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I am going to take the opposing view here on the likelihood of extraterrestrial life. But I do want to say that I think it is good someone is out there looking

by gpsx 10y ago

I am going to take the opposing view here on the likelihood of extraterrestrial life. But I do want to say that I think it is good someone is out there looking for it. I have been known to be wrong quite a bit. I don't think 10^22 is a very big number. If we try to guess the probability of life evolving at random, I can see it being negligible given that number of planets. First we can try to calculate something easier, the famous monkeys banging on keyboards to try to type Hamlet. If we put 1 trillion monkeys on each planet, and let them try for a trillion years, with three attempts per day to make the math easier, we get a total of 10^49 attempts. We'll consider a keyboard with 50 keys. 10^49 is roughly 50^29, which means we can expect one lucky monkey to get 29 characters into the play. That is impressive but not very far into a play with 30,557 words (150,000 characters?). (http://www.opensourceshakespeare.org/views/plays/plays_numwords.php http://www.opensourceshakespeare.org/views/plays/plays_numwo...) Now consider human DNA. I am not a biology expert so I may not have my DNA right. But it looks like a typical human DNA molecule contains 500,000 to 2,500,000 nucleotides (http://wow-really.blogspot.com/2006/11/your-dna-would-reach-moon.html http://wow-really.blogspot.com/2006/11/your-dna-would-reach-...). I believe there are 4 possibilities for each nulceotide. That means 4^2,500,000 or 10^1,500,000. That is a lot of possibilities. Worse even then typing Hamlet. And that would be if we just had monkeys supplied with adenine, guanine, cytosine and thymine putting DNA together. Never mind that these are each complicated molecules in themselves that have to be assembled at random. So how did we even get here? Well, thanks to quantum mechanics we have almost endless opportunities to end up here. It just seems unlikely that we and some other life ended up in the universe together.

na85 10y ago
I think the chemical reactions that could possibly give rise to life probably happen many many many orders of magnitude more often than 3 times per day.
firmgently 10y ago
It sounds like you're calculating the likelihood of a human evolving in an instant though? Which doesn't need to happen and isn't presumed to have happened here on earth. Intelligent life doesn't have to be like us at all, it doesn't even have to use DNA (although intuitively it does feel like it would need some similarly-complex form of reproductive instruction... eventually). According to evolutionary theory early life on this planet was something far simpler than us (eg. some form of self-replicating molecule - depending on your definition of life) and evolutionary forces (imperfect reproduction leading to variation along with 'survival of the best fit') do the rest of the work. It's vastly unlikely that it would take all the same forks in all the same paths and end up as something like humans (or even like vertebrates - the whole tree of life begun from scratch on another planet would likely be unrecognisable to us) but it seems (again, intuitively) like something akin to what we call intelligence would eventually arise due to the competitive advantages it offers.
- gpsx 10y ago
  My comment was trying to address the idea of big numbers. People can say there are so many planets there must be other life out there. But relative to the numbers that can be involved here, 10^22 is not that big of a number. You raise two very good points. The first (or really second) is multiplicity. For the DNA example I gave, there are many different valid human DNA patterns, and there are surely many non-human good patterns. We divide out number of parameters by the multiplicity. I don't think this generally have a big effect on the size of the _exponent_ we are talking about even if it does change the number by a large factor. The other point is that this was an evolutionary process. What this means is that we could stop and save our work along the way, due to reproduction/replication. When the monkeys try to type Hamlet, they have to start over each time. If one gets the last character wrong, it is back to the drawing board. A better evolution analogy would be if the scientist could stop a monkey when he got the first paragraph and then give that as a starting point for other monkeys. This _does_ seem like it could make a big difference in the size of the exponent. Back to the size of that exponent - it is roughly the number of components of the system. We are composed of 10^29 atoms. There aren't even that many planets, let alone a number raised to that exponent. Even the most simple life consists of many atoms, but the size of our universe only supports putting a small (100?) number of components together. Given this, I am personally still skeptical the universe is big enough to create life besides us. I do have one more thing I want to mention related to why life looks easy. When we look back at our evolution, it looks like it was easy, even inevitable. But there is one thing to consider. Imagine we lined up 10^300,000 monkeys or whatever it would take to type Hamlet, and we put a scientist behind each one to check the monkey's work. Imagine if you were the scientist behind that one monkey that actually pounded out all of Hamlet. Given that you did not see the other 10^300,000 attempts, what would that look like to you?

by gpsx 10y ago

na85 10y ago

I think the chemical reactions that could possibly give rise to life probably happen many many many orders of magnitude more often than 3 times per day.

firmgently 10y ago

It sounds like you're calculating the likelihood of a human evolving in an instant though? Which doesn't need to happen and isn't presumed to have happened here on earth. Intelligent life doesn't have to be like us at all, it doesn't even have to use DNA (although intuitively it does feel like it would need some similarly-complex form of reproductive instruction... eventually). According to evolutionary theory early life on this planet was something far simpler than us (eg. some form of self-replicating molecule - depending on your definition of life) and evolutionary forces (imperfect reproduction leading to variation along with 'survival of the best fit') do the rest of the work. It's vastly unlikely that it would take all the same forks in all the same paths and end up as something like humans (or even like vertebrates - the whole tree of life begun from scratch on another planet would likely be unrecognisable to us) but it seems (again, intuitively) like something akin to what we call intelligence would eventually arise due to the competitive advantages it offers.

gpsx 10y ago
My comment was trying to address the idea of big numbers. People can say there are so many planets there must be other life out there. But relative to the numbers that can be involved here, 10^22 is not that big of a number. You raise two very good points. The first (or really second) is multiplicity. For the DNA example I gave, there are many different valid human DNA patterns, and there are surely many non-human good patterns. We divide out number of parameters by the multiplicity. I don't think this generally have a big effect on the size of the _exponent_ we are talking about even if it does change the number by a large factor. The other point is that this was an evolutionary process. What this means is that we could stop and save our work along the way, due to reproduction/replication. When the monkeys try to type Hamlet, they have to start over each time. If one gets the last character wrong, it is back to the drawing board. A better evolution analogy would be if the scientist could stop a monkey when he got the first paragraph and then give that as a starting point for other monkeys. This _does_ seem like it could make a big difference in the size of the exponent. Back to the size of that exponent - it is roughly the number of components of the system. We are composed of 10^29 atoms. There aren't even that many planets, let alone a number raised to that exponent. Even the most simple life consists of many atoms, but the size of our universe only supports putting a small (100?) number of components together. Given this, I am personally still skeptical the universe is big enough to create life besides us. I do have one more thing I want to mention related to why life looks easy. When we look back at our evolution, it looks like it was easy, even inevitable. But there is one thing to consider. Imagine we lined up 10^300,000 monkeys or whatever it would take to type Hamlet, and we put a scientist behind each one to check the monkey's work. Imagine if you were the scientist behind that one monkey that actually pounded out all of Hamlet. Given that you did not see the other 10^300,000 attempts, what would that look like to you?