It took single celled organism 1 billion years to happen on Earth, it then took another 2 billion years for the first multi-celled animal. The jumps you're describing aren't easy at all.

And there's no such thing as evolution towards intelligence. Evolution does not favor certain traits and at this point the most successful organisms on Earth are bacteria and the most successful multi-cellular animals are the insects.

And actually intelligence requires big brains, which requires energy and thus fuel, so in constrained environments it can be a trait that's detrimental for survival. Even if multi-cellular life developed on other planets, to go from that to fairly intelligent dinosaurs or mammals is still very unlikely.

Obviously, the problem with extrapolating what happened on Earth is that we've got a sample of 1.

One could also argue that plants are the most successful because they have the largest biomass. Diagram here: http://www.pnas.org/content/pnas/early/2018/05/15/1711842115...

It's possible that evolution inherently drives life towards intelligence (as a likely outcome, not in the teleological sense). Three counter-points:

* Sure, an extreme minority of organisms are intelligent right now, but considering that intelligence is such a recent invention, we can't assume that this is the terminal state of affairs. Indeed, intelligence is making progress in taking over the biosphere that shows no signs of slowing down. Perhaps thousands or millions of years from now, we will have converted all biomass to sustain our own civilization and perhaps (artificial?) life entirely devoted to intelligence will be dominant.

* "Evolution towards intelligence" can be a "thing" even if this only occurs to a small minority of species. This is not to say that evolution is a linear progression from primitive to intelligent life; rather, if evolution makes life expand like a tree, and the degree of variation and complexity afforded by this tree is sufficiently large, it could be likely that some of the branches eventually reach intelligence (among myriads of other possible adaptations). This would be sufficient for intelligence to arise with high probability.

* Life is inherently concerned with representing and processing useful information about the environment. The chemical feedback loops that probably made up proto-life would have implicitly encoded information about their chemical environment (and the fundamental chemistry of life still echoes this information). Eventually the incorporation of more complex feedback loops combined with evolution led to the development of complex biomolecules, proper replicators, genetic code, multicellular organisms, nervous systems, brains, the mammalian neocortex, and whatever adaptations enabled human-level intelligence. What we see is a gradual progression through great many improvements towards more sophisticated information processing. It's plausible that a similar progression in information processing complexity occurs with high probability whenever life evolves, although the concrete steps could be radically different. Yes, it took billions of years on earth, but the universe has billions of years to spare and it's massively parallel. Again, there doesn't have to be a linear progression towards intelligence for all life; the conditions just have to be favorable for intelligence to occur as a particular adaptive niche in sufficiently complex ecosystems.

Of course, we can't really say much since we don't know what the actual probabilities given that we only have a sample size of n=1 for life and realistic experiments or simulations are far beyond our current capacity.

The question is: What could they possibly be using instead of some sort of electromagnetic signals?

There are only a limited number of fundamental forces in the known universe (unless our current understanding of physics is completely wrong), not all of which lend themselves to being used for long-range communication.

Gravity possibly could be used as a means of communication but I suppose it’d be rather slow and have a low bandwidth.

Some sort of quantum entanglement-based form of communication might be possible though that contradicts our current understanding of how information can be transmitted in the universe.

So, barring some fundamental shortcut such as Star Trek subspace, there aren’t too many options for interstellar communication.

Why not expect new physics we simply don't have the tools to see yet? Maybe something that only shows itself at very high energy or interacts only with neutrinos or antimatter or some exotic matter that isn't produced with fusion or supernovas.

What about beings that operate at very different time scales? What if there is some encoding scheme that blows our information theory out of the water so communication just looks like white noise?

What if evolution converges to a single shared consciousness or fierce independence and communication just stops being interesting after a certain stage? Or if non-interference is the very well enforced law of our corner of the galaxy?

I think it's hubris to think that we know the answers to all of the questions for physics or at least we know what we don't know. My assumption is that there are questions/problems/phenomena that we don't even have the context yet to imagine.

> What if there is some encoding scheme that blows our information theory out of the water so communication just looks like white noise?

You don't even need a new encoding scheme for that. Compressed data looks like white noise unless you know the decompression algorithm.

A signal with compressed data does not look like white noise. It looks like a sine or cosine wave that is around a well defined frequency, and the intensity/phase/frequency changes from time to time. The hops may look random, but the carrier signal is easy to spot.

If they use frequency hoping, the changes in the frequency are even more regular. It's more difficult to measure the exact signal, but all the hops are inside an interval.

You are describing FM, which does dump quite a bit of power into the carrier wave.... which is exactly why it's not used if you care about range/efficiency.

Check out things like "Olivia_MFSK" on wikipedia for something more current. It can transmit even with 14dB below the noise floor.

Seems like a any sane communication method for any galaxy spanning civilization would be: * encoded in such an advanced way that we wouldn't see it, even if using signals within our physics. * be highly directional

Maybe something like 1% of the asteroid belt would be converted into communication sats that could form a swarm that would over a few ns significant outshine the sun by focusing a signal on whoever you want to communicate with.

Of course typically the cloud of sats would be handling within the solar system communications or nearby stars that didn't require the entire cloud.

I do wonder if you could capture say 0.01% of the solar radiation for 24 hours and with 50% conversion frequency generate a single for 1 ns on the ideal frequency... could you outshine the galaxy on that frequency?

Of course the ideal frequency would be minimally blocked by dust and minimally generated by stars. The "Water hole" as mentioned by Seti (among others) would be a good start.

You’re probably more of an expert but what you’re saying is totally unintuitive to me.

If a signal carries the “this looks like a signal” information in addition to the source information itself... isn’t that a waste of bandwidth? Wouldn’t an ideally encoded stream be indistinguishable from noise?

I can understand for practical reasons leaving some bandwidth on the table to make it easier to detect signals, but when talking about advanced alien life forms we have to assume they are playing closer to the limits of physics.

Compressed data doesn’t looks like noise correctly encrypted data can.

That said however metadata will often be unencrypted and even encrypted data will have discernible patterns for example the transmission of say a 2.4ghz radio network with packets will look like white noise even if all packets are encrypted as you need to somehow modulate the signal for transmission control.

Under _our_ technology, yes. Why would that be so for a civilization even a hundred years more advanced than ours, never mind millions? Why would they be doing planet-scale broadcasts _ever_, instead of focussing the communication as tightly as they could in the right direction?

There's so many assumptions that they'll basically use a version of modern technology but bigger in the "why can't we hear them?" question. Tight-beam, fully encrypted data with sensitive receivers could easily be utterly undetectable by our understanding.

Well the beauty of the universe is that cannot be used as a good reason.

If civilizations are common then there are just as many less advanced civilization than us than they are more. Heck if technological progression leads to the downfall of a species than by default everyone we should be seeing is around our own level of development if not lower.

If intelligent life is an anomaly then it can be very well be that in the life span of an existing civilization they would be the only intelligent one in the galaxy or even beyond that and they would simply die out even 1M years is a blink of an eye for universal time scale.

And lastly regardless of what the civilization is today if they are on the other side of the galaxy we see a 100,000 year snapshot if they are in say another galaxy even a close one like the Andromeda galaxy we see them as they were 2.5M years ago.

Tight-beam, tachyon transmission, quantum entanglement with retro-causality suspension or w/e they might be using if they are so advanced beyond us that we look like anthills to them is fine but at some point they were just as advanced as we are and less so that's the noise that we should be hearing and we aren't.

That's assuming the exact opposite of this paper; that there's _infinite_ other civilisations, which is as obviously untrue as the idea that there are none.

If the period of time before all high-power communication is encrypted is short, then the likelihood that the period of our ability to pick up unencrypted high-power communications will intersect it is potentially very low.

The universe is _huge_. Most of our communications will not be audible above background radiation after a little way out - this could be no different for any other civilisation's communication technology. You don't use a nuclear reactor to power a cell tower, and if you don't put that much power into it then it's not gonna be detectable ten light years out.

I always wonder, if you draw a sphere around earth, some amount of light years away. How much surface of that outside sphere has our signal gotten in contact with. (for the sake of making it easier, say that all signals capable or reaching this distance, have done so)

Something like this:

http://www.planetary.org/blogs/emily-lakdawalla/2012/3390.ht...

Encoded data can sounds just like noise. Take Olivia for instance. It can transmit digital data at 14dB BELOW the noise floor. It's just a digital mode that hams use to try to transmit between countries for around 1 watt.

Then the answer is: we can only rule out intelligent life as we CAN immagine it. Sure, there could exist intelligent life of sorts that we cannot comprehend, that use physics outside of the standard model; God perhaps?

The fundamental forces are a starting point, but it's not right to assign special significance to EM. The great majority of mass in the universe does not feel electromagnetism. It's dark matter.

Humanity's expertise in electromagnetism is driven by our biologically EM-sensitive eyes, our physical size, the energy levels that permit classical chemistry, and the timeframe in which we live our lives.

Perhaps aliens exist with much larger physical forms, communicating with neutrinos over vast distances and larger time scales. Humanity would be completely blind to these signals.

EM is much easier, any moron wit a HAM radio can broadcast to the whole Earth, and a similar upgraded version that is still small and cheap can be used for interplanetary communication. So I'd guess EM for usual communications, but the idea of something weird like neutrinos for special purposes is nice.

I don't know the size of the current neutrino transmitter/receivers, but IIRC the size is about a big building. Even the initial EM device where smaller.

About dark matter, the current understanding is that it is diffuse and there are no "dark star" or "dark planets", but I always prefer to wait 10-50 (100?) years to call it definitive.

> Gravity possibly could be used as a means of communication but I suppose it’d be rather slow

Doesn't gravity "travel" at the speed of light just like EM radiation?

Yes but the frequency is way lower, so maybe less information/time.

Or an advanced civilization uses low power transmission with high compression codecs, maybe with spacial (cellular) dispersion.

Which of our modern transmissions would be decoded by someone from 75 years ago?

Two other factors that play a big role in not detecting life in the universe is:

1) it's a really big place. It's likely we can't see that far yet.

2) Will we be here a million years from now? Two million? Other civilizations could have come and gone dozens of times in our galaxy alone before we were here. And dozens may come and go after we're gone.

Milky Way is estimated to be what... 13.5 billion years old. Humanity is 200,000 years old. The time span in which we are actually able to detect anything outside our own planet is what.. 100 years old? I suspect it's a lot more than a dozen times. If life is more likely to develop, then humans have only been able to look out into our own galaxy for an entire 0.00000074% existence of our galaxy. Now, let's say a civilization does not last more than 1 million years for whatever reason, that means we exist for a whopping 0.00074% age of the universe to date. I don't know if I did my math all wrong, but if correct there is an enormous chance that 2 civilzation's paths may never cross. We could be living right next to the remains of a civilization before us and never know it.

#1 is a lot crazier, and more like: "we can only look at specific places, our detectors can only detect things which degrade as distance increases, and we might not be listening at the right frequency. So even if there were a civilization in this tiny, tiny region of the universe we are looking at, if they are too far away/obscured by debris/gas clouds, using wavelengths we aren't actively monitoring, we don't see them.

Okay that explains why we can't see them.

Why can't they see us? All the arguments for life say "the universe is so big there has to be more life, and highly advanced civilizations somewhere." Assuming that, sure, we can't see them. But why hasn't some advanced civilization seen us?

Some thoughts (in no particular order):

- some have, and have responded, but we aren't looking for them in the right place and in the right way

- humans have only been able to actively send information into space since only about the 1950s (radio waves), and physics dictates that locations 80 light years away are just now starting to see that, provided they are looking in the right location and in the right way (and that they are technologically advanced enough to do so.

- It could be that a sufficiently advanced civilization no longer has the capability to receive and transmit long-wave radio communications. Just like many computers now don't have any way to read a floppy disk, or if someone were trying to communicate via smoke signals, you'd be hard pressed to find anyone who could understand it.

- Space is so large that if a civilization several hundred light years away (an insignificant fraction of the size of our one galaxy, actually) sent us a message that we received and responded to, it's possible they could have collapsed by the time they receive our response. The converse is also true, they could have 'seen' us and sent a message, and we could collapse before we had a chance to receive it and respond.

I always thought that if a civilization was so advanced, why would it spend time interacting with a world like ours?

We may feel special, but that's only because we haven't found anything else. If they found hundreds (or more) of worlds like ours, then maybe we're just another dot on their galaxy map.

Plus if the media is anything to go by, all we do is shoot each other. Might not be too exciting for a civilization who can travel amongst the stars.

Why do humans spend time studying ants? Atoms? To further our understanding of the world. Seems illogical to think there isn't a civilization out there that wouldn't expand and explore other places.

Just seems unlikely that we assume, because the universe is so big, there are advanced civilizations out there - but not ones that can find us, not ones that we can find, for various reasons discussed in these threads.

If our understanding of the universe is true to a certain point, civilizations are far more likely to be essentially alone and "special" than many might think.

We study a billionth of a billionth if a percent of ants. Most ants we totally ignore.

Because there are an abundance of ants.

Is there a similar abundance of planets with life in the universe?

That's the subject of about a century of science fiction speculation.

The deal is, if we were one among hundreds or thousands, what are the odds nobody at all in any of those other civilizations would want to interact with us? Because we've received zero interactions. Dead silence.

Why is that? Well, it takes a lot of energy to broadcast, so they'd have to beam us a message. We're not really looking for beams. Don't even know what they'd look like? Laser pulses? Soliton trains? Neutrino bursts?

Someone would have to be very close (30 light years or so) to have noticed us and have time to signal back. Even among those, likely they would just watch us and then decide if they want to chance contacting a race that has thrown nukes at each other.

To put that in perspective there are about 400 stars within 30 light years of earth and among those stars we have found 26 exoplanets. This radius represents only about 0.00014% of just our own galaxy and an infinitesimaly small portion of the entire universe.

According to our knowledge of the universe.

And if that is accurate, then essentially we ARE alone in the universe. There simply isn't anything close enough - we'll be enveloped by the sun or some other catastrophe before that happens.

>Putting this altogether, it seems there's an excellent chance that primitive uni-cellular life evolves pretty readily and multi-cellular animals tend towards increased intelligence soon there after.

How much intelligence though? Dinosaurs were around for eons and, as far as we know, never used simple machines or mastered the use of fire. So far, the human branch is the only handful of species that ever has. Even fairly closely related primates haven't figured it out despite the fact that they watch us do it all the time.

Dinosaurs feel so much like a local maximum of evolution. Heavy investment in one "component" - exploitation over exploration.

"There is a next to infinitesimal chance that life started very quickly by some kind of once in billions of years magical circumstance."

Tautology? There is a very small chance that something with a very small chance of happening happened...

The intended meaning was that there's a small chance of something unlikely happening quickly. If it happened "quickly" (in geologic time) once conditions were favorable, that is evidence against it being enormously unlikely once those conditions obtained.

Multicellular life seems to be one of the biggest stumbling blocks. Life appeared very soon after it was possible, but a pretty huge chunk of the time since was limited to single cells.

Why? Once the earth is covered by single cell organisms there's going to be an incentive for even the simplest of cooperation. Quorum sensing can help reproduction, survival, collecting food, surviving drying out, etc. Once cells loosely cooperation that starts providing more specialization. Cells that have thicker cell walls, or better offense/defense, or more expensive pathways for breaking down more complex chemicals, etc. Seems like the natural tendency would be towards more complexity heading towards where you have cells that specialize being outside (and help control PH and water) vs inside (that specialize in other things taking advantage of the ideal conditions).

Keep in mind how many single cell organisms you can have in a single drop, how many drops are in the ocean, and how long a billion years is. Even a small competitive advantage turns into exponential growth for the community of cells. The noise of random mutations is going to eventually lead to a cooperation between cells that's going to cause a feedback loop.

Cell -> multi cellular seems easy and obvious compared to no cells -> cells.

Maybe the chance of life starting isn't so rare. It could be fairly common when a planet with organic matter cools and develops a magnetic field.

Meh. Much more likely they, and we, don't make it past planetary overpopulation, climate change or any of the numerous other self-made catastrophes.

Even asteroids, super nova's, cosmic radiation, bigger but dumber predators (Dinosaurs), etc.. lots of external factors could destroy a planet too, a planet is a fragile place, and keeping life on it is a fragile balance, it's a miracle we've lasted so long, imho.

None of these things is likely to actually be the end of life altogether, just life as it's known at the time. More asteroids won't make the Earth completely uninhabitable (just as it didn't the first time); nor will climate change (just as it hasn't before: https://en.wikipedia.org/wiki/Great_Oxygenation_Event). They'll simply be the end of our current human civilization, along with plenty of other current species. Other forms of life may benefit tremendously; things will evolve to take advantage of the new circumstances.

Quite, but it may turn out to be a great filter that no species, alien or terrestrial, has yet got past. Thus there may no end of life out there but none that has advanced far enough to be noticed.

Perhaps we'll be the first, though I have to say I'm far more pessimistic than say a decade or two ago.

I'm hopeful we can develop immortality tech, if we can do that, then also build generational ships...even if it takes 10,000 years we could colonize every habitable solar system, even without light speed travel and send findings back to earth on discoveries found. Obviously having a working Albucierre (Sp?) drive or similar would make things better, or some sort of wormhole tech. But we can get to alpha centauri in 100 years, sailors used to risk their lives to go on voyages, why is it too much to ask the same of scientists and their families?

Esp if we can figure out cryostasis, we should definitely make a trip to Alpha Centauri with actual people someday, if there's no-place habitable they could just keep moving on till they find a place. In the off chance something bad happens on earth at least they'd be able to reboot/restart mankind on a new planet.

Imagine if 10 generational ships set off in 10 different directions headed to 10 different solar systems looking for a habitable planet to setup camps. Even if it takes 500 years for each to reach their destination, if longevity increases into the 1000's of years, we'd still be able to witness it and it'd be pretty cool.

Those things probably won't escape the atmosphere, however. It would be much harder to bootstrap an energy-hungry civilisation any time within the next few billion years, as we've used most of the easily-accessible sources of fossil fuels. If human civilisation falls, whatever comes afterwards probably wouldn't be able to build a rocket, unless they wait for fossil fuels to regenerate.

Very true; the next global, technological civilization here would probably take tens of millions of years, if it happened at all.

Btw, how oxygenated is our neighbour Mars?

It took a very long time to go from single cell to multi-cell, implying it is unlikely.

A billion years is a very long time if you wait in a railway station. But in milliseconds, for instance, as powers of 10 is a blink of an eye compared to the magnitude of the search space of configurations of a single protein.

The context here is the lifetime of the universe. If that is 13 billion years, 1 billion is a considerable chunk.

If I interpret you right, you state that we might be extremely lucky hitting on a valid configuration so fast. In other words, the distribution might be at average at e.g. 1000 billion years. What shape would the distribution have?