----- Original Message ----- From: Hal Finney <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Saturday, January 10, 2004 12:24 AM Subject: Peculiarities of our universe
> There are a couple of peculiarities of our universe which it would be > nice if the All-Universe Hypothesis (AUH) could explain, or at least > shed light on them. > > One is the apparent paucity of life and intelligence in our universe. > This was first expressed as the Fermi Paradox, i.e., where are the aliens? > As our understanding of technological possibility has grown the problem > has become even more acute. It seems likely that our descendants > will engage in tremendous cosmic engineering projects in order to take > control of the very wasteful natural processes occuring throughout space. > We don't see any evidence of that. Similarly, proposals for von Neumann > self reproducing machines that could spread throughout the cosmos at a > large fraction of the speed of light appear to be almost within reach > via nanotechnology. Again, we don't see anything like that. > > So why is it that we live in a universe that has almost no observers? > Wouldn't it be more likely on anthropic grounds to live in a universe > that had a vast number of observers? Assuming the validity of the AP, we should expect to find ourselves in the most typical of circumstances. We should thus expect that most observers are similar to us. So, most observers are not part of a very advanced civilization. Maybe, as I wrote in the other posting, this is because those civilizations consist of only one individual. This should follow from the AUH, but it is not very clear how. If most observers are like us, then we shouldn't expect to find much evidence of intelligent life, even if there are hundreds of civilizations in our galaxy now. Maybe the fact that we are in a situation in which we don't have controll over our own bodies very much is a clue. This should again be a typical situation observers find themselves in. They are on the verge of understanding how the universe works, but they don't have a cure for deadly diseases or old age. They don't have the capacity to design and build observers like themselves. It should thus be the case that the moment they do develop such capabilities, their numbers should decline dramatically. This should be a universal property of civilizations evolving in a universe with large measure. > > The second peculiarity is the seemingly narrow range of physical laws > which could allow for our form of life to exist. Tegmark writes about > this at http://www.hep.upenn.edu/~max/toe.html. He shows a chart of > two physical constants and how if they had departed from their observed > values by even a tiny percentage, life would be impossible. In the > full paper linked from there he offers many more examples of physical > paramters which are fine-tuned for life. > > So why is this? Why does it turn out that our form of life (or perhaps, > any form of life) can exist for only a tiny range of variation? > Why didn't it turn out that you could change many parameters a great > deal and still have life form? > > I don't see anything a priori in the AUH that would have led to this > prediction. Now, it may just be one of those things that "happens to > happen", a fundamental mathematical property like the distribution of > primes or the absence of odd perfect numbers. Self-aware subsystems > just mathematically turn out to only be possible in a very tiny region > of parameter space. > > Now, you might be able to make the argument that "tiny" is not well > defined, that there is no natural length scale for judging parameter > ranges. Tegmark could as easily have zoomed in on the appropriate region > of his graph and shown a huge, enormous area where parameters could be > moved around and life would still work. > > However I think there is a more natural way to put the question, which is, > what fraction of computer programs would lead to simulated universes that > include observers? And here, if we follow Tegmark's ideas, the answer > appears to be that it is a very small fraction. (Of course, you still > need to use your own judgement to decide whether that is "tiny" or not.) I am not sure this is correct, I do agree that there is a problem here. Tegmark looks at what would happen if you change on or more parameters in the standard model and then concludes that the parameter space for life is very tiny. Most physicists believe that a fundamental theory with only a few parameter, e.g. superstring theory, could be behind the standard model. The standard model is what you get if you ''integrate out'' the as of yet unknown physics at the smallest length scales. Given that the fundamental theory is supposed to have only a few parameters, it should have a much larger measure than generic versions of the standard model. So, the problem is actually worse: Why does life only emerge in a tiny fraction of programs describing versions of the standard model? And of those programs that do give rise to life, at least one can be obtained from an atypically simple program (simulating the TOE).