[PassedOut]

DrTodd13, on Feb 1 2009, 02:31 PM, said:

No, I believe that unlikely things have occurred but the more unlikely it is a priori the more evidence I would like to see before believing that it really happened.

And what is more unlikely than a god who creates by magic?

[mikeh]

DrTodd13, on Feb 1 2009, 02:31 PM, said:

jdonn, on Jan 29 2009, 01:41 PM, said:

DrTodd13, on Jan 29 2009, 04:35 PM, said:

So, in short I would say that evolution is possible but failure to have a better explanation is not proof of the truth of the current best conjecture particularly when the same science giving us this explanation says its likelihood is extremely low.

If you are saying you only would believe an explanation for our existance if a priori it were extremely likely to occur, then I strongly disagree!

No, I believe that unlikely things have occurred but the more unlikely it is a priori the more evidence I would like to see before believing that it really happened.

That strikes me as a very sound approach.

However:

1. Speaking only for myself, I find it impossible to internalize the concept of 'billions of years' in terms of being able to sense whether something that is highly improbable in any time frame with which I am comfortable could become likely over that time line. Thus I can well imagine thinking, and I do think, that the odds of a self-replicating molecule, the presumed precursor to life as we know it, coming into existence through chemical and physical action in the early earth, are very small... but over a billion years or more? I can't internalize that, so I have to go with what science has suggested.. which is certainly that at least the building blocks for such molecules be generated without the invocation of a designer.

2. Common sense is an evolved ability. It allows our brains to leap to conclusions that, in the context of the decisions our ancestors had to make, were likely to enhance our survival and ability to reproduce. The problems were macroscopic, and involved immediate or short-term time-lines. The problems we wrestle with in terms of ultimate questions are of an entirely different nature.. they deal with issues we cannot directly perceive, over time lines we cannot grasp emotionally. So common sense, on which we rely very heavily in our day to day lives, may be a fallible instrument.

In particular, our internal grasp of probabilities is notoriously prone to error... hence the success of casinos, lotteries, bookies and so on.... as one everyday example..

While science cannot now and maybe never shall rule out the idea of some force or entity external to the universe 'created' the universe, the evidence so far available suggests that invoking that force or entity to explain what has happened since a trillionth of a trillionth of a second after the big bang is unnecessary, and that brings us back to Occam's razor as a compelling argument against such an invocation. Improbable tho life may be... the universe is an extremely large place, that has been in more or less its present form (ie low enough average density of energy to allow the formation of stars, planets, etc) for a very long time.... such that it seems highly probable that at some place (indeed, at many places) self-replicating life arose. There is nothing miraculous that it happened on this planet... given that it 'probably' had to happen somewhere.... the inhabitants of that somewhere will always be thinking 'why us?'.

[jdonn]

DrTodd13, on Feb 1 2009, 02:31 PM, said:

jdonn, on Jan 29 2009, 01:41 PM, said:

DrTodd13, on Jan 29 2009, 04:35 PM, said:

So, in short I would say that evolution is possible but failure to have a better explanation is not proof of the truth of the current best conjecture particularly when the same science giving us this explanation says its likelihood is extremely low.

If you are saying you only would believe an explanation for our existance if a priori it were extremely likely to occur, then I strongly disagree!

No, I believe that unlikely things have occurred but the more unlikely it is a priori the more evidence I would like to see before believing that it really happened.

Perhaps I could agree with that. But how can a priori likelihood of such things ever be judged?

[helene_t]

mikeh, on Feb 1 2009, 08:50 PM, said:

1. Speaking only for myself, I find it impossible to internalize the concept of 'billions of years' in terms of being able to sense whether something that is highly improbable in any time frame with which I am comfortable could become likely over that time line. Thus I can well imagine thinking, and I do think, that the odds of a self-replicating molecule, the presumed precursor to life as we know it, coming into existence through chemical and physical action in the early earth, are very small... but over a billion years or more?

If we knew the probability of a self-replicating molecule (or system of molecules) coming into existence in a given millisecond in a given microliter of primodial soup, then we could calculate the probability that it would ever occur somewhere in the ocean over a billion years. Roughly 10^49 times as high according to my quick head calculations. One problem is there is no concencus about how this replicator looked like so we cannot compute the probabilities.

For evolutionary biologist it doens't matter, though. We know it happened here on Earth so given that information obviously the probability is 1. But it is of interest for those who try to find life elsewhere in the universe.

[Winstonm]

helene_t, on Feb 1 2009, 08:42 PM, said:

mikeh, on Feb 1 2009, 08:50 PM, said:

1. Speaking only for myself, I find it impossible to internalize the concept of 'billions of years' in terms of being able to sense whether something that is highly improbable in any time frame with which I am comfortable could become likely over that time line.  Thus I can well imagine thinking, and I do think, that the odds of a self-replicating molecule, the presumed precursor to life as we know it, coming into existence through chemical and physical action in the early earth, are very small... but over a billion years or more?

If we knew the probability of a self-replicating molecule (or system of molecules) coming into existence in a given millisecond in a given microliter of primodial soup, then we could calculate the probability that it would ever occur somewhere in the ocean over a billion years. Roughly 10^49 times as high according to my quick head calculations. One problem is there is no concencus about how this replicator looked like so we cannot compute the probabilities.

For evolutionary biologist it doens't matter, though. We know it happened here on Earth so given that information obviously the probability is 1. But it is of interest for those who try to find life elsewhere in the universe.

Could one of the bright scientists here explain to me - if I have this correct to start - how and why NASA decided to search for a decrease in entropy as proof of life on Mars?

[helene_t]

Winstonm, on Feb 2 2009, 02:49 AM, said:

Could one of the bright scientists here explain to me - if I have this correct to start - how and why NASA decided to search for a decrease in entropy as proof of life on Mars?

According to wikipedia (http://en.wikipedia....ntropy_and_life) it goes back Lovelock who in 1964 suggested to look for entropy reduction because life can be defined as a mechanism that is capable of reducing entropy (or something like that). It sounds to me more like a semantic issue (how should we define life for the purpose of this project?) rather than a pratical one (how are we actually going to detect it?). But I may be wrong. Do you have any newer refs?

[Winstonm]

helene_t, on Feb 1 2009, 09:08 PM, said:

Winstonm, on Feb 2 2009, 02:49 AM, said:

Could one of the bright scientists here explain to me - if I have this correct to start - how and why NASA decided to search for a decrease in entropy as proof of life on Mars?

According to wikipedia (http://en.wikipedia....ntropy_and_life) it goes back Lovelock who in 1964 suggested to look for entropy reduction because life can be defined as a mechanism that is capable of reducing entropy (or something like that). It sounds to me more like a semantic issue (how should we define life for the purpose of this project?) rather than a pratical one (how are we actually going to detect it?). But I may be wrong. Do you have any newer refs?

No, sorry. I was relying on memory (hence was not even sure if what I thought I remembered was close to right.)

I seem to remember the debate began as you suggest - how is life defined and then how would such a form be located on a distant planet with the conclusion being as you suggest a reduction in entropy.