What is the probability of life in Universe?

[Chronos]

Agreed dave, oxygen is the byproduct of life, not a prerequisite. Almost no other explanation is known that can account for free oxygen in a planetary atmosphere. Water, on the other hand, is a necessary precursor for life [as we know it]. It's presence is merely makes life a reasonable possibility.

 

[Dmitry67]

In infinite Universe the probability is irrelevant. I suspect that probability of life is about something 10**-200. But even in such case there are infinitely many planets with life - beyond the cosmological horizon

 

[brother time]

I suspect that life is fairly likely (75%) to exist. But I am wondering what is the definition that classifies as life? And isn't life not requiring oxygen and can form based on any element? I did a report on diatoms and found that some in the Antarctic only require sulfur and iron to live.
Cheers, BT

 

[Gannet]

In the section Prospects for Life in the {Milky Way} Galaxy
http://www.tufts.edu/as/wright_center/cosmic_evolution/docs/fr_1/fr_1_future.html"

The following chart is shown (see attachment)

 

[phyzguy]

The problem with this figure is that the size of the boxes are complete guesses. We have a pretty good idea of the number of stars with planetary systems, but most of the other probabilities, such as:
(1) the probability that a planet is habitable, or
(2) the probability that if it is habitable that it has life, or
(3) the probability that if it has life that it has intelligent life

are complete guesses. Today we have no idea if these probabilities are 1 in 100 or 1 in 10^100.

 

[DaveC426913]

The problem with this figure is that the size of the boxes are complete guesses. We have a pretty good idea of the number of stars with planetary systems, but most of the other probabilities, such as:
(1) the probability that a planet is habitable, or
(2) the probability that if it is habitable that it has life, or
(3) the probability that if it has life that it has intelligent life

are complete guesses. Today we have no idea if these probabilities are 1 in 100 or 1 in 10^100.

Well not quite. We know that the worst the odds can possibly be at the highest level are 1 in 10^11 (one example in 500 billion stars).

 

[phyzguy]

Well not quite. We know that the worst the odds can possibly be at the highest level are 1 in 10^11 (one example in 500 billion stars).

How do we know that? Are you basing it on the fact that there is intelligent life on Earth? We cannot draw conclusions of the probability of an event based on one example.

 

[DaveC426913]

How do we know that? Are you basing it on the fact that there is intelligent life on Earth? We cannot draw conclusions of the probability of an event based on one example.

Your wording was a bit ambiguous.

You were suggesting that the chances of any given planet in our galaxy being habitable could be as low as 1 in 10^100. I am simply saying that the odds for life on a a planet in the galaxy cannot be worse than 10^11, because in the sample 500 billion so far, we've found one example.

i.e. There are 10,000 clover plants in a field. You claim the odds that one of them is a four-leafed variety could be 1 in 10,000,000,000. I'm saying "Nope, I already have one from this field. That means the odds at worst are one in 10,000."

I think what you are trying to say is "the odds of finding another four-leafed variety could easily be 1 in 100,000,000." Which is true, it's just an odd way of calculating probabilities. Kind of like every time you get a positive hit, you toss it away and start counting again.

 

[Dmitry67]

You were suggesting that the chances of any given planet in our galaxy being habitable could be as low as 1 in 10^100. I am simply saying that the odds for life on a a planet in the galaxy cannot be worse than 10^11, because in the sample 500 billion so far, we've found one example.

?
This is true only if most of galaxies have life at least on one planet!
You are assuming that the choice of our galaxy is random, which is not of course (anthropic principle) - the sample is not fair - even worse, for obvious reasons this sample is guaranteed to be unfair until you find planets except our own

I claim that that probablility is 10**-200
This number is not only consstent with the data we have, but it is even supported by the observational data - http://en.wikipedia.org/wiki/Fermi_paradox - so called 'Great Silence'

 

[DaveC426913]

This is true only if most of galaxies have life at least on one planet!
You are assuming that the choice of our galaxy is random,

It hasn't been an assumption. We have been talking only about our galaxy.

 

[phyzguy]

I am simply saying that the odds for life on a a planet in the galaxy cannot be worse than 10^11, because in the sample 500 billion so far, we've found one example.

You simply can't make probability arguments like this based on one data point. What you are saying is equivalent to the following reasoning:

(1) I deal out two poker hands. One is a royal flush.
(2) Therefore the odds of dealing a royal flush are at least 50%.

 

[DaveC426913]

You simply can't make probability arguments like this based on one data point. What you are saying is equivalent to the following reasoning:

(1) I deal out two poker hands. One is a royal flush.
(2) Therefore the odds of dealing a royal flush are at least 50%.

This analogy is flawed. A deck of cards is shuffled and then redealt. Our galaxy is not.

To keep your deck of cards analogy, we would say: this instance of the cards has dealt a royal flush, thus the probability of this instance dealing out a royal flush cannot be worse than 5 in 52 (the odds are, however, better than that, since there's 47 undealt cards that could still make a RF).


Is it possible that you are talking about galaxies, whereas I (and I thought everyone else) is talking about galaxy?

 

[Dmitry67]

Our galaxy is SPECIAL because WE are there.
Imagine that probability of life is 10^-200 per planet
So only one of 10^-189 galaxies has life
Observer in that galaxy (based on your logic) would conclude that life is very likely event - because in his sample (one galaxy) there is life.

 

[phyzguy]

I am simply saying that the odds for life on a a planet in the galaxy cannot be worse than 10^11, because in the sample 500 billion so far, we've found one example.

There are three problems with your argument. First, we have not examined 500 billion star systems and determined that only one has life. We've only examined one star system. Second, by your argument, why stop with only the galaxy? Why not include the entire observable universe, with ~ 10^23 stars? We haven't found any life anywhere. Third, even if we had examined 500 billion star systems, the fact that we only have one example means that the uncertainty in the estimate (which is proportional to the square root of the number of observations) is equal to the estimate itself. Back to my royal flush analogy. If I have two poker hands, and one is a royal flush, I can say that the odds of a royal flush are 50% +/-50% - in other words I know nothing about the odds of a royal flush. That is the situation we are in.

 

[DaveC426913]

Our galaxy is SPECIAL because WE are there.
Imagine that probability of life is 10^-200 per planet
So only one of 10^-189 galaxies has life
Observer in that galaxy (based on your logic) would conclude that life is very likely event - because in his sample (one galaxy) there is life.

But we have only been talking about our galaxy.

I must call a point of order here. While this thread is titled "life in the universe", the discussion has evolved since post 54 to "life in our galaxy".

In retrospect, this is not necessarily the shift everyone else has made (though I have been inserting it in every one of my posts), so I state retroactively that my discussions about odds are most definitely only applicable to our galaxy.

There are three problems with your argument. First, we have not examined 500 billion star systems and determined that only one has life. We've only examined one star system.

That is not a flaw.

If I turn over the top card of a deck and it's an ace, I can say with certainty that the odds of this deck containing aces are no worse than 1 in 52 (even if the chances are much higher than that).

Second, by your argument, why stop with only the galaxy?

Also not a flaw.

That is the premise of the argument we are in. My odds are based on this galaxy and this galaxy alone.

If you wish to set a different premise, I have no problem with that. The odds will change completely.

the fact that we only have one example means that the uncertainty in the estimate (which is proportional to the square root of the number of observations) is equal to the estimate itself. Back to my royal flush analogy. If I have two poker hands, and one is a royal flush, I can say that the odds of a royal flush are 50% +/-50% - in other words I know nothing about the odds of a royal flush. That is the situation we are in.

Hang on. You've twisted the analogy. You're not comparing apples to apples.

We're not talking about a hand; we're talking about the deck. The odds of a royal flush in the current configuration of cards cannot be 0; it is actually 1.

Deck = our galaxy
Hand = one planet

You are correct that the next hand that is dealt (i.e. the next planet we check) is not affected by the fact that the first hand dealt (the first planet we checked) turned up positive.

I was not saying otherwise.

 

[Dmitry67]

*OUR* galaxy is special because we are here.
Even we know that probability of life in OUR galaxy is 1 (at least 1 inhabited planet exists) it does not give us anything.

Returning to your statement:

I am simply saying that the odds for life on a a planet in the galaxy cannot be worse than 10^11, because in the sample 500 billion so far, we've found one example.

If we randomly pick any planet in OUR galaxy, the probability that there is life on is >10**-11 - TRUE

If we randomly pick any planet, the probability that there is life on is >10**-11 - FALSE

In general, this number (10^11) is absolutely useless, because it does not give us any estimation about how rare is the life in the Unvierse.

 

[phyzguy]

If we randomly pick any planet in OUR galaxy, the probability that there is life on is >10**-11 - TRUE

If we randomly pick any planet, the probability that there is life on is >10**-11 - FALSE

In general, this number (10^11) is absolutely useless, because it does not give us any estimation about how rare is the life in the Unvierse.

I agree completely. Stated another way, as you said, it is true that the odds of some planet in our galaxy having life is >10^-11, since there is life on Earth. However, this tells us nothing about the odds of there being life on some OTHER planet in our galaxy, which is of course what everyone wants to know.

Returning to your deck of cards analogy, it is correct, as DaveC said that if the first card is an ace, that then we know there is at least one ace in the deck. However, this tells us NOTHING about how many OTHER aces are in the deck.

 

[DaveC426913]

In general, this number (10^11) is absolutely useless, because it does not give us any estimation about how rare is the life in the Unvierse.

However, this tells us NOTHING about how many OTHER aces are in the deck.

Agreed. This whole side-thread came about because someone said the chances of life could be 1 in 10^100. There was some ambiguity about the scope that was applying to.

 

[Buckethead]

There may be some additional coefficiants that are not being considered. One has already been brought up, that of the definition of life. In biology the definition has been somewhat addressed: something that reproduces, assimilates, has parties and so on. In talking about life in the universe we might have a different defintion. If we consider quantum mechanics, then life (or more specifically, consciousness) is necessary for there to even be matter otherwise everything is just probability waves. So in cosmology perhaps the definition of life is anything that collapses probability waves. Considering that we have had a limited time on this planet, and assuming that the galaxy existed before us, we might conclude that there was intelligent life before us in order for matter to exist. Quite abstract, but just pushing the envelope here in a playful sort of way.

Also (and I suppose in the same vein) and as someone else here mentioned, without life a universe full of matter, well...doesn't matter, and may not really exist in any real sense of the word. I have felt for sometime that matter and life can't really be separated, you have to have both. With consciousness (which I'm using here as an alternative word for life) you have to have matter, or there is nothing, and with matter you have to have consciousness or there is nothing. So with this in mind, life or at least consciousness in some form or another, must have always existed with the universe or the universe could not exist.

Again, just being playfully abstract.

This may not be relevant to this discussion as I think it's safe to say that what we are searching for is recognizable life, i.e. bacteria or civilizations.

 

[PaulS1950]

While playing with the odds may be "numerically" or scientifically correct I think (perhaps even believe) that life permeates our galaxy. I also think (not believe) that intelligent life is going to be much more scattered.
We have what some members of the scientific community claim are signs of microbial life in rocks originating on Mars and if we accept that then there are two planets in our solar system that have supported life and more possibilities with the moons of our two gas giants planets. I think that your odds are scewed by a total lack of real knowledge of what it takes to give life a chance. Carbon and hydrogen are found in abundance throughout the galaxy and all we need in addition to that is some form of energy and a solvent that will allow the chemicals to combine. I don't believe we have the knowledge to limit that to water although our experience says that is necessary. For that matter can we limit life to only carbon based? The galaxy holds more wonders than we can imagine.
I will let you all go back to computing odds when you only know one small hand in a deck that is much larger than 52 cards.

 

[DaveC426913]

While playing with the odds may be "numerically" or scientifically correct I think (perhaps even believe) that life permeates our galaxy.

I will let you all go back to computing odds when you only know one small hand in a deck that is much larger than 52 cards.

It sounds like you think you're the only wisher in a sea of calculaters...

We all have our own beliefs about how abundant life is in the universe but those are private thoughts; there's little point in discussing them with others except when we wish to bolster my beliefs or defend them.

So, you've offered your opinion in a public place; so now you'll want to be defending it.

What makes you think life permeates the galaxy?

The Mars rock bacteria likely have the same origin as Earth bacteria - we still have only one abiogensis event.

"Carbon and hydrogen are found in abundance throughout the galaxy and all we need in addition to that is some form of energy and a solvent that will allow the chemicals to combine."

How do you know?

 

[Chronos]

I kinda like the probabilities for life elsewhere in our galaxy. Not so sure about intelligent life. I give life a 100% probability, intelligent life is much less probable. Too many special conditions required. I believe many intelligient species have arisen within our galaxy over the past 10 billion years. I also believe it entirely possible we may be the only one still standing.

 

[PaulS1950]

It sounds like you think you're the only wisher in a sea of calculaters...

We all have our own beliefs about how abundant life is in the universe but those are private thoughts; there's little point in discussing them with others except when we wish to bolster my beliefs or defend them.

So, you've offered your opinion in a public place; so now you'll want to be defending it.

What makes you think life permeates the galaxy?

The Mars rock bacteria likely have the same origin as Earth bacteria - we still have only one abiogensis event.

"Carbon and hydrogen are found in abundance throughout the galaxy and all we need in addition to that is some form of energy and a solvent that will allow the chemicals to combine."

How do you know?

I don't need to defend anything. As I stated some of what I was thinking I may not even believe myself. The parts I do believe are just that - belief. It needs no defence but that of my acceptance and reasons for that acceptance. I don't expect anyone else to believe what I do any more than I will just accept the beliefs of others.

As I stated in my post I don't believe that the "odds" being discussed can have much meaning because you/we (the human race) haven't enough facts to formulate meaningful statistics. Basing odds on our experience in a single star system when we haven't even studied all the planets and moons in our own system.