Originally Posted by Marx & Lennon

I think the argument is pure mathematics v. applied mathematics. Since I'm an 'applier', not a 'purist', I've stayed out of the discussion.

Yeah, but there isn't really a hard-and-fast distinction between pure and applied, it's more a matter of historical/cultural convention. (which one is information theory, for example?) Theorems in applied math still have to be proved just as rigorously as theorems in pure math--in principle you should be able to prove them using axioms and formal rules of inference, although in practice even pure mathematicians don't usually prove new theorems that way. I guess the main difference is that pure mathematicians try to prove new theorems that have some sort of intrinsic interest to other mathematicians, while applied mathematicians try to prove new theorems that will make various real-world practical problems easier to deal with.

Looking back over Croakmore's argument, there is a sense in which I agree with him--although I think statistics is genuine mathematics, if John Xenakis was claiming that his argument about the probability of life was totally rigorous I would disagree, because the application of statistical rules to real-world phenomena is much more heuristic...you have to worry about problems like the one of selection bias that I mentioned earlier.

WHEREAS: Probability theory, statistics, and pinochle are determined to be valid branches of mathematics.

THEREFORE: Astrology, poker, and rock, scissors and paper are hereby granted their own branches on that great tree of mathematics, too.

Exodus 8

The Green Geezer

Dear Jesse,

Originally Posted by Jesse '77

> Yeah, but there isn't really a hard-and-fast distinction between
> pure and applied, it's more a matter of historical/cultural
> convention. (which one is information theory, for example?)
> Theorems in applied math still have to be proved just as
> rigorously as theorems in pure math--in principle you should be
> able to prove them using axioms and formal rules of inference,
> although in practice even pure mathematicians don't usually prove
> new theorems that way. I guess the main difference is that pure
> mathematicians try to prove new theorems that have some sort of
> intrinsic interest to other mathematicians, while applied
> mathematicians try to prove new theorems that will make various
> real-world practical problems easier to deal with.

This is well stated, but I'm not sure I completely agree with the
distinction you're making between pure and applied math.

I think that all, or at least almost all, math is applied math in the
sense that, although it's being studied because of its interest to
other mathematicians, the reasons that it's of interest is because it
has some application somewhere, if only a distant one.

But the reason that you need pure (or abstract) math is because it
imposes a discipline. You have to study topological spaces because
you have to see how much you can prove when there's almost no
structure at all. Then you add measureable sets to see how much more
you have to add in order to do integrals. Then you add orthogonal
axes to see how much you can prove about Euclidean geometry without
worrying about the number of dimensions. Finally, you add a 1-, 2-
or 3-dimensional restriction to see what more you can prove about the
"real world" with the added assumptions.

You're right that it's hard to distinguish pure and applied math.
Over the years when I've talked to friends, if I mention 4 dimensions
or N dimensions, I often get a puzzled look, "But there are only
three dimensions." So multi-dimensional spaces appear, to the
general non-mathematician, to be the epitome of pure, abstract,
useless mathematics. And if 4-dimensional space is useless, then how
much more useless must infinitely many dimensions be. I mean, you'd
have to be an airhead to even think about that. Right? And yet, I
understand that infinite-dimension Hilbert Spaces are very important
to physicists who study quantum mechanics!

So of course you're right that theorems have to be proven just as
rigorously in applied math as they are in "pure" math.

One of the best statements of the need for discipline is the
following quote that I memorized when I was an undergraduate:

Originally Posted by Bertrand Russel

> "Now, in the beginning everything is self-evident, and it's hard
> to see whether one self-evident proposition follows from another
> or not. Obviousness is always the enemy of correctness. Hence, we
> must invent new and even difficult symbolism in which nothing is
> obvious."

To say that "statistics isn't mathematics" is not only wrong, but
it's self-defeating. What does that even mean? Does that mean that
you can say that 2+2=4 or 2+2=5 or 2+2=3 or whatever you're in the
mood for, and you can say whatever you want, because you don't have
to stick to mathematical rigor, because statistics isn't really math?

It's self-defeating when you want to prove that someone is "lying
with statistics." If you believe that someone is using a
"bend-and-fit model," how do you prove that he's doing so? Obviously
you need the rigor and discipline of mathematics to do so. In other
words, you need the mathematics of statistics not only to do
statistics applications, but also to have the tools available to
prove that someone else is lying or cheating with statistics.

Originally Posted by Jesse '77

> Looking back over Croakmore's argument, there is a sense in which
> I agree with him--although I think statistics is genuine
> mathematics, if John Xenakis was claiming that his argument about
> the probability of life was totally rigorous I would disagree,
> because the application of statistical rules to real-world
> phenomena is much more heuristic...you have to worry about
> problems like the one of selection bias that I mentioned
> earlier.

This is a very good statement of the situation.

Sincerely,

John

John J. Xenakis
john@GenerationalDynamics.com
http://www.GenerationalDynamics.com

Well, let’s try this one out.

Prove that:

a^n + b^n = c^n

for integers n greater than 2 (Fermat’s Last Theorem). This can be done rigorously with mathematics. Remember: n is a precise numerical value for which there is no ambiguity. I suppose you could call it “pure” mathematics.

Now, prove that:

(x1 + x2 + … + xn)/N = mean x

is a valid measure of a population’s central tendency. This cannot be done unambiguously by rigorous mathematics because the distribution of data in a population affects all measures of central tendency. You can do a X-square test and so on, but that will not prove anything precisely. Remember: mean x is an arbitrary value of central tendency that proves nothing about the distribution of data in a population. I suppose you could call it “applied” mathematics, but there is nothing really provable about it; all the operational proofs have already been rendered by “pure” mathematicians.

So what do you have with probability and statistics? A pinochle game? No, more than that. It is an important tool of science – and indeed a mathematical tool of sorts. But, for the love of Bertie Russell, it is not a branch of mathematics -- not at all like the true branches, such as the calculus, trigonometry, diff. eq., et al.

And, John, so far as universal life and intelligence goes, it’s good to know something about the distribution of populations before you draft assumptions about such important ubiquities. As Jesse'77 has said: You have to worry about bias. But, in the case of Fermat’s Last Theorem, there is no bias to worry about. Nothing arbitrary about it. However, all statistics derives from arbitrary measures of central tendency, and all statisticians must address this problem of bias by employing arbitrary tests that try to measure it.

When Newton reduced local gravity to a mathematical equation he altered the course of history. Something like that is happening now; it is the reduction of life to a digital code with a mathematical basis. Yes, it is still very ambiguous. But when I look at the Genetic Dictionary and reflect upon its meaning I am staggered by its 2^6 digital geometry, triangulated as codons, spelling out proteins. But, now, these genes are suspected of being controlled by epigenes and extraplasmic signals from the environment (What?). Who knows what the hell is going on?! Somewhere in the past Mother Nature or Whomever had a fancy for mathematics. And, frankly, I don’t think that Great Mathematician was rolling dice or flipping coins.

Why only one kind of life? And why only here? You have to be impressed by how little biologists really know about life and its origin. Codes that preserve themselves for millions and millions of years? Codes that can collectively evolve for survival purposes, rendering many of them immortal by all human standards. And I wonder, wonder, wonder: Is there something about Nature than is not "Darwinian all the way down”?

Exodus 8

The Green Geezer

Dear Richard,

Why do you say that calculus is mathematics? Newton's formula is
wrong because it doesn't take into account things like wind, moon
gravity, and so forth. Calculus isn't math, and Newton was nothing
more than an overrated pinochle player.

John

You can do better than that, John.

Look, I can offer you a draw on this valid-branches-of-mathematics issue (but it won't change my mind about it) for the sake of emphasizing my main point, which is: No amount of probabily theory or craftily applied statistics can overcome this "odd-singularity-of-life" problem -- only one kind of it, and only here. Why? You will reply that we don't know yet if it occurs anywhere else, and we don't know that it doesn't, so, for that reason, you can't rule out the probability of its ubiquity. Well, OK, I would say for that reason you can't rule out its utter uniqueness in form and habitat here on Earth, either. We know for sure that life occurs here on Earth. We just differ on the meaning of "...therefore it must occur elsewhere" vs. "...there is no statistical basis to support the contention that it therefore must occur elsewhere."

Any model that assumes that life ocurrs extraterrestrially must do so without the aid of probability theory and statistics. I don't think you can validly invoke probability and statistics on the question of universally ubiquitous life, and much less so on the question of universally ubiquitous intelligence.

Originally Posted by Croakmore

You can do better than that, John.

Don't bet on it.

Originally Posted by Peter Gibbons

Originally Posted by Croakmore

You can do better than that, John.

Don't bet on it.

Actually, I think John was on point. Croakmore's denigration of statistics by tying it to real world concerns doesn't make sense, because pure mathematics can also be used or misused to problems in the real world. And you can have proofs of statistical laws that don't reference the real world just as you can have proofs in pure mathematics.

Originally Posted by jeffw

Originally Posted by Peter Gibbons

Originally Posted by Croakmore

You can do better than that, John.

Don't bet on it.

Actually, I think John was on point. Croakmore's denigration of statistics by tying it to real world concerns doesn't make sense, because pure mathematics can also be used or misused to problems in the real world. And you can have proofs of statistical laws that don't reference the real world just as you can have proofs in pure mathematics.

I actually agree with Xenakis on a number of things. I believe life is abundant in the universe and that intelligent life is likely. And I believe that he's right about the stock market and the general economic clusterf*ck that's coming.

But, if you'll notice, Mr. E. (Croakmore) has been fairly pleasant during the conversation, whereas Xenakis is the one who is denigrating and condescending ("duh"). He just did the same to Liz in another thread. He asks for "objections" and then when people give them to him he calls it, and sometimes them, "stupid" and the like. This is besides the evasion and other annoying habits he can engage in.

Originally Posted by Peter Gibbons

Originally Posted by jeffw

Originally Posted by Peter Gibbons

Originally Posted by Croakmore

You can do better than that, John.

Don't bet on it.

Actually, I think John was on point. Croakmore's denigration of statistics by tying it to real world concerns doesn't make sense, because pure mathematics can also be used or misused to problems in the real world. And you can have proofs of statistical laws that don't reference the real world just as you can have proofs in pure mathematics.

I actually agree with Xenakis on a number of things. I believe life is abundant in the universe and that intelligent life is likely. And I believe that he's right about the stock market and the general economic clusterf*ck that's coming.

But, if you'll notice, Mr. E. (Croakmore) has been fairly pleasant during the conversation, whereas Xenakis is the one who is denigrating and condescending ("duh"). He just did the same to Liz in another thread. He asks for "objections" and then when people give them to him he calls it, and sometimes them, "stupid" and the like. This is besides the evasion and other annoying habits he can engage in.

Actually I think Mr. X is crushing on Liz, but that's another topic for a different thread ;-) .

Dear Richard,

Originally Posted by Croakmore

> You can do better than that, John.

Actually, no I can't, Richard.

In simplest form, my argument is to start from a set of assumptions
that evolutionary theory uses (what I call the "Nature's laboratory"
assumptions), and then to go from those assumptions, using logic and
math, to a conclusion about evolution on earth. You've denigrated
the Theory of Probability and Statistics and essentially said that
using logic and math is off bounds. You've even insulted me by
implying that I was dishonest.

When you ask questions like "Why only one kind of life? And why only
here?", or talk about the "odd-singularity-of-life problem," you're
essentially using statistical arguments yourself. But you've set
yourself up as the only arbiter of what kinds of statistical arguments
are OK (yours), versus what kinds are dishonest (everyone else's). So
you've positioned yourself so that you can say anything you want, and
no one can respond, least of all me. So you can say, depending on
your mood, that 2+2=3 or 2+2=4 or 2+2=5, and no one has any framework
for challenging you.

Like I said before, believe what you want, Richard.

John

jeffw & John,

How have it denigrated probability and statistics? By denying its wrongful place as a branch of mathematics? Isn't critical differentiation of analytic disciplines allowed on this forum? Jesus, you would think I did something bad -- like, I denigrated.

And, John, no specific insults were intended by me. Sorry. From my side of it, I was just arguing my case, but maybe I go too far sometimes with the words. However, I offered you a draw, so I can let most of it go. Except for one thing: I just don't go along with the idea that you can use probability and statictics as a means to support any argument about extraterrestrial life and consciousness, let alone ubiquous life and consciousness.

If you want to believe, as Sean does, that life is ubiquous and so is consciousness, then go ahead. But, boys, it's a belief built more on hope than on rigor.

If one can argue that life naturally crawls out of warm ponds, wherever they might occur, and eventually grows a consciousness like that of humans, just by virtue of the coin-tossing metaphor, then one should be expecting to hear from them any day now, because certainly some of them grew consciousnesses billions of years ago, and so they have had plenty of time to send out a few messages or a rocket ship or something.

Personally, I don't expect humans to ever discover extraterrestrial life. It's probably not there (but I don't know for certain). I think we're a one-off, a quirk, a glorious fudge of the lab results. And we're all alone out here on Earth -- all, all alone. (And, being an INTJ, that's the way I like it!)

Exodus 8

The Green Geezer

Originally Posted by Croakmore

How have it denigrated probability and statistics? By denying its wrongful place as a branch of mathematics? Isn't critical differentiation of analytic disciplines allowed on this forum?

But your denial of its rightful place as a branch of mathematics is based on your failure to differentiate between the pure theory of probability and statistics, which is based purely on reasoning logically from some set of axioms and which no mathematician in the world would deny is a valid branch of mathematics, and the application of statistics to actual real-world problems.

Originally Posted by Croakmore

If you want to believe, as Sean does, that life is ubiquous and so is consciousness, then go ahead. But, boys, it's a belief built more on hope than on rigor.

If one can argue that life naturally crawls out of warm ponds, wherever they might occur, and eventually grows a consciousness like that of humans, just by virtue of the coin-tossing metaphor, then one should be expecting to hear from them any day now, because certainly some of them grew consciousnesses billions of years ago, and so they have had plenty of time to send out a few messages or a rocket ship or something.

Personally, I don't expect humans to ever discover extraterrestrial life. It's probably not there (but I don't know for certain). I think we're a one-off, a quirk, a glorious fudge of the lab results. And we're all alone out here on Earth -- all, all alone. (And, being an INTJ, that's the way I like it!)

This I agree with. IMO, the feasibility of self-replicating probes makes the Fermi paradox into a very strong argument against any extraterrestrial intelligences having arisen within our past light cone (the set of points in spacetime that could send a signal that would reach our current point in spacetime travelling at the speed of light or slower). I have also seen some good arguments in the book Rare Earth about the number of factors that were critical to the development of complex life on earth that are unlikely to come together very often ('unlikely' in the sense of a rough guesstimate of the likelihood, not any formal mathematical argument). There's an online discussion of the rare earth hypothesis here.

Dear Richard,

Originally Posted by Croakmore

> I think we're a one-off, a quirk, a glorious fudge of the lab
> results. And we're all alone out here on Earth -- all, all
> alone.

As I said, this is a probabilistic or statistical conclusion. To
reach this conclusion, you have to construct some "bend-and-fit model"
of life on earth that explains how life can happen once, but not more
than once. Whatever model you're using, I doubt that it would pass
mathematical scrutiny.

Sincerely,

John

John J. Xenakis
E-mail: john@GenerationalDynamics.com
Web site: http://www.GenerationalDynamics.com

Originally Posted by John J. Xenakis

As I said, this is a probabilistic or statistical conclusion. To
reach this conclusion, you have to construct some "bend-and-fit model"
of life on earth that explains how life can happen once, but not more
than once. Whatever model you're using, I doubt that it would pass
mathematical scrutiny.

That's a strawman--you don't need a model that says life cannot happen more than once, ever. You just need a model that says that the probability of intelligence developing on a random star is less than 1 in 7*10^22, the number of stars in the observable universe according to current estimates (because of the speed-of-light limit, nothing outside the observable universe can possibly have any interaction with us). This seems like a giant number, but since probabilities multiply, all you'd need is 6 independent factors or events required for intelligent life to arise that each have a probability of less than 1 in 10,000, or 8 independent factors that each have a probability of less than 1 in 1000; it doesn't seem so implausible that a small number of such unlikely factors could be required for complex life to arise (again, read the book Rare Earth for a large number of plausible candidates for such factors).

Originally Posted by Jesse '77

Originally Posted by John J. Xenakis

As I said, this is a probabilistic or statistical conclusion. To
reach this conclusion, you have to construct some "bend-and-fit model"
of life on earth that explains how life can happen once, but not more
than once. Whatever model you're using, I doubt that it would pass
mathematical scrutiny.

That's a strawman--you don't need a model that says life cannot happen more than once, ever. You just need a model that says that the probability of intelligence developing on a random star is less than 1 in 7*10^22, the number of stars in the observable universe according to current estimates (because of the speed-of-light limit, nothing outside the observable universe can possibly have any interaction with us). This seems like a giant number, but since probabilities multiply, all you'd need is 6 independent factors or events required for intelligent life to arise that each have a probability of less than 1 in 10,000, or 8 independent factors that each have a probability of less than 1 in 1000; it doesn't seem so implausible that a small number of such unlikely factors could be required for complex life to arise (again, read the book Rare Earth for a large number of plausible candidates for such factors).

But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

Originally Posted by jeffw

But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

My argument was just to disagree with John Xenakis that it's totally implausible we're alone in the observable universe, not to make a positive claim that intelligent life must be rare. However, I still think the Fermi Paradox is a very strong argument against intelligent life being common in the galaxy, or even in the entire observable universe.

Originally Posted by jeffw

...
But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

I object to this for the specific reason that there is only one (1) kind of life and I cannot possibly imagine what other way it could have arisen beyond the way it arose on Earth. Do we know for sure that life originated on Earth rather than from some kind of alien infection? No! That's a pretty big gap in our already precarious knowledge about life. But one thing seems certain, at least to me, and that is the total historical absence of any "beta-max" competitor for supreme sovereinty of the living kingdoms. That is why I am bothered by the notion of "some other way elsewhere."

Life is still too great a mystery to make a stochastic model of its origin and distribution. I have to be impressed by the depth of this mystery: the few things we know for sure about life tell us only that it is organically cellular, its molecular genes are digitally coded, it self-replicates, it competes ecologically, and it evolves.

If Martha Stewart couldn't make a muffin from scrath then she wouldn't know didly squat about cooking. If a biologist can't make a virus from scrath then, relatively speaking, he or she is no better off than Martha Stewart. Fraudulent!

Exodus 8

The Green Geezer

Originally Posted by Jesse '77

Originally Posted by jeffw

But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

My argument was just to disagree with John Xenakis that it's totally implausible we're alone in the observable universe, not to make a positive claim that intelligent life must be rare. However, I still think the Fermi Paradox is a very strong argument against intelligent life being common in the galaxy, or even in the entire observable universe.

Or it could just mean that FTL travel just isn't possible and that making self-replicating robots is harder than it's proponents suggest.

Originally Posted by Croakmore

Originally Posted by jeffw

...
But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

I object to this for the specific reason that there is only one (1) kind of life and I cannot possibly imagine what other way it could have arisen beyond the way it arose on Earth. Do we know for sure that life originated on Earth rather than from some kind of alien infection? No! That's a pretty big gap in our already precarious knowledge about life. But one thing seems certain, at least to me, and that is the total historical absence of any "beta-max" competitor for supreme sovereinty of the living kingdoms. That is why I am bothered by the notion of "some other way elsewhere."

Could another mechanism of life have arisen but was out-competed by RNA/DNA life before they could have left any evidence? And what about other environments that are too hostile for DNA-life but how can you rule out some other mechanism that no one has thought of.

Given that it happened once, I find it pretty implausible to suggest that it couldn't have happened again somewhere else.

Of course this is all wild-speculation based on almost no data. And we know even less about the origins of intelligence and self-awareness.

Originally Posted by Croakmore

Life is still too great a mystery to make a stochastic model of its origin and distribution. I have to be impressed by the depth of this mystery: the few things we know for sure about life tell us only that it is organically cellular, its molecular genes are digitally coded, it self-replicates, it competes ecologically, and it evolves.

If Martha Stewart couldn't make a muffin from scrath then she wouldn't know didly squat about cooking. If a biologist can't make a virus from scrath then, relatively speaking, he or she is no better off than Martha Stewart. Fraudulent!

Hear, hear! Glad to see this thread finally move away from the purely abstract and focus more on concrete topics. To second Croaker's assertion, I came across this article in Der Spiegel while searching for the results of the Germany federal elections (ok, ok, so I'm not entirely weaned off of politics). It's a Spiegel Exclusive and it's not on their English site, so those of you who don't read German will have to make do with the Babelfish, which hardly helps with such a technical laden article. Here's my rough translation:

A Trip To The Great Beyond

Researchers bleed out pigs and dogs, fill them with chilled saline solution - and wake the dead animals hours later back to life. The technology, to turn creatures off and back on, could revolutionize medicine. Soon the first humans are to be sent into the "death sleep".

First the heart begins to beat, then a snort is heard. The pig straightens up and looks curiously at the man in the smock, who stands on the other side of the cage.

"This animal was dead for hours", says surgeon Hasan Alam, 39, of Massachusetts General Hospital in Boston. "But we brought it back. Now it's here again."

Magical powers also seem to be working in the Animal Research Institute of the Vienna General Hospital. There pigs open their eyes, after their hearts are stopped by an electric charge and they lie dead for half an hour. "The miracle is", says the emergency physician William Behringer, 39, "that the animals return to life without neurological damage."

In the past few years, the two research groups have sent hundreds of pigs through the round trip through the Beyond, always using the same trick: the doctors flood the bodies with liters of 2-degree-C chilled saline solution, and so send the animals into a mysterious limbo, that hinders the cells of the dead bodies from finally dying. All experiments are carried out after deep anesthesis, so that the animals feel no pain.

:idea: :idea: :idea:

After this, it seems a bit silly to be arguing about intelligent life, when we don't really even know what life is...


(Side note: notice that both lead researchers cited in the article are Atari-wave Xers.)

Originally Posted by jeffw

Originally Posted by Croakmore

Originally Posted by jeffw

...
But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

I object to this for the specific reason that there is only one (1) kind of life and I cannot possibly imagine what other way it could have arisen beyond the way it arose on Earth. Do we know for sure that life originated on Earth rather than from some kind of alien infection? No! That's a pretty big gap in our already precarious knowledge about life. But one thing seems certain, at least to me, and that is the total historical absence of any "beta-max" competitor for supreme sovereinty of the living kingdoms. That is why I am bothered by the notion of "some other way elsewhere."

Could another mechanism of life have arisen but was out-competed by RNA/DNA life before they could have left any evidence? And what about other environments that are too hostile for DNA-life but how can you rule out some other mechanism that no one has thought of.

Given that it happened once, I find it pretty implausible to suggest that it couldn't have happened again somewhere else.

Of course this is all wild-speculation based on almost no data. And we know even less about the origins of intelligence and self-awareness.

I would not know how to answer these questions without having some idea of what "another mechanism of life" could be. The only life we know of is all the same kind of life, so I don't have a clue about those alternative "mechanisms." What do you suppose they could be? And if they really do exist then why are they not found here on Earth (a notably fertile rock)? All I have is my opinion, but I can't feature those other guys in any way, shape, or form. But if I ever met one I would ask him or her or it this question: Do you have digitally coded genes or something like them?

Exodus 8

The Green Geezer

Originally Posted by Croakmore

Originally Posted by jeffw

Originally Posted by Croakmore

Originally Posted by jeffw

...
But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

I object to this for the specific reason that there is only one (1) kind of life and I cannot possibly imagine what other way it could have arisen beyond the way it arose on Earth. Do we know for sure that life originated on Earth rather than from some kind of alien infection? No! That's a pretty big gap in our already precarious knowledge about life. But one thing seems certain, at least to me, and that is the total historical absence of any "beta-max" competitor for supreme sovereinty of the living kingdoms. That is why I am bothered by the notion of "some other way elsewhere."

Could another mechanism of life have arisen but was out-competed by RNA/DNA life before they could have left any evidence? And what about other environments that are too hostile for DNA-life but how can you rule out some other mechanism that no one has thought of.

Given that it happened once, I find it pretty implausible to suggest that it couldn't have happened again somewhere else.

Of course this is all wild-speculation based on almost no data. And we know even less about the origins of intelligence and self-awareness.

I would not know how to answer these questions without having some idea of what "another mechanism of life" could be. The only life we know of is all the same kind of life, so I don't have a clue about those alternative "mechanisms." What do you suppose they could be? And if they really do exist then why are they not found here on Earth (a notably fertile rock)? All I have is my opinion, but I can't feature those other guys in any way, shape, or form. But if I ever met one I would ask him or her or it this question: Do you have digitally coded genes or something like them?

What makes you think that DNA is unique in being able to digitally encode the blueprints of life? We have only the history of one planet to look at in any detail and you seem to be willing to make a very big extrapolation out of a sample of one.

Originally Posted by jeffw

Originally Posted by Jesse '77

Originally Posted by jeffw

But we're so far from knowing what factors or events are necessary for life to arise that any attempt to apply an estimate is pointless. In fact, even if we knew what events on Earth led to the development of life, we can't rule out that life could arise in some other way elsewhere.

My argument was just to disagree with John Xenakis that it's totally implausible we're alone in the observable universe, not to make a positive claim that intelligent life must be rare. However, I still think the Fermi Paradox is a very strong argument against intelligent life being common in the galaxy, or even in the entire observable universe.

Or it could just mean that FTL travel just isn't possible and that making self-replicating robots is harder than it's proponents suggest.

I think FTL travel is very likely impossible, since according to relativity FTL travel would lead to the possibility of backwards time travel. But the timescale needed to send a probe across the galaxy is basically negligible compared to evolutionary timescales, even if the probe moves no faster than the Voyager spacecraft. Also, if you believe that a group of human colonists would be able to build new things upon arrival in a different star system, then as long as A.I. is not impossible, it should be possible to build a probe that could do the same thing. Yes, there's room for uncertainty, but the Fermi paradox is compelling enough so that I personally would be willing to bet a lot of money that no alien civilizations arose (and avoided destroying themselves) within our galaxy in the past, and I'd bet a slightly smaller amount of money that none arose within our entire past light cone.

edit: I looked it up, and I overstated things when I said that thing about the timescales to cross the galaxy being negligible compared to evolutionary timescales--the Voyager spacecraft only goes at about 0.006% light speed, and the galaxy is around 100,000 light years across, so it'd take a little under 2 billion years to cross it at that speed. But if you could get up to, say, 1% light speed (less than 200 times faster than Voyager) you could cross the galaxy in about 10 million years, which is pretty short on the timescale of evolution.

Originally Posted by Jesse '77

Yes, there's room for uncertainty, but the Fermi paradox is compelling enough so that I personally would be willing to bet a lot of money that no alien civilizations arose (and avoided destroying themselves) within our galaxy in the past,

The above doesn't seem to indicate very good odds for our civilization avoiding self-destruction, either! :shock:

I tend to agree. :cry: