Why hasn't life evolved on other planets?

According to atheists, evolution is bound to happen given enough time (4.5 billion Years, or 100 Qaudrillion seconds). If so, why have we not been visited by aleins from other planets? Surely, at least one of 10(24) stars (quite a large number, it is a billion times more than the number of seconds that have elapsed since the big bang) contains a species which is interested enough, and technologically advanced enough, to visit us. Yet, they never have. Why?
Atheist Answer: 

What we have here is a case of large numbers vs other large numbers, preventing a clear-cut case for high or low probability.

A simple version of the Drake equation applies here. The probability that we will be contacted by aliens is:

A. the probability of intelligent life evolving on at least one other planet, multiplied by
B. the probability that a given intelligent species will develop interstellar exploration, or intergalactic exploration as the case may be, before it becomes extinct, multiplied by
C. the probability that a given species with interstellar/galactic exploration will actually find us before we become extinct ourselves.

(I say "exploration" rather than "travel", because the aliens might not have to be in our vicinity to find and contact us.)

If you remove the "other" from A to make, "the probability of intelligent life evolving on at least one planet," its probability becomes 1 (certain), as our existence proves it has already happened. If it happened here, nothing prevents it happening elsewhere, so A is indeed very close to 1 and very likely indeed. In other words, they're probably out there.

B is where the trouble starts. Interstellar or intergalactic travel or communication within reasonable timeframes (say, between any two stars in a galaxy within a lifetime) might actually be impossible, if the universe's inherent speed limit of 300,000km a second cannot be circumvented. B could be zero, and therefore alien contact might simply be impossible.

If instead there is a way to cross the cosmos which we haven't discovered yet, we won't know how long that takes until it happens. The danger is that it requires a species to spend a very long time working from a baseline of technologies with which it might inadvertently destroy itself. We're at that stage right now; our theories of deep space travel stem from some of the same research and the same minds as our atomic weaponry. The terrible risk of this particular period in a civilisation's existence appears to lower B considerably.

Finally, C is a function of A and the possibly infinite size of the universe. If every intelligent species which will ever arise has an volume of space to itself so big it will take the rest of its lifespan to explore (likely so far, since we've found nothing in the places we can see properly), no two may ever cross paths. Since the universe is expanding, the chances of contact are shrinking all the time, especially if the species are in separate galaxies, clusters or superclusters.

Tragically, the most likely case appears to be that there's intelligent life all over the universe, forcibly segregated by the tyranny of time and distance. Of course, ET could show up tomorrow and waggle a glowing finger at our flawed view of the universe.

- SmartLX


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You say that the probability of there being another human-like species is "1." You ignore that according to evolution there MUST be numerous (possibly millions) of humanlike species. You never include this crucial point into your equation.

Read it more carefully. I

Read it more carefully. I said the probability of there being a human-like species is 1. It's obvious, because we are a human-like species and we exist. As for other human-like species, I said the probability is only close to 1, which means there's a chance there are none. Therefore, "MUST be" is an overstatement.

It's still likely that there is lots and lots of intelligent life out there, and I did factor that in. This is why I mentioned "large numbers vs other large numbers": the likely abundance of alien intelligence is countered by the odds against two things: that a given species will explore space beyond their own solar system, and that a given spacefaring species will find us. The first may be impossible, and at the very least is made difficult by the destructive applications of rocket science. The second is a gargantuan task given the vast and increasing scale of the universe. Even if aliens found other aliens, what are the chances that it would be us?

Sure, imagine millions of humanlike species. Then remember that we know of approximately ten thousand million million million (10^22) stars in the visible universe. That puts the number of stars per species around one to ten thousand million million (10^15 or 10^16). Exploring just one species' share of the universe would take longer than the universe is expected to last before heat death.

That's why I think there's a good reason we haven't been contacted. The unlikely parts of the process are more unlikely than the likely part is likely.


I do not want to go back and forth about this topic. But I feel I must clarify a couple of things. First of all, you make it sound as if it is a hard thing to explore the universe. It is not. All the aliens have to do is send us intergalactic radio signals.
For example, we have already sent a radio message to a star cluster 25,000 light years away from us. This star cluster contains thousands of stars. Why have they never (at least any time before 25,000 years ago), sent us any radio signals.
Of course you will, as you have done before, respond with some cutesy answer. But are you seeking the truth?
In fact, had you been there when Jesus (supposedly) walked on water, you would have also tried to explain it away. You would have said, "just because we do not know why it happened, does not mean that there is a God."
As Richard Dawkins admits, it is a lot of fun to be an atheist (despite the fact that they are lonelier, live shorter, and are more depressed: do a search about it). Are you not willing to give up that fun for the sake of truth, and well-being?

Ridiculing my responses by

Ridiculing my responses by calling them "cutesy" doesn't actually refute them, you know.

Intergalactic radio signals, and all other kinds of electromagnetic radiation, are limited to the speed of light. The Milky Way galaxy is 100,000 light years across, and the nearest other galaxy Andromeda is 2.5 million light years away. By the time Earth got a radio signal from our nearest neighbours, either they or we are very likely to have moved on or died out in the previous 100,000 to 2.5 million plus years, or else we aren't at a stage where we can recognise or even pick up what they're sending. The radio spectrum is really, REALLY narrow compared to the full range of signals available, and we're still not listening for all of it.

Just what signal have we sent to a star cluster 25,000 light years away that has arrived there, and given any inhabitants a sign of intelligent life on Earth? What were we sending out 25,000 years ago? It would have to have been 50,000 years since the signal went out before we received a reply at any rate.

I am seeking the facts. "Truth" can be redefined too easily and too broadly. There are those with an attitude along the lines of, "What's true for me is true for me." This has no bearing on reality.

Given that I've seen Penn and Teller walk on water, and immediately demonstrate how they did it, I would indeed try to explain how Jesus had done it in front of me. So would many other witnesses. The difference is, if it really were a miracle, we would fail. It would be a fairly obvious circumvention of physical laws of buoyancy and displacement, and we would be forced to consider supernatural explanations. (God isn't the only one of those, by the way.) However it has not happened in front of me, and the veracity of the accounts of this miracle is unsupported outside of the New Testament itself.

The "supposedly" in your reply tells me you're not a Christian, or at least not a fundamentalist Christian, so what would you do if it happened in front of you?

You've changed the subject now, but okay. There is statistical evidence that religious people are happier and less stressed on average. There is also evidence that less intelligent people are happier and less stressed, but I'm not about to throw away my education and forget what I know in order to sink into a contented stupor. People who've just dropped acid are incredibly happy, but...no thankyou.

Ultimately, just because belief has its advantages doesn't make it justified by historical fact (evidenced by the fact that the advantages you mention are common to contradictory religions), and I have an aversion to deluding myself. Neither does it mean that religion is without its disadvantages. It costs to believe, anything from an hour a week to 10% of your income to all your friends to your entire life.

Quick reply

Just a couple of points. True, there are starts 2.5 million miles away. However, there are PLENTY of starts that are very close. The closest star is a mere 4.3 light years away. While scientists do not believe that evolution should happen in every solar system, they do estimate that it could happen in 10% of the stars in the milky way (they are so sure of evolution), according to Stefan Lovgren in an article in the national geographic (although, I admit, I might have misunderstood the article).
Personally, I am between 30% and 50% sure that Jesus walked on water (and I do not beleive Pascal's wager applies to individual religions). So no, I am not a christian. However, I do not believe that it is irational to be one.
Next, you admit that a theist has a better life. But you cannot force yourself to believe what you think is false. My question is then, why do you sadistically try to convince those who believe religion is true, that it is false? If you successfully convince them, they will live shorter, and less happy lives.
Furthermore, many argue - this website included - that pascal's wager is stupid becuase God would know that you do not really believe. So he would not reward you for "believing" in Him. Yet you try to convince people who fully believe (and will therefore, even according to your logic, be rewarded) not to believe. Why? - Aren't you CAUSING then to possibly lose an afterlife. Second, even if you do not believe in God and therefore can never be rewarded, it seems axiomatic that this God who might exist would rather that you do not convince people not to believe in him. Why do you subject yourself to punishment?

Stars again

I think I've found the right article by Stefan Lovgren. It says that a certain ring within the galaxy, containing 10% of the total stars, is where life is most likely to evolve.

That's not saying much. The largest estimate of planets per star I've ever read was one planet for every five stars. That's not bad, but this is where another part of the Drake equation comes in: what proportion of planets can naturally generate and sustain life? Since we haven't yet found a viable planet besides Earth, the odds against this particular prerequisite currently have no upper bound.

With my extension of your logic to include happy fools and oblivious trippers, I was trying to show that being happier and less stressed does not necessarily mean leading "a better life". The billions of people who worship false gods are happily wasting large amounts of their lives. If they realised this, they would regret it and spend their time on other pursuits. Even those worshipping the real god, if any, may be going about it the wrong way and thus wasting their efforts as well.

This is what freedom from religion offers: a chance at real fulfillment, and a chance to be unambiguously useful. Without a hypothetical afterlife to prepare for and a distant father figure to please, people have more space in their lives to devote to earthly pursuits - mathematics, art, medicine, charity work, whatever - with tangible goals and rewards, not just for the individual but for the world. Religion has of course sponsored many such achievements, but without religious influence these pursuits are fully focused on the real world, the here and now, and can achieve more where it counts.

If you've read my piece on Pascal's Wager, you know I've got more than one objection. Perhaps I do cause people to lose a chance at a particular afterlife. I also relieve them of an infinitely greater chance of facing a god other than theirs, having allied themselves with a false, rival god, and thus being subject to the full wrath of whoever the real god might be. Throwing in with any one god is the ultimate long shot, and I hate to see people take it. Furthermore, to consider my own case, if there's a real god then I'm most likely pleasing him/her to some extent by combating beliefs in false gods, because chances are it's not one of the major ones.