Is there life in the universe, and if so has it visited Earth?

[imaplanck]

The way I see it, is even if we even get to plug actual figures into the drake equation: The distances will in all likelihood be too restrictive for us too ever be able to reach the percentage of life that has reached technological civilization, and the reverse is also true.

 

[Ivan Seeking]

I agree; our existence might be against all odds, however there is no evidence to suggest that this is true. Also, since there is no reason to believe that we are special, it is entirely possible that intelligent life is nearly as common as planets.

If we randomly select a grain of sand on the beach, is it more logical to expect that grain of sand to be unique, or typical. Does our observation of that grain change the odds? Were the odds for intelligent life on Earth different before we [humans] came to be? Unless we can cite reasons why we are unique, it seems to me that our very existence is evidence that life is common. Again, the only hard evidence for the odds is measured as 1:1, for intelligent life on earth-like planets.

I wanted to clarify what I meant here a bit: As far as we know, we earthlings are unique or could be a rare event, but most likely, we couldn't possibly know otherwise as yet. By "unique" I am referring to our solar system, our part of the galaxy, the chemistry of our sun and the planets, etc. In this sense it appears that we may be a typical system with no particularly notable features. In this sense, considering our system may be like considering any other typical system. However, the selection of our system for consideration is certainly not random.

 

[imaplanck]

As a UFO believer, how do you feel about the upcoming interferometry missions and other scientific searches for life?
Are they just a complete waste of time to you, seeing as a few retired pilots (with a interest in making a few bucks) have reinforced your fantasy that Aliens have visited earth?

 

[DaveC426913]

That seems a bit harsh.

 

[fournier17]

1] Unless I'm mistaken, CO2 and methane are both organic compounds.QUOTE]

CO2 is inorganic carbon compound, and methane is an organic compound. However, the vast majority of the gases, which were believed to have composed the Earth's early atmosphere, were inorganic compounds. These inorganic compounds were needed for chemical evolution to occur, which gave rise to the organic building blocks that make up the macromolecules of the cell. Earth did not start off with organic molecules such as nucleotides, or sugars. However after reading an article linked to by Ivan Seeking, it seems that our planet may have been seeded with amino acids. Amino acids alone arent enough though for the evolution of life. You would still need chemical evolution to provide the Earth with sugars, nucleotides, and lipids for the biological evolution of life.

2]
IMO, you're over-complicating it the requirements.
- For water to be liquid, there must be enough energy to make it so. Sufficuent energy is a given.QUOTE]

-The formation of life is like a cooking recipe. If you want to talk about the ingredients and steps needed for the formation of life, its best to use as much detail as possible.
We should consider energy and the sources of energy. Just because water is liquid does not mean that there is enough energy for many of the reactions that preceded biological evolution to occur. If only the minimal amount of energy required by water to be in a liquid phase was present, the reactions that took place in early Earth would have occurred very slowly. Water in early Earth was bombarded by ionizing radiation which provided energy for a lot of the reactions, since there wasnt very much ozone in our atmosphere at that time. In todays earth, which has abundant amounts of liquid water, the rate of the reactions that occurred in the past, would occur today at an almost infinitly smaller rate. This is due to almost all of the high energy radiation being absorbed by the ozone layer.

- No surface is needed. Oceans work nicely.QUOTE]

-What does the ocean rest on top of? A surface is needed. Your not going to see biological evolution in gaseous planets.

- The range from the parent star is covered under the "liquid water" requirement. It is not in-and-of-itself a requirement.QUOTE]

-The range of the planet to a parent star is important, if a planet is to close, it would be like Venus, which would be to hot for life, to far and its to cold.

- I don't think a large amount of time betwwen catastrophes is a requirement. We're just talking about the origin of life for now, not the evolution of complex organisms. I doubt the biggest asteroid could wipe out ocean life across a planet. QUOTE]

Life needs a stable environment in order to start. If there is continuous bombardment of asteriods into a planet, your not going to see the formation of life.

 

[imaplanck]

That seems a bit harsh.

Why is it?

There is absolutely no forensic evidence to back up these alien stories, but plenty of evidence of ulterior motives i.e. a desire to cash in on the impressionable dreamers.

 

[fournier17]

The way I see it, is even if we even get to plug actual figures into the drake equation: The distances will in all likelihood be too restrictive for us too ever be able to reach the percentage of life that has reached technological civilization, and the reverse is also true.

What about worm holes. We could theoriticaly bend space/time and use a worm hole to punch through space/time. Heres some food for thought. Our planet has been around for about 4.5 billion years, it took about a billion years for the formation of the first prokaryotes. What if life began somewhere close to the beggining of the universe. Let's say life began somewhere when the universe was 1 billion years old, and that it took life there about 3.5 billion years to evolve an intelligent civilization. That civilization would be 10.5 billion years older than ours. Look how much we have done in the past 100 years, what if there is a civilization out there that has had 10.5 BILLION years to advance. I am sure if worm hole travel is possible, they would be using it. This hypothetical civilization would be almost god like compared to us, with their technological capabilities.

 

[imaplanck]

What about worm holes.

What about if fairies magic us across the galaxies/clusters/universe?

Heres some food for thought. Our planet has been around for about 4.5 billion years, it took about a billion for the formation of the first prokaryotes. What if life began somewhere close to the beggining of formation the Universe. Let's say life began somewhere when the universe was 1 billion years old, and that it took like there about 3.5 billion years to evolve an intelligent civilization. That civilization would be 10 billion years older than ours. Look how much we have done in the past 100 years, what if there is a civilization out there that has had 10 BILLION years to advance. I am sure if worm hole travel is possible, they would be using it. This hypothetical civilization would be almost god like with their technological capabilities.

The bigbang itself is estimated to be around ten billiuon years old, and didnt settle down to well in on that time.

 

[fournier17]

What about if fairies magic us across the galaxies/clusters/universe?



The bigbang itself is estimated to be around ten billiuon years old, and stars and planets didnt come about to well in omn that time.

-People use to think human flight was impossible as well. Given enough time, what do you know, we humans are in the sky. Now we can travel across the Alantic in less then a day when it took our ancestors months.

-I read some where that our universe is 15 billion years old, but that besides the point. What if there is a civilization out there that is billions of years older than ours. Dont you think they would be FAR more advanced then us? I think they would be able to do a lot of things that we think is impossible.

 

[imaplanck]

-People use to think human flight was impossible as well. Given enough time, what do you know, we humans are in the sky. Now we can travel across the Alantic in less then a day when it took our ancestors months.


-I read some where that our universe is 15 billion years old, but that besides the point. What if there is a civilization out there that is billions of years older than ours. Dont you think they would be FAR more advanced then us.

Yes you are right its 15(sorry). `


Yeah I think they would be FAR in advance of us, but (given the vast improbability of abiogenesis) I also think they could quite possibly be billions, if not trillions of light years away, if they exist at all. Never the less- Wormholes are purely a hypothesis, and even so how would one pinpoint a single inhabited star in 10^9999999999999 stars, say?

 

[Schrodinger's Dog]

I don't think we're quite there yet. The last the I saw, we can only detect relatively large planets, like Jupiter. And I recall the comment being made that this [finding Jupiters] is a very good sign because large planets make life on smaller planets possible by clearing the system. So finding big planets bodes well for life.

I think the current smallest planet is in the order of ten or eleven times the size of Uranus, but that's from memory it might be a bit larger.

 

[russ_watters]

-People use to think human flight was impossible as well. Given enough time, what do you know, we humans are in the sky. Now we can travel across the Alantic in less then a day when it took our ancestors months.

That is a very commonly used strawman. The huge difference between flight and ftl travel is that there never was a scientific theory that ruled-out flight. Flight was always a technological problem, not a theoretical one.

Look forward a couple thousand years and compare it to the view the ancient Egyptians would have had of us. Since the Egyptians knew about birds, I don't think they would be terribly surprised to see us flying. Flight fit with what they knew about reality. But looking forward, and seeing ftl travel a few centuries from now would require a scientific framework incompatible with the reality we see around us today.

That all said, I don't think the distance problem is very big one, though I'm not one who is looking forward to seeing a flying saurcer land on the White House lawn and taking day-trips to the Vegan system (I'm a meat eater anyway, so I'd hate that place). I believe it is possible with technology currently under development to prove to a level of certainty acceptable to scientists (but not laypeople or True Believers) whether or not there is life in any system within a thousand light years or so. Once that is done, communication becomes a relatively straightforward (if ultimately pointless) exercise.

 

[fournier17]

To get elements for life (Carbon/Oxygen and all the other elements of the periodic table), you need these made in a first-generation star which creates these as the products of nuclear fusion. This star then has to explode to create the dust/gas for a second generation star (like our Sun). QUOTE]

Is it known at what age of the Universe, the first second generation stars started to appear?

 

[imaplanck]

Very constructive of you to just say someones point of view is a 'fantasy'. Although the 'evidence' at present is certainly far from conclusive, it's not all totally dismissable (IMO).
Personally, I find less than a few percent of cases to have some merit to them, but that few percent is what makes the difference.
Any further scientific effort is always welcome.

At least you make a point here:



I partly agree with you here as I know a lot of people are in it for the money ( and publicity) and I haven't seen any physical evidence so far. But there also a lot of people NOT in it for the money and any real evidence COULD have been put out of public view by governments.
[As a sidenote, I remember seeing a clip of Stanton Friedman on a UFO program a while back (He's an ex-nuclear physicist who now seems to make a living doing the UFO-talk circuit and is a pro-UFO beleiver) . Anyways , he got filmed doing a behind-the scenes book-signing at one point and my impression was that he was very happy to talk to people if they bought his book, but wasn't interested at all otherwise!]



The timescale of our evolution:
Universe started approx 13Billion years ago (+/- a couple of billion).
The Earth/ Solar system is approx 5Billion years old.
To make life you need complex elements, that is, higher elements than Hydrogen/Helium.
To get elements for life (Carbon/Oxygen and all the other elements of the periodic table), you need these made in a first-generation star which creates these as the products of nuclear fusion. This star then has to explode to create the dust/gas for a second generation star (like our Sun).
So sometime during the first 8Billion years of the Universe our 1st generation progenetor star existed.
When our Earth started to form, after the first Billion years or so, basic single cell life forms existed for the next 3 Billion years and only the complex life (multicellular) started 4Billion years after the Earths formation. All the larger scale life forms have only been around for the last 600Million years or so.
So small and large differences in evolution time could exist between different alien races and hence in different levels of advancement and understanding.
.

I have studied the big bang to a degree, from the forming of hydrogen onto more complex elements etc, and the supernova event and the subsiquent settle down etc. I just fail to remember the details. Anyway I concede that life elsewhere could possibly be billions of years ahead of us.

It was only a few hundred years ago that the leading scientists of the day stated it would be impossible for people to travel faster than on horseback as the force-fullness of the air would make it so people would be unable to breathe.
If you were to tell a stone-age man that you could speak instantly to someone anywhere in the known world or fly like a bird or go to the moon I think he would say your point of view would be a 'fantasy'.

That is crap! the steam locomotive is 200 or so years old. Also one the flight front- Cayley invented the glider(heavier than air flight) over a century before the wright brothers famous flight, and I refuse to believe the rubbish touted, that no one could have thought powered heavier than air flight was possible before the Wright bros.

At any rate this type of naive analogy(used to allude that anything you can possibly conceive of, will eventually be achieved), is perilously foolhardy to say the least.

 

[Ivan Seeking]

As a UFO believer, how do you feel about the upcoming interferometry missions and other scientific searches for life?
Are they just a complete waste of time to you, seeing as a few retired pilots (with a interest in making a few bucks) have reinforced your fantasy that Aliens have visited earth?

That was intended for me?

First of all, I don't know what you mean by a UFO believer. You will have to explain to me what I believe.

Next, you will need to explain exactly what my fantasy is.

Also, keep up the insults and you will be penalized.

As for SETI and the question: What if ET was here? You can be the judge of the implications.

Psssssst: I ran SETI@Home on multiple computers for seven years.

Oh yes, to say that the entire UFO phenomenon boils down to a few retired pilots shows that you have no knowledge of the facts.

 

[russ_watters]

You think a stone-age man would have believed in people flying?

I absolutely do. It is known for certain that people have dreamed of imitating birds for thousands of years. They knew even then that there was no theoretical limitation: what prevented humans from imitating birds was always known to be a matter of power to weight ratio. History of flight: http://www.ueet.nasa.gov/StudentSite/historyofflight.html

And remember to differentiate flight from powered flight. The ancient Chinese flew kites (which is one way the Wright bros tested their designs).

It was only a few hundred years ago that the leading scientists of the day stated it would be impossible for people to travel faster than on horseback as the force-fullness of the air would make it so people would be unable to breathe.

Scientists? do you have any quotes? The wind blows faster than a horse runs and people certainly knew that hundreds of years ago.

Regardless, lack of understanding of a scientific principle is not the same as having a working scientific theory that forbids a phemonena.

I said this was a strawman before, but it is really half straman and half misunderstanding of the difference between science and technology.

Another important concept here is that as science progresses, we gain a better understanding of what we don't know. Ie, at one time, the speed of light was thought to be infinite. But that was only because the ability to measure it didn't exist. Now, we can measure it to a known and ever increasing level of precision. This provides an [ever decreasing] margin for error in our theories. The potential for them to be wrong exists in those shrinking margins for error and any theory that replaces an existing theory will have to incorporate the theory as footnotes or limited/special cases in the same way that for many applications Newton's theory of gravity still works depending on the case and margin for error required.

There may be unusual ways to circumvent theories like SR (and FYI, things like wormholes do not provide those avenues - they have properties that forbid it as well), but we certainly will never be able to go through it, meaning an action-reaction rocket will never travel faster than C. How can I be so sure? Because we've already put lots and lots of energy into particles and found that we can't accelerate them to a speed above C.

 

[DaveC426913]

Also, keep up the insults and you will be penalized.

From the strike through his name, I guess he did.

 

[DaveC426913]

Just because water is liquid does not mean that there is enough energy for many of the reactions that preceded biological evolution to occur. If only the minimal amount of energy required by water to be in a liquid phase was present, the reactions that took place in early Earth would have occurred very slowly.

Granted, and conceded. So,
4] Energy.

What does the ocean rest on top of? A surface is needed. Your not going to see biological evolution in gaseous planets.

Why do you bring up gaseous planets? We've already placed the requirement for liquid water; it could be a rocky planet or gaseous - as long as there is sufficient liquid water. Again, no surface is needed.

- The range from the parent star is covered under the "liquid water" requirement. It is not in-and-of-itself a requirement.QUOTE] [/B]
-The range of the planet to a parent star is important, if a planet is to close, it would be like Venus, which would be to hot for life, to far and its to cold.

Again, covered under liquid water. Any planet that's too close or too far will not have liquid water. The corollary holds true as well: if it does have liquid water, it is (by our current understanding of life) the right temp for life.

Life needs a staple environment in order to start. If their is continuous bombardment of asteriods into a planet, your not going to see the formation of life.

I disagree.
Life needs a stable environment to evolve to complex forms.
If a planet is continuously bombarded, you're not going to see complex life.

My point here is that a planet will be no less interesting for us to study just because it has "merely" the simplest kinds of life that could evolve on its battered home.


And my bigger point is that only the 4 requirements are required for us to examine a target in earnest for life. Any of the requirements you mention above should NOT disqualify a target for a search.

 

[Ivan Seeking]

Iam feeling rather ill after writing out a full page reply to Russ_watters and having it disappear when trying to post it. I can't face writing that out again. I haven't the will.

I know the feeling all too well. This is especially likely to happen when you have spent a great deal of time writing a response. If I'm not using Word as an editor, what I do is highlight the entire response and hit [Ctrl C] before hitting the post button. That way you can always paste it back in if the post fails.

 

[vanesch]

That I happen to share the same sentiment as you in believing that there are lots and lots of planets out there with life, I'm quite simply stating that we cannot logically extrapolate from a single instance we know of to the probability of its universal occurrence.

Yes, that was exactly my point. The fact that intelligent life developed on Earth is *no indication at all* that intelligent life has a relatively high probability to develop, because it is a totally biased statistic. The only thing that it indicates is that it is not totally impossible. It would be like me being on a desert island, assuming that there must be a serious fraction of all human beings with the name patrick van esch, because that's my name, and it is the only name I know off.

Now, the day that we find other, independent life somewhere is a totally different issue. From that moment our set of un-biased observations is non-empty. But as of now, we haven't gotten any clue, and the fact that WE are here doesn't mean anything.

EDIT: I should maybe clarify. I'm not thinking that the entire universe is completely devoid of life, or the opposite. I'm totally agnostic about it. I only wanted to point out that Carl Sagan kind of reasonings are very romantic, but they are not scientific per se, because of the inherent bias. In fact, the same applies to that part of biological evolution that is in our direct ancestry: it is also potentially biased. Even if there would be a totally improbable step in the evolution that leads up to us, that is no reason to discard it, because it has been "post-selected" by our very presence.

 

[DaveC426913]

Yes, that was exactly my point. The fact that intelligent life developed on Earth is *no indication at all* that intelligent life has a relatively high probability to develop, because it is a totally biased statistic.

Right, but the other side of the coin is that, if we are given a planet that has virtually the same parameters of Earth, temp, chemical makeup, etc. is there any logical reason WHY the same processes would not occur?

One could argue that, in the vast array of the galaxy, there will be a number of planets that are very Earth-like. I'm sayin' a probability of ~1.0 that there is at least one.

If you start that Earth going on its path, the likelihood that it will develop life is ~1.0 - MINUS the accumulating ways its future deviates from Earth (impacts, solar disturbances, etc.)

Looking at it this, way, we CAN deduce the likelihood of ET, based on what we DO know could happen.

 

[Schrodinger's Dog]

Now this is the sort of debate that the Drake equation is supposed to promote, well minus the insults, worthless my foot.

OK can we agree that the galaxy has 100billion stars then

 

[russ_watters]

Yes, that was exactly my point. The fact that intelligent life developed on Earth is *no indication at all* that intelligent life has a relatively high probability to develop, because it is a totally biased statistic.

Basically, it is the same as trying to construct a line (or curve) from a single data point.

 

[russ_watters]

Right, but the other side of the coin is that, if we are given a planet that has virtually the same parameters of Earth, temp, chemical makeup, etc. is there any logical reason WHY the same processes would not occur?

Sure: probability. We don't know whether what happened on Earth was a guarantee based on the starting conditions or a one in a quadrillion shot.

 

[Ivan Seeking]

Sure: probability.

False. We have no idea of the probablity. It could be 100%.

Edit: Okay, actually, Dave's post could read either way. I see what you meant.

Probability could be a limiting factor, but we don't know that it is, and there is no evidence to say that it is, but there is some probability that probability is a limit...

 

[Ivan Seeking]

In order for life in the univserse to be rare, the events that led to life would have to be phenomenally rare given the number of atoms and molecules that make up the biosphere; not to mention the millions or billions of years that they have to occur. How rare would the events leading to life have to be in order to be rare on the grand scale?

 

[Schrodinger's Dog]

TOO CLARIFY THESE ARE PARAMETERS FOR INTELLIGENT LIFE.

OK maybe it might be better to analyse this from the point of view of what we know to start and then extrapolate, for example what do we think are the basic requirements for life, I'll start with a basic list feel free to add to it.

A planet who's gravity is not so high or two low so as to preclude the formation of life forms and which has a stable surface, ie rock.

A sun formed hopefully of a size and energy output which promotes a good amount of planetary formation and is hot enough to sustain life but not too hot.

Water at higher than freezing point, ideally at a temperature where more chemical reactions can happen more quickly.

Inorganic compounds such as Cyanide and a good supply of minerals (PolyAromatic Hydrocarbons)PAH's and so on. Perhaps a second or so generation star, so there are more basic elements.

Perhaps a good amount of Cometary material to bring more water to the planet, and or seed it with more chemicals, although not essential.

Conditions so that a stable atmosphere of some sort can form.

A distance from the sun that does not mean a runaway greenhouse effect forms and is not too cold to inhibit life forming. Ie a temperate zone.

Large gaseous giants to help soak up some of the meteors flying around amongst the suns left overs.

If you agree these are the basics, what do you think the likelihood is of finding these types of conditions?

 

[Newbie says Hi]

OK maybe it might be better to analyse this from the point of view of what we know to start and then extrapolate, for example what do we think are the basic requirements for life, I'll start with a basic list feel free to add to it.

A planet who's gravity is not so high or two low so as to preclude the formation of life forms and which has a stable surface, ie rock.

A sun formed hopefully of a size and energy output which promotes a good amount of planetary formation and is hot enough to sustain life but not too hot.

Water at higher than freezing point, ideally at a temperature where more chemical reactions can happen more quickly.

Inorganic compounds such as Cyanide and a good supply of minerals (PolyAromatic Hydrocarbons)PAH's and so on. Perhaps a second or so generation star, so there are more basic elements.

Perhaps a good amount of Cometary material to bring more water to the planet, and or seed it with more chemicals, although not essential.

Conditions so that a stable atmosphere of some sort can form.

A distance from the sun that does not mean a runaway greenhouse effect forms and is not too cold to inhibit life forming. Ie a temperate zone.

Large gaseous giants to help soak up some of the meteors flying around amongst the suns left overs.

If you agree these are the basics, what do you think the likelihood is of finding these types of conditions?

Sorry Schrod, but I don't think I can agree with 1 of the points on your list (specifically #7). Computer models of Europa show that it may have a liquid water ocean under it's ice crust. Europa is far from the sun to maintain liquid water where it is too cold. It is not using the sun's energy to maintain liquid water (if it infact has liquid water) but using tidal heating thanks to Jupiter. So if Europa has liquid water, it opens up the possibility, I think for life that is NOT in the "habitable zone" of the parent star.

 

[Schrodinger's Dog]

Sorry Schrod, but I don't think I can agree with 1 of the points on your list (specifically #7). Computer models of Europa show that it may have a liquid water ocean under it's ice crust. Europa is far from the sun to maintain liquid water where it is too cold. It is not using the sun's energy to maintain liquid water (if it infact has liquid water) but using tidal heating thanks to Jupiter. So if Europa has liquid water, it opens up the possibility, I think for life that is NOT in the "habitable zone" of the parent star.

Agreed but the life there is liable to remain stuck in the water, I know the volcanic activity could lead to a water based life form evolving, given a thin layer of water and an ice crust on top, but there it stays, I think without land your liable to get only "sea" based creatures, and given it's almost lightless environs, life isn't likely to develop beyond a certain stage.

Point taken though.

 

[DaveC426913]

OK maybe it might be better to analyse this from the point of view of what we know to start and then extrapolate, for example what do we think are the basic requirements for life, I'll start with a basic list feel free to add to it.

A planet who's gravity is not so high or two low so as to preclude the formation of life forms and which has a stable surface, ie rock.

A sun formed hopefully of a size and energy output which promotes a good amount of planetary formation and is hot enough to sustain life but not too hot.

Water at higher than freezing point, ideally at a temperature where more chemical reactions can happen more quickly.

Inorganic compounds such as Cyanide and a good supply of minerals (PolyAromatic Hydrocarbons)PAH's and so on. Perhaps a second or so generation star, so there are more basic elements.

Perhaps a good amount of Cometary material to bring more water to the planet, and or seed it with more chemicals, although not essential.

Conditions so that a stable atmosphere of some sort can form.

A distance from the sun that does not mean a runaway greenhouse effect forms and is not too cold to inhibit life forming. Ie a temperate zone.

Large gaseous giants to help soak up some of the meteors flying around amongst the suns left overs.

If you agree these are the basics, what do you think the likelihood is of finding these types of conditions?

Again I disagree. I think you are being way too limiting.
It really only requires 4 ingredients:
- liquid water
- organic molecules (and inorganic material)
- energy
- time
+ sufficient quantities of the above

eg. You don't even need a solid surface. Life on Earth formed in the oceans.

 

[Schrodinger's Dog]

Again I disagree. I think you are being way too limiting.
It really only requires 4 ingredients:
- liquid water
- organic molecules (and inorganic material)
- energy
- time
+ sufficient quantities of the above

eg. You don't even need a solid surface. Life on Earth formed in the oceans.

Ok for life to form you need oceans, but for intelligent life? guess I didn't make it clear, my fault obviously. We're talking about intelligent life, life can form with those four, but are they really of interest to the OP?

 

[DaveC426913]

Ok for life to form you need oceans, but for intelligent life? guess I didn't make it clear, my fault obviously. We're talking about intelligent life, life can form with those four, but are they really of interest to the OP?

Well, the OP stated the assumption of life in the universe:

My question is two fold, we're fairly certain that probability indicates there must be life elsewhere in the universe,

This was contested as a premise. I think that's how we got talking about the creation of life.

The question of intelligent life, granted, requires a lot more criteria.

 

[russ_watters]

False. We have no idea of the probablity. It could be 100%.

Edit: Okay, actually, Dave's post could read either way. I see what you meant.

Probability could be a limiting factor, but we don't know that it is, and there is no evidence to say that it is, but there is some probability that probability is a limit...

Right - there is some probability, somewhere between 0 and 100% (it can't be either 0 or 100%) and we don't know what it is. That's the entire point.

In order for life in the univserse to be rare, the events that led to life would have to be phenomenally rare given the number of atoms and molecules that make up the biosphere; not to mention the millions or billions of years that they have to occur. How rare would the events leading to life have to be in order to be rare on the grand scale?

What do you get if you divide a big number by another big number? There is no basis for saying that the probability must be "phenomenallly rare" given that we don't have any idea what it takes to make that event happen. Heck, we don't even really know what that event was that may or may not have been a "phenomenally rare" event.

Along the same lines, how far does "same parameters" go? Does it include stability of the host star? Rotation rate? Axis orientation? Absence of planet-killer meteors? How close does the mass of the planet have to be? Fractions of certain elements? See, the constraining of the parameters and the probability of intelligent life arising are inversely proportional to each other, so you don't really gain as much as you might think by constraining them tightly. If, for example, the tightness of the parameters that leads to a 90% probability of intelligent life arising is itself a 1 in a hundred billion shot, you've just about ruled-out other intelligent life in our galaxy. If we don't even know how tight the parameters really need to be, there is no way to know how many times you need to pull that handle to have a reasonable chance hit the jackpot. It can't be claimed that we know that there are enough chances out there to overcome an unknown probability. That's what it means to be unknown!

Ok for life to form you need oceans, but for intelligent life? guess I didn't make it clear, my fault obviously. We're talking about intelligent life, life can form with those four, but are they really of interest to the OP?

Why does intelligent life require dry land?

 

[Ivan Seeking]

What do you get if you divide a big number by another big number? There is no basis for saying that the probability must be "phenomenallly rare" given that we don't have any idea what it takes to make that event happen. Heck, we don't even really know what that event was that may or may not have been a "phenomenally rare" event.

We are mostly saying the same thing.

I was assuming that life is rare on earth-like planets.

 

[vanesch]

Right, but the other side of the coin is that, if we are given a planet that has virtually the same parameters of Earth, temp, chemical makeup, etc. is there any logical reason WHY the same processes would not occur?

One could argue that, in the vast array of the galaxy, there will be a number of planets that are very Earth-like. I'm sayin' a probability of ~1.0 that there is at least one.

If you start that Earth going on its path, the likelihood that it will develop life is ~1.0 - MINUS the accumulating ways its future deviates from Earth (impacts, solar disturbances, etc.)

Looking at it this, way, we CAN deduce the likelihood of ET, based on what we DO know could happen.

The easy part (also the easy part in the Drake equation) are the physical/geological parameters: earthlike planets, stable star, long time, water or something similar etc... All that is modelable, INDEPENDENTLY of what happened on earth, so we can obtain relatively unbiased estimates of that.

But the hard part is linked to the crucial steps in life itself:
- the genesis of life (this might have been a quite probable event a la Miller experiment, or an incredibly improbable thing to happen: as long as we don't have an INDEPENDENT model or estimation, disconnected from our own ancestry, WE HAVEN'T GOTTEN A CLUE).
- the evolution of complex life: the same comment applies. We shouldn't look at our own ancestry to infer whatever probability estimation.
- the evolution of intelligent, civilisation-bearing life. The same comment applies.

I'm not saying that these have to be small probabilities. I'm saying that, because these events are linked to our own existence, we cannot say anything unbiased about them. You could just put all the double winners of lotteries on an island, and the general impression on that island would be that a good way to make a living is to play on the lottery.

So they COULD be very small probabilities, way smaller than we might reasonably expect, given our biased (lottery-winner) viewpoint ; UNLESS we have a specific model or experimental input which allows us to say anything sensible about each of these steps. Imagine that each of the probabilities for this to happen is 10^(-40000). This is not impossible. In that case, chances are that we are unique in the universe. They could also be 1/100. In that case, we'll soon get some visit from the neighbours.

But the point is, we simply don't know.