(arxiv.org)

113 points | by monort 279 days ago

• poppingtonic 279 days ago

The conclusion of this paper is, paraphrasing, "We should stop using point estimates for what should be distributions. When we do that, we get much lower bounds and have a better chance at being more precise, whether or not we are alone." It opens up avenues for more questions, which is the correct stance given how little we know.

• PaulHoule 279 days ago

Ecosystems are limited by the availability of water, not sunlight. Also there are more "habitable" places in the universe which are underground oceans (the default condition outside the frost line) as opposed to a tiny fraction of rock worlds which have to parametrically fine tuned to have water -- ex. there are 10-20 worlds that have underground oceans in our own solar system.

Why would a spacefaring civilization care about dry worlds inside the frost line? The most absurd thing about "Battle: Los Angeles" is not that aliens would come to Los Angeles (as opposed to Detroit) to steal water, but that they would come to a planet which has a thin layer on the surface as opposed to being just a run-of-the-mill dwarf planet or asteroid or comet or whatever you call it that is closer to 50% water.

If civilizations of the dark had deuterium fusion they might see very little reason to mess around with the puny resources to be found close to a star. It's entirely plausible that a generation "starship" could live off the land and hop from comet to comet to the next star in 10,000 years but probably the crew would lose interest long before the first millenium.

• TeMPOraL 278 days ago

> The most absurd thing about "Battle: Los Angeles" is not that aliens would come to Los Angeles (as opposed to Detroit) to steal water,

Hey, they landed near all major coastal cities; the movie was just following one group of soldiers fighting off one part of the invasion force.

> but that they would come to a planet which has a thin layer on the surface as opposed to being just a run-of-the-mill dwarf planet or asteroid or comet or whatever you call it that is closer to 50% water.

Fair enough.

Disclaimer: I really liked the movie and wish there was a sequel made.

EDIT: My guess would be that the alien military tech was running off water (probably hydrogen/oxygen), so they started the invasion on the coasts to have essentially unlimited supply of water, but the actual purpose for the invasion was something else entirely. The "aliens need our water" hypothesis was AFAIR proposed by some talking head in the movie, not stated as in-universe fact.

• squirrelicus 278 days ago

H2O isn't exactly rare in the universe, it's the third most common molecule after H2 and CO. Getting water into orbit is absurdly expensive compared to getting it from the other rocks with lower gravity and atmo, like Ceres.

Weird premise for a movie

• TeMPOraL 278 days ago

It's a weird premise indeed, and I've seen it only in two places - as an in-movie speculation I mentioned, and as something the director alluded to[0]. Personally, I've discarded it in my headcanon - as it makes little sense, and one can imagine alternative explanations.

--

[0] - https://screenrant.com/battle-los-angeles-comiccon-2010/, C-f water.

• PaulHoule 278 days ago

Exactly, H2O is rare on rocky planets. It makes more sense to mine it from Pluto.

• onychomys 278 days ago

Or to just go to the rings of Saturn, which are mostly water ice, and which give you the added advantage of having something pretty to look at while you refuel.

• PaulHoule 278 days ago

Exactly, go outside the frostline and you are swimming in it. If you want to get away from it (or move it around) you can use some of it to make fuel or use it directly as reaction mass.

Beyond the frost line the scale is so much bigger. A population of 1 trillion beings in the Oort cloud is not going to be in a position of taking over the Earth and moving population there because it doesn't move the needle. They could create more "living space" by cutting up a Kuiper Belt Object and turning it into small ringworlds. I am not joking when I talk about Pluto as a better space colonization target than dry Mars.

Space technology from outside the frost line would have to be reconfigured to work inside the front line, why bother?

• PaulHoule 278 days ago

I liked the movie too, not so much as science fiction but in how the relationship is developed between the staff sergeant and the junior officer.

• woodandsteel 276 days ago

The problem with intelligent creatures that live in an ocean is they can't have fire, which seems to be essential for technological development.

• Sniffnoy 278 days ago

I'm going to repost the same comment I made on Reddit:

This is quite interesting. It certainly sounds like this does dissolve the Fermi paradox, as they say. However, I think the key idea in this paper is actually not what the authors say it is. They say the key idea is taking account of all our uncertainty rather than using point estimates. I think the key idea is actually realizing that the Drake equation and the Fermi observation don't conflict because they're answering different questions.

That is to say: Where does this use of point estimates come from? Well, the Drake equation gives (under the assumption that certain things are uncorrelated) the expected number of civilizations we should expect to detect. Here's the thing -- if we grant the uncorrelatedness assumption (as the authors do), the use of point estimates is entirely valid for that purpose; summarizing one's uncertainty into point estimates will not alter the result.

The thing is that the authors here have realized, it seems to me, that the expected value is fundamentally the wrong calculation for purposes of considering the Fermi observation. Sure, maybe the expected value is high -- but why would that conflict with our seeing nothing? The right question to ask, in terms of the Fermi observation, is not, what is the expected number of civilizations we would see, but rather, what is the probability we would see any number more than zero?

They then note that -- taking into account all our uncertainty, as they say -- while the expected number may be high, this probability is actually quite low, and therefore does not conflict with the Fermi observation. But to my mind the key idea here isn't taking into account all our uncertainty, but asking about P(N>0) rather than E(N) in the first place, realizing that it's really P(N>0) and not E(N) that's the relevant question. It's only that switch from E(N) to P(N>0) that necessitates the taking into account of all our uncertainty, after all!

[Note afterward: Over on Reddit, hxka points out that that should be P(N>1), not P(N>0). Or really it should be P(N>1|N>0)...]

• btilly 278 days ago

I have trouble calling it a paradox, because there is nothing that needs explaining in my view. Just throw in the fact that known fudge factors are important, and throw in the fact that there are more fudge factors that we don't know.

For example the traditional Drake equation doesn't include as a major factor "large moon that stabilizes the axial tilt over evolutionary time". And yet that seems to be needed and at least somewhat rare.

The traditional Drake equation doesn't include as a major factor "life not wiped out by a supernova over evolutionary time". And yet per http://earthsky.org/astronomy-essentials/supernove-distance there are estimates that this might happen on average once per 15 million years. From the Cambrian explosion to the present is around 540 million years. The odds of that forbearance is on the order of 7 billion to 1 against. How much does THAT change the Drake equation?

• jobigoud 278 days ago

It doesn't have to include these specifics. They are just sub-factors contributing to higher level factors.

Your first is covered by "fl, the fraction of those planets that actually develop life", and your second is covered by "fi, the fraction of planets bearing life on which intelligent, civilized life, has developed".

What you are saying seems to be the same as OP. It's not a paradox because the chances are insignificant, so we are indeed alone.

• stephenwinter2 275 days ago

I agree, I also can't see a paradox in terms of nature. And I would like to add an aspect of sociology (sociology is rarely discussed at this topic): Given mankind's industrialization period and decline of the ecosystem is normal it takes longer to get to an exoplanet than to ruin it. - So, what interstellar space travel really would be is this: The living mankind on Earth gives up itself and its home planet to spread the genes of those who plan its demise. http://www.hashsign.eu/html/blog/dominance/hadfield-hawking-... My answer to the Fermi Paradox is this: These bastards shouldn't get away with it.

• light_hue_1 279 days ago

It's "papers" like this by people that are either clueless or malicious that make everyone pine for the pre-arxiv days.

Everyone considered this option. From the very first day the paradox was posed. We don't know the parameters well, it's within our margin of error that no one else is out there, so it's an option. This is such an absurd claim to take as your own that it's literally on the wikipedia page!

It's also extremely shortsighted in order to get media attention. This resolves nothing about the paradox. What about the universe prevents other intelligent species from existing nearby? Sure, it's within our margin of error, but where is this coming from? Too few planets, too little abiogenesis, etc? Many factors or a single one? Is our existence simply a consequence of the fact that we're here therefore the dice must have landed well for us? Or is there something fairly unique about our solar system / planet / species / etc.

That's the real scientific question that keeps people up at night.

• titzer 279 days ago

I dunno, I kind of doubt that Eric Drexler is clueless or malicious. Maybe if you read the paper and understood their approach you'd have less of a knee-jerk reaction. They are arguing (as pointed out in comments elsewhere) that the math on probabilities should be using distributions, and this is what they do, and they go on to show that the resulting probabilities are far, far lower than the simplistic Drake equation would suggest.

• thraway180306 279 days ago

doubt that Eric Drexler is clueless or malicious

Someone however, does not.

https://scottlocklin.wordpress.com/2010/08/24/nano-nonsense-...

• jessriedel 279 days ago

> the math on probabilities should be using distributions

Do you really think that this is novel in any way whatsoever? There is some yearly chance of nuclear war, and I don't know about geopolitics so I have a prior distribution over that yearly chance. Should I cite this paper?

I actually really like the authors, and for all I know the paper may have some new insights or perform a calculation that hasn't been done before, but let's not pretend that prior distributions over probabilities is a new idea.

• true_religion 279 days ago

What does novelty have to do with dissolving the Fermi Paradox?

Is Fermi is some well established science, with repeated experimental proof, upon which numerous other conjectures have been built on?

Does it really require a novel approach to attack its basis?

• jessriedel 278 days ago

The top-level commenter wrote

> Everyone considered this option. From the very first day the paradox was posed. We don't know the parameters well, it's within our margin of error that no one else is out there, so it's an option.

And the person I replied to was rebutting this point (that the approach is obvious and considered long ago).

It's fine to write review articles, or clean up old arguments and repackage them, but it shouldn't be presented as a new idea, and in particular it should point to the prior work.

• titzer 278 days ago

I don't think they are claiming to have invented math on probability distributions and I didn't mean to suggest that that is what is novel about this paper. They used a different, more powerful technique to look at the math of the Fermi Paradox and came to a conclusion different than that following from the normal treatment of the Drake equation. That's a reasonable contribution, IMO.

• gwern 279 days ago

Can you point to a single person making the point previously that even small amounts of uncertainty in the distribution of each variable in the Drake equation often implies a small or near-zero number of ETI even when the best mean point-estimate of the distribution for each variable, when multiplied together, predicts a large mean number of ETIs?

• jessriedel 278 days ago

I don't understand. Your point ("even small amounts of uncertainty ... a large mean number of ETIs?") sounds just like a rephrasing of his ("We don't know the parameters well, it's within our margin of error that no one else is out there"). In particular, how could your statement be false while his be true?

• gwern 278 days ago

His point, as suggested by the comments agreeing with him and the claims that it's 'obvious', is that the parameters could be small. The problem with that is the parameters look large. Adopting a distribution and calculating it out gives much broader predictive distributions. You can have all the parameters not be that small but small enough, combined with minimal uncertainty, that on many draws from the posteriors, you get underpopulated universes once all the uncertainty and probabilities are integrated. What he wants to take by theft from individual parameters, handwaving them away as being small and thus causing the paradox, can be obtained without any trickery for a wide range of parameter values and 'margin of error's simply by the nature of the pipeline process producing a wide range of final outputs. It's akin to confusing the confidence interval around a mean for the predictive interval.

• jessriedel 278 days ago

I asked how his statement could be true while your statement could be false (which would show that even if his statement was granted then your statement could be new and non-obvious). You replied by claiming that his statement isn't justified while your statement is. This is a formalization of an intuitive argument, not a surprising dissolution of a paradox.

In other words, if other researchers had considered his statement and dismissed it without doing the sort of analysis being formally written up in this paper, then those dismissive researchers would have been making a mistake.

As I said elsewhere, I think these sorts of formalizations are really very helpful. Perhaps, given the sloppy thinking in this area, even more helpful than novel results. I generally think review articles are distillation is vastly undersupplied

• mirimir 279 days ago

Agreed. This is just picking parameters consistent with no detection of extraterrestrial civilizations. The point of the Fermi paradox is that it's a stretch to assume such parameters. It's not prediction about extraterrestrial civilizations collapsing or whatever. It's just an alternative to consider. And perhaps a warning about shouting at the Universe. Although it's probably too late to fret too much about that.

• jerf 279 days ago

The article is not about picking parameters. The article is one meta layer up from that; they examine the distribution of parameters.

I can't guarantee this is novel paper in general, but it's not something I've seen treated this formally before. I mean, it roughly conforms to what I've been saying for a while, but I only worked the math very intuitively and in a manner that could have been flawed, so I get no credit. They've worked it formally and put it on a solid basis. Plus as we adjust our probability ranges in the future, the analysis can be re-run with new numbers easily and produce concrete, or at least, concretely-vague answers, instead of vaguely-vague intuitions.

• jessriedel 278 days ago

> I can't guarantee this is novel paper in general, but it's not something I've seen treated this formally before

Yea, I'd be very happy if they just said "here we make formal the possibility, considered since the paradox was first proposed, that there is enough uncertainty in each parameter that seeing zero ETI is perfectly compatible with expectations". That would have been a modest but useful contribution to the lit that would have informed further research. The issue I have is with claims that they are "dissolving" anything.

• mirimir 279 days ago

OK, picking distributions. I can't imagine that there's enough data to even do that.

• scott_s 279 days ago

I think you (and some others) are being dismissive of a good-faith attempt to formalize thinking of a problem with many unknowns. I can't access the paper itself, but commenter carry_bit posted a link to the slides, and the conclusion slide says:

The Fermi question is not a paradox: it just looks like one if one is overconfident in how well we know the Drake equation parameters.

• Doing a distribution model shows that even existing literature allows for a substantial probability of very little life, and a more cautious prior gives a significant probability for rare life.

• The Fermi observation makes the most uncertain priors move strongly, reinforcing the rare life guess and an early great filter.

• Getting even a little bit more information can update our belief state a lot!

I think their arguments deserve more consideration than what they are getting in this thread.

• jerf 279 days ago

You should be able to access the paper. Arxiv doesn't require any logins or credentials or anything; just check the "download" section in the upper right. This should go straight to the PDF: https://arxiv.org/pdf/1806.02404 (Unless, you just mean you're on a device that can't render PDFs or something. It's a simple PDF, though, even a phone should be able to handle it.)

• jerf 279 days ago

"OK, picking distributions. I can't imagine that there's enough data to even do that."

Of course there is enough data to pick the distributions of estimates given by various people. We have all the estimates given by people in hand.

You seem to be being dismissive without even remotely engaging with what is being discussed here.

Let's skip over the part where you fall back to the claim that the distribution of probabilities given by people isn't relevant to anything, because that's not important to the paper. The entire point is to examine the distribution of such probabilities, and compare it to the observed universe, and that's it. Nothing more.

• 08-15 278 days ago

There is quite a bit of literature on picking distributions in the absence of observations. "Probability Theory: The Logic Of Science" by E. T. Jaynes has a whole chapter on "ignorance priors", where he shows how to pick prior distributions in the absence of quantitative information.

Generally, these ignorance priors are improper (unnormalizable) distributions. One example is scale parameters, where the approriate prior is 'ds/s', which makes any order of magnitude equally probable. It doesn't have a mean, and it favors small values. A tiny bit of evidence will immediately turn it into a proper posterior distribution; I think this prior has zero information content.

Of course, if one applies that approach to the Drake equation, one ends up with an equally uninformative posterior distribution, unless one can add evidence for each single variable. But that evidence just isn't there for some of them, so the result remains the same: It's impossible to estimate N, but it's probably very small. As it should be, given the total lack of data.

• ExactoKnight 278 days ago

> And perhaps a warning about shouting at the Universe. Although it's probably too late to fret too much about that.

Any civilization sufficiently advanced to threaten us already has the capability to see we exist. For those with a large enough telescope, we have been emitting signs of life to the rest of the galaxy for billions of years.

It's only more recently that we have been showing signs of intelligent life (through radio waves and changes to our environment). These signs have not yet propagated throughout much of the galaxy yet, and there is a good argument we ought to get as advanced as possible as quickly as possible, so we can defend ourselves before others become aware of our intelligent existence.

• jawns 279 days ago

> This is such an absurd claim to take as your own that it's literally on the wikipedia page!

• Luc 279 days ago

But it's posted in the pop-physics category. It doesn't seem inappropriate as a popular science article.

• tgb 278 days ago

Thanks for pointing this out, it changes my perception of this article entirely.

• uniformlyrandom 279 days ago

The paper just says that Fermi estimation method is not applicable in this case. It does not say that there is no life, it says that is not the right way to estimate life existence. You can as well flip a coin, and then be amazed that aliens do not turn up when you guess heads right.

• vertexFarm 279 days ago

The most interesting option (danger: my dumbass opinions ahead) for why there's no other communicating species in radio range is whether there's a great filter right under our nose.

If we can ever prove that there's plenty of planets and plenty of abiogenesis and plenty of multicellular things out there that just don't know how to make radio waves, then either the leap to technology is exceedingly rare or we are in very big trouble very soon. I could see that keeping some people up at night.

Of course it could just be that, like us, other technological beings don't constantly broadcast super-directional radio transmissions at super-high power into random areas of space. We sent the Arecibo message a couple times for a few minutes, but it was really not enough to ever hope it got noticed by anyone out there. Even if space is bursting with intelligent life. Not even close. Cute project, though. Why do we expect more from others?

There was once a fairly mature plan, back in the 60s I believe, when nukes were still all the rage and people were discussing lots of exciting ways to use them for space exploration, wherein some physicist calculated how much power you'd need to make meaningful, intelligible radio contact a few stars over using an omnidirectional radio source. It involved setting off lots of nuclear bombs somewhere around Jupiter's orbit, in fact modulating the detonations and using the EMP as the signal. Those are the extreme methods needed get a signal out there up and over the noise of our own star, to defeat outrageous inverse square losses, to have it even barely intelligible at a very low baud rate a few light years away. Have we ever actually done that, even once? No.

So that should also tell you that nobody is listening to our old TV broadcasts and it's no surprise we aren't able to pick up anyone else's. No sane technological race is going to do an omnidirectional burst of communications meant for local use at such an enormous magnitude of power. It would be wasteful and destructive. Directed, focused transmissions only reach a billionth of the sky, so that has its own odds against it. SETI is a highly optimistic program considering the physics at work here.

The other argument for Fermi's paradox and why, if there are intelligent beings out there, we should know about it: If there's an advanced race even a couple million years ahead of us--just a blink of an eye in astronomical terms--they should have proliferated through the whole galaxy by now. We wouldn't be listening to their broadcasts, we would be them. Even discounting how unlikely it is that any race will ever be able to get to another star, this assumes that life (or Von Neumann machines) will spread and replicate endlessly, until they fill an extremely large space and convert an astronomically large amount of mass into themselves. We don't really see that with life we have on Earth. Most of our biome is still matter which is not life, and it's been here for billions of years. I don't understand the assumption that life will spread infinitely instead of staking out a reasonably large area that is barely manageable and then cull down, as life does here in our data set.

Even if there's a lot of technological species out there, and they're broadcasting with rational amounts of power, and they've expanded to cover rational amounts of space, it's still no surprise that we haven't found one yet. It's almost impossible to keep in mind just how big it all is. We also haven't been searching exhaustively or for a very long period of time. Would an alien SETI comparable to ours be able to detect our own transmissions? It's actually really unlikely.

• perl4ever 278 days ago

"Most of our biome is still matter which is not life, and it's been here for billions of years."

Our planet is called Earth you know, which also means dirt. Because it seems to be covered in organic matter. If your perspective was correct, wouldn't we call the planet "Rock" or something?

• 279 days ago
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• not_a_moth 279 days ago

How can we be expected to take seriously a probability estimate of life being "out there"? Only 10 years ago we discovered how many Earth-like planets are likely in our galaxy (I didn't see this aspect mentioned in the paper...), and they are also calculating a probability of abiogenesis (emergence of life), which, while I'm not an expert, seems highly speculative.

• Anderkent 278 days ago

Why can't you estimate probability of something speculative? Of course it must be speculative if you're talking probabilities; otherwise you'd just know if the life is out there or not.

If the assumptions are very speculative, you just end up with very wide probability distributions, which is exactly what the paper argues for.

• gmuslera 278 days ago

The reasoning seem to be "as we don't have enough data, lets conclude whatever I want".

The Fermi paradox assumes that if there are aliens more advanced than us somewhere for a long time, they should be here by now. Maybe more advanced technology enables interstellar travel (maybe not, maybe is not practical at all), maybe they may not have all our motivations (expansion, technological advancement in our own focus, exponential growth, etc), maybe they don't want to expand or announce themselves because they went cyber or try to pass unnoticed in the dark forest, or things that we can't even imagine yet, as we are not advanced enough.

We just don't have enough data to give a meaningful answer. And maybe never will. The only way to decide if we are alone in the universe or not is actually finding someone else. But with so much outside our physical or practical line of sight we can't just say that there is no one else because we didn't see anything.

• jobigoud 278 days ago

When talking about the Fermi Paradox it's not about what this or that extra-terrestrial civilization might do. It's about what none of them is doing.

When you say "maybe they don't want to expand", if you want this to explain the paradox, you actually mean "none of them want to expand". Because if just one did, we would see it.

• gmuslera 278 days ago

Is not "none of them" but "all the ones that reached certain knowledge level", after you know something, you avoid expanding or showing yourself.

The dark forest idea comes from Liu Cixin Three Body Problem trilogy, if you show yourself you risk being destroyed by even more powerful civilizations that are hidden in the dark. And they are hidden because are afraid that the same happens to them, with a third one or with the one they destroyed after they advanced enough.

It is not the only possible reason, just one of the possible things that we don't know (or even don't know that we don't know) that can disprove or at least atenuate enough the paradox hypothesis.

Can be like explaining a caveman why you can't make a building high enough to reach the moon, so far he knows would be doable and even desirable for us, so why we didn't built one yet?

• posterboy 278 days ago

We would see it? Do you have any idea how big the universe is, and how little we see? If there were astronauts on pluto right now, we could not detect them, I suppose -- I might be wrong, but the statement is bound to be true at some order of magnitude that's certainly smaller than the theoretically visible universe.

• mechsquirrel 278 days ago

The thesis of the article is not "lets conclude whatever I want"

The foundational assumption is that (a) historically people have just picked the values for the Drake Equation that "felt right", and this is wrong, biased, and stupid, and (b) we should not be surprised if the Drake parameters fall in any order of magnitude. So let's Monte Carlo in a log-scaled distribution (roughly). Thus, given what we actually do know, median civilizations per galaxy is 0.32, average is 27 million.

Interestingly, this suggests that optimistic Drake Equation parameters must be wrong, lest they create an empirically impossibly-populated galaxy.

• sulam 278 days ago

>Maybe more advanced technology enables interstellar travel (maybe not, maybe is not practical at all)

We have practical interstellar travel today if you don't artificially constrain your thinking to sending blobs of mostly water with lifespans measured in decades.

• maxerickson 278 days ago

What are your parameters for practical?

Like, how much mass, how fast, cost, etc?

• sulam 278 days ago

Voyager-class.

• carry_bit 279 days ago
• jl2718 278 days ago

I would rephrase the question as: What are reasonable bounds on the number of intelligent civilizations, given that we have observed exactly one in the archeological record of our own planet, and no others elsewhere with current technology?

So, tiny sliver of time over billions of years, and communications technology that only reaches to a few nearby stars.

Trying to use probability of certain chemistry is, I think, highly subject to errors and failure to consider some alternative possibilities.

Life itself, however, is a totally different equation because it’s nearly as old as the earth. This might suggest that there is a lot of it out there.

• sbensu 278 days ago

Related recommendation: this podcast episode[1] was very good, covered many solutions to the Fermi Paradox, and discussed the OP's article.

• chmike 277 days ago

In my opinion, takling the ET existence using the drake equation is not efficient because it boils down to estimate or guessing values.

I favor the following reasonning. For simplification, let consider the universe as homogene. Now, let p be the probability that life emerges in one unit of time and space. (1-p) is the probability that life does not emerge in the unit of volume and space.

If v is the number of volume units in the universe and t the age of the universe in unit of time, then the probability that life never emerges in the universe is (1-p)^(v * t). If p is bigger than zero, this probability will tend to 0 with a growing v and t, regardless of the magnitude of p. This always converges to 0. Soon or later, life will emerge in the universe as long as it can emerge spontaneously.

What is the probaility that our solar system is the only place in the universe where life emerged. Let s be the volume of our solar system. That probability is (1-p)^((v-s) * t). Since s is very small relative to v, that probability is very close to the above probability. And with growing v and t this probability tend to zero. In other words the probability that life emerges elsewere in the universe after removing the volume of our solar system is not much affected. It still tends toward 1.

This should give you the idea. The only unknown variable is p. But even if we don't know it's value, we can draw two important conclusions from this. 1) it doesn't matter how small p is, soon or later life will emerge. 2) the probability that we are alone in the universe is tending toward 0 with increasing t and v.

Could we be the most advanced ? Why discarding the ufological data ? It's time this non-sense and ostrich attitude stops.

• ISL 279 days ago

If the argument stated above is correct, there is an awful waste of space. (Thanks, Carl!)

There is nothing in physical law to suggest that here is substantially different from anywhere else in the universe. To believe that here is manifestly different from every other place in the universe is a really surprising claim.

• mdpopescu 279 days ago

First, we know with absolute certainty that here is substantially different from anywhere else: we know there's life here, we haven't found life anywhere else. (And the null hypothesis is that we haven't found it because it doesn't exist.)

Second, it's a waste of space only if 1) it was created on purpose and 2) the purpose wasn't "to allow us space to expand". If either of those is false, I don't see how it can be called "a waste of space".

• goatlover 279 days ago

> First, we know with absolute certainty that here is substantially different from anywhere else: we know there's life here, we haven't found life anywhere else.

We haven't even ruled out life existing on Mars or under the ice of Europa, let alone X light years away.

• ISL 279 days ago

First, we know with absolute certainty that here is substantially different from anywhere else: we know there's life here, we haven't found life anywhere else.

I'll take the other side of that bet. What odds are on offer (10^15:1? 10^80:1?)?

• Anderkent 278 days ago

Wait, are you saying you'll take a bet where you pay 10^15 to 1 if we do not find life out there? I'll take you up on that for \$0.01 on my side.

• gnaritas 278 days ago

> First, we know with absolute certainty that here is substantially different from anywhere else: we know there's life here, we haven't found life anywhere else

No we do not. We haven't looked anywhere else, we don't yet really have that ability. There's no reason at all to believe this place is special.

• 8bitsrule 278 days ago

expectation that the universe should be teeming with >intelligent life<.

It's only a paradox if you're capable of entertaining such an expectation. Based on my life experience, I'd estimate the probability is about the same as finding a bottle of my favorite drink sitting on the doorstep.

• jackconnor 278 days ago

I feel like if aliens come they might keep themselves hidden, rather than announce their presence. If so, it could be Fermi was right, we just haven't seen the evidence of it yet, since the Fermi Paradox presupposes that their should be intelligent life and the we actually can point to evidence of it.

• carapace 278 days ago

We're in quarantine.

To other life forms humans look like H.R. Giger's xenomorph aliens from the movies.

We're obviously intelligent, yet we absolutely refuse to communicate with other life forms. we're not even interested in the possibility.

We consume other organisms with rapacious abandon, converting them into more of ourselves as fast as we can. We are strip-mining the oceans of protein, our chattel livestock out-mass all other land animals by several times, and still we consume. We clearcut forests leaving patterns visible from space.

We cover everything with asphalt and concrete to create huge sprawling nests that are inimical to life other than our own (and a few species that can live with us.) Again, this is clearly visible from space.

From orbit we look just like a disease.

There's a place in Washington (state), a lake, where the UFOs take off and land (underwater) and the cheeky fuckers will wave back at you from windows in the ships.

We're not alone. We just suck.

• 278 days ago
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• taylorswift_ 278 days ago

where is this lake in WA state? have you been there? are you reptilian?

• carapace 278 days ago

> where is this lake in WA state?

I' don't know. Even if I knew I wouldn't say in a public forum like this, it would be irresponsible.

> have you been there?

No. If I wanted to talk to aliens I wouldn't go rubbernecking at them like a yokel.

> are you reptilian?

We're all reptilian. ;-) https://en.wikipedia.org/wiki/Triune_brain https://en.wikipedia.org/wiki/Recapitulation_theory

The "reptilian" thing is a human psychological issue, there are no reptile aliens secretly ruling Earth.

• taylorswift_ 278 days ago

but how do you know it exists if you've never been there? who told you?

> there are no reptile aliens secretly ruling Earth.

perhaps not ruling it...

• carapace 278 days ago

Look, my basic point is that we're not alone, rather nobody wants to talk to us because we're terrifying ravenous monsters.

> but how do you know it exists if you've never been there? who told you?

I can't tell you that in a public forum. And again, even if I could I wouldn't. Either you don't believe me in which case what's the point? Or, worse, you do believe me and want to go there.

I'm not interested in helping anyone talk to aliens, it's just frustrating to me personally whenever the subject of the Fermi Paradox comes up because it's such a foolish question.

The critical issue people are dealing with whether it's UFOs, reptilians, crop circles, bigfoot, pyramid power, crystals, etc... it's all one thing: where is the edge of consensus reality?

To me, the important thing is this: if we don't learn to live in harmony with Nature, and damn quickly, we're going to crash our world civilization.

We don't need aliens to fix our shit. We have the technology and the understanding, it's really down to our fundamental nature: do we wake up and course-correct fast enough or will the oceans rise and wipe us out, leaving a world-wide desert and tropical regions at the poles?

• taylorswift_ 278 days ago

Oh I'd love to go to that lake...

I agree it's foolish conjecture and I believe we are certainly not "alone". I had an experience when I was 10 that infused fear and curiosity in me.

I'd like to say I am hopeful about our future but we are just evolved organisms from a long chain of creatures designed to compete for survival... it's in our own nature to self-destruct.

• mchahn 277 days ago

Can some tell me what the "{\em ex ante}" I see in several places means?

• tachkotic 267 days ago

The time span of human civilization is too small to witness the emergence and extinction of intelligent civilization elsewhere. Universe is really very vast in terms of distance and time.

• jpm_sd 279 days ago

TL;DR - It's not a paradox, because we're probably alone. Kind of a letdown!

• jandrese 279 days ago

The Drake equation is the epitome of garbage in garbage out. Trying to draw a line using a single data point.

There was recent news from NASA about the discovery of organic molecules on Mars and the possibility of life there at some point in the past. Discovery that life once existed on Mars would blow up the assumptions in the Drake equation.

As for the Fermi paradox I'm still of the opinion that its solution is simple but depressing: Interstellar travel is so difficult that by the time you're capable of it you don't need it anymore, and even when you're capable of it you still don't get very far outside of your stellar neighborhood. Unlimited power systems, reactionless drives, and FTL travel (or even high-c travel) are depressingly impossible. And then the cold hand of entropy and the aggregate chance of disaster make it extremely dangerous to even attempt. Basically without Sci-Fi propulsion/power you end up traveling at an interstellar snail's pace, and the longer the trip the more likely it is that a random meteorite smashes through your vessel, or you simply run out of spare parts and materials to make them, and the amount of fuel you need to just keep the lights on becomes enormous.

If you can build a starship that can travel between solar systems with our current understanding of physics, then you can build orbital colonies for basically unlimited living space much much easier. For one, they can be powered by solar cells instead of needing to carry fuel. It's not like we are going to run out of raw materials either. Even restricting yourself to the belt the amount of material available would last basically indefinitely. Worst case you can start breaking up moons.

So even in a universe full of life everybody is alone. Especially if you think about how genetic algorithms tend to get hung up on local maxima, so lots of planets waste millions of years with dumb dinosaurs with no space program or radio telescopes.

• jcranmer 278 days ago

Only two variables of the Drake equation can be meaningfully estimated: rate of star formation and fraction of stars with planets. The number of life-supporting planets per star is surprisingly ill-defined (what number is that for Sol?). All of the other variables are basically knobs that let you control what you want the answer to be.

> There was recent news from NASA about the discovery of organic molecules on Mars and the possibility of life there at some point in the past.

It should be pointed out that the organic molecules in question are known to be created by abiotic processes.

> As for the Fermi paradox I'm still of the opinion that its solution is simple but depressing: Interstellar travel is so difficult that by the time you're capable of it you don't need it anymore, and even when you're capable of it you still don't get very far outside of your stellar neighborhood.

Well, there's an even more depressing possibility: interstellar communication itself is effectively impossible, let alone travel. Any beam will spread out over a larger and larger radius, so even the most focused laser beams will become too weak to detect within I think a few hundred light years, so we're not even talking about trying to find aliens in the galaxy, we're talking about trying to find aliens in the nearest stars.

• jandrese 278 days ago

It doesn't help that we have a giant noise source in the middle of our solar system that shoots the noise floor through the roof when you're trying to detect laser comms over light years.

Plus, even at lightspeed you're talking multi-year roundtrips to our nearest interstellar neighbors.

Our entire history of radio emissions has only made it to around 500 solar systems currently. Even if someone was listening and responded immediately the response probably wouldn't have made it back to Earth yet.

• bena 278 days ago

> Plus, even at lightspeed you're talking multi-year roundtrips to our nearest interstellar neighbors.

That's something I think people ignore. It takes 4 years to get to the next closest star at the fastest possible speed.

And that's ignoring all of the other issues with long term space travel. 4 years. To a place where we're relatively certain doesn't have life capable of technology.

The assumption that other intelligent life will conveniently find a way around the speed of light is a big one.

• calebh 278 days ago

You're completely ignoring the time dilation effects of relativity. From the perspective of a fast moving spaceship, the distance between stars contracts, and from the perspective of an outside observer, the time experienced in the spaceship slows down. This is why I believe that interstellar travel will be feasible, although creating any sort of empire will be impossible. Here's a quote from the Wikipedia article on time dilation:

"Theoretically, time dilation would make it possible for passengers in a fast-moving vehicle to advance further into the future in a short period of their own time. For sufficiently high speeds, the effect is dramatic.[2] For example, one year of travel might correspond to ten years on Earth. Indeed, a constant 1 g acceleration would permit humans to travel through the entire known Universe in one human lifetime.[12] Space travelers could then return to Earth billions of years in the future. A scenario based on this idea was presented in the novel Planet of the Apes by Pierre Boulle, and the Orion Project has been an attempt toward this idea."

https://en.wikipedia.org/wiki/Time_dilation#Velocity_time_di...

• jandrese 278 days ago

Constant 1 G acceleration requires three things:

1. An infinite power source

2. A reactionless drive

3. A spacecraft made of material so strong that it can survive collisions with rocky material at velocities very close to c. Or a Star Trek style deflector shield.

Warp drive is probably easier to achieve.

Detonating nukes behind your spaceship will never give you anything close to 1G constant acceleration over a long period of time.

Time dilation has some definite drawbacks as well. Say for example you have a very redundant ship that can repair damage from micrometeorite attacks in a few minutes. The hits are very rare, maybe once a year at most at normal velocity. But now you're traveling at a high fraction of C and you're hitting tens of fragments per second, and always at a high fraction of C. Your repair process is effectively working in slow motion and could very easily get overwhelmed. Without a sci-fi energy shield your spacecraft is ablated to death long before you get anywhere.

• Zimahl 278 days ago

> multi-year roundtrips to our nearest interstellar neighbors.

At lightspeed it's an instantaneous trip to the traveler. It's only a multi-year trip to those who are still on Earth.

• jandrese 278 days ago

That comment was in reference to communicating with the star system. Nobody is traveling in that case.

• TeMPOraL 278 days ago

Also, VR. I already fear the future of humanity is not exploring strange new worlds, but creating virtual ones, and converting the solar system into more computronium.

(And the weird thing about that is that I feel it's a bad thing for some reason, but I can't articulate a coherent argument against it.)

• strkek 278 days ago

As long as humans continue to be like we have been so far, i.e. with the mentality of destroying our own planet and not caring about it, or committing crimes like kidnapping, etc... as long as there are individuals like that, every time we humans learn something new, things will inevitably turn way more scarier.

Whether it's colonizing other planets or making a full-dive VR; just thinking about the time when we can do any of these things gives me a headache.

• greglindahl 278 days ago

There are a bunch of scifi novels that explore the issue, and most of them feature bad things that result.

• jandrese 278 days ago

To be fair, if it turned out all hunky dory then the novel wouldn't be very exciting. Sometimes the downsides are rather contrived.

• dosshell 279 days ago

And some numbers from the paper:

> we find a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe (53%–99.6% and 39%–85% respectively).

> ’Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological horizon and forever unreachable.

• ssijak 279 days ago

How did you/they calculate that probability of being alone? Anybody who tries to slap some number on such things as the probability for life to emerge is dishonest at least.

• mdpopescu 279 days ago

That's the whole point of Michael Crichton's rant in "Aliens caused global warming" [1]

• amelius 279 days ago

Imagine a two-dimensional grid of squares, where all the squares are randomly chosen to be either black or white. Imagine that somewhere in this grid there's the appearance of a smiley in a 12x12 rectangle. How would this smiley compute if it's alone in the grid, and how close the nearest other smiley can be expected to be?

• amelius 279 days ago

> because we're probably alone

... in the observable universe.

• mikeash 279 days ago

Which is another way of saying “within our light cone,” and anything outside it might as well not exist as far as we’re ckncerned.

• psychometry 279 days ago

• goatlover 279 days ago

I find it interesting because if N=1, then we're an incredibly statistical fluke, and yet there's no reason to suppose that our solar system or planet is that much of an anomaly.

• vertexFarm 278 days ago

I feel like this is about the same as wandering out into the antarctic pole of inaccessibility, whispering "is anyone out there" one time in 1974, waiting a couple minutes, and then pondering on how it's such an incredible statistical fluke that nobody has responded.

• psychometry 278 days ago

Maybe for me the issue is that since N=1, we have nowhere near enough information to construct reasonable priors on the equation's parameters. This makes the variance in the outcome explode. The ballpark is so huge that basically any interpretation is fair game.

• FreekNortier 278 days ago

They are here just not in a way most people would think. When you are ready to know you will know.

• shawn 279 days ago

It has always seemed arrogant to think that aliens exist anywhere within our galaxy. Look at how many galaxies are out there. Now realize that the universe extends far beyond our Hubble sphere.

We can’t hope to colonize even a fraction of 1% of our galaxy, even with wildly futuristic technology.

There is one option, though: Become our own aliens. If we set up colonies separated by time and distance, we will culturally diverge within a century, and genetically within a few millennia-ish.

• OscarCunningham 279 days ago

>We can’t hope to colonize even a fraction of 1% of our galaxy, even with wildly futuristic technology.

If you can do any colonization at all it shouldn't be that much harder to colonize the whole galaxy. Once you've got the ability to colonize exponential growth will take over and pretty soon* you'll be everywhere.

*In the context of the Fermi paradox, we're wondering why no aliens have already colonized the galaxy (including our solar system). So by "pretty soon" I mean relative to the time interval between when such aliens might have appeared and now.

• jcranmer 278 days ago

There is a basic epistemological flaw that goes on in the Fermi Paradox (and similar arguments): the argument rests on the idea that, given enough time, an event which has non-zero probability will eventually happen. The flaw is that there is no consideration of if enough time has actually passed, since the probabilities we talk about are often characterized on the level of "we don't conclusively know it to be impossible."

If you look at the statement you yourself make, it requires a lot of assumptions:

* Interstellar colonization is possible (this is explicitly taken as a hypothesis, though)

* The ability to colonize another star system is the ability to colonize a large number of star systems. This is to say, the social consequences of colonization are not going to grow larger with size. A possible counterfactual would be that large civilizations might put more energy into securing control of known systems rather than embarking on further colonization--and the anecdotal evidence from the history of Earth is that this is indeed the case.

* Colonization is a logistic process (which is probably what you really meant when you said exponential, but the difference is a technicality for this discussion). If interstellar travel is really as difficult as our knowledge of physics suggests it to be, then interstellar colonies are likely to develop as completely independent civilizations without maintaining strong ties to their parent motherlands, and subsequent colonization efforts are going to include attempts to "colonize" already-colonized systems and consequently logistic growth wouldn't be achieved.

• pfdietz 278 days ago

We're also wondering why we haven't seen any other galaxy that's been fully colonized and industrialized. K3 civilizations would be detectable at cosmological distances.

Von Neumann probes could probably colonize a good chunk of the Milky Way given a few hundred thousand years.

• vertexFarm 278 days ago

I think that's an overly simplistic assumption, even if we assume they weren't designed by a rational actor who programmed a generation limit into them to keep them from totally converting all matter in the galaxy into probes (an absolute must, obviously).

Life on Earth consists of Von Neumann machines. That's exactly what life is. Yet our life has not converted the entire mass of Earth into itself, and there's still plenty of places where you can't easily find signs of life. And our life has had billions of years. The assumption that Von Neumanns will very cleanly and exponentially increase in number until they are all over the galaxy is too ideal.

• krapp 278 days ago

It also assumes that all bodies in the galaxy are equally amenable to colonization and conversion into the necessary resources, and that for machines as complex as Von Neumann probes would need to be, there would be no such thing as mutation or evolution over innumerable generations which might halt the process of expansion.

And that most if not all probes in every generation will even find something other than empty space because the universe is very very very big and the likelihood of traveling in any direction and ever hitting anything is very very very small.

Although if you assume the universe is simple enough to describe on the back of a napkin then it probably is straightforward.

• rtkwe 278 days ago

That also makes an assumption about the actual ability to make a machine capable of self replication. That in and of itself is a really hard problem as it has to replicate the entire high industrial base needed to create itself which is a LOT of stuff. Just our current technology requires hundreds of processes and chemicals to create critical things like the circuit boards and the components (capacitors, ICs, etc) on it. Then it needs the intelligence and sensors to identify all the constituent sources and address production problems (eg: impurities in source stock) and breakdowns of it's own internal equipment.

Earth is full of machines that are capable of self-reproduction (e.g. bacteria), and some of them are clever enough to build rockets, so I don't think it's such a big stretch to assume that von Neumann probes are possible.

• rtkwe 278 days ago

That doesn't get us any closer, unless we stretch the idea of a Von Neumann probe to it's limits and include life seeding. Also we're a long ways away from anything near the scale required even surviving a trip to space much less actually living there.

• drjesusphd 279 days ago

Yes, this is the essence of the Fermi paradox, and it's often overlooked. 100k years is nothing on cosmological scales.

• ghaff 279 days ago

That in turn makes assumptions about the practicality of interstellar travel etc. But, yes. The counterpoint to space is big is that so are timescales.

• bramgn 278 days ago

This. I always wonder why discussions about the search for alien civilizations don't take the massive timescale more into consideration. Say you're watching a summary of our universe compressed to a hundred years. Each time a civilization pops up, it might just hold on long enough to last a nanosecond. We're just living that in that blip of a time.

Interstellar travel is definitely possible. The only question is how long the trips take. You can build nuclear pulse propulsion vessels fairly easily that can reach a few percent of the speed of light. Those things can cross the Milky Way in less than ten million years.

• ghaff 279 days ago

I wouldn't use the term "definitely." But it looks like "just" a (very hard) engineering problem [i.e. no known fundamental reasons why it's impossible]. And humans are pretty good at solving engineering problems over relatively short periods of time.

ADDED: There are also questions of resources, motivations, and e.g. whether we'd even want to build self-replicating probes.

No, speed is the hard engineering problem. The Voyager probes for example have reached escape velocity from our solar system. That's fairly primitive rocket technology.

• Cthulhu_ 279 days ago

What if we are the aliens though?

Panspermia?

• mirimir 279 days ago

Maybe, but not necessarily even that. The flow of chemical evolution that leads to carbon-based life is just so highly likely. We see some key molecules just about everywhere we look out there. And various simulations (physical, not virtual) create nucleic acids, amino acids, fatty acids, carbohydrates, etc. So there's no reason to think that the Earth is special.

• pbhjpbhj 279 days ago

Something I don't get, people say something along those lines -- that with earth-like conditions, blah-blah, earth-like planets, ... then life!

But also experts claim life only arose once on Earth. So, in a place with perfect conditions, the perfect distance from the sun, the perfect atmosphere, perfect trigger, perfect environmental conditions, life only started once! Doesn't that make it so infinitesimally unlikely that even with millions, billions, of planets with the right conditions we still shouldn't expect abiogenesis to occur.

The same arguments that make for extraterrestrial life surely stand against the uniqueness of anything. We know things that are unique. Seems like it's mostly faith based assertion.

• burlesona 278 days ago

Or an anti-faith based assertion. It’s in many ways much more terrifying if we are, in fact, special.

If we are just one of billions of places that life is going strong then we’ll do the best we can but if we don’t survive the eons who cares.

If Earth is the one and only seed of life, then don’t we have an incredible moral imperative not to wreck things here, and if possible to spread life into the darkness?

Being truly alone in the vast dark is a much scarier idea to live with.

• nervousvarun 278 days ago

Just curious how can anyone conclusively claim life arose only once? Don't they just say we only have evidence that it arose once?

Maybe it started twice or 100M times but 100% of those times the newly started life was "consumed" in some way by already existing life etc.

• mirimir 278 days ago

Yes, that seems a dubious claim. There's no way to know, except though simulations, how many dead ends there were. What we know is that all existing organisms share basic biochemical features. More or less the same nucleic acids, amino acids, and so on. So other paths arguably got competed out. Or merged, as we know for nuclei, mitochondria and chloroplasts in eukaryotes. Probably also components of bacteria. Flagella, maybe? The whole DNA/RNA/protein thing could well be a kludge.

The especially cool aspect of searching for life elsewhere in the solar system is the possibility that we'll find other variants that dominated.

• jobigoud 278 days ago

It's also because we have tried all sorts of approaches for the past 70 years or so and we haven't been able to bootstrap it ourselves.

• mirimir 278 days ago

I doubt that any of the experiments have run for longer than a few years. And probably less.

• transfire 279 days ago

"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space."

There is no way we are alone.

• Buttons840 279 days ago

Every once in a while we see a headline that says something like "There are more planets than we previously thought", or "There are more galaxies than we previously thought". When people see these they often conclude that the odds that life exists elsewhere are greater than previously thought, but it's also perfectly logical to see those headlines and concludes that the odds of life forming are lower than previously thought, because (per Fermi) "Well then where is everyone?"

Look at the math:

odds of life existing elsewhere = (10^n planets) / (10^(-m) odds of life forming on a planet)

We don't know what n and m are. It may be that m is much larger than than n. Yes, the number of planets is very large, but the odds of life forming is apparently very small. It may be that there is a very large number of planets, but a very very very very small chance that life would form on a planet.

• bena 278 days ago

We're still working out how to get to Mars. Currently it will take close to a year. The longest time someone has spent in space has been just over a year.

It is not easy. It is not quick.

Even if we travel at the fastest possible speed, it takes 4 years to get to the next star. So, where are they? Too far away to reach.

The assumption that these problems are possible to overcome is a big one.

• jobigoud 278 days ago

The Universe is old. Really old.