac3198b3bb7446a738d252233861 8ba380465181f544d900f8cc20b1544b6022f05bc5 266917d2ef5a8f6afe41245862b66c3c3f1874df84 c3bf6c4362455e2c4c66d08be68c1b1a0ab073619a c5626e7719c4bc75d96ebb42daee9f147fe60aae71 85a482939c62ded6e05ac9728e7edf65c97c868535 63f697a45e75d325824e4bea051c1c3781fa284d86

And wow there are 10 to 556 (1 with 556 zeroes) possible numbers that big, and I've got exactly that one! Isn't it amazing? Hint: it isn't.

I provided some examples.

You obviously don't agree with the argument, but not that long ago you were pretty obviously questioning whether anyone had ever even made the argument. Did you make sure to call and check for buried cables before digging the new holes to move those goalposts into?

I questioned the use of "improbable" by anybody who knows what "improbable" in mathematical sense means and uses it in that way about the "universe we observe" giving any exact evidence. I still haven't seen such an example. I don't care about these who don't want to even understand what they talk about, or those who make claims with no actual support. My question was with the goal to point to exactly that: those who claim actually don't have any physical evidence for their claims. The wikipedia article mentions "theists," "philosophers," "theologians" etc. Some scientists also write something on the subject but not with the actual scientific support, just in their role of some of the above.

The number of random people claiming something doesn't make the claim more true. The validity of physical claims can be evaluated only based on the physical evidence, and only processed according to the mathematical rules that are valid in our Universe. Anything else is not physics.

Once in a time, there was one constant that physicists talked about as "special" (in that non-physical sense) being at that moment "exactly" 137, according to the best measurements of the moment. It was measured much more precisely since. 137.0359. Then 137.03599. Then 137.035999. Wow, isn't it something special? Maybe it's exactly 137.036? Does it have some special "meaning"? But now we know using much more precise measurements that it's 137.035999139... So it turned out to be quite unspectacular.

What is spectacular is that we have so precise measurements today: for that constant we are uncertain only for "0.23 parts per billion." And by the way, whichever computer or mobile phone you use now, the CPU in it has the basis of 99.9999999% pure silicon. That's also spectacular, it's one grain (i.e. 1 gram) of dirt in 1000 tons of silicon (at least 12 railroad cars needed)! And because it is also a result of a lot of hard work, and available to everybody including "theists" and "philosophers."

> But it tells you nothing useful whatsoever.

Exactly. Existence of our civilization is not an evidence for the high probability of life emergence, nor for the low probability of that.

And the lack of observations of extraterrestrial civilizations is evidence for low probability of life emergence.

Rigorously speaking, probabilities are not attributed to singular events, but to sets (possibly, in the discrete case, single-element sets such as {heads}, {tails}).

To be even more precise: a sigma-algebra is a concept of set-of-all-sets that avoids continuous-case paradoxes through technical stuff you can ignore.

A filtration is a decreasing sequence of sigma algebras: for example, if your event space is the six numbers a die might show, you could have

F(0) = { {}, {die number is odd}, {die number is even}}

and

F(1) = { {}, {die number is 1},...{die number is 6}, {die number is 1 or 2},...} (a sigma algebra is closed under intersections)

What this means is that earlier probabilities are defined on coarser spaces of sets of events as compared to later probabilities. This is how you get dynamic stochastic processes that don't look into the future.

Imagine an intergalactic astro physicist raising three eye brows, wondering, "only?!"

The point is that, if you rolled the dice on a new universe that had a decent chance of producing something like our Earth, there are lots of sources of variance, such that the "95% confidence interval" during which something like us might have evolved is probably hundreds of millions of years wide. Given that, the chance that two independent civilizations would reach a particular level of technological development during the same million-year period is less than 1%.

An advanced civilization has antennas that don't waste energy by beaming signals into space.

But, I'm not sure if the signals will appear to be from intelligence though.

I didn't find that. For example, there is the following paragraph; it clearly distinguishes between our galaxy and the universe:

> In the end, the team’s conclusions do not mean that humanity is alone in the Universe, or that the odds of finding evidence of extra-terrestrial civilizations (both past and present) is unlikely. Instead, it simply means that we can say with greater confidence – based on what we know – that humanity is most likely the only intelligent species in the Milky Way Galaxy at present.

The Milky Way is only 100,000 light years across, which is a blink of an eye in geological time.

A different matter is "too short lived", which is taken into account in the Drake equation (the last factor, L).

This doesn't mean we are alone, given the uncertainties. It just means that if we don't see anyone, we don't have to come up with all sorts of crazy scenarios to resolve the paradox, as people often do.

(If you find it implausible that we're the only ones, note we could also be one of just a few, separated by billions of light years, in which case we still wouldn't see anyone.)

We "figured out" unconstrained growth could be catastrophic a couple of hundred years ago at the very least. And in fact we guessed prematurely as technology extended the date of the catastrophe multiple times.

So we then bounced into a phase of overconfidence whereby some of us decided that technology could overcome all problems.

(Arguably we are still in this phase - or at least some of us hope this turns out to be true as we've lost hope in the possibility of political solutions to problems caused by growth)

In fact, you can sum up the problem as a pithy slogan: Doomsday predictions are always wrong. Until they aren't.

Someone should make T-shirts.

Unless your fellow technological life is within a few hundred light years, communication of any kind starts to look like throwing messages in bottles. Of course the closer your target is, the less wistfully academic it is. If Proxima Centauri had a planet with a civilization like ours, you’d have to consider what they could do other than just talk. At that point, the issue switches from insane time scales rendering the whole process moot, to potential forms of dark forest detente.

The discussion at that time assumed vanishingly little would survive that long - potentially just a thin layer of radiation from atmospheric nuclear testing that would be hard to place in time with accuracy more than +/- a couple million years.

I say this more as a thought experiment than a serious suggestion, but if a "technologically advanced" civilization did previously exist on earth, 100+ million years ago, what evidence of it would we expect to find at this point?

All of that assumes that the arc of technology doesn’t terminate in a cosmic eyeblink after the current era, which it might. Either way, there is a sort of childish assumption that we’re always going to be as exploration-minded as we are today. If ‘c’ really is the cosmic limit, then it makes more sense to stick closer together, because any significant travel will imply either speciation, or a one-way cultural trip.

If life is constrained to a reasonable fraction of the speed of light when moving mass, and light when communicating then the universe could be teeming with life out of temporal spatial sync with each other. We might not be alone, but we’d be effectively isolated, and still see ourselves as being alone. It’s only under the assumptions of unlimited growth and expansion that the Fermi Paradox is a paradox.

Mind you, the idea that life which is likely evolve, adapt, and develop significant technology being ultimately self-destructive a la The Filter also seems very likely. The article offers squat in rebuttal to that.

Run-away climate catastrophe, nuclear war, or alternatively, the physical impossibility of interstellar travel are not crazy scenarios that explain the paradox. They are real threats that we have put far too little into mitigating. [1][2]

[1] I think we are putting the right amount of effort into mitigating the latter.

[2] A few smart people are playing with mental what-if toys like 'If we could send 100,000 people to a planet which has already suffered a run-away climate catastrophe!' The rest of us are digging our heels in, and finding every excuse to do nothing.

You state this like it is a problem. I think it's more like a feature?

My take on the main point of the paper: it is commonplace to derive probabilities for being alone in the universe by plugging in point estimates into Drake Equation, but one should take into account that, in fact, we have lots uncertainty in our estimates for the parameters, and without quantifying that uncertainty, the Drake's Equation indeed will produce biased estimates. And if we quantify the uncertainty, we end up with wide distributions (that have some of their mass near zero).

edit. Your point about N = 1 is interesting, though.

edit2. Concerning N = 1: They don't elaborate on it in writing, but if I'm reading the sec 4.0.2 correctly, they do account for our existence in their spatial Poisson update: P(no detection | N, d) = 1 - exp(-(4/3) pi d^3 lambda) = 1 - P("number of civilizations in sphere of radius d when rate is lambda" = 0) = P("number of civilizations in sphere ..." > 0).

edit3. wait, that does not make sense, does it. shouldn't P( no detection | N, d) be P("number of civilizations in sphere when rate is lambda" = 1) = (4/3) pi d^3 lambda exp(-(4/3) pi d^3 lambda), as per spatial Poisson process P(K = 1). now I'm just confused.

The anthropic principle is the correction. Observing ourselves is a prerequisite of analysis - independently of probabilities which can be any low! So it is not an "independent" observation. Otherwise we could easily say from armchair, that:

1. Probability of civilization in a certain place is extremely low

2. Universe is huge, with plenty of places

3. https://en.wikipedia.org/wiki/Poisson_limit_theorem

4. Expected number of civilizations in universe (without noticing anthropic principle): 1 (at least!)

5. So take Poisson dist. with lambda=1, as a conservative estimate

6. Probability of more than 1 civilization, if we know that there is at least 1 (again without noticing anthropic principle): P(X>1 | X>0) = P(X>1)/P(X>0) /Bayes/ = 0.718

So with around 72% probability there is a another civilization. ;)

Not to creatroll the discussion, but the probability of occurrence for each individual independent event that led up to what is life on Earth, in each branch of the tree of life, on each evolutionary path, is so low that number of planets in the Universe multiplied by all the milliseconds in the history of the Universe will not get very far toward reasonable chances. Take, for instance, a protein of 100 aminoacids. 23^100 possibilities, to put it naively, yields a quite low probability. And there a many types of proteins needed for life.

IF one knows of any study that touches seriously on this topic, I'd happily want to know and be corrected!

Overall life might be an inevitable outcome of our universe as our universe is predisposed to create carbon and life is the most efficient process of hydrating carbon we currently know off if increasing entropy is a natural lawful state of the universe it will be predisposed for creating life to serve that purpose.

That said it’s unclesr if complex and not to mention intelligent life is a predisposition or an anomaly as out of the nearly 4 billion years life existing on Earth and now it seems it started only a few 100Ms of years after the early bombardment period technological intelligence evolved so late into the game that it might have been a fluke.

Other types of intelligence exist we have pretty darn smart animals but despite many of them predating mankind and our ancestors none of them has ever evolved further.

For example if we take self replicating proteins these will self optimize to an exact letter order which would improve their ability to self replicate in the environment and this isn't conscious since the random assortment that would be better would simply over take the other types in a fairly short amount of time.

Beyond that you still have some random process of "mutation" and that is proteins that were not replicated correctly which can happen for multitude of reasons something bumped into them, temperature changed, acidity changed, random high energy cosmic ray hit them and boom one is not like the other.

If that new protein is now better at replicating in that environment whether it's because this new protein can replicate faster or is more resilient to it's environment and it degrades slower it will take over it's environment and the same holds true for the opposite as if that protein replicates slower it will eventually die out because it cannot compete faster proteins for the available raw materials and so it replicates slower until eventually it's gone.

This is the true beauty of natural selection it works on all processes even those we don't consider biological.

And as life complexity increases, so does the the complexity of the processes that make it possible. Humans are the result of a huge number of individual, albeit not all independent, events, each with a very low probability. Multiplying those probabilities, as it's required when determining the probability of occurrence of a sequence of independent events, yields numbers that are hard to event write down without special notations.

As I see it, the only way out is to postulate evolution based on other non-probabilistic evidence, and then to conclude that in spite of the low probability those events still happened.

Specific details of a given example (us, the one example we know about) are irrelevant.

In other words: take a coin, throw it 1000 times and record the results. Now calculate the probability of the exact outcome you just got. Pretty low, yet you just did it. Now ask another question -- how likely is that at least 200 of those results are heads? Pretty high.

How unlikely life is is a question of just how big the set of results qualifying as _life_ is. We are (probably) just one possible configuration.

In reality its chemical reactions. And there are only a few ways in which they happen.

Again search/combination space argument suggests there is a process that resets to 0 and moves to the last possible state incrementally, and that process repeats endlessly until a desirable state is reached, avoiding previously reached final states.

The problem with the above argument is words like 'reset', 'desirable state'.

In reality there is no 'search space'. Its really uni directional chemical reactions that go on, each one happening now was due to the reactions before. These reactions go on until you reach a set of chemicals that either just don't react with each other, or the chemical reactions just continue seemingly forever.

Out come of some these reactions could be life.

In this case if we have self replicating proteins in a puddle of amino acids then those which would replicate the best in that environment and that process would be governed by multiple factors such as what is the most "cost effective" combination and what is the most "resilient" combination that will hold up to environmental factors.

For the amino acids themselves it's not that different which ones would appear and at what ratio would also be governed by the laws of physics based on the compounds available, the make up of the solvent existing energy sources and more.

If for example you have amino acids that can survive dehydration and those who cannot then the only ones which will be left after a few cycles of that puddle drying up and filling with water will be those which can survive. Same will go for the proteins the protein which will be able to survive dehydration the best and or the proteins that would assemble and self replicate the fastest during the wet period would be the ones that are the "desirable state" as these would be the ones that survive this specific environment and process.

    Infinite monkey take 1, Atlas Srugged written? yes : no
    Infinite monkey take 2, Atlas Srugged written? yes : no
    ...
    Infinite monkey take n, Atlas Srugged written? yes : no

And this process is happening between the most commonly naturally occurring elements. So these triggers and process would have happened in almost every star system.

A naive 1-in-23e100 calculation is probably the wrong way to go about it. After all, the probability of any poker hand is 1-in-2.6M.

The count is one. Either the "multiple universes" are causally disconnected and therefore irrelevant, or are actually connected and therefore part of the same universe.

It is tempting, because we exist, to assume the probability of life arising can't be that low.

But if life is so rare that the odds of one arising in any given (causally disconnected) universe means life almost never arises, and more than one civilisation is unimaginable more rare than that again, if you imagine an infinite number of universes there will still be an infinite number of civilisations.

But being alone might be the most likely scenario if life is present, and nobody would be present in the empty universes to take them into account.

In which case our existence might easily trick us into over-estimating the odds of life arising.

Framed in a less depressing way: It might be we're not seeing the aliens because something is preventing us from observing them rather than because they don't exist.

I interpreted the original post to be saying that if life is very improbable then it is unlikely we would be here. And If there were only one universe then yes, it would be unlikely we are here. But if there are many universes, this could support a vanishingly small probability of life with most universes being empty, but a small fraction having life.

So these different universes are meaningful only to the extent you are asking philosophical questions like this, but not to most practical considerations.