3 ms·

I use to think the same as you for the same reason as you, but there's actually a surprisingly strong argument that life forms that develop independently should

I use to think the same as you for the same reason as you, but there's actually a surprisingly strong argument that life forms that develop independently should still look like us at the lowest level. The idea is this: Although it's likely possible for alternative forms of life to develop, we should expect the probability of abiogenesis (i.e., the chance that life develops in a given pool of chemicals, per unit time per unit volume) to vary dramatically depending on the form of life. This is because abiogenesis is (almost certainly) an extremely improbable event which requires individually unlikely random events to all occur in sequence. In other words: given the fundamental particles and interactions of physics, it would be very surprising if the chance of abiogenesis for two different forms of life were within, say, an order of magnitude of each other, since there are so many conditional probabilities that need to multiply for a given sequence of improbable events. This implies that, looking across the universe, there is a preferred form of life that is much more likely to be generated than all other forms. Therefore, with high probability it will be the form of life that we are and that any aliens we meet are.

blauditore 10y ago
Hm, interesting approach. So the assumption is that abiogenesis is highly complex, thus probabilities for fundamentally different life forms (likely) vary wildly. Hence either foreign life form X were far more likely to develop and we would see it all over the place (actually, maybe not), or it were far less likely and hence we'd rather find one similar to ours. But how does one estimate probabilities of abiogenesis, or their relative magnitudes? Are there e.g. scientific papers published on this subject?
- jessriedel 10y ago
  > Hence either foreign life form X were far more likely to develop and we would see it all over the place (actually, maybe not), or it were far less likely and hence we'd rather find one similar to ours. Yea. The argument is actually independent of whether the probability of abiogenesis is large enough for life to independently arise multiple times in the solar system or (conversely) small enough that it's very unlikely for it to exist elsewhere in the observable universe. I think all it requires is that abiogenesis is a combination of several small probabilities distributed over several orders of magnitude. (If the probability is large enough that multiple forms routinely develop on the same planet, then we probably also have to assume something about, say, the first-mover dominating.) > But how does one estimate probabilities of abiogenesis, or their relative magnitudes? It's really hard. > Are there e.g. scientific papers published on this subject? Yes, but I don't know them off the top of my head, or whether any are any good.
- jerf 10y ago
  "But how does one estimate probabilities of abiogenesis, or their relative magnitudes?" You probably covered some of this in school, though it tends to be an aside in your chemistry or biology book and easy to miss. But people have done the basic experiments with taking a bunch of likely looking chemicals, based on what we think the old Earth looked like, and shooting electricity through them and other such things that seem like they may have contributed to life. Those experiments came up negative; life isn't that easy. That has been so thoroughly absorbed into modern consciousness that it can be easy to forget that they were perfectly legitimate experiments to conduct, and had they come out positive, that pretty much would have ended all debated about how common life is in the universe, moving the discussion firmly into the "intelligent" part of the issue. You can also try to create "minimal organisms" that are sufficiently simple that they perhaps could be randomly created. However, last I knew, computing odds of abiogenesis is still effectively impossible because there are still some steps that we simply do not know how to get past via random processes, such as ensuring the chirality of the molecules matches. That's not to say there's a lot of ideas out there on how to get over various elements of the problem, but at the moment I think it's fair to say that the best science we current have puts the odds of abiogenesis at simply "impossibly unlikely". Stay tuned for more "best science", of course.
  - jessriedel 10y ago
    > effectively impossible because there are still some steps that we simply do not know how to get past via random processes To be clear, there is always a lower bound on this probability that comes from brute force randomness (e.g., a quantum fluctuation in which all the molecules of a bacteria assemble spontaneously). This lower bound is extremely, extremely tiny, taking the form 10^(-10^(large)), and there are almost certainly easier ways to make a simpler replicator that later evolves to become a bacteria. But since we don't have an upper bound on the volume of the universe, and we don't have evidence for life arising somewhere else in our observable universe, it's formally possible that it's simply that stupendously rare (but still not impossible).

blauditore 10y ago

Hm, interesting approach. So the assumption is that abiogenesis is highly complex, thus probabilities for fundamentally different life forms (likely) vary wildly. Hence either foreign life form X were far more likely to develop and we would see it all over the place (actually, maybe not), or it were far less likely and hence we'd rather find one similar to ours. But how does one estimate probabilities of abiogenesis, or their relative magnitudes? Are there e.g. scientific papers published on this subject?

jessriedel 10y ago
> Hence either foreign life form X were far more likely to develop and we would see it all over the place (actually, maybe not), or it were far less likely and hence we'd rather find one similar to ours. Yea. The argument is actually independent of whether the probability of abiogenesis is large enough for life to independently arise multiple times in the solar system or (conversely) small enough that it's very unlikely for it to exist elsewhere in the observable universe. I think all it requires is that abiogenesis is a combination of several small probabilities distributed over several orders of magnitude. (If the probability is large enough that multiple forms routinely develop on the same planet, then we probably also have to assume something about, say, the first-mover dominating.) > But how does one estimate probabilities of abiogenesis, or their relative magnitudes? It's really hard. > Are there e.g. scientific papers published on this subject? Yes, but I don't know them off the top of my head, or whether any are any good.
jerf 10y ago
"But how does one estimate probabilities of abiogenesis, or their relative magnitudes?" You probably covered some of this in school, though it tends to be an aside in your chemistry or biology book and easy to miss. But people have done the basic experiments with taking a bunch of likely looking chemicals, based on what we think the old Earth looked like, and shooting electricity through them and other such things that seem like they may have contributed to life. Those experiments came up negative; life isn't that easy. That has been so thoroughly absorbed into modern consciousness that it can be easy to forget that they were perfectly legitimate experiments to conduct, and had they come out positive, that pretty much would have ended all debated about how common life is in the universe, moving the discussion firmly into the "intelligent" part of the issue. You can also try to create "minimal organisms" that are sufficiently simple that they perhaps could be randomly created. However, last I knew, computing odds of abiogenesis is still effectively impossible because there are still some steps that we simply do not know how to get past via random processes, such as ensuring the chirality of the molecules matches. That's not to say there's a lot of ideas out there on how to get over various elements of the problem, but at the moment I think it's fair to say that the best science we current have puts the odds of abiogenesis at simply "impossibly unlikely". Stay tuned for more "best science", of course.
- jessriedel 10y ago
  > effectively impossible because there are still some steps that we simply do not know how to get past via random processes To be clear, there is always a lower bound on this probability that comes from brute force randomness (e.g., a quantum fluctuation in which all the molecules of a bacteria assemble spontaneously). This lower bound is extremely, extremely tiny, taking the form 10^(-10^(large)), and there are almost certainly easier ways to make a simpler replicator that later evolves to become a bacteria. But since we don't have an upper bound on the volume of the universe, and we don't have evidence for life arising somewhere else in our observable universe, it's formally possible that it's simply that stupendously rare (but still not impossible).