The Fermi Paradox

Sounds like a hell of a book/movie plot.

> until all of a sudden the most distant stars go dim

Why the most distant?

I feel there's a language used here to conceal some questionable reasoning;

"Why don't we see a civilizations spanning a galaxy? How would that work? No idea but why don't we see it?"

We could ask why we don't see Lovecraftian gods or giant life forms that each stars. We don't know how that works either.

There is actually a pretty good explanation for it in my opinion, that it takes about this long since the big bang for life forms of our complexity to exist. (meaning our planet was seeded at some point with some primitive life forms that than continued on their evolutionary tracks towards this point in time).

So you have many planets starting to get to the point where space exploration on a wide scale is feasible. Maybe a few are a hundred thousand and some change years ahead or behind us but the likelihood is low that many are significantly well established, or established long enough and close enough for us to detect.

I had this idea recently myself and to the best of my knowledge you're the only other person who's mentioned it. The closest I've found is the "galactic preemption" hypothesis published in the 80's, but that's more an explanation for why only one civilization would exist in a single galaxy, rather than for why a newborn civilization such as our own would look at the sky and see no signs of civilization in the whole universe.

Have you seen this idea published anywhere?

This model assumes that interstellar travel is profitable. There is no evidence that this is the case, even if we had Star Trek technology.

If it isn't profitable, then it turns into a drain on the home planet. That isn't sustainable.

But the Milky Way is only 50,000 light years in radius (~ average distance between stars?). That's not much at all on a evolutionary scale. So your argument explains why we're not currently observing an alien civilization (i.e. they would expand so close to light speed we would likely either be conquered or observing nothing -- so observing nothing is a consistent scenario). But it does not explain why no Type III civilizations (continuing with the assumption that civilizations all quickly go on to become Type III) has risen at all in the past hundreds of millions of years.

You can close that gap that via an anthropic principle by saying that if some civilization were colonizing our solar system, life on Earth would be extinguished/not possible.

I actually posted about this very topic a few days ago here.

Once you have von Neumann machines spreading they will take over each new star system pretty much as soon as they reach it. Assuming the von Neumann machines are small and are being powered by an energy source (i.e lasers) from their origin star system they will spread through the galaxy at close to the speed of light. This spread method creates an interesting effect in that we would not see the stars go out until the von Neumann machines had almost reached us if the origin star was within our galaxy - basically the von Neumann machines would be traveling only a little behind the light front from the origin star system (this would make a good science fiction story).

If the origin star system was far enough a way, then the slightly slower speed that the von Neumann machines would travel at should allow us to see them progressing though a distance galaxy. Such a galaxy would look to us like part of the galaxy had a chunk taken out of it. It would be worth looking through the galaxy classification data set [1, 2] to see if there are any galaxies like that out there that look like this. My feeling is we won't find any as I think intellegent life is near unique within the visible universe, but it is at least a testable hypothesis.

1. http://www.galaxyzoo.org

2. http://en.wikipedia.org/wiki/Atlas_of_Peculiar_Galaxies

Speed of light is fast enough, considering how long the universe has been around. Our galaxy is 100 thousand light-years - a blink in geological time. We can see everything that ever happened in our galaxy right now, excepting the last few moments.

I'd instead be looking for evidence civilizations are expanding by ways we don't yet suspect. Soliton waves through gas clouds? Wormholes? Multidimensional folds? What would those things look like? Maybe they look like dark matter or something.

We can't calculate the probability of life arising though because even if we did know how it arose here—which we don't exactly—we don't know all the possible different ways it can arise, which may or may not also be a number raised to a large power.

This is essentially the problem that I have with the Drake equation. It encourages--whether that's the intent or not--taking a reasonably known and very, very large number (number of stars) and multiplying it by probabilities/percentages, some of which (we think) we know with at least order of magnitude accuracy. But others we have absolutely no idea. And saying some of those events (such as the evolution of intelligence as we understand the term) has a 1 in a billion probability of occurring SOUNDS like a worst case for-the-purposes-of-argument plug-in. But it's really not.

Depending of whether life is a fluke or normal outcome. Until we know how life on Earth began, we will have no idea for what to look for in the sky.

http://www.scientificamerican.com/article/a-new-physics-theo...

This theory could be quite important or wrong. Or both. But it gives very interesting definition of what life is.

Agreed. It's a common error to think that the smallest fraction of something is 1%.

A very short distance. IIRC something like 20 or so light years, but I'm having trouble finding the citation. That's for radio waves (and the number is getting smaller as the technology is getting better -- EM radiation blasted into the universe is considered waste by hardware engineers).

For direct detection of life, that's still an open question. I remember a poster done by a grad student who looked at whether life would be detectable from the Moon, looking at the Earth. This was tested with data from one of the outer solar system probes which did a lunar flyby on its way out (Cassini?). The result, IIRC, was inconclusive -- you could see signs of life, but not anything that was absolutely definitive proof.

Indirect evidence might be provided by spectra of the atmosphere observed via solar transit. A biome is likely to have different spectra than would be predicted by inorganic atmospheric physics. Still, that's making some assumptions about what extraterrestrial life would be like, and only only visible along the elliptic plane.

Life, or intelligent life?

We can infer life based on atmospheric compositions NOW, but only if that planet fits an extremely narrow margin... meaning, Earth. Earth three and a half billion years ago had life on it, but you'd be hard-pressed to tell it from orbit.

If you want to move to unambiguous (intelligent) life then.......

The largest radio telescope we have (the 305 meter diameter Arecibo) would need to have it's sensitivity increased by around two orders of magnitude JUST to pick up our TV/FM/AM signals from outside the solar system. So, the crap we pump out the most couldn't even be detected by Voyager 2, if we had strapped a giant dish to it.

If we move into the narrowband signals then, depending on the source-strength, Arecibo could potentially pick up signals at up to a few thousand light years... if it happened to be pointed in exactly the right direction at exactly the right time.

So, our most sensitive instrument is only capable of measuring a fraction of a percent of the spectrum in a fraction of a percent of the possible-directions-it-could-be-pointed if the point source happened to be sending a strong enough signal (aimed at us) at exactly the right time (which would be anywhere between 2 and a few thousand years ago).

I haven't done the math, but I suspect that regardless of the frequency and amount of energy we dump into sending out a signal (within the realms of not being scifi, anyhow), it would be impossible for anyone to detect us a thousand or two lightyears out (using EM radiation) without knowing when/where to look. They also wouldn't be able to "see" that for quite a long time yet. I couldn't find a list of "when did we start sending out signals at X frequency" (and I suspect it doesn't exist), but if we take 50 years ago as a guess and we assume we pumped out noise at a frequency that could make the distance at a power level sufficient to be noticeable and that there wasn't anything to get in the way of the signal then we're only looking at something like 2000 star-systems.

I agree. Why the assumption the Type 3 capable civilisations will necessarily wish to metastasise across the entire universe? One would hope that civilisations' ideas of what constitutes fulfilling and worthwhile activity will evolve and improve along with their technology.

The SUN is visible everywhere within a Dyson sphere; it's the STARS that you can't see any more. The idea isn't that a civilization wants to do this; the idea is that it needs that much energy to continue with whatever industrial or infrastructure processes it requires to support a very large population. Dyson reasoned, we need steadily increasing amounts of energy input to support what we are doing; if the trend continues, what's the limit? (Typical physicist question, no?) The limit is to harvest all the energy emitted from your star. The only way to do that is to build a spherical collector, so that every photon can be captured. Then where do you live? On the sphere's inner surface. Of what material could you build a stable sphere one AU in radius? Where would that bulk of material come from and how be processed and positioned? How would you provide gravity on its inner surface? We have no fucking idea -- but we are not a Type-whatever civilization.

The laws of any potential biology and the messiness of the world could together effectively limit a civilization's energy usage to much lower than indicated by the easily deducible laws of physic (the explicit laws of physics might limit the output of an internal combustion engine to a certain but the effective maximum winds up less than that. Human biological systems experience serious damage by being weightless for significant periods, etc).

I only recently realized that this "paradox" looking at the possibility not of "earth advanced" civilization but supposed advanced civilizations that would put out much more energy than humans put out.

The whole thing seems to rest on false-extrapolations of mid 20th century hard-science fiction authors. Our Western Civilization has experienced an exponential growth of some things, has expanded it's "frontiers" quickly in a variety of ways, conquering the rest of the globe and then labeling space "the final frontier".

But all this has been low-hanging fruit. We're reaching the end of population expansion, space is fundamentally hostile to human life in a way that would take tremendous progress to overcome and we're facing longer term consequences of the rapid expansions we have achieved (global warming is just one of the consequences). If humans survive this, we'll have to have somehow achieve a steady-state for energy consumption and related things. But once we do achieve that steady state, why would we want or need to suddenly start using the energy of an entire star (after the thousand years of scientific progress we'd need to under how to do that)?

I often wonder this as well. The speed of light isn't really a physical limit to expansion - generation ships are theoretically possible. It may just be that the Great Filter takes the form of relatively benign[1] economic and/or sociological obstacles.

At least, if you take a diff between typical beliefs at the time the Fermi Paradox was formulated vs. typical beliefs now, I would say the experience of the shutting down of Apollo and overall reduction of human space exploration is probably the most relevant new observation we have made since then.

[1] In the sense of: You don't need nuclear armageddon to stop humans from spreading to other solar systems; the price tag of interstellar travel is sufficient.

> I am surprised a more common argument was not mentioned: ... maybe the speed of light really is a fundamental limit ... they still can't violate natural law and are thus unable to reach us.

One of the assumptions of the article and of most serious scientific discussion of the topic is that the speed of light really is the fundamental limit that it appears to be. It's not mentioned because it's axiomatic. The only thing in favour of the speed of light not being an absolute limit is that people don't want it to be. And wishful thinking is a very weak argument.

This does not make interstellar travel impossible, just very difficult. It is not feasible for us at this time, but it does not "violate natural law".

Even without FTL, if civs can travel across stars, they should have already colonized the galaxy.

Imagine a civ arising 50 million years ago (a majority of the other stars in the Milky Way are billions of years older than the Sun). It takes 50,000 years to become interplanetary, and then 1000 years later it's ready to launch a mission to the nearest neighbor, 8 light years away. It travels at 0.02c and then arrives 400 years later. After 2000 years it has colonized that system enough that it has local resources to repeat the process.

The galaxy is 100,000 light years across, so that allows a spread from one edge to the other in 30 million years, which is long ago for us. Forming closer to the center and allowing for the mixing of star systems with galactic rotation would shrink that number.

Wormholes or warp drive would actually explain the Fermi paradox for me: since the other civs are used to their stars that are older and hotter, and they only pay attention to the prime real estate. But limited to the speed of light, a civ will spread by filling each nook and cranny it can live in.

... or, how about the hypothesis that we were intended to be a seed package (a.k.a. "biological rootkit") but due to a bug in the programming, we failed to develop properly. Just a mistake playing itself out...

Exciting for a movie plot I guess. But, what could they win from exterminating another inferior intelligence? By your context, they are already inferior, and thus, no threat to the apex civilization.

What responsibility? I can see absolutely zero responsibility attached to that scenario.

Humans also may be the most responsible intelligent life that ever exists in the universe. What's the basis to judge such things to begin with?

There's an exceptionally low probability that human survival has any bearing on whether other intelligent life comes to exist (in the we're first scenario). Being first bears no responsibility because future life in the galaxy or universe is not inherently dependent on what we do.

I had the same thought and agree with what you wrote. But when you think about this set of evolutionary steps you still end up with the same scenarios: you are rare, you are first, you are fucked. So in that regard, you can subsume all of these steps into a filter.

Even if we wipe ourselves out tomorrow, that still means that a civilization was able to broadcast its existence for about 80 years. If the Great Filter is now or ahead of us, that at least implies that pre-filter civilizations can be advanced enough to signal their existence.

At some point our signals will be too weak for anyone to pick up or distinguish from cosmic background noise, which probably limits the radius of the sphere of stars that can hear us, but anyone inside that sphere gets at least 80 years to be listening to potentially hear us.

So, even if civilizations only last for say 100 years on average, and you can only hear other civilizations within N light years, if N is big enough eventually someone should hear someone, and if N is really big enough, somewhere in that 100 years everyone should hear at least one other someone.

I'll add another guess.

A resource crunch, i.e. we simply use up the required resources before we figure out how to explore our planetary neighbourhood. e.g When we figure out that a helium engine is possible, very efficient and very safe, we no longer have sufficient quantities left.

A lot of people consider nuclear annihilation a big threat but I'm not too worried about tbh. I mean if you think about it, every major player has got a trigger to end all life at any given point, doesn't it seem reasonable that at some point you invest a lot of money into systems that can safeguard and prevent this type of catastrophe. I know a lot of people may consider the governments dangerous and selfish but they aren't stupid, major players have definitely got systems in place to neutralise these threats.

At least they do in my optimistic viewpoint.

Of course no one can now right now, it's not one of these things that can be solved by theoretical work alone. At some point - assuming we don't go extinct before reaching it - we will know.

But it's still open to useful speculation, as there might be something we still need to consider in order to avoid said extinction.

The Fermi Paradox is one of the more thought-provoking signs that something might be amiss (at least in our part of the galaxy), and especially because our culture is predisposed to not take anything happening on the interstellar stage very seriously this provides an impetus for reflection that would otherwise not happen.

One of the most benign (but ultimately depressing) possibilities is that biogenesis is somehow extremely unlikely. There is no reason to assume this is true, given that we know even the more complex building blocks of life are actually very prevalent throughout the universe - but it may still be statistically unlikely that cells form from them. On the footsteps of that possibility follows the hypothesis that technological intelligence is rare. Again, that's not exactly in line with what we can observe on Earth, but it might still be the case.

Most of the other options should be positively troubling, though.

Of course we can't know for sure. The article presents a large number of hypotheses and arguments for them, most of which are fairly reasonable.

Or we just haven't observed them yet because we aren't technologically advanced enough? What if they don't use radio?

4 seems likeliest. Interstellar colonization is simply impossible because of the vastness of the distance that must be covered. It requires more energy than can be summoned to get a useful amount of hardware across multiple lightyears.

If AIs were taking over left and right we'd still expect to see some kind of evidence of their existence. Since they'd only be replacing biological civilizations I don't think it would count as the Great Filter, not in the context of Fermi's Paradox at least, as you'd end up with roughly the same number of technologically capable civilizations after the filter.

Or maybe the long living civilisations never existed, or we aren't knocking on the right doors, or in the right areas?

There are humans that try to talk with ants (and bees, and dolphins) using those creatures' own methods. Unless there were strongly-enforced no-contact laws, then some alien researcher would want to inspect those Terrans and see if we can talk. Even if they are way smarter, they'll use that smarts to talk with us in a way we can understand.

that exact possibility was listed in the article.