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People often use the argument that there must be a God, for example, because Earth and the laws of physics are perfectly situated for humans to exist the way we do.

However, if Earth, or even the universe as a whole, were not situated so that life could evolve, then we wouldn't even exist to be able to question our own existence. So there's nothing interesting or special about our existence at all - this is just the only "scenario" in which humans exist, and another scenario easily could have occurred in which we do not exist; but of course humans would never be around to observe such a thing.

Is this some type of fallacy, and is there a name for it?

Julius Hamilton
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    It seems like just the general "not understanding probabilities". If there's no possibility how we could observe the universe if life wasn't possible, then the fact that life is possible gives us no evidence that the universe was fine tuned. It has no value in a probability calculation. And in the weaker form, "humans existing the way we do", ignoring that there's no universal law saying that observers must be humans existing the way we do. If we had four arms, we would still have exactly the same "evidence". – Luaan Oct 07 '16 at 10:06
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    Seems pretty unlikely that life would evolve in a way that it didn't form appropriate to its environment. If we'd arisen as methane ice critters on Titan, we'd possibly have the same argument and view Earth as the embodiment of Hell. – user2338816 Oct 08 '16 at 01:42
  • Note that the question wrt to the Earth vs the Universe is very different. We now know that the Earth is only one planet out of likely trillions or more in the universe. Whereas the Universe, as far as we know is singular. This argument was traditionally made about "Life on Earth", but this was in the 18th century when we didn't know much about other stars, and solar systems, etc. – RBarryYoung Oct 08 '16 at 18:45
  • @RBarryYoung: Odds of any planet meeting the necessary constraints: 1 in 10^99. Maximum number of attempts: 2 *10^23. (The 2 is false precision coming from expected number of attempts per star system.) – Joshua Oct 09 '16 at 16:19
  • @Joshua, where you getting those numbers from? I am not aware of any current science that says the chances of a random planet supporting life are anything even remotely like 1/10^99. The lowest I've seen recently is more like 1/10^9. – RBarryYoung Oct 09 '16 at 21:18
  • @RBarryYoung: How many distinct factors do you have? If it's less than 50 it's incomplete. To be fair though, some of the factors in mine would only exclude terrestrial life, and one only excludes hominid life (maximum partial O2 pressure sets a limit for intelligent life that must have cooked food). – Joshua Oct 09 '16 at 21:39
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    @Joshua not the question I asked. Where are you getting your numbers from? I know of no credible source that supports them. And counting distinct factors is meaningless if they are not independent and virtually none of them truly are. Finally, and most importantly none of this addresses my original point which still stands: Life on Earth vs Life in the Universe are very different questions. – RBarryYoung Oct 10 '16 at 04:59
  • Related: Fermi paradox. – user Oct 10 '16 at 06:01
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    Throw a dice one billon times, and write the numbers down. What was the probability of obtaining that sequence? But you got it! Incredible! – Michel Billaud Oct 10 '16 at 16:03
  • Isn't that just called sampling bias? – I'm with Monica Oct 11 '16 at 12:47

11 Answers11

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I believe you're thinking of the anthropic principle. There are actually two variations:

The strong anthropic principle says that the universe was made the way it is so that humans could exist.

The weak anthropic principle says that the universe must be such that humans could exist, since here we are.

The strong anthropic principle is considered fallacious. The weak version, however, is perfectly valid. It's used e.g. in cosmology to dismiss hypotheses that would exclude the possibility of human life ever developing.

Era
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    John Leslie (quoted by William Lane Craig in The Case for a Creator by Lee Strobel) argues something like: "Suppose you were to be executed by firing squad, and you were blindfolded and heard a loud bang, but you did not die. You would not accept someone saying, 'oh well, if they had shot you, you wouldn't be around to observe it, so it requires no explanation.' " – EMBLEM Oct 07 '16 at 01:31
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    That's not a very good description of the anthropic principle. The weak anthropic principle says that we must take into account in our calculations that the space and time which we are examining is not randomly selected but picked based on the presence of an observer. (E.g. the chance of life arising on a planet might be tiny, but if there are a zillion planets in the universe, the chance of life arising on Earth is a zillion times that since Earth is by definition that one planet where life arose.) – Tgr Oct 07 '16 at 06:48
  • ...The strong anthropic principle extends this logic to some hypothetical mechanism which would completely explain away the improbability of intelligent observers, such as a multitude of parallel universes. – Tgr Oct 07 '16 at 06:49
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    @EMBLEM - actually, as a believer in the many-worlds interpretation of quantum physics, I would be required to believe that. Under such circumstances, in most world-lines I would die but in a few I would survive, and therefore the survivors in those world-lines would be forced to accept such an explanation because there is no other. – Periata Breatta Oct 07 '16 at 09:15
  • @PeriataBreatta The point of that example is whether one should believe that the firing squad planned to intentionally miss the target or everyone just happened to miss. The idea of "requires no explanation" in the example is that you don't need to consider the firing squad planning to miss because the latter option (chance) requires no explanation. In the many-worlds interpretation, there are still more world-lines where the firing squad had a secret plan you haven't observed than world-lines where the firing squad didn't have a secret plan and everyone just happened to miss. – JiK Oct 07 '16 at 11:00
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    @PeriataBreatta: When you look at the so-called multiverse as a whole, you find that it totally pushes the issue under the carpet, because there is only one multiverse in your viewpoint. Why does that one multiverse follow the laws it does (whatever they are)? Are you going to appeal to an infinite regression of nested multiverses? Even if so, the whole regression must obey some laws that govern how they interact, so the problem remains in full force... – user21820 Oct 07 '16 at 14:28
  • @JiK If there are infinitely many universes, then there are infinitely many in which they all missed and infinitely many in which they conspired to let you live. – EMBLEM Oct 07 '16 at 17:03
  • @user21820 laws? we can only observe and expect the same conditions will yield the same results. But formally proving causality? that's another problem entirely. from the firing squad shooting and you not dying, you can assume they missed, or that some laws stopped to be valid. – njzk2 Oct 07 '16 at 20:25
  • @njzk2: Science is based on empirical evidence, which rests on the fundamental assumption that there are underlying laws governing the world. You yourself claim that we expect the same conditions to yield the same results, which is in agreement with this. Whether or not we can figure out the causal relations is completely orthogonal to the assumption that there are laws. The very notion of a multiverse has in itself the gigantic assumption that the individual universes in it only interact weakly, and there must be a law to govern the nature of interaction. – user21820 Oct 08 '16 at 02:19
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    @njzk2: If my point is not clear enough, consider the fact that the very idea of a multiverse was in the first place concocted to purportedly 'explain' why the universe we live in has the properties it does, but it utterly fails because the properties of the multiverse itself remain unexplained. It is no different from the simply meaningless proposal that you are reading this comment because either you are or you are not and you just happen to be in the universe where you are. In sum, the multiverse idea is not only totally unverifiable but also has zero explanatory power. – user21820 Oct 08 '16 at 02:44
  • @EMBLEM Yes, but the probability measures of those sets need not be equal. – JiK Oct 08 '16 at 16:14
  • @user21820 it is still only a hypothesis, demonstrating anything will take time. – njzk2 Oct 08 '16 at 22:00
  • @njzk2: You don't get it; the multiverse hypothesis is just as unverifiable as the hypothesis that there is a flying spaghetti monster, and equally useless because it does not even provide any reasonable explanation of anything. Read my first sentence of my last comment carefully.. – user21820 Oct 09 '16 at 04:28
  • @user21820 the operative verb in it being "remain". Give it time. – njzk2 Oct 11 '16 at 02:03
  • @njzk2: And the hypothesis that there is a flying spaghetti monster who created us dumb humans remains a better hypothesis that explains no less than the multiverse hypothesis. Yup, give it time. More seriously, you don't get my point: the multiverse hypothesis does not even reduce the question, because it comes down to the same exact question for the multiverse that it was supposed to explain for our universe, and this implies that the multiverse hypothesis is useless. It is analogous to the hypothesis that the world rests on a world turtle and that it is all the way down. – user21820 Oct 11 '16 at 03:33
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The underlying problem (and fallacy) with this argument is sometimes referred to as the 'Texas Sharpshooter' fallacy.

One is standing from a position of a known situation and asking what are the odds that everything turned out exactly as it has, which is always going to be incredibly improbable. If one shuffles a pack of cards, then looks at the order and declares 'the odds of this particular order coming up are astronomical, so it must be a miracle', this is not sound reasoning. There are indeed near-infinite ways the universe could have turned out, and this happens to be the permutation we got, but whatever happens there would have been some outcome.

Essentially, it's declaring the target after the event has occurred.

Ant
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    Not to detract from your answer, but I always found it funny that the name of the Texas Sharpshooter fallacy, seemed like an faulty generalization fallacy itself... Why Texas? – Dryden Long Oct 07 '16 at 13:55
  • Probably some random story. Interestingly enough, (I can't remember what study it was) I recall in the past year or so hearing about a study where they published results and said, "oh these outliers are just random noise," effectively. However, when they finally went back and really looked at the study it turns out that the "noise" was actually the signal. It was something fairly foundational, too. – Wayne Werner Oct 10 '16 at 13:13
  • @DrydenLong - As someone from a neighboring state, I think I can fairly say that if you knew a lot of Texans you wouldn't have to ask that question. – T.E.D. Oct 10 '16 at 16:49
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    This analogy doesn't quite fit; you're not looking for just any arrangement out of many, you're looking for a specific arrangement, say, all cards of a suit together, suits arranged black-red-black-red, and all cards arranged in order low to high. Given one chance (that we're certain of) to draw that pattern, the odds against it go up significantly (52!:1), IIRC. If you bet me you can shuffle the deck and end up with that arrangement in one try, and then you do it, the most likely reason is that you cheated. It's POSSIBLE that it's a chance event, but I highly doubt it. – Terry Lewis Oct 10 '16 at 20:00
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    @TerryLewis that's the thing, you're NOT looking for an arrangement, it's already there. – Pieter B Oct 11 '16 at 08:32
  • @PieterB, the fact that is is there does not explain how it came to be there. Assume that my scenario is a game where you shuffle the deck, and then deal them out, face up, one by one. If you match the pattern I specified, the most likely reason is not a chance arrangement of cards, but that you stacked the deck. It's the fact that the cards turned in a specified order. Similarly, the universe seems to be specifically arranged to permit life. Yes, the chance of being in our universe is 100%... but what is the chance that a random universe would allow us to exist in the first place? – Terry Lewis Oct 12 '16 at 16:02
  • no, the assumption made in this answer is that there are many targets for the Texas Sharpshooter to hit. but, unless you make the case for a Multiverse (something as falsifiable as is a notion of God), then what is really the case is that there was one target, the target is small and far away, and the shooter is remarking about how fortunate he is to have hit the target. – robert bristow-johnson Jul 24 '17 at 19:40
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Your description is somewhat vague so that the reasoning might mix several things.

1) Base rate fallacy. "The laws of physics are perfectly situated for humans to exist the way we do" is either tautological or it is unclear how probabilities are being assigned to "collections" of laws of physics that allow "humans to exist the way we do." The sample space and the base probability measure on it are not particularly intelligible. "It seems rather unlikely" that the universe should allow humans to exist is a "gut feeling" with no prior basis for estimation. The no miracles argument for scientific realism suffers from a similar affliction. "It would be a miracle if the science were as useful without also being true" does not follow from any intelligible base probability assignment, we'd need something like an ensemble of "sciences" describing "reality," and access to what reality "truly is" over and above those "sciences."

2) Intelligent design fallacy. The "perfectly situated for humans" claim assumes that even granting that they are "unlikely," conditions allowing human existence could not have evolved over time from something much more generic, the way Earth evolved from conditions rather inhospitable to life. Similar to arguing that "irreducible complexity" prevents the gradual evolution of intricate structures like the eye, which therefore must be "pre-designed." In this case, it's assumed that conditions favorable to human existence have to be "pre-designed" in the laws of physics.

3) Anthropic reasoning. We observe what we see because otherwise, we wouldn't be here to observe it. This is fine as long as it is only meant as a constraint on theories describing our observations. However, typically anthropic reasoners offer it as something more, an explanation of what we observe. For it to work as such one needs a bloated ontology of the multiverse, where a whole ensemble of universes with different physical laws is instantiated. Then it would naturally be "likely" (when conditioned on our existence) for us to find certain (unconditionally) "unlikely" features in it. This also needs a meaningful assignment of probabilities to the universes to avoid problems with the base rate fallacy. While not necessarily fallacious this sort of reasoning is highly speculative and metaphysically loaded, making it controversial among physicists.

Obito
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It's not a fallacy.

The first argument you mentioned is known as the teleological argument, which goes: Look at all the minutiae of cosmology, geology, and biology, and marvel. If anyone of them were slightly different we could not have existed. Therefore there must be some fine-tuner, because it is too improbable that everything would have lined up so perfectly.

Indeed, if you were to draw from the distribution of all possible universes, and find that the one you drew harbored life, that would be a huge coincidence (probably, I can only speculate about that distribution). But the teleological argument fails to consider that we have a VERY strong prior, in the statistical sense: that our existence and ability to ask the question is contingent on those parameters being fine tuned in the first place.

The anthropic principle acknowledges this observer/selection bias. We should not at all be surprised to find that our universe is "fine-tuned", unless we have some reason to believe that it is exceptional beyond some minimal configuration to support intelligent observation (I'd point to the fact that is is 99.9999% vacuum with a smattering of rocks, and that we are organic slime on the surface of one of those... does it honestly look that fine-tuned?)

John K
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I don't know if this answer exactly matches your question. But one variant on this sort of thing started out as creationism, then became "Intelligent Design." As I understand it, the idea is that we are special not because we are improbable, but because we are impossible - not the sort of thing that could be the result of natural processes.

But note this is not a fallacy; it is not even an absurd argument. The uncomfortable fact is that creationists are correct when they say e.g. that evolution is "just a theory." Of course, it is, just like all science! Science is not itself something that can be studied by science; it rests on various articles of scientific faith (like "the world is orderly"), just as religions rest on their articles of faith. The mistake the creationists make is to go from "we're naturalistically impossible" to "therefore there must be a God, namely the one I believe in." Even worse, they try to enlist science in support of obviously non-scientific propositions. But their core idea - that science is not the only arbiter of truth, it's impeccable.

Whether we are naturally impossible, or even just improbable, is not a scientific question. Even if we were to discover a population of humans on a distant planet we would not be able to definitively "prove" that both they and we are the products of nature. You can't put probabilities on supernatural events. Something like that is why some of our best scientists are devoutly religious.

Obito
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  • Science makes assumptions, yes. But all of those are disprovable - if we find that something isn't orderly, we don't ignore it - we investigate it all the more. And I don't see why you'd note creationism specifically - most mythologies have a creation myth, because that's just the kind of thing kids ask you - how did we come to be? Science is no "arbiter of truth"; it's just a set of processes that tries to get us from "no knowing" to "knowing a bit more". That's why science doesn't have to be afraid of change - change is what drives our understanding forward. – Luaan Oct 07 '16 at 09:56
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    @Luaan: thank you for making my point wrt to anomalies. but the assumptions of science are disprovable? how would you even begin to disprove the fundamental assumption that the world is orderly? the fact that we investigate anamolies, rather than declaring them miracles, illustrates my point. –  Oct 07 '16 at 23:51
  • @Luaan : creationism and intelligence design deserve special attention precisely because they claim to be scientific, which traditional mythologies do not do. –  Oct 07 '16 at 23:54
  • "science is not the only arbiter of truth" and "it cannot be rigorously proven that science is the only arbiter of truth" are different claims. The second is true, the first is at least questionable. Wrt. the vacuousness of requiring rigorous proof, What the Tortoise Said to Achilles from Lewis Carrol is recommended reading. – Tgr Oct 09 '16 at 06:55
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What you describe is called the fine-tuning argument - that out of the full possibility space of the laws of physics, only a very small fraction permits intelligent life, so some creator must have fine-tuned physics. Whether it is a valid claim is an ongoing debate in philosophy of religion, so it would be unfair to call it a fallacy per se, but one can certainly argue that it is based on a fallacy. In your argument, that fallacy would be the observational selection effect. The Stanford Encyclopedia of Philosophy (always a great resource) gives a formal version of such an argument (see section 4.1.1.2 here for the full version): the usual formulation of the fine-tuning argument P(universe is suitable for life|universe was designed) >> P(universe is suitable for life|universe is random), so upon observing that the universe is suitable for life, we conclude that it must be designed. But that ignores the observation bias: what we actually can calculate are P(universe is suitable for life|universe was designed & observers exist) and (universe is suitable for life|universe is random & observers exist), and clearly both of those values are 1 (the universe must be suitable for life if observers exist) so we don't actually learn anything from observing that the universe is suitable for life.

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    But doesn't the argument consider "observers exist" an observation? So it should be in the left side of | somewhere. – JiK Oct 07 '16 at 11:07
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    At least the way I have understood the argument is: "P1: P(observers exist|universe was designed) >> P(observers exist|universe is random). P2: The prior P(universe was designed) is not that much smaller than the prior P(universe is smaller). C1: Ergo P(universe was designed|observers exist) >> P(universe is random|observers exist). P3: Observers exist. C2: For posterior probabilities, P(universe was designed)>>P(universe is random)". – JiK Oct 07 '16 at 11:14
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    (cont'd): A frequency version which might be a bit more intuitive (although doesn't seem to make sense per se): There are 10^100+10^10 universes, 10^10 of then designed and 10^100 of them random. A designed universe has observers with probability 1, a random universe has observers with probability 10^-95. Thus there are 10^10 designed universes with observers and 10^5 random universes with observers. Thus a universe with observer is much more likely to be designed. There's no observational selection fallacy in this version. – JiK Oct 07 '16 at 11:20
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    (cont'd): To be honest, I've found it a bit hard to figure out what people making this argument actually mean, so I don't know if I've understood and paraphrased the argument in its original meaning. – JiK Oct 07 '16 at 11:23
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    You can read the full argument here (I'll admit I didn't). Personally I think the claim boils down (in a very unclear way) to denying the validity of the implicit permise that we as observers have been picked at random from some probability space of observers in all possible universes. Compare the doomsday argument which uses the same premise to arrive at paradoxical results. – Tgr Oct 07 '16 at 18:53
  • ...only a very small fraction permits intelligent life... Unfortunately, that's an assumption. If some universal constant had a slightly different value and the laws of physics otherwise remained the same, then intelligent life would seem impossible. But with different laws of physics, universal constants might take any number of different values and still allow intelligent life. No way to know what different physics allows. – user2338816 Oct 08 '16 at 01:37
  • the case that Tgr makes requires the existence of a very large number of other universes, as a statistical population, to select from. then selection bias is applicable. but if our Universe is the only Universe (and we have no way to ever know differently), then selection bias does not apply and the remarkability of fine-tuning continues to beg for an answer. – robert bristow-johnson Jul 24 '17 at 19:36
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Era answered with the anthropic principles. Let me make it more clear how that relates to your question:

  • The strong anthropic principle: Earth/the universe has been made the way it is so that it could and would produce human beings.
  • The weak version: Humans are the way they are because the universe is like it is.

The strong variant almost necessarily needs a God figure (i.e., an intention for the creation of the universe); it also violates Occams Razor, falsifiability and is as egocentrical as believing that the stars and Sun rotate around Earth. Hence a fallacy. N.B., it nearly enforces humans as observers, and proponents will likely also argue that there can only be humans, because the argument is made to let humans seem to be special.

The weak one is just a more or less bemusing statement that is obviously true for every possible universe and every possible observer. It triggers no further philosophical or physical questions. It allows for any kind of (un)imaginable observer to evolve. It does not make humans special in any way and allows for multiple different types of observer (a.k.a. aliens).

Note that it makes not that much difference if you replace "human" by "intelligent being" or "observer"; the most important point about it is whether there was an intention to create observers that went into the design of the universe.

AnoE
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    This is a very good first answer and one can clearly see that you know what you are talking about. It could become great though, if you would add sources and references, especially for the definitions. – Philip Klöcking Oct 09 '16 at 00:13
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    @PhilipKlöcking, I was not aware that citations are required here; as I did gave none, I thought it is clear that what I wrote is at least partly my interpretation of those concepts. I have especially put them into a nutshell in regards to the question (in which respect is it a fallacy). A quick look at https://en.wikipedia.org/wiki/Anthropic_principle#Variants makes me believe that it would support at least my "bullet pointed" descriptions of the WAP/SAP (c/f the part "Barrow and Tipler" there); I have not read their work directly though and cannot quote anything. – AnoE Oct 10 '16 at 16:30
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I'd like to give a different kind of answer than the ones above, in the hope of shedding light on your question from a different angle: rather than talk about the subject matter of teleological arguments and anthropic principles, I'll just say a bit about how arguments work.

"Fallacy" is a term we use to describe how an argument fails to be logically valid - that is, how the premises fail to entail the conclusion. For instance, I might say, "A implies B; B; therefore A." We call this "the fallacy of affirming the consequent" in order to communicate where that argument went wrong. If that second premise had been "A" rather than "B," we would have had a valid argument with the conclusion "B."

So "fallacy" is only a good term to use insofar as the thing you're talking about is purported to be a deductive argument. But the argument you gave in your question does not have a form anything like a deductively valid argument, so (even if it is indeed an invalid argument in some way) it will be hard to say where exactly a fallacy lies, or what it is - hence the multiplicity of answers here.

Or, to speak more generally, since it's hard to say exactly what the argument that you're asking about is, it's also hard to say what, if anything, is wrong with it. If, as your tags suggest, you're interested in the logic of this question as well as the subject matter, you'll have to be a bit more specific.

EDIT: I don't say this, by the way, just to be pedantic. Some versions of the teleological argument are logically valid, and others are not. I'm of the opinion that you'll have the most fruitful and enlightening discussion only after you've figured out what sort of argument you're evaluating.

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A general, logical way of analyzing that argument would be,

i) the less random something is, the more non-arbitrary it is, and the more information it contains. (This is a common idea from information theory.)

ii) Something non-arbitrary is something borne of logical structure. The more constrained a set of relationships, such as propositions “following” from each other, the more that something attains what is commonly caused “causational” aspects (which, as I currently view it, is just the subset of “physical” propositions of logical consequence, from the enclosing set of all chains of logically consequent truths.)

iii) Therefore, if something appears non-arbitrary, then it must have highly particular logical, causal principles by which it came to be.

I have more to say on this. But for now, I believe the “fallacy” is about an interesting intersection of observation and observer.

Perhaps, to give one example: if the “observer” (say, a sentient being) has the scope of their observation ability delimited in a particular way, it can create the illusion of non-randomness, but that may be a small pocket of order in a broader context of randomness.

I believe in psychology this may be called “cohesion”: things only manifest on the horizons of our conscious, cognitive apperception, which are predetermined to do so, due to having some characteristic which “gets them in the door”. Thus, the “dynamic” between observer and observation I mentioned above, is that they are causally/logically linked: only that which the human mind, being situated in highly particular circumstances, predetermines to be made observable, becomes observed.

I am willing to go out on a limb here and say that my idea is not optimally developed or clear, but intuitively, I feel there is something strong here I am getting at. On a far deeper level, it is about things which we do not realize are far more profoundly causally and inherently logically linked, than we realize. We sometimes find the coherence between things in our universe to be deep, because, with our limited point of view, we do not realize that two separate things are so intrinsically logically linked to one another, so as to be fully identifiable with one another; and I think this is a very Wittgensteinian idea.

We can’t fathom how two seemingly different things could be connected, because we do not grasp that the two separate things are actually deeply interconnected to the point of being mutually necessary or dependent, or even essentially 100% mutually causally linked.

I will try to develop what I am saying in a more formalized way.

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First some corrections, because your premise is wrong: Earth and the laws of physics are perfectly situated for humans to exist.

No, it isn't. Earth was until a very, very recent time completely uninhabitable for humans. Almost half the time Earth had no oxygen at all. 90% of Earth time there was nothing to eat at all. Only during the Perm period (300 million years) and after the mesozoikum (< 70 million years) carbon dioxide levels were low enough to allow breathing for us. But during the Perm giant insects existed, pointing to high oxygen levels (35%) which are detrimental for us. So "Earth" allowed only a very small timeframe for us.

It is also not plausible that the laws of physics (or natural sciences in general) are perfectly situated. Protozoa do not need to die. Humans have trouble with the upright stance. If it is perfectly situated why did smallpox exist and why could we eradicate it without noticing that something very important is missing now ?

So, if anything, the question should be if life itself is improbable. As observers it is very hard to carefully judge the evidence because we do not know what is reliable or simply an assumption.

  • Let's look at the argument of the fine-tuned parameters. If we change some fundamental constants and interactions only a tiny bit, life becomes impossible. The problem is: Are the parameters independent of each other and could they have other values ? If someone can develop a theory that automatically restricts many or all of those parameters the very, very small probability can become noticable.

  • Another option: If we assume that life cannot exist in space and lifeforms are bound on their planet, we could actually use multiclipation of probabilities to arrive at very low probalities because each lifeform must form independently. If we for the sake of argument assume that panspermia is possible (lifeforms can be propelled in space, survive there and seed planets), then the probability that life forms on a hospitable planet is rather high.

My stance is that the final probability depends on so many unknown knowledge that it is currently more an intangible riddle and while arguments for the improbability of life are existing and may even be right, they are currently not very strong.

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    One could argue that the laws of physics being what they are also led to us being able to defeat smallpox and, well, the species is still here. Life doesn't need to be perfectly peaches and roses... it just needs to continue. And continue it does. But I guess now we're arguing as to what "perfectly suited" or even just "suited" really means in this context, which could be deemed a moving target. – Lightness Races in Orbit Oct 08 '16 at 14:52
  • @LightnessRacesinOrbit I use the definition "perfect" as "being entirely without fault or defect". It was explicitly stated in the premise and for that, IMO it simply fails because you cannot have two different situations (before and after smallpox eradication, it does not matter if some germs under control exist) and declare them both as perfect. If you come with a theodicy argument and say, smallpox suffering is necessary, then you have to claim a less perfect world after smallpox. "Perfect" does not leave room to wiggle. – Thorsten S. Oct 08 '16 at 15:39
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    All you've done is move the goalposts. Now tell me what the world must look like in order to satisfy the condition "entirely without fault or defect" from the perspective of being hospitable to human life. Again, bearing in mind the unequivocal fact that we're here and thriving. – Lightness Races in Orbit Oct 08 '16 at 18:23
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    @LightnessRacesinOrbit Please tell us how you reconcile the existence of smallpox with "perfectly suited". And what are you exactly claiming by "thriving" ? The fact that more than 800 million people (2014) are malnourished, that 800 000 people per year are killing themselves because they feel otherwise ? To be frank, the fact that we experience so many negative sides and the ability to imagine that it could be better are proof that we are not living in a "perfect" world. In that one people could not imagine better alternatives or better Earth conditions per definitionem. – Thorsten S. Oct 09 '16 at 16:44
  • The human population of earth is seven billion. I am saying that "perfect conditions" need not necessarily mean that every single one of those people enjoys the epitome of health and happiness: the species is doing more than just fine. Hence my point, which I shall repeat one final time: it depends on your definition. I think you should broaden your view a little. – Lightness Races in Orbit Oct 09 '16 at 16:50
  • Well, perhaps I may broaden your view in return: The human race was nearly wiped out. 70,000 years ago one of the most catastrophic supervolcanoes, the Toba eruption, is very likely to have caused a genetic bottleneck of humans, a very sharp decline in population...almost extinction. In the 14th century, the "Black Death" killed 20% of the world population. In both cases humans the cause was not human influence, but the environment of Earth. And the people just not felt a little miserable, they died. Please continue about what "perfect" conditions are. – Thorsten S. Oct 09 '16 at 17:21
  • "Nearly." "Nearly." As a "did we or did we not survive it", we perfectly well survived it! But you seem insistent on missing that point... I'm not saying my interpretation is the only valid one; I'm just trying to get you to realise that yours is also just one of many. – Lightness Races in Orbit Oct 09 '16 at 17:21
  • @LightnessRacesinOrbit And that are "perfect conditions" ? The only thing disproving your claim is if humans do not exist anymore and then we could not discuss it per definitionem ? Are you really trying to defend this ? – Thorsten S. Oct 09 '16 at 17:27
  • That's not what I was saying at all but, even if it were, there's nothing invalid about that: it is called the weak anthropic principle. As far as trying to help you improve this answer goes, though, I give up. Have a nice day. – Lightness Races in Orbit Oct 09 '16 at 17:29
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    I am not missing the point, it simply seems that you are not seeing that there are many, many other adjectives: mediocre, fair, good, very good, excellent. "Perfect" is a superlative, the highest degree of...perfection. And you cannot defend this adjective for the environment of Earth. We adjusted ourselves pretty good to its conditions during evolution, but we are by no means "perfectly suited", "perfectly conditioned" or whatever you want to call that. – Thorsten S. Oct 09 '16 at 17:41
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We're probably not very special - and regarding the physical conditions required for our existence, these apparently existed on this planet long before we did.

If conditions had been radically different on earth, some other intelligent life form may have evolved - and may have asked the same kind of question.

The semantics of logic are not ever going to solve this conundrum.

steve kando
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