Would we really know they are there?

[Warped9]

One of the arguments for lack of intelligent life is that we're not detecting any radio signals. But is it possible something is being overlooked?

For arguments sake lets say there is at least one world with intelligence within a hundred light years of us. Is it a given we could know they're there? We certainly wouldn't if they weren't broadcasting anything or not using radio we could detect.

Conversely is it possible they couldn't notice us either? Of course not if they didn't have sufficient technology, but if they did is it at all possible either of us might not notice the other for some reason or other?

Thoughts anyone?

 

[RobertVA]

After a century or two a civilization might discover a more effective technology or find it advantageous to use a frequency band that is lost among the natural background noise to anyone more than a few light years away. For that matter, a signal used for a high bit rate might be indistinguishable from a natural signal to a less advanced civilization, especially if they lack the proper decryption key(s).

 

[Bill Morris]

I don't thiink SETI is going to find anything.

But if you want an answer, here's the NICAP free online book download link. The books are rather old and some were best-sellers in their time. I just downloaded four, read the first three, and started the fourth, which builds a very strong case with a compilation of evidence from highly qualified people. That's the second one in the second column, titled The UFO Evidence. I guess that's the one to look at first, although the first three provide historical and other background information and make the fourth easier to digest.

http://www.nicap.org/onlinebooks.htm

And there are quite a few main-sequence (sunlike) stars within 100 light-years, some as much as a blillion years older than ours. So there could easily be aliens not so far away that are millions of years ahead of us that perhaps observe the Prime Directive with regard to us as a prewarp culture not ready for contact. And people on many planets may have models of Trek ships on display in their homes.

 

[MacLeod]

Well first of all they have to be broadcasting a signal of sufficent strength and on a frequency that we are monitoring. It is possible that an alien race has detected our signals and have sent back a reply on a frequency that we can detect. I believe it was the mid 30's that we started to broadcast signals of sufficent strength so they have been ttravelling for what 80ish years o they have travelled 80ly., so an alien race 40ly distant detecting a signal we send iif they send one back we wouldn't hear it until 2012.

 

[YellowSubmarine]

Well, there are many things that you need to take into account:

1. Signal strength: Currently the strength of the signals of Earth is weak enough that they are barely recognizable at any significant distance. I haven't done the math, but you'd have trouble receiving Earth's signals even from Mars, you'd pick them and recognize their artificial origin, but for making out what we are saying you'd need a significantly big radio telescope if not something bigger.
2. Not enough radio telescopes: Our radio telescopes are way too small. Cover the entire far side of the moon with an enormous array and then we're talking.
3. Directed signals: The number of unidirectional signals that we are sending and receiving is going down. Satellite TV is directed towards the Earth, interplanetary communications are directed at the planet they are for, cellphone networks are directed in the plane parallel to the surface. It's to be expected that an advanced civilizations would leak only a small portion of its communication signals into space.
4. Digital signals and shy aliens: When encrypted, digital data is unrecognisable from random noise. Of course, that's not necessarily true for the signals carrying it, but if the aliens wanted to hide their signals they could. They could create an artificial signal that looks exactly like a natural one if they wanted to.
5. The universe doesn't have to be overpopulated: While it's foolish to think we are alone in this vast universe, it's not unthinkable if our closest neighbours are really really far away. We might be lucky if there's another civilization in our galaxy, let alone the nearby stars.
6. There are way too many stars: We can't listen to all stars at the same time, if you want to pick something you need to isolate a really small area of space. The smaller the area the bigger the chance of finding something. It would take a lot of time to cover it all.
7. Too much noise: There are way too many natural signals to filter out.
8. We might have picked alien signals already: Just because you can't confirm the artificial origin of something it doesn't mean that it's not artificial. The signals might be barely recognizable against the background noise and we didn't work hard enough to tell them apart. Or perhaps we told them apart but we couldn't confirm their origin. Remember the WOW signal? It could have been an artificial signal directed to our location, but we would never be able to tell – it might have had a message encoded, but because of (1) and (2) we weren't able to read it. It's a bit disingenous to say “if there are aliens where are their signals” when we did get some signals that do not seem to conform to something natural.

 

[MacLeod]

Who knows with that WOW signal, perhaps it was from an alien race but after decades/centuries of looking for life and beaming singals into space and hearing nothing back. Gave it up. We could simpluy have caught the last bit of the signal

 

[farmkid]

Well, there are many things that you need to take into account:

1. Signal strength: Currently the strength of the signals of Earth is weak enough that they are barely recognizable at any significant distance. I haven't done the math, but you'd have trouble receiving Earth's signals even from Mars, you'd pick them and recognize their artificial origin, but for making out what we are saying you'd need a significantly big radio telescope if not something bigger.
2. Not enough radio telescopes: Our radio telescopes are way too small. Cover the entire far side of the moon with an enormous array and then we're talking.
3. Directed signals: The number of unidirectional signals that we are sending and receiving is going down. Satellite TV is directed towards the Earth, interplanetary communications are directed at the planet they are for, cellphone networks are directed in the plane parallel to the surface. It's to be expected that an advanced civilizations would leak only a small portion of its communication signals into space.
4. Digital signals and shy aliens: When encrypted, digital data is unrecognisable from random noise. Of course, that's not necessarily true for the signals carrying it, but if the aliens wanted to hide their signals they could. They could create an artificial signal that looks exactly like a natural one if they wanted to.
5. The universe doesn't have to be overpopulated: While it's foolish to think we are alone in this vast universe, it's not unthinkable if our closest neighbours are really really far away. We might be lucky if there's another civilization in our galaxy, let alone the nearby stars.
6. There are way too many stars: We can't listen to all stars at the same time, if you want to pick something you need to isolate a really small area of space. The smaller the area the bigger the chance of finding something. It would take a lot of time to cover it all.
7. Too much noise: There are way too many natural signals to filter out.
8. We might have picked alien signals already: Just because you can't confirm the artificial origin of something it doesn't mean that it's not artificial. The signals might be barely recognizable against the background noise and we didn't work hard enough to tell them apart. Or perhaps we told them apart but we couldn't confirm their origin. Remember the WOW signal? It could have been an artificial signal directed to our location, but we would never be able to tell – it might have had a message encoded, but because of (1) and (2) we weren't able to read it. It's a bit disingenous to say “if there are aliens where are their signals” when we did get some signals that do not seem to conform to something natural.

One more to add to your list:
Even if a nearby system were to develop intelligent life, it would be highly unlikely that would coincide with our own technological development. Say evolution is slightly faster or slower on that planet, or started slightly before or after our own, and we could miss them by millions of years. Earth is something like 4.5 billion years old, if I remember right. Say the other planet is 4.4 billion years old and is exactly like our planet in terms of evolution (not likely, of course, but just for the sake of argument, let's go with that). That means that planet is still 100 million years away from developing a civilization capable of talking to us, and dinosaurs are still roaming around. Humans have been around for so little time, and capable of sending or receiving radio signals for such a small fraction of that time, that it's no wonder we haven't found anything. The odds of another civilization developing close enough to Earth that we could detect their signals, and for that civilization's development to coincide with our own such that we could detect them is vanishingly small.

 

[YellowSubmarine]

If there wasn't evidence on the subject, it would be normal to expect that we are in the middle of time – that is, half of the civilizations come after us and half come before us.

Of course, there is evidence – complexity increases over time, you are more likely to find a civilization with a further generation of stars with more heavier elements, the first generations of complex life on Earth also weren't particularly clever, etc. But I haven't seen any attempts to put that together in a prediction, also the probability will start declining with entropy at one point, so it's quite complicated even if you forget the hairy details.

Still, I think it would be quite crazy if we are the first, one of the first, or even one of the early ones, though at the same time it is possible... And it drives me crazy to think that we could be the first (well, say in the galaxy, because first in the universe would be a bit too much).

 

[Tau Ceti III]

I did some digging on this a while back, and if I remember correctly, and this was directly from the SETI people:

- Our ability to receive a signal assumes the sender is putting out a signal far stronger than what Earth currently sends out

- The distance from which we could detect "ourselves" is about 0.1 light years

So an identical civilization to ours hypothetically could be on Alpha Centauri, and we would not be detecting them.

So any conclusions made from SETI efforts to date are worth exactly diddly / squat.

 

[YellowSubmarine]

What SETI is useful for is picking signals directed at us. Alien civilizations might be doing active SETI and sending signals to random stars and we might happen to be the receiver of such signals from time to time, and SETI might pick them up if they are listening in the right direction.

If civilizations are very common in the universe it's very likely that some of them would do active SETI and we'd pick them up, and I think that we should entertain the possibility that the Wow! signal was such active SETI attempt that didn't last long enough for us to pick it up again.

We can assume that we an average civilization, and we can also assume that we will be making many active SETI attempts even if the majority of us think it is a dangerous idea – you can't stop a group with a huge antenna and money to transmit signals, and it will be more difficult as technologies advance. From that we can infer that extraterrestrial civilizations would be doing it too, and far often, and it is a safe assumption to think that the number of civilizations that exist is tied to the number of signals picked by our current SETI attempts.

--- A crude example of the chances ---

Let's say there are 260 000 stars in a 250 light-year radius. Let's suppose that 260 harbour civilizations that are doing active SETI now, and let's assume that each has a telescope array sending a message continuously to at least 4 stars at a time, for 4 hours continuously. Let's assume that they all narrow down the list of stars to about 1/10.

With these figures, approximately 6240 out of the 26000 nearby star systems are targeted each day, which means that the Solar system is targeted roughly once every four days. With 26000 possible sources, this means that if we use 10 listening arrays we would pick one signal every 28 years.

 

[farmkid]

What SETI is useful for is picking signals directed at us. Alien civilizations might be doing active SETI and sending signals to random stars and we might happen to be the receiver of such signals from time to time, and SETI might pick them up if they are listening in the right direction.

If civilizations are very common in the universe it's very likely that some of them would do active SETI and we'd pick them up, and I think that we should entertain the possibility that the Wow! signal was such active SETI attempt that didn't last long enough for us to pick it up again.

We can assume that we an average civilization, and we can also assume that we will be making many active SETI attempts even if the majority of us think it is a dangerous idea – you can't stop a group with a huge antenna and money to transmit signals, and it will be more difficult as technologies advance. From that we can infer that extraterrestrial civilizations would be doing it too, and far often, and it is a safe assumption to think that the number of civilizations that exist is tied to the number of signals picked by our current SETI attempts.

--- A crude example of the chances ---

Let's say there are 260 000 stars in a 250 light-year radius. Let's suppose that 260 harbour civilizations that are doing active SETI now, and let's assume that each has a telescope array sending a message continuously to at least 4 stars at a time, for 4 hours continuously. Let's assume that they all narrow down the list of stars to about 1/10.

With these figures, approximately 6240 out of the 26000 nearby star systems are targeted each day, which means that the Solar system is targeted roughly once every four days. With 26000 possible sources, this means that if we use 10 listening arrays we would pick one signal every 28 years.

I think your numbers are wildly optimistic. Even if 260 (which might be very conservative or unrealistically high or anywhere in between, but based on the planets we have discovered, it's probably high) of those star systems had a civilization that would at some point engage in SETI-like activities, the chance that even one of them being engaged it now is nearly 0. In the 4.5 billion years this planet has existed, a civilization capable of SETI has only been around for a few decades. Based on that, the odds of a planet that will develop a civilization with the technology only has about a 2 in a billion chance of being engaged in SETI-like activity at the same time as us. Remember, ~90% of the earth's history passed before the dinosaurs came along. Humans have been here a mere blink.

 

[Yminale]

There is a project starting that looks for signs of cosmic level engineering (Dyson spheres, Ringworlds, Time-space gates etc.) that could only be done by an advance civilization.

 

[Yminale]

One of the arguments for lack of intelligent life is that we're not detecting any radio signals. But is it possible something is being overlooked?

The assumption is that radio is the only effective way for alien civilization to communicate. That's really a statement about our limitations in not just in technology but also in basic physics.

Think of it this way. You are walking in the forest and you see a trail. Do you get curious? Probably not since you don't know if it's made by humans or animals. Now you stroll around and you find a road and it's not on your map. Do you get curious? You better be. Aliens maybe the same way. They may have concluded that radio is just too inefficient and are actually looking for some form of FTL which maybe easier to detect and less ambiguous and more useful.

 

[YellowSubmarine]

I think your numbers are wildly optimistic. Even if 260 (which might be very conservative or unrealistically high or anywhere in between, but based on the planets we have discovered, it's probably high) of those star systems had a civilization that would at some point engage in SETI-like activities, the chance that even one of them being engaged it now is nearly 0.

Yup, the chances are wildly optimistic, but it's not their point – all the figures do is try to roughly illustrate give some perspective in a possible relation between the number of civilizations that currently do active SETI and the numbers of signals received, and it would seem that even if my figures are off by a lot they show that the chances of finding another civilization are very small even in the most optimistic cases, but listening for them is not in vain.

In the 4.5 billion years this planet has existed, a civilization capable of SETI has only been around for a few decades. Based on that, the odds of a planet that will develop a civilization with the technology only has about a 2 in a billion chance of being engaged in SETI-like activity at the same time as us. Remember, ~90% of the earth's history passed before the dinosaurs came along. Humans have been here a mere blink.

I would disagree with this a bit – it might be so or it might not be. We don't know what the odds are for that other civilizations to exist at the same time as us. There are several things to consider:
1. We still don't know what events would trigger the end of a civilization, and how probable is this. Most civilizations might survive until their stars survive... at least. It's true that looking at ourselves it seems that the average age of a civilization is a few thousand years, but it could be million or billion.
2. Civilizations are not the first thing to appear, in fact we are almost certain that they would appear late in the stellar and planetary development. There are a lot of stars with an age similar to ours, and there the peak possibility for a civilization could be exactly now.

These things can lower the odds significantly, and this means that 260 is wildly optimistic but not completely implausible. Let's not underestimate that possibility.

What's more, if we were to assume that the Wow signal is of artificial extraterrestrial origin, unless such a wildly optimistic figure is true, it would be incredibly and impossibly lucky that we have picked it up. (Which kinda means that the signal most probably originated on Earth though...)

 

[Mysterion]

There is a project starting that looks for signs of cosmic level engineering (Dyson spheres, Ringworlds, Time-space gates etc.) that could only be done by an advance civilization.

Do you have a link or something for further info on this project?

 

[scotthm]

I don't thiink SETI is going to find anything.

Agreed. I think it's highly unlikely.

there could easily be aliens not so far away that are millions of years ahead of us that perhaps observe the Prime Directive with regard to us as a prewarp culture not ready for contact.

But I disagree with your characterization of "easily" here. There is no basis for that. If you had said "conceivably" then I'd agree with this also.

The odds of another civilization developing close enough to Earth that we could detect their signals, and for that civilization's development to coincide with our own such that we could detect them is vanishingly small.

I agree. I think many people grossly overestimate the "window of opportunity".

it drives me crazy to think that we could be the first...

So that's what it was...

the chances of finding another civilization are very small even in the most optimistic cases, but listening for them is not in vain.

It is in vain if you never receive signals from an extra-terrestrial intelligence, unless you consider the technological innovations of the search itself to be sufficiently fruitful.

We still don't know what events would trigger the end of a civilization, and how probable is this. Most civilizations might survive until their stars survive... at least. It's true that looking at ourselves it seems that the average age of a civilization is a few thousand years, but it could be million or billion.

The lifespan of a civilization will depend on the availability of energy to sustain it. At some point, we will deplete our planet of easy to extract fossil fuels, and we may or may not come up with a way to adequately replace them. But even if we do, the chances of a global catastrophy sufficient to disrupt or destroy most of civilization (and with a global economy that isn't very far fetched) are not zero. With a diminished technological capacity, would we be able to extract enough energy from our depleted planet to jump-start an "advanced" civilization again? I think it may be tougher the second time around.

---------------

 

[YellowSubmarine]

It's not a question of whether it is possible to destroy a civilization, it's a question of how likely it is. Do you think that it is likely that we will go extinct soon? If there's a 50% chance for a civilization to survive as long as its star does, 50% of the civilizations that ever existed on active stars around us still exist today. I'd dare to say that it's even more likely than 50%.

Now, whether a civilization would retain enough of its technological capacity to do active SETI is another matter, but I'd say it will (let's be optimistic!). Technology might become less ubiquitous, might become more expensive, but I'd say it's here to stay, it's not reasonable to expect that suddenly all the resources or know-how would disappear. It's dangerous that most of our technology is very hard to replicate from scratch and the knowledge behind it is often proprietary and not available to the public, but even then you'd need a pretty unimaginable disaster to lose it. The bad part is that I can imagine some such scenarios, the good part is that I don't think that we can be that stupid to let them happen.

Even in a fallen civilization, as long as it hasn't lost its technology completely, I imagine you'd find crazy groups of people determined to build active SETI transmitters despite of the world's wretched state, or even because of it. What's more, if some wacko gets the power he could decide to use 10% of the world's energy for SETI even though 90% of the population doesn't have enough energy to meet its basic needs. If ancient leaders spent ridiculous amount of resources to build pyramids with passages through which the soul ascends to the heavens, I see no reason why post-disaster leaders won't try to spend ridiculous amount of resources to talk to the heavens while still alive.

If a civilization has fallen to a state in which it doesn't have a space and SETI programs any more, I'd expect some crazy emperor to create a huge SETI project for his own amusement in the next 1000 years or so.

 

[CorporalCaptain]

It's a certainty that mass extinction has occurred on the Earth in the past. It seems pretty likely that it will happen again in the future, unless technology somehow can prevent or mitigate it. I imagine this state of affairs is probably pretty common on other inhabited planets, if any, and on many of them the frequency and severity could be much worse than here.

 

[scotthm]

I see no reason why post-disaster leaders won't try to spend ridiculous amount of resources to talk to the heavens while still alive.

Of course you don't. After all, you believe "the chances of finding another civilization are very small even in the most optimistic cases, but listening for them is not in vain."

I have no problem with SETI or its mission, but I'm not what you'd call optimistic about its prospects.

---------------

 

[Yminale]

There is a project starting that looks for signs of cosmic level engineering (Dyson spheres, Ringworlds, Time-space gates etc.) that could only be done by an advance civilization.

Do you have a link or something for further info on this project?

I heard it on the Mysterious Universe podcast but I can't find the original article.

This is the best I can do.
http://io9.com/5797597/are-we-surrounded-by-dyson-spheres