Why we're the only intelligent life in our galaxy

[Bouncing Zabaglione Bros.]

true, this is why such a statement is not really scientifically acceptable, but just looking at the abuncance of life that has permeated this planet in this solar system of ~4.5 bn years age, it is not such a large stretch to imagine billions earth like systems (one estimate was 30 billions in Milky Way) even in our own galaxy which is estimated at about ~14bn years old, giving us more than double the time for the same process to repeat in similar conditions on another place.

I think you're making a basic mistake here a that a lot of people make. You're saying "gee we were so lucky to get this great planet, and there's so many other stars out there, there must be other places where there's intelligent life and other lucky planets. If there wern't all these great planets out there, how could we have got one?" However, because Earth is so amenable to life (for a short time anyway), it's almost a certainty that life would evolve here. If this was the only place in the galaxy where life could form, this would then be the most likely place we'd see life in the galaxy.

Finding life on Earth doesn't really tell us anything about life elsewhere. Statistically we could very well be the most amenable place to life, and thus the most likely place to have it. We just don't have any evidence of complex life elsewhere to be able to use statistics to tell us about the greater galaxy. Sometimes things happen in a given place because it's something that happens often, and one place is as likely to see this particular happening as another. Sometimes things happen in that place because that's a particularly good place for it to happen.

Even when you take into account the large numbers of stars and try to do some statisical handwaving, you have to take into account the very few places with all the requisite physical parameters, and then the complex chain of events that led us to becoming a dominant, intelligent species in a relatively short timescale. Then you have to do it all again for another species, and factor in the chances of them being physically close in space as well as time. The chances of all these things coinciding are very small indeed. The numbers, space and time involved are just too big for the chances to be anything more than one in billions of billions ad infinitum that we're next door to each other.

I might as well claim that statistically it's far more likely that there are no civilizations near us (because there's a lot more space that isn't near us), and they are long gone or not yet formed (because there's a lot more time in the past and in the future than now). But that would just be conjecture. The difference is my conjecture is based on the evidence we have in front of us. Your conjecture is based on evidence that we're just making up out of thin air and pulling from sci-fi books.

You have to reverse your thinking on the "chances of things" happening. Look at it this way: what were the chances of you getting into an auto accident on your way to work this morning? It didn't happen, so after the fact, we can say that your chances were a complete zero percent. The accident didn't happen. Were the probabilites any different before you set out for your journey as when you arrived at work? Just because you "could have" had an accident?

If the galaxy was teeming with life, wouldn't some of it have travelled? Wouldn't the numbers be big enough that we'd see some evidence of a technologically advanced starfaring race? If they never became starfaring, they would have died out with their home star, but surely some of them must be technologically more advanced than us and colonising? But I can say that we've not got that evidence, so we statisically can say with certainty that it's not happened to us, despite all the billions of stars and billions of years that should have given that opportunity if the numbers were there to favour your argument that the vast numbers of stars ensure intelligent life.

If you can say "all these stars guarentee intelligent life", why can't I say that "all these stars guarentee intelligent life, some of which will be starfaring and should have already visited us publicly with FTL spaceships"? But that's not what happened. Or are you suggesting that there's lots of life out there (lots of stars) but none of it is starfaring, and none of it was living anytime before us? They just all sat at home and waited for their stars to go out, none of them ever got more advanced than us and decided to go travelling?

 

[Frank]

No, unless you have a population of 1. A sufficiently advanced civilization puts the power of space exploration in the hands of individuals. If you have billions of intelligent life forms, and universal molecular assemblers, all it takes in one interested hacker to create a probe.

Yes, but is that probe, with or without hacker, going to pay a visit to all planets in the Galaxy?

And don't forget, that in the human model people crave power and some are going to do their utter best to regulate all such things.

 

[Frank]

I think our experience on Earth seems to indicate that most civilizations will want to colonize (space exploration is a multinational, multicultural effort), so if we took many planets with intelligent life at random, I would expect the vast majority to want to colonize their local area.

Ah, but if you make that single example into a general rule, you also state that intelligent (humanlike) life is a vast majority at the same time. So, either the Galaxy is teeming with humanlike, intelligent species who for the most part want to colonize their local area and see the Earth as a yummie target, or things might be more random and intelligent life much rarer.

A sample of one cannot be statistical significant in one case, and unlikely in the other, especially if the orders of magnitude are in the same ballpark.

 

[Frank]

And for another interesting notion: how many Dyson spheres do we need to make up all the alleged dark matter and energy?

 

[KimB]

Ah, but if you make that single example into a general rule, you also state that intelligent (humanlike) life is a vast majority at the same time.

Except it's not a single example. There are many rather different cultures on Earth. The cultures which wish to spread themselves are the ones that have come to dominate. And it shouldn't be any surprise that this is so.

If you were to argue that it is likely that other intelligent species would not wish to colonize, then one would have to find some process by which such a culture comes into being. Since the desire to spread seems to be universal for all life on Earth, which includes a great many different organisms, I have a hard time believing that such a process would happen frequently, if at all.

 

[KimB]

And for another interesting notion: how many Dyson spheres do we need to make up all the alleged dark matter and energy?

Hehe, nice try

Dark matter is required to have existed in the very early universe to explain the growth of structure, as in before there were any stars or galaxies. Thus dark matter is not made out of protons, neutrons, and electrons, but rather something else.

Dark energy behaves differently from matter altogether, and thus cannot be made up of it.

 

[DemoCoder]

Yes, but is that probe, with or without hacker, going to pay a visit to all planets in the Galaxy?

And don't forget, that in the human model people crave power and some are going to do their utter best to regulate all such things.

Hahaha, yeah, like we regulate VIRUS/WORM writers today?

Your scenario now requires every civilization in the universe to be an orwellian police state.

 

[DemoCoder]

Excellent explanation BZB, people don't understand that belief in a hypothesis requires both evidence in favor of, and lack of evidence against.

The people in this thread say "we have made one observation for life, and that observation is positive! Life on earth!" But they overlook the millions of negative observations: everyday we fail to see any evidence of life elsewhere. It's selection bias.

Imagine that you want to know the probability that the sun will rise tommorow. Let's use white and black stones to represent observations, white = saw sun rise, black = sun didn't rise. Let us put the stones in a bag, and let the bag represent our belief in the hypothesis "the sun will rise"

Now lets assume the prior probability of the Sun rising, in absense of ANY evidence, is 50/50. So we put 1 white stone, and 1 black stone in a bag. What's the probability of pulling a white stone out of the bag? 1/2, which is the probability we assign to the hypothesis of the Sun rising to be true.

Now, today I observe the sun rise, so I put another white stone in the bag. What's the probability of pulling a white stone? It's now 2/3rds. And tommorow if I observe it to rise? 3/4s. And after 10,000 days? 10000/10001. The more I observe the run, the closer the probability converges to 1 that the hypothesis is true.

Now let us consider life on other planets. I place 1 white stone everytime I encounter a evidence of life on a new planet, and 1 black stone everytime I encounter evidence against life on a new planet. We let this represent the probability of encountering life.

I start with zero planets, and 1 black stone. I encounter the earth. I place a white stone. The probability of a life encounter is 1/2. I then start surveying the universe. Everytime I found a planet with no life, or I make an observation that is supposed to detect like elsewhere and fails, I place one black stone.

Well, lets put millions of black stones for SETI, lets put black stones for the few extra-solar planets we have found in telescopes that seem to be gas giants or too close to their stars corona. Let's put black stones for every moon and planet in our solar system.

Every observation that does not fit our hypothesis contributes more and more strength the the probability of it not being true.

So, contrary to the idea that life on earth implies it is likely elsewhere, in fact, the vast majority of negative observations override this one data point, and suggest it's less likely.

But the hopeful dreams will ignore this, or say the universe is too big, and our negative observations too few. But then why act like a sample size of 1 for successful observations implies anything? If you complain of small negative sample sizes being inconclusive, you must also have the same complain of small positive samples.

This is why people believe in psychics, or synchronicity. They only count positive evidence, positive predictions, and forget or ignore the millions of negative unsuccessful predictions or coincidences.

 

[KimB]

Well, lets put millions of black stones for SETI, lets put black stones for the few extra-solar planets we have found in telescopes that seem to be gas giants or too close to their stars corona. Let's put black stones for every moon and planet in our solar system.

Every observation that does not fit our hypothesis contributes more and more strength the the probability of it not being true.

Well, that's not completely applicable. We may have found some large planets, but we only expect to have ever seen large planets to date with current observational techniques (though Earth-sized planets are apparently not far off at all). The findings of these extrasolar planets that are not Earth-like aren't of much consequence, then, because we didn't expect to find any Earth-like ones.

SETI can only search for intelligent life, of course, not all life, but is a good consistency check of the hypothesis that there is no nearby intelligent life.

And as for the planets within our own solar system, we believe that there still is some possibility of life having once existed on Mars, and may currently exist on Europa (microbial life in both cases, of course). And the lack of life on other planets within the solar system isn't really evidence of of lack of life elsewhere: it just means that life needs the right conditions to form.

Then we're back to the question as to how common those conditions are. For that we have no real data at all, since we don't yet have instruments and analytic techniques accurate enough to detect planets similar to the Earth.

 

[Frank]

Except it's not a single example. There are many rather different cultures on Earth. The cultures which wish to spread themselves are the ones that have come to dominate. And it shouldn't be any surprise that this is so.

If you were to argue that it is likely that other intelligent species would not wish to colonize, then one would have to find some process by which such a culture comes into being. Since the desire to spread seems to be universal for all life on Earth, which includes a great many different organisms, I have a hard time believing that such a process would happen frequently, if at all.

But it's still a single example of life. A single biosphere, in which all the participants are build alike, and behave in a certain way. You cannot count them all as possible candidates of life that could evolve on other planets. Those other planets might evolve their own, unique biosphere. NOT a selection of life as we know it, with some other organisms thrown in. It's not a selection of species from a premade pool. Like, they do have rabbits, but not elephants, and they have curipas, which don't exist on Earth. That's not how it works.

It will be different, and follow it's own rules.

 

[Frank]

Hahaha, yeah, like we regulate VIRUS/WORM writers today?

Your scenario now requires every civilization in the universe to be an orwellian police state.

No, I just have no idea whatsoever how all the other possible civilizations would be, only that they would be different from ours.

 

[DemoCoder]

Well, that's not completely applicable. We may have found some large planets, but we only expect to have ever seen large planets to date with current observational techniques (though Earth-sized planets are apparently not far off at all). The findings of these extrasolar planets that are not Earth-like aren't of much consequence, then, because we didn't expect to find any Earth-like ones.

We've actually detected rocky/icy earth-like planet 5x the mass of earth. But it doesn't matter. Every little bit of circumstancial or indirect evidence slides the probability up or down, adjusting our strength of belief in the proposition. Yes, the detection mechanism has a selection bias, but the orbits of some of the gas giants detected (close to main sequence star, as close as earth or mercury) ever so slightly increase the likelihood that there is no hidden earth-like planet in that system, resulting in a clear negative reading. Every star we can eliminate as a possible earth harboring solar system, removes one possibility from observation. We used to have zero information about the existence of extra solar planets, now we have slight evidence that atleast 100+ stars don't have earth like planets (due to closely orbiting mega gas giants on highly elliptical orbits, probably not good for stability of other small planet orbits)

SETI can only search for intelligent life, of course, not all life, but is a good consistency check of the hypothesis that there is no nearby intelligent life.

It's just yet more negative evidence, which causes us to revise the confidence in our overall hypothesis.

And as for the planets within our own solar system, we believe that there still is some possibility of life having once existed on Mars, and may currently exist on Europa (microbial life in both cases, of course). And the lack of life on other planets within the solar system isn't really evidence of of lack of life elsewhere: it just means that life needs the right conditions to form.

Ok Chalnoth, what if it was the reverse. What if, everywhere we looked in the solar system. Icy moons, titan, neptune, gas giants like Saturn, Mercury, you name it. The coldest, the hottest, the most inhospitable, we found evidence for some form of life? Wouldn't that tend to raise your confidence that life was alot more likely elsewhere? Now explain why the converse, lack of life detected anywhere else, does not lower your confidence that life is elsewhere? Yes, you rationalize that it means those other planets don't have the right conditions or that we have not widened our detection methods enough, but that's irrelevent as far as the probability goes if you were a Bayesian Reasoner. Each time you eliminate a possibility from the set of possibilites, you adjust your confidence level.

Sure, SETI doesn't search all frequencies. But before SETI, we searched none. Now we search a portion and we have negative results. Does that increase or decrease the probability of the hypothesis being true?

Then we're back to the question as to how common those conditions are. For that we have no real data at all, since we don't yet have instruments and analytic techniques accurate enough to detect planets similar to the Earth.

But again, those newer techniques would merely serve to either confirm or rule out, another set of possible observations. Let's say we had a space-based nulling interferometer, and we could not detect any earth-sized planets. Then people would say "well, maybe non-earth like planets can have life" and we'd then have to search that set.

But this excuse does not mean that people's belief in a hypothesis won't be revised by null evidence. It will. The more and more null evidence, the less belief in the hypothesis will be justified. One can always invent more and more reasons why null evidence is continually seen, and the dreamers will hold onto this explanation to try and avoid revising their confidence in the extrasolar life hypothesis, but the rules of probability say you should in fact, revise your belief confidence level.

This is the fundamental problem people have in dealing with statistics and probabilities: they ignore null evidence, because human beings only react to surprising or "new" evidence.

 

[KimB]

It will be different, and follow it's own rules.

To an extent, clearly. But some simple rules still must be followed by any life, and one of those is evolution. Evolution is nothing more than the logical conclusion that arises from having a random element to reproduction along with the possibility of death, and therefore any life will be subject to the pressures of evolution.

Now, consider if you will that life on Earth has been subject to a huge variety of evolutionary pressures, both due to existing in different environments, and also just due to having different responses to the same environment. Thus I claim that any universal property of life on Earth that is derived from evolution should be a universal property of all life everywhere.

And one property that seems to be universal is that every life form on Earth seems to want to spread itself as much as it can. Colonization seems to be a universal, evolution-derived property of life on Earth, and thus should be a universal property of all life.

 

[Frank]

Well, lets put millions of black stones for SETI, lets put black stones for the few extra-solar planets we have found in telescopes that seem to be gas giants or too close to their stars corona. Let's put black stones for every moon and planet in our solar system.

SETI: we wouldn't hear our own most powerful broadcast station if it was on a planet on the closest star. And who is to say that advanced civilizations use extremely high power, omnidirectional radio broadcasts for communication? Can you say unlikely?

And do we know for sure there hasn't been life on Mars, or on one of Jupiter's moons? Or on Jupiter itself? Let alone the possible planets around other stars. If we devise a method that can only spot gas giants, and we assume by default that gas giants cannot possibly hold life, you have no way to add white stones until you encouter life on a gas giant.

You can only state for sure, that we haven't found planets yet that would support the same biosphere as the Earth. And that's it.

 

[Ty]

And do we know for sure there hasn't been life on Mars, or on one of Jupiter's moons? Or on Jupiter itself? Let alone the possible planets around other stars. If we devise a method that can only spot gas giants, and we assume by default that gas giants cannot possibly hold life, you have no way to add white stones until you encouter life on a gas giant.

We don't know but the issue is that, "to prove that life exists elsewhere, you need to provide evidence of it".

You can only state for sure, that we haven't found planets yet that would support the same biosphere as the Earth. And that's it.

Correct and it doesn't DISprove that life exists elsewhere (which can't really be done - proving a negative) but it certainly doesn't prove that it does.

 

[Frank]

Do we know for sure that there is no life on Jupiter? No, we don't. We only know that humans wouldn't have a chance surviving there. That's it. Could we find/make some life that could survive Jupiter? Yes. So, why again are we so sure there is no life on Jupiter?

And if there is/can be life on a gas giant, how does that make the chances?

 

[Ty]

Do we know for sure that there is no life on Jupiter?

First of all, ask yourself, how would one even go about proving that there is no life on Jupiter? Unless you are truly omniscient, it can't be done.

No, we don't. We only know that humans wouldn't have a chance surviving there. That's it. Could we find/make some life that could survive Jupiter? Yes. So, why again are we so sure there is no life on Jupiter?

And if there is/can be life on a gas giant, how does that make the chances?

Probability goes up no doubt, but probability is not evidence of existence.

 

[Frank]

Yes, I understand the dilemma. But it works both ways: you cannot make definite statements either way. We still only have a sample set of one. Or two with one negative, if we count our moon as well.

 

[DemoCoder]

DiGuru, we are discussing probability, not proof or disproof. You can't prove a negative. You can never prove that no form of life exists somewhere. But each detection method that fails, constricts the space of possibilities, and lowers the confidence you should have in the hypothesis.

I'm not going to keep reiterating how this works. Go read an article on Bayesian reasoning. There is no better statistical methodology.

 

[Frank]

I'm *NOT* trying to prove that there is other (intelligent) life in our Galaxy, or the universe. This whole thread, I'm only trying to show that we don't know, and there is not even a probability we can work from.

Statistics is fine, but you cannot just state that there is no life somewhere, like on gas giants, and add them to the negatives. Considering the scales involved, that would be like finding a microscopic spot on Earth and seeing no life there for a second, and using that as evidence that there is no life on Earth whatsoever.

That's all.