It's about signal and noise. Let's say there is a civilization out there, and we know about each other and want to talk. We point a big parabolic antenna at each other and start exchanging radio massages. That's what we are doing with Voyager right now, we point some high-gain antennas at each other and talk. At the rate of 7.2 kb/s [1], or one quarter of the bandwidth of the old dialup connections. But Voyager is close, stars are far. The closest star is about 2000 times farther than Voyager 1. Radio waves decay with the square of the distance, so if a Voyager-size antenna were to transmit towards us from 2000 times farther away, we'd get a signal 4 million times weaker. So, our friends out there need a much bigger antenna than the one on the Voyager, and we need them to point it straight at us, and we need them to blast a mighty strong radio signal towards us. We should also point a bigger antenna at them (the one we point at Voyager is 70 meter wide, not really a toy). Somehow between their bigger antenna and our bigger antenna, we need to overcome the 4 million decay factor. If our friends are 10 times farther away from us than Proxima Centauri, then we need to overcome another factor of 100.

But, our friends out there don't know about us, and they don't set up a mighty large antenna and align it perfectly in our direction. They simply chatter locally using radio waves, in many cases, their antennas are pointing towards their intended receivers, and not randomly towards some exoplanet far far away (the Earth).

SETI never had a chance to find anything.

[1] https://voyager.jpl.nasa.gov/mission/spacecraft/instruments/...

The more significant 'silence' is the fact that every star in the Milky Way galaxy has not already been colonized and turned into a Dyson sphere.

Species with language and toolmaking capabilities seemingly grow in technological sophistication at an exponential rate, so on the geological timescale, will quickly acquire space flight, grow to populations of trillions, harness the resources of their star system, then move onto settling a new star, and so on.

Why do you believe that?

You're making the assumption that the problems involved with prolonged space travel are solvable with the time and resources we have here.

It could not be. It could be too expensive to colonize beyond the immediate area. If even the immediate area can be colonized.

There's also the assumption that there's going to be a good reason to make a non-returnable investment. Because, at some point, that's what it is. The speed of light is a limit we have not even come close to exceeding, much less approaching. And even if we do, and the people on the ship, time dilation, yadda, yadda. It does not matter. The people on Earth will still experience time normally. It taking the ship no time at all does not matter if it takes 1000 years on Earth. Or even 50 years. The return has to be phenomenal or the cost negligible.

I assume the cost of settling other stars would become negligible at some point. If our solar system becomes a Dyson Sphere, and we have a population of thousands of trillions of people, I can't imagine how launching laser propulsion spacecraft that can travel at 0.2c toward other stars wouldn't be easily within reach of any moderately wealthy coalition of space enthusiasts.

You're right though. I haven't actually done a careful estimate of the resources required vs the resources available to a Type II civilization. If the former is significant relative to the latter, and there is no Return that can motivate that magnitude of an investment with the type of investment structures that will evolve on a solar-system-wide economy - where investment time horizons have no need to be extraordinarily long - then maybe interstellar colonization is not inevitable.

This is getting close to imagining a perfectly spherical cow in a frictionless environment.

Why do you assume the cost of settling other stars would become negligible?

Our solar system is not a Dyson Sphere. What makes you think it will become one?

We don't have a population of thousands of trillions. Why do you think we'll get there in a manner in which all of them will be coordinated under one banner?

What makes you think that laser propulsion will be practical for such applications? Considering we haven't had a single laser propelled craft used in space exploration. Also, 0.2c is a clever way of not saying 20% the speed of light. Or 100 million miles per hour. How long do you think it will take to get a person to that speed? At 3g, it would take over a month of pure acceleration. The human body can withstand 3g for about an hour. You'd have to accelerate closer to 1g once you've broken Earth orbit. And now you're talking months. Months to accelerate, months to decelerate.

So yes, if we solve all of these other really, really, really, really hard problems, some of the other problems aren't that hard.

>>Our solar system is not a Dyson Sphere. What makes you think it will become one?

Because 1. of the accelerating rate of technological progress that we've seen over the last 2 million years, and 2. the deduction that preferential selection leads to economic systems that harness more energy and replicate themselves becoming more common

>>We don't have a population of thousands of trillions. Why do you think we'll get there in a manner in which all of them will be coordinated under one banner?

They wouldn't need to all be under one banner.

>>What makes you think that laser propulsion will be practical for such applications?

Because we understand the physics of it. It's theoretically possible, and assuming sufficient advances in science and engineering, will become practically possible.

>>And now you're talking months. Months to accelerate, months to decelerate.

I don't see such a requirement preventing interstellar colonization.

> Because 1. of the accelerating rate of technological progress that we've seen over the last 2 million years, and 2. the deduction that preferential selection leads to economic systems that harness more energy and replicate themselves becoming more common

So, in other words, no clue, just wishing. You've seen a logarithmic rise and don't even consider that it could level off in the same fashion. The graph of technological advancement could be an arctan.

> They wouldn't need to all be under one banner.

So everyone handles their part of the sphere? And how do we decide where to go once we get it moving?

> Because we understand the physics of it. It's theoretically possible, and assuming sufficient advances in science and engineering, will become practically possible.

In theory, there is little difference between theory and practice, in practice there is a hell of a lot of difference.

Also, I'm not granting your assumptions. Why do you believe those assumptions? You've not given a reason besides that you believe that we will continue progressing at an exponential rate.

> I don't see such a requirement preventing interstellar colonization.

Then you don't understand the problems.

>>So, in other words, no clue, just wishing. You've seen a logarithmic rise and don't even consider that it could level off in the same fashion.

The logarithmic rise has been in place for a long time. The likelihood that it ends in the near future, before long-range space flight, seems unlikely.

This is especially so because the resources and capabilities being unlocked by new innovations seem to be inherently expand human civilization's rate of innovation.

For example, the cutting edge of technology today, like reusable rockets, NN-based machine-learning, and 3D printing, seem very likely to exponentially increase the resources/productive-output of our civilization.

Intuitively, I don't see any reason this accelerating progress will stop until physical laws become the only major limiting factor, and these laws allow for an exponentially expanding, seafaring civilization.

Of course, I don't know for certain. It goes without saying that these sorts of discussions are speculative.

>>So everyone handles their part of the sphere? And how do we decide where to go once we get it moving?

We don't need to propel the entire Dyson Sphere. Some group(s) needs to create a massive laser emitter, and use it to propel an artificial craft.

>>In theory, there is little difference between theory and practice, in practice there is a hell of a lot of difference.

Theory tells us what is possible. History tells us what to expect in terms of long term trends.

Based on the longstanding trend and intuitions about the nature of technological/economic evolution, I think we can expect anything that is theoretically possible to do with a small fraction of the resources extractable by a Type II civilization, will be done by human civilization, and hence interstellar colonization will be possible.

Yes, I agree. Just note, that this is assuming however, that no alien civilization has developed any vessels that would bring them closer to use, e.g. in our solar system so we could detect their signals

Even the focus on on radio is potentially misguided. Perhaps there are alien species who's home planet is under some heavy fog so they have evolved to see the reflection of radio waves, to then go bouncing high power radio signals around could potentially blind themselves so they have evolved some other means of distant communications.

That's just one failure scenario, if you took a Wifi signal and could somehow transport it back in time 100 years and blast it out at 1000 times the normal energy how long would it take past us to notice?

I think even 100 years ago, a kilowatt microwave transmitter would probably draw attention to itself by the way that eggs explode and cups of water boil when near it.

Fair point. Call it 60w or even 1w if that feels better. It's still many orders of magnitude over what you would be receiving across space from another solar system.

Also, for mild amusement, your comment reminded me of this video https://www.youtube.com/watch?v=b9UO9tn4MpI

You would have to stand right next to a 1kw microwave transmitter to notice any heating effects. That wouldn't help you locate it at any distance.

The SETI Institute has a very active YouTube channel if you are interested in updates: https://www.youtube.com/channel/UCzQdkHKOTVT_chwgDcau4sg

They also provide publicly available audit for their financials so you can see where they are at: https://www.seti.org/about-us/financials

As far as I can tell, they are still going strong. And the YouTube channel is always very interesting, and cutting-edge! It's not always about alien life directly, many times it is tangentially related (helpful [to the search] technologies, breakthroughs, panel discussions, etc). Perhaps not the most refined broadcasts, but they are always very educational and informative.

We are the only animal species capable of sending radio waves in space. For all we know it's an accident. Dinosaurs or scorpions lived longer than us as species but would probably never reach that level.

So the universe may well be teeming with life, but not the kind that sends radio waves.

We have only covered ~200ly with radio waves. That is a small spot in our galaxy, let alone universe. The core is ~25.000ly away. I think the original signal would be highly distorted by then. I still think seti@home was worth it, but it cannot answer the question about alien life negatively if it doesn't net a positive result.

True. I have always wondered why no other species on Earth have evolved in a way Humans have. Every other species maintains the balance in nature but we are the only species actively creating imbalance and destroying the planet. Prometheus might have been true after all.

All the species evolve the same way.

None of the species care about any specific "balance".

Humans are not destroying the planet (talk about hubris), but the biosphere and possibly the civilization.

I don't know about that. One species poisoned most other to death, a long time ago.

What species might that be?

There are five known big mass extinction events in Earth life history, the first one is caused by... drumroll... small plants. https://www.youtube.com/watch?v=mAkjETPM1s4

That lead me to this one, he's funny: https://www.youtube.com/watch?v=FlUes_NPa6M

That's because sooner or later every species enters an equilibrium state with the amount of energy available in the ecosystem. In the process it may out-compete quite a bit of other species, and so we speak of 'invasive species'.

> Maybe something is out there, but out of reach, or deliberately silent?

Have you read The Three Body Problem series by Cixin Liu? It's a terrific (and recently quite famous + awarded) sci fi trilogy that explores this idea. That all sufficiently advanced civilizations have learned to be extremely radio silent in order to escape detection. Reason being that they all eventually conclude that, from a game theoretic standpoint, the only reasonable thing to do when you detect another civilization is to eliminate them before they do you.

The problem I see with this idea is that it depends on either FTL travel, or on a horizon of time much larger than I would imagine. If we were discovered by a war-like civilization in one of the nearer stars today, it may well take them hundreds or thousanfs of years to get here even with a probe. Is it really a plausible threat?

This is exactly the scenario in the books ;)

Those book's are absolutely great, the 2-D probes pack t to 3-D..ah man have to read them again!!

When malicious eavesdroppers are involved, some fates are worse than death...

http://freefall.purrsia.com/ff400/fv00307.htm#anunsecuredlin...

Others like Vernor Vinge have speculated that the galactic net has really bad malware.

This assumes that alien civilizations purely see us as competition and not an organism they can achieve synergy with.

What if organisms could choose other ways of allying and joining together? What if, say, you had the strong, dominant, ambitious sub-population of a race trying to ally with other strong, dominant, ambitious life forms without thought to race? What if the organisms in the universe which favored peace decided to seek each other out and unite for a common cause?

> What if organisms could choose other ways of allying and joining together? What if, say, you had the strong, dominant, ambitious sub-population of a race trying to ally with other strong, dominant, ambitious life forms without thought to race? What if the organisms in the universe which favored peace decided to seek each other out and unite for a common cause?

That could be true.

Judging by history, that's not a very good bet. Peace sort of works among humans, in part because we are so close genetically. But Pre-WWI Europe showed that you can't engineer peace even by inter-marrying rulers.

Stepping away from humans a small amount, even today people regularly eat primates of various sorts (i.e. "bush meat").

Why do you think humans would ever make peace with alien cultures?

> Why do you think humans would ever make peace with alien cultures?

Great question. Maybe we need interstellar mutually-assured destruction. Seems to be the only thing, short of dominance, that has worked to preserve peace(-ish).

> Maybe we need interstellar mutually-assured destruction. Seems to be the only thing, short of dominance, that has worked to preserve peace(-ish).

It seems unlikely to me that when 2 alien cultures meet, that their technology levels are so similar that MAD is possible.

It might not need to be about technology, but biology, à la War Of The Worlds.

Whilst I doubt that (all of?) our viruses would have any effect on them (as they require our own cells to reproduce - aliens are unlikely to have a similar makeup), but things like funguses and bacteria could be very very bad for them.

Seems fairly unlikely though.

Random bacteria and fungii that are introduced to humans don't kill us all off. Bacteria especially are everywhere, it stands to reason that over all of the exploring, investigating and just plain spreading that we do, we'd encounter some bacteria that are new to a population. If those had any great chance of killing us off, shouldn't at least local examples exist of that happening?

Instead I think what we see are the organisms that affect us are those that coevolve with either us or with related species. We're killed by the things we spend a lot of time with, not random out-of-context bacteria that's never seen a mammal before.

If that's true of us, seems hard to say why it wouldn't be true of aliens, no?

> We're killed by the things we spend a lot of time with, not random out-of-context bacteria that's never seen a mammal before.

We're mostly killed by things that have never been in humans before because we haven't developed defenses. Sure, most of those things don't kill us, but you really only need the right one to come along and basically wipe us out. Part of the reasons we're ultimately able to develop a defense is because it is Earth life and we've seen all the tricks. Any alien microbe that is able to establish itself inside our bodies might not have to worry about any of our defenses.

I think you've really got the wrong model. Think of the introduction of non-native species to various ecosystems. A lot of the time, the non-native species either can't hack it, or they find an equilibrium. But some of the time you get kudzu or eurasian watermilfoil.

In any case, the point is largely moot. Any civilization we are likely to meet in the next thousands of years will necessarily have to visit us and if they can do that, they can just lob a couple space rocks at Earth and wipe us out from a distance.

> it stands to reason that over all of the exploring, investigating and just plain spreading that we do, we'd encounter some bacteria that are new to a population. If those had any great chance of killing us off, shouldn't at least local examples exist of that happening?

We have examples of exactly this! It was very bad: https://en.wikipedia.org/wiki/Native_American_disease_and_ep...

Those were diseases already in humans moving to an untouched population of humans, not what I was talking about.

A bacterium that hasn't seem humans before is pretty unlikely to be able to do anything to us. One that hasn't even been in mammals before is even less likely, etc.

They definitely could choose. The problem is: communication. Light speed, although fast, isn't fast enough for communication between vast distances. How can you establish any sort of trust when messages take decades/centuries to deliver? It'd simply be safest to expect the worst.

this is where i lost interest in the book. the idea that destroying another civilization is the only reasonable choice is beyond ridiculous.

first of all, game theory is based on our current experience and conditioning. if we raise a society where cooperation is valued, then the outcomes of game theory will change too. it is absurd to assume that game theory is universal.

but even if it were, and we'd have to assume that all aliens are hostile, the recources necessary to mount an expedition to another inhabited solar system are much larger than the benefits of exploiting a remote planet. it's simply not worth it.

what would be the point?

my expectation is that before we are able to send ships we'll be communicating for a long period, giving us enough time to share scientific discoveries.

i'll even go as far as to claim that developing space travel that can take us to another inhabited solar system will only happen in collaboration with the civilization that we want to visit.

Probably in universe time, equivalent intelligent civilizations will only be using radio waves for communication for maybe few hundred years. To be able to find radio signal from another civ in that window of time is unlikely. A more advanced Comm method is used.

In this series they move on to gravitational waves.

I have not, I will definitely check that out, thanks for sharing. I feel that SETI is something I'm woefully uneducated on, and can't find good places to jump into research before sources seem to go wildly off the rails.

Yeah I can testify that it's one of the best Sci-Fi novels these years. I read the original Chinese version but I heard that the translation of 1st and 3rd book (by same person) is excellent.

Wouldn't someone send communication signals to lure or bait other civilizations? For example, spam a friendly hello message on every potential communication channel and encourage new civilizations to reply. When they do, destroy them.

No, because that'd just be endangering your own civilization unnecessarily. There's always a bigger, badder civ out there :)

But earth debunks that theory, no body came to destroy us yet.

We can't send a strong enough radio signal to be detectable at any other nearby stars

The Three Body Problem is great, but it assumes the existence of weapons of ludicrous destructive power.. The only other time I've ever seen a piece of fiction where someone had that amount of destructive power was in a cartoon. (And even then I only saw it once)

If you assume that there's no faster-than-light space travel, it doesn't really make any sense to engage in interstellar conflict IMO. The same tech that would let you travel between the stars would also let you live in comfortable artificial habitats around your own home star, close enough to the rest of your civilization to be able to watch TV and keep up with HackerNews.

> The Three Body Problem is great, but it assumes the existence of weapons of ludicrous destructive power.. The only other time I've ever seen a piece of fiction where someone had that amount of destructive power was in a cartoon. (And even then I only saw it once)

That part doesn't seem to hard to me. A robotic spacecraft could install solar sales on a comet in such a way as to crash it into the target planet a few hundred years later. This could go unnoticed until it was too late by the target planet. Alternatively, a beam-powered probe (e.g. 'starwisp' or similar) moving at relativistic speeds could be crashed into the target planet.

Neither of these require cartoon physics.

how detectable would the EMP from nuclear explosions be? Obviously that is strong, but not very directed..

You do realize that there is gigantic nuclear reactor sitting about 93 million miles from where you are right now, right? An energy source so massive, it would only take a small fraction of it to heat and power several full planets. It would be like billions of nuclear explosions every second.

The Sun dwarfs anything we can do on Earth. Any arbitrary explosion of that sort wouldn't even register as noise next to the Sun. Our radio transmissions are directed and deliberate in a way that is noticeable even among the noise. Like watching scrambled HBO on an old cable box.

Yes. However I don't know if that is different. That is a roaring fire, whereas the https://en.wikipedia.org/wiki/Tsar_Bomba was a 58 megaton event which would have created a pulse. Electronic devices can sit in the sunshine all day, exposed to the roaring fire of the sun but a singular EMP can take them out? When you look for things, you look for what is different to its surroundings. Even when our own people are looking for planets around other stars, they are looking for an incredibly small change. They found something nearly 30,000 light years away like that.

Yes, we're close enough to Earth that it has a lot more affect on us than the Sun. And the Earth has a magnetic shield. Etc.

The Tsar Bomba did not destroy all life on the planet, did it? A simple solar flare is 5 to 10 magnitudes larger. Yes, small changes, but small changes that don't belong.

We are close enough to the Sun that even if that were detectable at the scale of the cosmos, the distance between the Earth and the Sun is a rounding error at the scales we are talking about.

Appreciate this. We are effectively in the Sun's atmosphere. The entire solar system is. Scale matters.

Maybe they're still on the way. We didn't start radio broadcasts until quite recently ago.

As other commenters have covered, SETI makes a whole lot of assumptions about what extraterrestrial contact would look like and wastes time exploring the hypothesis that another civilization would behave just like us in our infancy, except at a time when they have the capability and surplus energy to transmit signals many orders of magnitude stronger than we do.

To my knowledge, we are not currently transmitting sustained signals that would be detectable through the noise by any neighboring systems, and to do so for any sustained period of time, let alone a significant enough amount of time to be noticed (geological time scale) AND then wait for a response would take a ridiculous amount of energy, and provide no return on investment for literally thousands of generations. And even then, that return on investment might just be an invasion.

So in my opinion, SETI is a poor use of compute and investigating the more credible of the tens of thousands of as-of-yet unexplained UFO reports would be a better use of time. Either they are already here, or we will not have the tools to discover neighbors (if they exist) until our technology is far more advanced.

Carl Sagan has a nice example for this: " we take a glass of water from ocean and assuming there is no fish exist"

Is it possible that the universe is teeming with intelligent life, just randomly distributed throughout cosmic timelines and therefore unlikely to be detected?

It's the possible that every single star has a civilization at the level of our's, actively transmitting and detecting, yet find nothing. IE, Earth couldn't detect the signal of Earth if they were transmitted from the nearest star.

This is seldom mentioned in the press. I learned it here, on hackernews a decade ago, I think. I was shocked. It's shame you get people not knowing basic stuff like this.

> The Arecibo Observatory and FAST could each detect the TV carrier wave leakage out to a distance of about sixteen lightyears. That’s a little bit further away than Tau Ceti is.

https://www.forbes.com/sites/quora/2017/01/27/how-far-into-s...

That's for detecting a TV broadcast. But how far away could one Arecibo observatory detect another Arecibo?

> The answer is, that except for obscuration and dust in certain places, it could be anywhere in the galaxy and we would pick up the signals. That means at least one hundred billion stars that you can listen to for signs of extraterrestrial intelligence.

https://www.rollingstone.com/culture/culture-news/carl-sagan...

How far away can our own technologies detect our own transmissions? If a planet 100 light years away was making as much RF noise as us, could we detect it? I thought we could.

One easy way to think about this is:

If our radio signals would make it to a planet 100 light-years away (even if you ignore Inverse-square law), you could probably power them down and still reach all of earth. Why would one pay for that extra, unneeded, power?

Because antenna gain is a function of both the transmitter and receiver, and detection is different from getting a high-quality signal. Most high-power radio signals on earth are aimed at transmitting to fairly low power, small, cheap devices which need to recover a good amount of information from the signal. This is very different from the requirements of a radio telescope (which has a gain many orders of magnitude higher because it has a much larger space, power, and cost budget) detecting a signal (which requires far lower signal-to-noise than reconstructing something high quality from it).

Our own people on this mote have only been teeming with radio communications for but a blip of time (in the grand scheme of things).

Perhaps we will disappear only to be a part of the fossil record in just as short a blip.

If all radio-species come and go so briefly, consider a signal from another planet serendipitous.

But, you know, you have to try.

Except, not even

If an earth-like society existed on the nearest star, transmitting as we do. Neither society could detect the other.

Ideas that we could find stuff that is "out there" presuppose societies that are more advanced, and more advanced on our terms, transmitting as we do but loud enough to "hear".

PLUS what you mention, we in our current incarnation have existed as a blip.

> Except, not even if an earth-like society existed on the nearest star, transmitting as we do. Neither society could detect the other.

Proxima Centauri, the nearest star, is 1.301 parsec away (4.25 light years), so sufficient time for a signal to travel between them and us, no?

Maybe you are saying we couldn't detect each other due to a linguistic or intelligence gap?

It presupposes they use radio and that they’re specifically sending a message to us. We have the technological capacity to send such a message. Listening is much cheaper and safer so most civilizations would probably opt to listen.

There is a glimmer of hope!

https://en.wikipedia.org/wiki/Wow!_signal

Last I checked the wow signal was proven to come from microwave interferrence.

Source?

It's just that the speed of light is too slow for any relatively recent signals to reach us from such distant sources. Most of what we can receive is very old news.

nit: teeming

fixed, thanks

The first SETI-specific NASA grant in over three decades was just awarded so there is still hope we will see something in our lifetime.

https://www.cfa.harvard.edu/news/2020-12

Space is enormous! While our capacity to search it for signs of intelligence is miniscule.

Dark Forest.

Let's hope we do not contact anything until we have really, really good weapons.

Its a novel.

and it's probably the best hypothesis why we don't seem to find much.

What hypothesis?