Seti Results Conclusive Proof?

[Radrook]

Recently during a conversation about the possibility of intelligent life on other worlds someone suggested that the silence SETI has experienced is conclusive proof that there is none. Otherwise, the argument went, something would have already been detected. How srong of an argument is this? I for one think it's weak.

[The_Fire]

Note; This is based on my memory, so I suggest checking out the SETI webpage , but that argument can be considered flawed due to the following reasons:

1: SETI is only listening to a narrow spectre of frequences. They filter out things they consider "background noise". While the specific frequencies are selected from a somewhat educated guess on where an alien transmission may be, this means they could be listning to the wrong thing. Or that a signal in the "Background noise" doesn't get recorded at all.

2: It is possible that a more advanced civlisation have already started using some sort of alternate communications which means they are no longer emitting radiowaves and that their old stuff have already passed us.

3: Due to distance, it's possible that "their" transmission haven't reached us yet. Our first transmission have barely reached the next starsystems yet.


There are probably more reasons, but those are the ones I get of the top of my head.

[Radrook]

Yes, I agree! Also, many of the civilizations might not have the technology we possess. We have to remember that during most of human history we were unable to emit any radio waves. That we are able to now is a consequence of our specific history. So maybe, just maybe we are the only ones who have achieved this? Unlikely though it may seem it might just be so-well, it isn't an impossibility.

On the other hand, we might really be alone in terms of being the only material creatures with intelligence, or perhaps the only creatures period. That too is unlikely in view of the vastness of the universe but also not an impossibility.

In any case, as you said, the present silence isn't sufficient to justify a definite conclusion.


BTW

Since I am not an atheist I am not basing my speculations on evolution as I am certain most of those who will respond to this thread will.

[NobbyNobbs]

Two more reasons:

4) SETI can only inspect one very small section of sky at a time. it's possible that while they are facing north, the signals are coming from the south.


5) The logical fallacy inherent in the argument: lack of evidence is not evidence of non-existence.

[my_wan]

If there were dozens of technological civilizations we are capable of detecting it is highly unlikely we would have found any of them yet given the time we have been searching. Due to the distance if we ever do find one it means by definition that they are thousands if not hundreds of thousands of years ahead of us technological. Given the time spans and our recent technological emergence the odds are vastly in favor of them being at least hundreds of thousands of years ahead of us regardless.

So long as we remain tied to this planet our extinction is assured in the long run. Regardless of our environmental effects or lack of it.

[BenBurch]

Why do we assume that these ET civilizations would be using radio at all? They might use lasers for everything, or use such tight RF beams that there is little chance of one of them pointing at earth.

[Arkan_Wolfshade]

Originally Posted by Radrook

Recently during a conversation about the possibility of intelligent life on other worlds someone suggested that the silence SETI has experienced is conclusive proof that there is none. Otherwise, the argument went, something would have already been detected. How srong of an argument is this? I for one think it's weak.

It is extremly weak, in that "abscence of evidence is not evidence of abscence".

[sphenisc]

Originally Posted by Arkan_Wolfshade

It is extremly weak, in that "abscence of evidence is not evidence of abscence".

However evidence of absence is evidence of absence.

And 52 terabytes is evidence.

http://www.astrobio.net/news/article710.html

[Jimbo07]

Originally Posted by NobbyNobbs

Two more reasons:

4) SETI can only inspect one very small section of sky at a time. it's possible that while they are facing north, the signals are coming from the south.

The Allen Telescope Array may help. It has a wide field of view and a wider frequency band.

Even a few years of silence from ATA won't be strong evidence of absence.

Quote:

5) The logical fallacy inherent in the argument: lack of evidence is not evidence of non-existence.

However, like any good science, searchers should at least be prepared that there really is no one out there! It's a question of how many generations worth of data will be convincing. I'm sure some already are. There aren't any Martians, but it's still illuminating to explore there...

[Radrook]

Originally Posted by Jimbo07

The Allen Telescope Array may help. It has a wide field of view and a wider frequency band.

Even a few years of silence from ATA won't be strong evidence of absence.




However, like any good science, searchers should at least be prepared that there really is no one out there! It's a question of how many generations worth of data will be convincing. I'm sure some already are. There aren't any Martians, but it's still illuminating to explore there...

I once read a Sci Fi short story where only one other "intelligent" space-faring race was found. Result? War! The "This town isn't big enough for both of us" scenario. But in this case, ironically, the universe wasn't big enough. Weird!

[my_wan]

Originally Posted by BenBurch

Why do we assume that these ET civilizations would be using radio at all? They might use lasers for everything, or use such tight RF beams that there is little chance of one of them pointing at earth.

Very true. I would also suspect that for broader transmissions they would use spread spectrum. If this is the case then unless you know exactly which set of frequencies to listen to it would sound like normal background noise. This remains true even if you listen on a broad enough range of frequencies to be getting their whole range of frequencies. If some kind of encryption was encoded between a pair of sets of frequencies then even prior knowledge of the frequency sets would sound like static.

There is also the possibility of even more advanced stuff. If something roughly akin to Quantum encryption was used then the very act of trying to listen would mean there is no signal to listen to. They could also know that you tried.

The speed of light limitation would remain an issue for communication as well as for the home planet waiting on the ship to reach its' destination. That is assuming such a race would even be dependent on any given planet (which I doubt). The light speed issue is no issue at all from the ships point of view. From the ship perspective it can essentially get from anywhere to anywhere as fast as they want to. If they travel very far at these speeds we might actually catch up to them technologically.

Personally I think SETIs only chance would be to find a race that only fairly recently gained technological status. Similar to our technological status. The laws of physics indicate that early technologies would be fairly consistent across all races. As technology progresses the way a races technology is expressed can increasingly vary, within certain very broad parameters.

[Jimbo07]

Originally Posted by my_wan

There is also the possibility of even more advanced stuff. If something roughly akin to Quantum encryption was used then the very act of trying to listen would mean there is no signal to listen to. They could also know that you tried.

The speed of light limitation would remain an issue for communication as well as for the home planet waiting on the ship to reach its' destination.

That, or light speed isn't even a problem. Maybe they communicate by spacefolded micro-wormholes (or to quote Fry, "Magic. Got it.").

Maybe they are life-forms made of some exotic substance (or to quote Homer, "Silli foam.").

The point is, anything beyond what we are capable of detecting is sheer speculation and not a good justification for resources spent (or not) on SETI.

Quote:

Similar to our technological status... As technology progresses the way a races technology is expressed can increasingly vary, within certain very broad parameters.

I agree, as our communications technology progresses, it may be more reasonable to speculate on what is happening in those media...

[roger]

SETI has examined something like 1 hundreth trillionith of the available search space. If I'm looking for my keys,and I am not sure if they are in my house or not, I don't examine a few molecules at the entrance, shrug, and conclude that the keys are not here.

ETA: yes, that's a silly analogy, don't bother pointing out the logical fallacy contained within, and focus on the size of the search space left unexplored.

[Arkan_Wolfshade]

Originally Posted by sphenisc

However evidence of absence is evidence of absence.

And 52 terabytes is evidence.

http://www.astrobio.net/news/article710.html

But if the total possible data that could be collected for analysis is 520 or 5200 TB, then 52 TB of not finding anything is not significant.

[Kopji]

Of course, maybe after seeing what we have been transmitting into space for the last 75 years, they are all hiding from us.

[Diagoras]

And what if the closest intelligent life form is in a galaxy 4 billion light years away? SETI is looking at stars within our galaxy; if they find nothing around our neighborhood, that doesn't mean there isn't any intelligent life out there anywhere. If it's really, really, really far away, maybe they just don't have any reason to send an extremely powerful signal our way announcing their existence, and even if they tried we're not looking for it, assuming it's had enough time to travel here for us to detect it. At this point, it seems unlikely we'd notice an intelligent civilization in another galaxy, unless they exploded a whole bunch of supernovae in a pattern that spelled out "Hi, we're aliens" in their alien language.

[TX50]

And, of course, for all we know the universe may well be pullulating with
intelligent alien civilizations that haven't progressed to a radio-telescope-
using technological level yet.

[Jimbo07]

Here's a nice response to some potential criticisms of SETI:

No Tax Dollars Spent!

Of course, this response won't appeal to people who are not predisposed to exploratory pursuits (Everest climbers, for example, really anger someone close to me).

[BenBurch]

Originally Posted by my_wan

If some kind of encryption was encoded between a pair of sets of frequencies then even prior knowledge of the frequency sets would sound like static.

Data waterfalling and redundancy in a digital stream are nearly as unrecognizable as an encrypted stream, and likely to be used between civilizations that already know each other, or deep space assets of a single race.

[my_wan]

Originally Posted by Jimbo07

That, or light speed isn't even a problem. Maybe they communicate by spacefolded micro-wormholes (or to quote Fry, "Magic. Got it.").

I know that Robertson-Walker manifolds allow the spacial and temporal components to vary independently but personally I doubt that very seriously, at least not without producing the same relativistic effects as standard high speed travel. That's leading off topic though so start a new thread if you want to call me on it.

Originally Posted by Jimbo07

Maybe they are life-forms made of some exotic substance (or to quote Homer, "Silli foam.").

Perhaps something like this;
http://www.space.com/scienceastronom...asma_life.html

Originally Posted by Jimbo07

The point is, anything beyond what we are capable of detecting is sheer speculation and not a good justification for resources spent (or not) on SETI.

Yes I agree. Most anything more advanced would likely not be targetable by SETI even if we understood the technology well anyway. That was my point in the broad (technically reasonable) examples I used. I do feel like we understand enough now to understand at least very broadly the individual components of such an advanced technology, with only a few caveats.

Originally Posted by Jimbo07

I agree, as our communications technology progresses, it may be more reasonable to speculate on what is happening in those media...

I can identify dozens of communication schemes that are physically if not technologically possible. The number of protocols that can be used with each of those technologies expands the possibilities exponentially. We can't even be sure they wouldn't use different technologies and/or protocols to transmit different components of the same message. So I disagree in that I think it is reasonable to speculate about those technologies now. However, such speculation now or after we develop similar technologies is likely not to be of any use to a SETI program.

Sorry for nit picking but I've thought quiet a bit about it. Your points were very reasonable.

[Fnord]

Originally Posted by Radrook

Recently during a conversation about the possibility of intelligent life on other worlds someone suggested that the silence SETI has experienced is conclusive proof that there is none. Otherwise, the argument went, something would have already been detected. How srong of an argument is this? I for one think it's weak.

The argument couldn't fight its way out of a wet paper bag. Absence of proof is not proof of absence.

The possibility exists for extraterrestrial life. That it has not been found yet means: (1) our instruments are not sensitive enough; (2) we've been listening in the wrong places; (3) we have not been listening long enough; (4) we've mis-interpreted intelligent signals as noise; (5) "they" do not want to be found; or (6) we're already here.

[Jimbo07]

Originally Posted by my_wan

Sorry for nit picking but I've thought quiet a bit about it. Your points were very reasonable.

Wow! Thank you for calling me reasonable!

Seriously, my point is remarkably simple. Either they exist, or they don't and either we will find evidence, or we won't. At some point we'll have to ask ourselves how much absence of evidence constitutes evidence of absence?

The speculation about technologies and civilization development and other things can help answer the question about evidence, but not about the existence of the ETIs themselves. As our technology advances, there may be fewer plausible places for their technology to hide, or fewer likely answers to the absence.

...

There's, of course, speculation of the other kind! We might not have heard them yet, but next week we will, because some civilization is deliberately broadcasting a detection signal with something we would easily recognize (e.g. amplitude modulated radio).

Originally Posted by Fnord

The argument couldn't fight its way out of a wet paper bag. Absence of proof is not proof of absence.

The possibility exists for extraterrestrial life. That it has not been found yet means: (1) our instruments are not sensitive enough; (2) we've been listening in the wrong places; (3) we have not been listening long enough; (4) we've mis-interpreted intelligent signals as noise; (5) "they" do not want to be found; or (6) we're already here.

You've forgotten possibility (7) They just don't exist.

Your post reads like: they exist, here's why he haven't heard from them. Your use of the word possibility suggests to me that you meant, "IF they exist, here are some reasons why we might not have heard from them," and my point (7) becomes redundant.

[my_wan]

Let's see how many possibilities we can list.

1) They don't exist.
2) We simply haven't looked in the right place yet.
3) Their technology is too advanced for us to know what to listen for.
4) Their signal is cloaked.
5) They are not technologically advanced enough yet.
6) Their signal hasn't had time to reach earth yet.
7) They already died out.
8) They will not evolve intelligence for another X years.
9) They are aquatic on a water world.
10) They are already here checking us out.

Any other suggestions? Yes I know that last one don't count as it would automatically mean one of the other options is true.

My own estimates of the Drake equation only gives me 1 or 2 civilizations per galaxy at best. The major limiting factor in my numbers was planetary stability. This lack of stability may be meteors, environmental, orbital, wars, etc. Given that a solar system forms by accretion makes meteors a huge issue. Our moon has a major stabilizing affect for us that may be responsible for allowing our existence. It seems the Earth itself has apparently both been frozen pole to pole and burned to a crisp on more than one occasion since life began here. I would expect microbial type life to be quiet common and higher life forms to be rare finds. Intelligent life would be downright rare in the extreme. Then again this is admittedly an Earth/planet centric estimate.

If you want to place your bets on finding life within a year read this;
http://www.cnn.com/2007/WORLD/europe...ing/index.html

So long as we forever remain dependent on this Earth for survival we are doomed to extinction in the long run. Maybe sky daddy will save us .

[NobbyNobbs]

I once heard an argument that explains the theory that we will not find evidence of ET life. If I recall correctly, it goes like this:

A) It's highly unlikely that the ETs are at the same level of technology that we are. Therefore, they are either significantly ahead of us (teleportation, FTL drives, etc) or significantly behind us (Just coming up out of the seas, banging bones on rocks).

B) If they are behind us, there aren't any signals to detect.

C) If they are ahead of us, one of two things is bound to have happened. Either they've flourished, or they've killed themselves off.

D) If they've killed themselves off, there's no signal to detect.

E) If they've flourished, they should be all over the place by now (two rabbits breed four, four rabbits breed 8, etc). Since they're obviously not all over the place, they haven't flourished.

I know there are a ton of holes in this logic, but I thought I'd throw it out there.


Who knows, maybe all the pulsars we've detected are actually alien semaphore flags?

[Big Les]

Even assuming there are currently no sentient lifeforms within range of us, isn't the probability of such life existing at some time in the past or some future point actually pretty high? Forgive my statistical ineptitude and possibly logical failings, but it would still be an amazing thought to think that somewhere, somewhen, there have been/are/will be intelligent creatures of some kind. Even if we can never meet any.

[T'ai Chi]

Heck, just use the highly scientific Drake Equation to solve for the number of alien civilizations out there, any get anywhere from 1 to 100 billion.

[my_wan]

Originally Posted by Big Les

Even assuming there are currently no sentient lifeforms within range of us, isn't the probability of such life existing at some time in the past or some future point actually pretty high? Forgive my statistical ineptitude and possibly logical failings, but it would still be an amazing thought to think that somewhere, somewhen, there have been/are/will be intelligent creatures of some kind. Even if we can never meet any.

Yes exactly. Any such guessing at the odds has to be figured at a particular point in time.

Originally Posted by T'ai Chi

Heck, just use the highly scientific Drake Equation to solve for the number of alien civilizations out there, any get anywhere from 1 to 100 billion.

Yes also very true. The Drake equation can essentially be broken down in an essentially limitless series of other assumptions. Even if absolutely perfect conditions are met (for life as we know it) on a given planet we don't even have any clue of how likely it is to produce life. Life here started almost from the start. Was that just a winning lottery ticket. Other planets here seem pretty lifeless but that could still change. Each assumption in the Drake equation is so full of unidentified assumptions that any real determination is absurd. It does have value in that if we start with the most optimistic assumptions and adjust down with better knowledge we can see how extraordinarily rare we are.

Consider that a single meteor or even a change in timing of a previous meteor would mean we wouldn't be here now. Had a meteor not hit at a time it did we likely wouldn't be here. Even a bacterium could evolve that changes the climate so drastically we wouldn't be here. Reason exist to think that without our moon not many higher life period would be here. Look at how the tiny variations in Earths orbit have traditionally moved us from ice ages to tropical conditions. Five billion years of a reasonable degree of stability is not an easy lottery to win. Even winning this lottery doesn't necessarily mean evolution will lend itself to a high degree intelligence. Many of the dinosaur epochs had as much time with stable environments than we've had.

[Georg]

Is there any reliable explanation for the wow signal that I´m not aware of?

[Big Les]

It just seems incredibly unlikely that we could be the only vaguely intelligent life in the history of everything. Of course, even in Star Trek intelligent life was originally very rare indeed - all those bumpy-headed humanoids were seeded by one master race (which kind of flips off evolution on Earth in favour of intelligent design (gasp), but explains why the aliens in Trek were so dull).

[my_wan]

Originally Posted by Georg

Is there any reliable explanation for the wow signal that I´m not aware of?

Unfortunately no. The argument for and against the alien origin theory is equally as valid and problematic. It's a bummer how we have to sometimes say, I dunno .

[my_wan]

Originally Posted by Big Les

It just seems incredibly unlikely that we could be the only vaguely intelligent life in the history of everything. Of course, even in Star Trek intelligent life was originally very rare indeed - all those bumpy-headed humanoids were seeded by one master race (which kind of flips off evolution on Earth in favour of intelligent design (gasp), but explains why the aliens in Trek were so dull).

Yes it is in fact astronomically unlikely. However it may in fact be the case for our galaxy, meaning the only races we can conceive of finding. The flipside is that even if the odds of a technological race are so low that only one in a thousand galaxies have such a race there remains a LOT more of these races in the Universe than star trek had. Say about 1/2 billion of these races with the above numbers.

[Big Les]

So my geeky daydreams of faraway planets full of intelligent beings are not unrealistic?

Never mind FTL travel, we need to skip straight to the intergalactic stuff!!!

[my_wan]

Originally Posted by Big Les

So my geeky daydreams of faraway planets full of intelligent beings are not unrealistic?

Never mind FTL travel, we need to skip straight to the intergalactic stuff!!!

There are roughly 15 Galaxies within a million light years of here. I haven't run the numbers but neglecting escape velocities etc. it might be technically conceivable to get to another galaxy within a lifetime. This is without FTL and using normal relativistic acceleration without sleep chambers. If you ever decide to come home though expect your brother to be 100+ million years older than you.

[Diagoras]

Originally Posted by my_wan

Consider that a single meteor or even a change in timing of a previous meteor would mean we wouldn't be here now. Had a meteor not hit at a time it did we likely wouldn't be here. Even a bacterium could evolve that changes the climate so drastically we wouldn't be here. Reason exist to think that without our moon not many higher life period would be here. Look at how the tiny variations in Earths orbit have traditionally moved us from ice ages to tropical conditions. Five billion years of a reasonable degree of stability is not an easy lottery to win. Even winning this lottery doesn't necessarily mean evolution will lend itself to a high degree intelligence. Many of the dinosaur epochs had as much time with stable environments than we've had.

I have also heard credible theories that there was a significant genetic bottleneck early in the history of our species, when we were still all in Africa, saying there were only ~10,000 of our ancestors around. The only species on the planet to develop radio technology nearly went extinct before its technology could even get off the ground!

[my_wan]

Originally Posted by Diagoras

I have also heard credible theories that there was a significant genetic bottleneck early in the history of our species, when we were still all in Africa, saying there were only ~10,000 of our ancestors around. The only species on the planet to develop radio technology nearly went extinct before its technology could even get off the ground!

Yes the genetic bottleneck is in general on a very solid scientific footing, though the width/breadth can be argued to some extent. Some factoids; Chimpanzees have about twice the genetic diversity we do regardless of race. In a sense there is more genetic diversity within a human race than there is between human races. Lewontin's Fallacy has been used to argue against this but whether or not it is a fallacy really depends on what question you are asking. The difference is if you choose a large enough arbitrary number of traits the fallacy stands. If you simply choose a random set of traits it's not a fallacy. The thing is that if the arbitrary number of traits is large enough we would have to classify every individual as a unique race.

In the past there were many subspecies of the genus Homo. We are the only ones that still survive.

[roger]

Doing math like that I can prove anything. Let's see, my father was one of 2 billion males on the planet, my mother 1 of 2 billion females. Multiply those by # of sperm my father generated by # of eggs my mother had and you get the odds of me existing based on the previous generation. Do it again for their parents, then their parent's parents, etc. The chances of me existing is 1 in a squint-zillion. Therefore, I must be extremely unique, and no other human could possibly exist.

Thus, you are all figaments of my imagination.

[tofu]

Originally Posted by BenBurch

Why do we assume that these ET civilizations would be using radio at all?

I think you're making the assumption that communication is the only thing SETI would be able to detect.

Look at it this way, if you were a few dozen light years away and looked back toward Earth, what would be the most powerful, most obviously unnatural signal coming from our solar system? Hint: it's not a communications signal. It's not TV or cell phones.

You (and others who have said the same thing in this thread) are partially right, a very advanced civilization may not use radio very much for communications. They may only use fiber or lasers. But every advanced civilization *must* protect itself from comets and asteroids and other junk. And the best way to do that is with radar.

So the answer is, the most powerful signal currently being emitted by Earth is the Pave Paws radar system. It was originally built to watch for ballistic missiles, but it also serves a vital secondary role of tracking space junk. I submit to you that *every* advanced civilization will have a similar system, or else they run the risk of having their satellites and space stations destroyed by nuts and bolts and other assorted garbage. I also submit to you that a really advanced civilization will also have an even more powerful system scanning for rouge asteroids and comets.

If SETI happened to find a solar system where something like Pave Paws was operating, they could identify it as unmistakably artificial. I don't know the range at which they could detect it though, but it's a lot farther away than TV or FM radio would be detectable. And the best part is, as I said, every advanced civilization has to have this.

[my_wan]

Originally Posted by roger

Doing math like that I can prove anything. Let's see, my father was one of 2 billion males on the planet, my mother 1 of 2 billion females. Multiply those by # of sperm my father generated by # of eggs my mother had and you get the odds of me existing based on the previous generation. Do it again for their parents, then their parent's parents, etc. The chances of me existing is 1 in a squint-zillion. Therefore, I must be extremely unique, and no other human could possibly exist.

Thus, you are all figaments of my imagination.

Exactly what math are you refering to as "math like that"?

[my_wan]

Originally Posted by my_wan

Exactly what math are you refering to as "math like that"?

Never mind it just occurred to me who you were.

[BenBurch]

Originally Posted by Georg

Is there any reliable explanation for the wow signal that I´m not aware of?

Yeah there is; People getting excited over data they cannot explain and jumping to conclusions.