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

[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 probability. 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 probability. 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.

 

[Schrodinger's Dog]

That's what it means to be unknown! Why does intelligent life require dry land?

You'll note I have both water and dry land, an all ocean planet I think would be less likely to develop intelligent life, considering our manual dexterity is one of the primary factors that lead to our language and intelligence, but the point is the best chance for intelligent life is on a non gaseous giant with both water in the form of seas ideally, and rock. Not that an all ocean planet couldn't develop life, just that ideally a bit of both I think would promote or increase the chances of intelligent life developing.

Well, the OP stated the assumption of life 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.

I've edited my post now so as to avoid confusion, apologies.

TO 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?

 

[arildno]

Well, I don't see why mermaids can't weave sea-weeds together in a useful manner.

To have some appendage that is eminently suited for manipulating objects around us is certainly crucial for the evolution of intelligent life.

It doesn't follow, however, that intelligent life can only develop on dry land

 

[Schrodinger's Dog]

Well, I don't see why mermaids can't weave sea-weeds together in a useful manner.

To have some appendage that is eminently suited for manipulating objects around us is certainly crucial for the evolution of intelligent life.

It doesn't follow, however, that intelligent life can only develop on dry land

I didn't say that. I thought I'd cleared that up?

Mermaids aren't real btw just in case you didn't know

You'll note I have both water and dry land, an all ocean planet I think would be less likely to develop intelligent life, considering our manual dexterity is one of the primary factors that lead to our language and intelligence, but the point is the best chance for intelligent life is on a non gaseous giant with both water in the form of seas ideally, and rock. Not that an all ocean planet couldn't develop life, just that ideally a bit of both I think would promote or increase the chances of intelligent life developing.

 

[Newbie says Hi]

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

Are you saying that you think life doesn't even require a planet(oid) to begin?

By these simple requirements, it looks to me that we should expect to see a universe that is swarming with life as we explore further out of our solar system (it seems like liquid water may be the only "rare" requirement)?

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

Note sure I entirely agree here, so, you got a reference for that? Should we effectively rule out even puddles or other "localized" scenarios? I say that because we can make the conditions for abiogenesis on Earth even less stringent, and extend that to other places in the cosmos (assuming puddles are more common than oceans). (Or maybe you meant life on Earth formed in a liquid-watery environment, possibly ocean.)

 

[DaveC426913]

By these simple requirements, it looks to me that we should expect to see a universe that is swarming with life as we explore further out of our solar system (it seems like liquid water may be the only "rare" requirement)?

Don't discount the imporatnce of the "metarequirement" (i.e. a requirement of the requirements) : that there is suffiocient quantities of the above.

The implications here, are that your planetless, freefloating body of H2O must be both liquid and long-lasting. I'm not holding my breath on this one.

Not sure I entirely agree here, so, you got a reference for that? Should we effectively rule out even puddles or other "localized" scenarios? I say that because we can make the conditions for abiogenesis on Earth even less stringent, and extend that to other places in the cosmos (assuming puddles are more common than oceans). (Or maybe you meant life on Earth formed in a liquid-watery environment, possibly ocean.)

Whatever bodies of water you want to consider of suffiicient size and longevity and contain the appropriate organic compounds. It doesn't matter.

All I'm saying is a solid surface is not a requirement for life (though it might be a large part of the requirement for long-standing liquid water.)

The point is, it would be folly to look at a planet, see it has no rocky surface, and summarily disqualify it on that basis as a candidate for life.

 

[fournier17]

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?

I know that planets like Jupiter are being found in solar systems, astrobiologist are optimistic that there will be Earth like planets around the planets that are similar to jupiter. These Earth like planets could possibly meet the criteria above.

Another basic ingredient that i just read about is that the atmosphere in which chemical evolution is occurring must be reducing and not oxidizing. An oxidizing atmosphere is believed to inhibit the formation of macromolecules.

 

[Schrodinger's Dog]

I know that planets like Jupiter are being found in solar systems, astrobiologist are optimistic that there will be Earth like planets around the planets that are similar to jupiter. These Earth like planets could possibly meet the criteria above.

Another basic ingredient that i just read about is that the atmosphere in which chemical evolution is occurring must be reducing and not oxidizing. An oxidizing atmosphere is believed to inhibit the formation of macromolecules.

Not so much of an issue if life first formed under the sea, which of course it did at least from our perspective. Another reason I suppose why water is very important.

 

[SGT]

I know that planets like Jupiter are being found in solar systems, astrobiologist are optimistic that there will be Earth like planets around the planets that are similar to jupiter. These Earth like planets could possibly meet the criteria above.

Another basic ingredient that i just read about is that the atmosphere in which chemical evolution is occurring must be reducing and not oxidizing. An oxidizing atmosphere is believed to inhibit the formation of macromolecules.

It is not enough to have an Earth like planet. It must orbit a Sol like star.
Huge, very bright stars (A,B,O in the main sequence) are too short lived to allow complex life to evolve in their planets.
Small, dim stars don´t output enough energy for life. So, we are probably limited to class G stars (about 1/1000 of all starts)

 

[Ivan Seeking]

It is not enough to have an Earth like planet. It must orbit a Sol like star.
Huge, very bright stars (A,B,O in the main sequence) are too short lived to allow complex life to evolve in their planets.
Small, dim stars don´t output enough energy for life. So, we are probably limited to class G stars (about 1/1000 of all starts)

How do you arrive at that number?

Class G stars are probably the best known, if only for the reason that our Sun is of this class. They have even weaker hydrogen lines than F, but along with the ionized metals, they have neutral metals. G is host to the "Yellow Evolutionary Void". [1] Supergiant stars often swing between O or B (blue) and K or M (red). While they do this, they do not stay for long in the G classification as this is an extremely unstable place for a supergiant to be. These are about 8% of all main sequence stars.

http://en.wikipedia.org/wiki/Spectral_class

 

[SGT]

How do you arrive at that number?


http://en.wikipedia.org/wiki/Spectral_class

I stand corrected. I wanted to write 1/10 and not 1/1000. Thanks for pointing my mistake.

 

[hayshed]

my idea of life is that life really just huge complex numbers of reactions that form into 1 aparnet entity. a lot of the stuff up there is about "is this planet fit for life?", but wat is life? people can't even decide if viruses are living. so basically "life" is things that react in a human like way...we think of it as animals and plants, but because the universe is basically infinatly, there is a 100% chance on my book that life exists out there. if we ever met it? probably 100% didnt we find some bacteria on mars? please correct me on any of this if I am wrong

 

[SGT]

my idea of life is that life really just huge complex numbers of reactions that form into 1 aparnet entity. a lot of the stuff up there is about "is this planet fit for life?", but wat is life? people can't even decide if viruses are living. so basically "life" is things that react in a human like way...we think of it as animals and plants, but because the universe is basically infinatly, there is a 100% chance on my book that life exists out there. if we ever met it? probably 100% didnt we find some bacteria on mars? please correct me on any of this if I am wrong

Let´s answer your questions one by one:

lifeThe property or quality that distinguishes living organisms from dead organisms and inanimate matter, manifested in functions such as metabolism, growth, reproduction, and response to stimuli or adaptation to the environment originating from within the organism.

Any complex system that fits all those properties is a living being. Viruses don´t, so they are not alive.


As far as we know, the Universe is finite.

The probability of life existing in the Universe is very high, but we are discussing the existence of intelligent life and technological civilization. Even if it is very likely that other technological civilizations exist in the Universe, we don´t know if they are concomitant and, if they are, are they near enough to communicate?

No bacterium was found on Mars. Meteorites found on Earth, that for their characteristics seem to come from Mars, show patterns that are similar to what paleontologists believe are fossils of bacteria on Earth.

 

[Newbie says Hi]

didnt we find some bacteria on mars? please correct me on any of this if I am wrong

Well, if you are referring to the "positive results" of '76 NASA Viking missions to Mars, the scientific consensus now is that the "positive results" were due to chemical reactions with the Martian soil and, therefore, of a non-biological origin.

 

[DaveC426913]

We need to define our goals. I was talking about life of any sort, complex or not. In terms of what we as a people are searching for, I can't see us canceling a mission to a planet teeming with life simply because they're simple.

So, it is not necessary to have a long-lived sun for OUR interest to be piqued in the planet's life.

To state it explicitly: I am arguing what conditions are necessary for life to form (and thus pique our interest), regardless of how complex it may or may not get.

 

[SGT]

We need to define our goals. I was talking about life of any sort, complex or not. In terms of what we as a people are searching for, I can't see us canceling a mission to a planet teeming with life simply because they're simple.

So, it is not necessary to have a long-lived sun for OUR interest to be piqued in the planet's life.

To state it explicitly: I am arguing what conditions are necessary for life to form (and thus pique our interest), regardless of how complex it may or may not get.

I agree with you that the existence of life, regardless of its complexity is of interest to us. But the original question is about intelligent life and the possibility of technological aliens being visiting or at least trying to communicate with us.