Basis of science's belief that extraterrestrial life is likely?

[Lemur866]

To take one point, how do we know what the sun is made of?

Well, that’s an interesting story. For a long time, no one had any idea what the sun or other extraterrestrial bodies could be made of.

Then a guy named Fraunhofer discovered that if you looked carefully at a spectrum caused by passing sunlight through a prism, there were mysterious dark lines. Further experiments showed that these sorts of lines were present when spectra were created when different substances were heated to glowing hot.

And when the lines created by incandescent hydrogen was compared to the sun, they matched. And so we now realized that the sun was composed of hydrogen.

However, something mysterious was also discovered. There was a band that corresponded to no known substance. And so it was theorized that there was some unknown element in the sun, and the substance was named “Helium”, after the greek god Helios. Of course, that gives away the later discovery that helium was also present on Earth, and is now used in all sorts of applications.

And the same spectroscopic technique can be applied to all sorts of things. We can directly observe spectroscopic lines in incandescent substances, but it turns out that cold substances absorb and reflect light in characteristic ways, and so we can often tell what something is made of merely by looking at it through a specialized prism called a spectroscope.

[Stoid]

@Lemur866

To take one point, how do we know what the sun is made of?

Well, that’s an interesting story. For a long time, no one had any idea what the sun or other extraterrestrial bodies could be made of.

Then a guy named Fraunhofer discovered that if you looked carefully at a spectrum caused by passing sunlight through a prism, there were mysterious dark lines. Further experiments showed that these sorts of lines were present when spectra were created when different substances were heated to glowing hot.

And when the lines created by incandescent hydrogen was compared to the sun, they matched. And so we now realized that the sun was composed of hydrogen.

However, something mysterious was also discovered. There was a band that corresponded to no known substance. And so it was theorized that there was some unknown element in the sun, and the substance was named “Helium”, after the greek god Helios. Of course, that gives away the later discovery that helium was also present on Earth, and is now used in all sorts of applications.

And the same spectroscopic technique can be applied to all sorts of things. We can directly observe spectroscopic lines in incandescent substances, but it turns out that cold substances absorb and reflect light in characteristic ways, and so we can often tell what something is made of merely by looking at it through a specialized prism called a spectroscope.

thank you! I understood that well enough.

[Baboonanza]

@Lemur866

If we discovered life on Mars, or Europa, or Alpha Centauri 6, and determined that life was the result of an independent abiogenesis, that would definitely be strong evidence that life is likely on lots of other planets. But our observation of life on Earth isn’t.

The reason Blake is going on and on about the Anthropic principle, is that we humans observe life on Earth. But if there was no life on Earth, there wouldn’t be humans to observe the lack of life, just like there are no intelligent species on the Moon observing that the Moon lacks life.

So therefore, any species that observes life on its own planet must have evolved on a planet where life evolved. This is a subtle point. But it means that our sample is biased. We know there are plenty of planets without life, we can observe dozens of them in our solar system.

Suppose for the sake of argument that there is only one planet in the entire universe that has life. And on that planet intelligent life appears. They observe that their planet has life. What can they conclude about the likelihood of life evolving on other planets? Nothing–because if life hadn’t evolved on their planet, they wouldn’t be able to observe the life on their planet.

However, if they observe a second instance of life, and that instance of life arose independently, then they have an independent instance of life. And NOW they can do some back of the envelope calculations. Of course, it could be that life really is fantastically rare, and they just hit the jackpot. But that sample isn’t biased by the fact that it had to exist before the observation could be made.

So, if tomorrow we discover another planet with liquid water, and that planet has life, suddenly the odds of life arising on a suitable planet can be estimated at somewhere near 1. Our estimate could be way off, but now we have some reason to trust that we don’t have an unbiased sample, and since we pulled out a red jellybean we have some justification for betting that the next jellybean we pull out might be red. And if we pull out two red jellybeans, then our confidence increases. And if every time we pull out a jellybean (a planet with liquid water) that jellybean is red (has life), then we can put very clear numbers on our confidence in the outcome of the next sample.

But we should throw out the sample that generated the observer of the experiment, because we know that sample HAD to generate the observer, because otherwise there would have been no experiment.

Thanks, that was very informative. If Blake had explained himself even half as well as you this whole debate would have been a lot more straightforward.

I was thinking about this last night and I think I’ve found the fundamental problem I have with the issue, and I’ll outline my thinking. We start with a simplified version of the Drake equation:

P (Probability of life in the universe) = N (number of stars) * S (the probability of life arising at any star, which is a compound of a load of other factors)

Obviously we don’t know S or N, though we can assume N is any non-infinite very large number.

From this we can see that as S approaches 1 / N then P approaches 1. So there is a threshold above which other life existing in the universe is almost certain. Given that N is a very, very large number this threshold is very low.

Lets say for our purposes it’s 110^-40. Surely that means that it’s more likely P is more than 110^-40 than less? Unfortunately set theory says that the number of rational numbers in the range 0 < 110^-40 is just as infinite as the (numerically) much larger range 110^-40 < 1. Both set are equally likely.

The problem is that while I know that this is the case, I have a hard time actually believing it. It’s just more intuitive to believe that the larger, higher probability range is more likely than the smaller low probability one.

[Acid_Lamp]

@Frylock

The idea that nature is uniform is a methodological assumption. What this means is, we proceed as though it were true and we hope this will give us good results. So far, it hasn’t done us wrong. But why put our hopes in this methodological assumption and not some other one? That gets complicated and there’s disagreement here among those who bother to think about it much, but basically, (I should maybe put an IMO here) the uniformity assumption is the only one that allows for any basis of prediction at all. In other words, if you don’t assume uniformity, you can’t make any predictions of any kind. And if you don’t make any predictions, you can’t… act. So to act, you have to assume uniformity.*

Snip.

I’m noticing some cognitive dissonance here. If science proceeds on the methodological basis of assumed uniformity, the only rational reason for taking a negative stance on the existence of life elsewhere is that earth is somehow unique to an unbelievable level. That really strikes me as nothing more than a thinly veiled type of pseudo religious thought, wishing for us to be special or unique. This becomes more the case as we learn more about the scale of the universe, and the uncontested fact that our galaxy alone is packed with planets and moons.

[wintertime]

@Acid_Lamp

I’m noticing some cognitive dissonance here. If science proceeds on the methodological basis of assumed uniformity, the only rational reason for taking a negative stance on the existence of life elsewhere is that earth is somehow unique to an unbelievable level.

Once again, who argued that the probability of life elsewhere is miniscule? To say this, you need to know the numbers for any calculation that is more than a thinly veiled wild guess – do you know them?

I certainly don’t.

“Assumed uniformity” is a useful proposition because it works in dealing with processes in physics, chemistry, biology etc. But it relies on the knowledge how this processes proceed precisely and what we can observe during all the stages involved.

We don’t know, how life came to be yet; and as Blake pointed out, you will find competing theories about its origin that use the same observations to come to sometimes opposing explanations.

Maybe a theory we already know will prove to be right, maybe it will be an amalgam of currently competing ideas or something new. We don’t know yet.

We do know that life exists on one planet. We also do know that is was here, that it became robust enough to survive a multitude of catastrophes. But we don’t even know for certain that it originated here and we certainly don’t know how it came to be.

[Frylock]

@Acid_Lamp

Snip.

I’m noticing some cognitive dissonance here. If science proceeds on the methodological basis of assumed uniformity, the only rational reason for taking a negative stance on the existence of life elsewhere is that earth is somehow unique to an unbelievable level. That really strikes me as nothing more than a thinly veiled type of pseudo religious thought, wishing for us to be special or unique. This becomes more the case as we learn more about the scale of the universe, and the uncontested fact that our galaxy alone is packed with planets and moons.

The assumption is that things work the same way wherever you go.

But if you don’t know how something works here, then you don’t know how it works anywhere else even (especially?) assuming uniformity.

So if you don’t know how reliably natural processes produce life on Earth, you don’t know how reliably they produce it anywhere else in the universe.

And, according to Blake, we don’t know how reliably natural processes produce life on Earth.

If you grant him that, then his conclusion (that there’s no basis for speculation about the probability of life appearing elsewhere) follows pretty well.

[Baboonanza]

@wintertime

Once again, who argued that the probability of life elsewhere is miniscule? To say this, you need to know the numbers for any calculation that is more than a thinly veiled wild guess – do you know them?

I certainly don’t.

That kind of what I’ve been trying to make, though badly. To say that ‘we don’t know if there is life elsewhere in the universe’ implies that the probability of it accurring must be (or at least could be) miniscule. Because if the chance wasn’t miniscule then given the size of the universe it would have to happen more than once.

That’s why the idea that the Earth isn’t exceptional and that the universe is uniform is important. For me, without some evidence to show that something incredibly exceptional happened here the default position has to be ‘life’. But I do agree that this position isn’t scientific because there is insufficient evidence to support it. Science would have to say ‘we don’t know’.

[Acid_Lamp]

@Frylock

The assumption is that things work the same way wherever you go.

But if you don’t know how something works here, then you don’t know how it works anywhere else even (especially?) assuming uniformity.

So if you don’t know how reliably natural processes produce life on Earth, you don’t know how reliably they produce it anywhere else in the universe.

And, according to Blake, we don’t know how reliably natural processes produce life on Earth.

If you grant him that, then his conclusion (that there’s no basis for speculation about the probability of life appearing elsewhere) follows pretty well.

Gotcha, Thanks for clearing that up. I still think that Blake is grossly overreaching by applying the Anthropic principle to such a concept, but I get the logic now.

[Cheesesteak]

@Frylock

And, according to Blake, we don’t know how reliably natural processes produce life on Earth.

If you grant him that, then his conclusion (that there’s no basis for speculation about the probability of life appearing elsewhere) follows pretty well.

Knowing something isn’t a black and white proposition.

I don’t know how to make a rocket that can be launched into space. However, if my next door neighbor was about to launch a Lunar probe using a rocket made of tinfoil, elbow macaroni and Sterno, I would have a basis for believing that it won’t work.

Once you gather a certain amount of knowledge on a topic, like biology and chemistry, there is reason to believe that experts can have a basis for speculation on the beginnings of Life.

[GIGObuster]

@Frylock

If you grant him that, then his conclusion (that there’s no basis for speculation about the probability of life appearing elsewhere) follows pretty well.

Oh, I grant him that as well, but it does not follow really well.

Looking around, the Anthropic Principle is a favorite of people attempting to get religion into the scientific discussions, even if that is not the case for you or Blake that effort does have the result of producing critics with power to tell the people involved in the research to stop what they are doing. And I’m not referring to people on message boards, but to elected ignorant congresscritters.

What it should follow always is a clarification: Yes, there is no direct evidence of life out there, but so far the circumstances in favor of it being there are strong or so far research has not discredited most of the theories in favor of life being out there.

[Frylock]

@GIGObuster

Oh, I grant him that as well, but it does not follow really well.

It is a pretty simple inference.

If nature is uniform, and we don’t know how reliably Earth produces life, then we do not know how reliably earthlike planets produce life.

I can’t see a way around that. You can disagree with the premises, but the inference is basically valid.

Looking around, the Anthropic Principle is a favorite of people attempting to get religion into the scientific discussions, even if that is not the case for you or Blake that effort does have the result of producing critics with power to tell the people involved in the research to stop what they are doing. And I’m not referring to people on message boards, but to elected ignorant congresscritters.

What it should follow always is a clarification: Yes, there is no direct evidence of life out there, but so far the circumstances in favor of it being there are strong or so far research has not discredited most of the theories in favor of life being out there.

If I understand him correctly, Blake is critical of anthropic reasoning. He’s saying its anthropic reasoning (a confused version of it at that) that makes people optimistic about extraterrestrial life. (I think. To be honest I wan’t 100 percent clear on exactly what he was saying about the Anthropic Principle. Nonetheless the thrust of his argument seemed clear enough, and I’ve summarized it a couple of times in this discussion without reference to the anthropic principle.)

Anyway, ignorant congressment are going to be ignorant congressmen no matter what anyone says.

And what Blake is saying invites further research, rather than discouraging it. I’m not sure why you think otherwise.

[Frylock]

Creationists use the anthropic principle? This surprises me, actually. The anthropic principle is an attempt to explain away the apparent fortuitousness of many of the features of our environment. A creationist explains these by saying they’re there because of God. Someone deploying anthropic reasoning, instead, says there’s nothing really to explain.

[Frylock]

So after some digging around, I think I’ve found that there are two fundamentally opposed lines of reasoning that go around under the name “anthropic principle”.

One version is:

Apparently coincidental facts about our planet and our universe are not as surprising as they may seem–since they are coincidences that would have to occur for us to even be here talking about them. There is no need to invoke a special explanation for these coincidences; our own existence is explanation enough.

The other version is:

There are alot of coincidences that occured–and had to occur–in order for intelligent life to develop on Earth. There must be some extraordinary cause for these coincidences.

As far as I can tell, the first version is the “real” anthropic principle, and the second version seems to be some kind of massive misunderstanding of the anthropic principle.

The second provides impetus toward creationism. The first does the opposite.

Blake is referring to the first version, not the second, I think.

[Diogenes_the_Cynic]

I was referring to the second. I had an impression that it basically referred to the fine tuning argument.

[GIGObuster]

@Frylock

And what Blake is saying invites further research, rather than discouraging it. I’m not sure why you think otherwise.

Actually that was what I was going to say or imply so far. I have no idea why you think what I said objected to that.

Just saying that scientists have no evidence the OP’s position is indeed encouraging very critical positions to the current research.

The clarification is important to prevent that and indeed, because there is uncertainty therefore more research is needed. My overall point here is that yes, just recently we only could guess at the probabilities, nowadays many of the holes are being plug and it seems to me that insisting that there is no growing circumstantial and actual evidence of the optimistic view is becoming silly. (Or I should say: I’m beginning to dismiss the position of the ones claiming scientists have nothing to base the idea that life is probable out there, as they seem to not bother to check that the new evidence is changing the probabilities)

Regarding the creationists/IDs using the anthropic principle:

Anthropic principle

The modern form of a design argument is put forth by Intelligent design. Proponents of intelligent design often cite the fine-tuning observations that (in part) preceded the formulation of the anthropic principle by Carter as a proof of an intelligent designer.

Many criticisms focus on versions of the Strong Anthropic Principle, such as Barrett and Tipler’s anthropic cosmological principle, which are teleological notions that tend to describe the existence of life as a necessary prerequisite for the observable constants of physics. In a lecture titled “The Confusion of Cause and Effect in Bad Science,” the paleophysicist Caroline Miller said:[57]

“The Anthropic Principle is based on the underlying belief that the universe was created for our benefit. Unfortunately for its adherents, all of the reality-based evidence at our disposal contradicts this belief. In a nonanthropocentric universe, there is no need for multiple universes or supernatural entities to explain life as we know it.”

Similarly, Stephen Jay Gould [58] ,[59] Michael Shermer[60] and others claim that the stronger versions of the Anthropic Principle seem to reverse known causes and effects. Gould compared the claim that the universe is fine-tuned for the benefit of our kind of life to saying that sausages were made long and narrow so that they could fit into modern hotdog buns, or saying that ships had been invented to house barnacles. These critics cite the vast physical, fossil, genetic, and other biological evidence consistent with life having been fine-tuned through natural selection to adapt to the physical and geophysical environment in which life exists. Life appears to have adapted to physics, and not vice versa.

[Voyager]

@Frylock

It is a pretty simple inference.

If nature is uniform, and we don’t know how reliably Earth produces life, then we do not know how reliably earthlike planets produce life.

I can’t see a way around that. You can disagree with the premises, but the inference is basically valid.

While we don’t know the exact probability, it is not true that we can’t say anything about them. Would you agree that the probability of abiogenesis is higher if the initial form of life arising is simple rather than complex? The famous 747 in a windstorm argument only makes sense if one thinks that the first life form was a complex cell. Given that we see pseudo-life forms like viruses and prions that are very simple, we can reasonably say that the probability of life arising is not too low. With this, and the argument that Earth is not exceptional, we can say that the probability of life arising elsewhere is not too low either.

Blake’s incorrect argument is that if you don’t know the exact probability you can’t say anything at all about the likelihood of something happening. He also doesn’t like the absence of an exact answer to how life arose. Actually, many hypotheses about how it happened, all saying it was likely, makes me more confident that whichever one happens to be true will include life being likely to arise.

[Frylock]

@Voyager

While we don’t know the exact probability, it is not true that we can’t say anything about them.

I said the inference is valid: if you agree with the premises, you have to agree with the conclusion.

You’re disagreeing with one of the premises.

That’s fine! But I was talking to someone (Gigobuster) who thought he could grant the premises without granting the conclusion.

Blake’s incorrect argument is that if you don’t know the exact probability you can’t say anything at all about the likelihood of something happening.

Not at all. He’s saying that in order to calculate a probability (call it “exact” or not as you like) you have to have a certain kind of basis, and we don’t have that kind of basis when it comes to the question of biogenesis. You may think we have some kind of basis for such a calculation (exact or inexact, whatever). That’s something to discuss. But let’s get his argument right before we discuss which bits of it to agree with and disagree with.

[BrainGlutton]

@Lanzy

No facts here but if there is no life anywhere else, it kinda makes the universe pointless.

As Jodi Foster put it in Contact: “If we were the only ones, wouldn’t that be an awful waste of space?”

Well, yes, it would. When rain falls on the ocean, that is an awful waste of fresh water. Nevertheless, rain falls on the ocean. We have no grounds to assume the universe is set up in a way that is not “pointless” in human judgment.

[Lemur866]

I think I can improve on the jellybean analogy.

The question is to estimate the frequency of red jellybeans in an jar.

So we pull out jellybeans one at a time, and observe whether the jellybean is red. If the first jellybean is red, we’re justified in thinking that red jellybeans are common. Not strongly justified, but at least we have some justification.

However, suppose the experiment has another rule. If we don’t pull a red jellybean out of the jar on the first try, we have to throw out our notebooks, erase all the data, wipe our memory of the experiment, and start over again.

And so, after an unknown number of trials, we find we draw a red jellybean on the first try. Well, all that tells us is that there was at least one red jellybean in the jar. We don’t know if we’ve been drawing jellybeans for millions of years, because we can’t start recording the experiment until we draw that first red jellybean.

And so under these rules, it’s obvious that we have to throw out the result of the first trial. And so, what happens is that we’re looking at the jar, and trying to guess how many red jellybeans are inside, and we haven’t been able to draw a single valid jellybean sample from the jar.

And this is Blake’s argument. Sure, we’ve got one red jellybean (life on Earth), but that was just what was needed to start the experiment. We need to throw out that sample, because it’s biased, and wait for the next sample.

The trouble is that it’s going to take a lot of effort to collect that second jellybean, and lots of people don’t want to wait. And so they say, hey, we got one red jellybean, and so why can’t we guess that the jar is 100% red jellybeans?

But that’s what we are justified in guessing only when the NEXT jellybean shows up red.

[Frylock]

@Lemur866

I think I can improve on the jellybean analogy.

The question is to estimate the frequency of red jellybeans in an jar.

So we pull out jellybeans one at a time, and observe whether the jellybean is red. If the first jellybean is red, we’re justified in thinking that red jellybeans are common. Not strongly justified, but at least we have some justification.

However, suppose the experiment has another rule. If we don’t pull a red jellybean out of the jar on the first try, we have to throw out our notebooks, erase all the data, wipe our memory of the experiment, and start over again.

And so, after an unknown number of trials, we find we draw a red jellybean on the first try. Well, all that tells us is that there was at least one red jellybean in the jar. We don’t know if we’ve been drawing jellybeans for millions of years, because we can’t start recording the experiment until we draw that first red jellybean.

And so under these rules, it’s obvious that we have to throw out the result of the first trial. And so, what happens is that we’re looking at the jar, and trying to guess how many red jellybeans are inside, and we haven’t been able to draw a single valid jellybean sample from the jar.

And this is Blake’s argument. Sure, we’ve got one red jellybean (life on Earth), but that was just what was needed to start the experiment. We need to throw out that sample, because it’s biased, and wait for the next sample.

The trouble is that it’s going to take a lot of effort to collect that second jellybean, and lots of people don’t want to wait. And so they say, hey, we got one red jellybean, and so why can’t we guess that the jar is 100% red jellybeans?

But that’s what we are justified in guessing only when the NEXT jellybean shows up red.

I think you hit the nail on the head here Lemure. This is how I understand Blake’s argument,* as well. I don’t think it can be as easily dismissed as a lot of people here think.

*One of them anyway. I think he’s got two going here. One is an that we can’t generalize from the presence of life on Earth because that presence is a biased sample, and we don’t know how to measure the bias. The other is that we can’t generalize from the presence of life on Earth because we don’t know enough about the underlying mechanisms to be able to say with any justification how common the mechanism is in Earthlike environments.