Abstract: I argue that we are likely the only intelligent beings currently present in the (observable) universe. Lest my derivation sounds too much like the Anthropic Principle, which people scoff upon, I do a careful analysis of the latter.
In this essay, I will first argue that the universe changes dramatically after the emergence of an intelligent species, so much that either no other civs will emerge, or if they do, they will witness a very different universe. Since only one species can evolve from scratch, we must be it, thus resolving the Fermi Paradox.
The "we must be it" argument must sound uncomfortable. Anthropic-y arguments make us uncomfortable. Let's examine first where that discomfort comes from. Consider these 4 anthropic-y arguments. I will argue from Bayesian logic that in 2 of these 4, it is okay to invoke the Anthropic-y logic.
A2: If there were a billion living species to choose from, why did I end up a human? Isn't that weird? Why should I be the lucky one? Something is not right.
A3: The universe must team with life. If we don't find any, we just happen to be lucky enough to be the first ones.
A4: There is only once that intelligent life will emerge. Therefore, we are the ones.
Bayesian logic is always the answer. It provides us a deeper look at why we dislike the Anthropic argument. It also helps us find out when it is okay to invoke this Anthropic-y logic. Let's examine the 4 arguments one by one:
AA1: The fact is that we have a lot of theories of physics to choose from. New ones emerge each day. Candidate T1 (the theory implicit in the question) involves a very small chance (extreme fine-tuning of parameters, p=1e-100) to explain the current situation. Candidate T2 is much more likely to lead naturally (p=.5) to current conditions (ripe conditions for intelligent life). Then, since we know intelligent life has emerged, we simply need to adjust the probabilities of the correctness of T1 and T2 via Bayesian logic. In other words, T1 becomes very unlikely as compared to T2, and that's what the physicists who dislike Anthropic arguments are saying. Their reasoning is valid even if we didn't have currently have a T2 -- new theories are after, all being proposed all the time -- there's certainly a better than 1e-100 chance that someone in the next 100 years will propose a T2. That's the point. Thus, this Anthropic argument is wrong, and it is very valid for physicists to become uncomfortable at the invoking of this Anthropic argument.
AA2: This anti-Anthropic argument is wrong. It is okay to be the "lucky one" in this case. The only kinds of persons that can pose such a question are, after all, humans. So, the probability of the poser of this question being a human is 1. There is nothing wrong. (There is no equally likely competing theory T2 in which animals can pose such questions. Or, any such theory is extremely unlikely because of other reasons.)
AA3: That is an bad Anthropic argument. If the universe had 10^10 civs, the probability of us being the lucky ones is 1e-10. The competing theory T2, which simply says that we simply haven't looked hard enough, is much more likely to be correct.
AA4: Now that we have argued out the existence of more than one civ, there's nothing wrong with us being the ones. In this universe, the only being asking this question will have to be the first intelligent life. Thus, from a Bayesian standpoint, there's nothing weird about the poser being one of those intelligent beings - in fact, it is the only possibility. Thus, this Anthropic-y argument is okay.
Having argued that A4 is okay because of AA4, the only remaining task is to argue out the existence of other civs that will witness the universe like we do. That comes very naturally if you believe in Technological Singularity. Say, intelligent species are likely to emerge once every 10^8 years (that is 10 species every billion years). The first intelligence to emerge will attain immense technology very shortly (within 10^4 years, or perhaps a much shorter time - for example, we are within some 10^2 years of our attainment of immense technology.). Since species emerge some once every 10^8 years, there are still no species yet, and the first species has become the Gods of the universe. They will greatly modify the universe. If and when any other species are allowed to evolve, they emerge in a very different universe - a very modified one - imagine being born on a tree in a forest versus in the middle of New York city.
Thus, the only species that will witness the nascent, void, lifeless universe in its "natural form", with a "natural nightsky, with no roads or highways paved through it, will be the very first species. Other species may or may not emerge, but if they do, they should do so in the very visible shadow of the first civ. Since we are the ones observing a very natural universe, we are the very first species. And, as I argued in A4 above, there's nothing wrongly Anthropic about this argument.
Yes, I can almost hear the criticisms - "Learn some physics! Don't you know there's some a fundamental limit called the speed of light? Even a great civ. cannot surpass it." First, the speed of light is a currently accepted limit, considered valid during a very small sliver of the history of our understanding of Science. At one point, it was believed manifestly obvious that heavy things can't fly. Anyway. Secondly, if you really care that much about the speed of light, replace the word "universe" by "observable universe" in this essay, and all conclusions remain the same. Another criticism would be: what if the first civilization chose to keep itself very invisible to the others. In the unlikely scenario that this would happen (and I do believe this is unlikely): then, we are the second only civ. to emerge. But, even then, the question of "Where are they" gets answered - there are either no other civs yet, or if there's one, it's keeping itself invisible - by the very premise of the criticism.
My Conclusion: We are most likely, the very first ones on the block.
Given the conclusions of this essay, it is even more important to pay heed to the OneBasket article.
-- Deepak Goel (deego3 @ gmailNOSPAM period com), August 2006 -- March, 2008.
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