Originally Posted by britb

If it does exist somewhere, it probably wouldn't even be considered life by Earth standards - some Si based bacteria or something crazy like that.

This. We've designed the definition of life around ourselves and what we experience (which in my opinion, is quite selfish). I can say quite easily that despite the size of the universe, finding life out there that is considered life by our standards is a very miniscule chance. Unless you're suggesting that somewhere there's an exact copy of our planet, the same distance (proportionally) from a single sun, with the exact same elemental composition, atmosphere and initial conditions spawning life...

Does this mean there are no such things as sentient beings? No, it simply shows we need to be careful with the word life. "Life" in this thread has a very different meaning from the word "Life" in everyday usage. Perhaps rocks are living things by some universal extension of the laws of life.

----------

Also note that we need to be careful with arguments such as Carl Sagan's "grains of sand" idea. While conceptually, it demonstrates his view quite vividly and is a nice analogy, no matter how many stars there are, and no matter how massive the universe is, it is still finite. It's existed for a finite amount of time, and is expanding at a finite rate...it's finite (even relativistically, light only travels a finite distance in finite time, so matter must also).

What's my point? It's simply that if the probability of something occuring is low enough, in any finite space, then it remains low in an arbitrarily large (but finite) space. The probability increases, yes, but it doesn't jump up to "definite occurance" as people seem to suggest (this would be true in an infinite universe, where life had "infinity-many" chances to occur).

EDIT: To give an example of what I mean, even things with relatively high probability are not definite. In theory, it's possible that I flip a coin 1,000,000,000...000,0 00 (a many zeroes as you like) times, and get nothing but heads. It isn't until I pretend that I flip it "infinitely many" times that I know for sure that I've gotten tails. (In fact, I would know I've gotten as many tails as I did heads, since the probability should converge to 50/50).

So the big question is, how unlikely was our life? Did it defy all odds in the sense that the probability remains arbitrarily low, even in such a large universe? Or did it occur with a low, but large enough probability that there's definitely life out there? A key assumption made by Sagan, Hawking, and other "big dreamers" is that the second is true. I'm not saying it's wrong (or right), but we need to stop and realize the fact that we don't really have any evidence either way.

Namely, given that we have no idea how to create life, we can't clinically test this probability and determine how likely it is, particularly since we're not even sure what exactly triggered life on this planet (and how probable that event was). Alternatively, if we could somehow see the entire universe at once, then we'd simply count up those planets (or stars, galaxies, etc.) that have life, versus those that don't, and then simply take their quotient to find out the approximate probability, since there should be an approximate* correspondence between probability and real life (*in theory, there's always exceptions as in my EDIT above). If the likelyhood of having life was say, 1% (definitely not this high) then we'd expect to see 1 planet in 100 have life.

My mathy 2 cents.

Originally Posted by Faer

I don't know. I saw this documentary that strongly advocated the presence of aliens with reference to the Egyptian and Aztec civilizations - how those people didn't have enough tools to design the pyramids, and even in the heiroglyphs, the 'gods' are supposedly the aliens.

I saw that too. I gotta say, they raised some pretty good points and brought up some pretty convincing evidence.

Though the universe is finite, it is safe to assume that the scope of the universe is in fact so incredibly large, that the chances that we are the only intelligent life in the entire universe must be zero. If you flip a coin 5 trillion times, and the chances of it landing on it's side (like the Scotiabank commercial) is one in 5 trillion, then it probably would have happened once. Extrapolating the idea, if the chances of life developing on a given planet is the same, then there should be some kind of life somewhere, albeit extremely rare.

I suppose I'm more optimistic that we'll find SOMETHING... Even if it IS under the ice on Europa or in the ice caps on Mars. It just won't come knocking on our doors anytime soon unless someone develops the almighty Pinewood Derby car...

Last brief note on the Egyptian thing... I'm no conspiracy theorist, but it makes sense in a weird way that we could have been eased into the transition to civilization by some other being. Maybe they saw potential, so they helped us out? If I were an ancient Mesopotamian or Egyptian and some random super-intelligent came and taught me the basics of civilization, I would probably worship it as a god of some kind.

I firmly believe in the Na'vi.

It would be pretty narrow-minded to think that life only existed on just on Earth. There is so much information out there about the universe that we haven't uncovered. As for other beings visiting Earth, I don't really buy into this modern UFO mumbo-jumbo. I think that it's just people out to make a quick buck. I believe that in the more distant past, visitations quite possibly could have occurred.

I think it's pretty silly to believe that we're the only beings in the universe, or the most advanced technologically for that matter. They've found all sorts of strange things on the moon, and remains of a civilization on Mars...and I wouldn't be surprised to find out that we've already been contacted and just haven't been told yet.

whut? They have? Link?

Originally Posted by Ownaginatios

I saw that too. I gotta say, they raised some pretty good points and brought up some pretty convincing evidence.

I'm pretty sure we didn't see the same one, since mine wasn't even in English...but yeah, some of the points raised made so much sense in context. Especially about the Egyptian civilization, that almost sold me to believe.

Though the question then is, if aliens did indeed come to earth long long ago to help build all of those things, then why the heck did they leave? Or rather, why didn't they come back? Unless they ARE back and merging silently with humans and...I dunno, monitoring us?

Originally Posted by Faer

I'm pretty sure we didn't see the same one, since mine wasn't even in English...but yeah, some of the points raised made so much sense in context. Especially about the Egyptian civilization, that almost sold me to believe.

Though the question then is, if aliens did indeed come to earth long long ago to help build all of those things, then why the heck did they leave? Or rather, why didn't they come back? Unless they ARE back and merging silently with humans and...I dunno, monitoring us?

Maybe they already retrieved what they were in need of here, and have no reason to come back.

Originally Posted by Willmountain

Extrapolating the idea, if the chances of life developing on a given planet is the same, then there should be some kind of life somewhere, albeit extremely rare.

But this right here is your non-trivial assumption, we can't extrapolate the data because for all we know, we're comparing apples with oranges. For something "tangible" where the probability of success is sufficiently high (like flipping a coin, 50%) it seems reasonable that the so-called law of large numbers will take effect after a trillion trials.


Let's put it differently, in strictly mathematical terms, here is Sagan's argument:

The universe is very large, so large that life has had N chances to occur, for some large (astronomical) number N.

The probability of life occurring successfully is small, let's call it m.

Since the probability of life not occuring is (1-m)^N this must be very close to 0, since N is so big. So it is almost certain that life exists elsewhere.

His argument is an example of something called the Archimedean Principle, that is, if you take any two numbers, one larger than the other, then I can always multiply the smaller one by some number to make it bigger than the larger one.

ie. 2 and 200,000,000. I can do 2 * 1,000,000,000 and my product is greater.

To bring the point home, the chance of failure to produce life is much greater than the chance of success, and so if we multiply by a big enough N, then the chance of success is now greater.

-----------

And now here's my point: Unlike in mathematics, we don't have the luxury of choosing numbers as arbitrarily high as we like. There is a definite number N, we're not allowed to pick and choose. Some N dictating how many "chances" life has had to occur.

Since we don't know just how unlikely the success of life on this planet was, we don't know just how big N needs to be in order to apply the Archimedean Principle.

So again, I'm just making up numbers here to illustrate my point, but suppose N is 1,000,000,000,000, and m is 0.0000000000000000000 000000000000000000000 000000000000000000000 000000000000000000006 78%, then even though it's a bit more likely after N trials, it's by no means a sure thing.

This leaves us with two cases:

1) Either N is sufficiently large (or conversely, m is), and so life must most likely exist
2) N isn't large enough (or conversely, m is too small), and so life may not exist

We don't have any real evidence to support either claim. We know the universe is huge, we know the probability of producing life is very small...and so as I mentioned, the ultimate question is, "which one 'wins out?' "

Sagan and yourself are convinced it's the first case. I'm not convinced it is to the point of completely throwing away the second possibility. I'm not suggesting which side I agree with, I'm simply saying it isn't "obvious" that it's the first case.


(Also note that N is growing with time, while m is presumably not shrinking. So perhaps the argument that "someday" there will definitely be life somewhere else would hold...but who knows how long we'd have to wait).

I beleive in aliens.

As others have already said, when you consider the size of the universe and the number of planets they keep discovering, and many, many more that have not been discovered, I think it is safe to say there is life out there. I don't know if we will ever meet them or hear from them since they are trillions of light years away, but i do believe in it.

what if they're not trying to hide