AJ113

Your opinion please, learned friends.

In a discussion on another board it has been stated that the presence of many stars in the known universe indicates a high probability that there is life other than that on Earth.

I have agreed that it is possible that the conditions exist to support life, not just on Earth-type planets, but anywhere outside of Earth.

But my argument is that since we know nothing about how life started, the presence of many stars indicates only that there are many stars, and it is a non-sequitur argument to conclude from this fact that other life exists.

I do not ask for your opinion on the subject itself, but the validity of my argument.

wade-w

This looks more like a Science and Skepticism thread.

Santas little helper

If we indeed didn't know anything about how life
started then I would say that your point was valid.
But we do know a bit or perhaps it's more
accurate to say that we can make some plausible
speculations.
So for example , for life to get started and be
maintained , a source of energy is needed and stars provide that.Existence of stars increases the probability for the existence of planets which
also helps.

I'm not claiming that this adds up to a "high
probability" of life existing elsewhere but it does count for something.
Anyway have you checked this thread ?

andy_d

The true value of a scientific model lies not in it's ability to provide explanation for observed phenomenon, but in it's ability to make predictions which are subsequently found to be accurate.

Therefore, it's quite appropriate for exobiologists to use our knowledge of the development of life on Earth to make predictions about life on other planets.

AJ113

Agreed, but is it reasonable to declare those predictions as fact?

Rhaedas

Given that we aren't sure yet how life got started in the only place so far we find life, plus we don't know if our type of life is the only type possible, or if there's a few varieties possible (silicon, methane, ammonia based), then I'd have to agree with your argument on the basis of what we know...that all we can confirm right now is the likelihood of finding life sustaining conditions is good, given the number of stars.

But at least we can speculate...

Shadowy Man

Well, we do know that the probability of life forming on a planet is greater than zero and most likely less than one.

gcameron

Interesting... I had this exact conversation with a friend of mine the other ngiht. Rather heatedly. I took the position of skepticism -- that we have, at the moment, a sample set of one, and until we have more data, or a better understanding of the processes behind abiogenesis etc., we will be unable to make a determination as to the likelihood of life. I.e., if there are 7 sextillion stars in the universe (or whatever), but the odds of abiogenesis occurring on a Goldilocks planet are 1 in 700 sextillion, then we'd be lucky to have life even once...

He argued that it was statistically more reasonable to guess that there *is* more than one occurrence of life in this universe than that there *isn't.* He said as we learn more about the outside universe to a closer and closer approximation, we find it is more like our own backyard (i.e. there are stars elsewhere, and now we know many of those stars are orbited by planets). This upward trend, he argues, indicates that even a closer approximation (i.e. the existence of tiny replicators on some of those planets) will probably turn out to be true as well. I'm not sure that follows, myself.

I still maintain there isn't enough data to make a guess. I accused him of relying too much on "the assumption of mediocrity." Fortunately we didn't come to blows.

Pyrrho

We do not know the exact odds of life occurring, as even if we knew the odds of a planet having the conditions necessary for life (which we also don't know), we don't know the odds of life actually developing on a planet with the necessary conditions for life to be possible at all.

To address your specific argument, you are mistaken when you say, "we know nothing about how life started". True, we do not know everything about how life started, but this is not the same as knowing nothing about the matter. So your argument, even if valid, is unsound.

In any case, we have absolutely no reason to believe that intelligent life exists anywhere in the universe, or that it is even possible for it to exist. After all, we have absolutely no experience of even one case of intelligent life.

Tim Thompson

I would say so, but then, who does that? For the most part, the problem of "overstating" what is or is not fact, exists only in popular circles, rarely between scientists. I've been in quite a few meetings of scientists, and one of the prime factors in every one, is the small amount of fact, and large amount of speculation, which ranges from the well informed and likely to be true, all the way to "wild ass guess".

Here I disagree, we have plenty of data, from which we can make some very good guesses. For instance, life as we know it, here on Earth, is entirely based on the organic chemistry of hydrogen, carbon, nitrogen and oxygen (commonly rearranged as CHON). But those elements are all the most common elements in the universe, save helium, which doesn't do much of anything in the chemical sense. That fact alone leads to the reasonable conclusion that life (minus intelligence), should not be unique, or even all that uncommon.

A simple foray into radio astronomy holds that guess well, as there are well over 100 molecules, many of organic interest, visible in the molecular clouds of the interstellar medium ( The 123 reported interstellar and circumstellar molecules. Updated 2003 Apr 17 by HAW.). The ubiquitous presence of water almost everywhere, and the almost equally ubiquitous presence of organic molecules in space, cerdtainly lends credence to the notion that life is actually likely to be rather common, and that's what I think.

Also consider that, at least on Earth, it certainly appears that life got started as soon as conditions permitted; certainly there was life by 3.8 billion years ago, maybe earlier. That observation, added to what I have already noted, only adds to the sense that life is common.

While we only have the one datum, "life on Earth", so far as the known existence of life goes, the other data are literally cosmic in extent, and so our vision is not limited simply to Earth.

The real question seems to me to be whether or not intelligent life is common (depending on how generous you want to be about defining "intelligent"). Along these lines, the Planetary Society hosts a very interesting set of web pages: Carl Sagan and Ernst Mayr Debate. Sagan, ever the SETI optimist, believed that intelligent life is common. Mayr, who is no slouch when it comes to evolutionary biology, did not agree. he held that if intelligence were a big evolutionary advantage, then there should be more than one "intelligent" species on Earth, and there isn't. Anyway, read the webpages and see what y'all think.

Personally, i'm with Mayr (or perhaps I just don't feel like arguing with him). i think life is common, probably ubiquitous. But i think that intelligent life is less common than we might wish.

Cheers.