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In this case N=2 is very different from N=1. The probability of detecting further Earth-like planets is not influenced by the existence of Earth, because what w
by dodobirdlord 7y ago
In this case N=2 is very different from N=1. The probability of detecting further Earth-like planets is not influenced by the existence of Earth, because what we're actually measuring is the conditional probability of detecting Earth-like planets given the existence of Earth, which already factors Earth in. In this case N=1 is a lot more like N=0 and N=2 is a lot more like N=1.
- solipsism 7y agoThat's silly. The type of world we're interested in is ones that could support life as we know it. We knew one of those exists. We're trying to find more.
- dodobirdlord 7y agoCalling it silly seems a bit harsh, it's just statistics. We are interested in knowing the frequency of earth-like planets existing. If we assume that the existence of earth is a pre-condition for life existing and performing the measurement, then the existence of earth tells us nothing about that frequency. Regardless of the frequency in question the count of earth-like planets starts at 1, because in scenarios where the count is at 0 the measurement is not being performed. There could be millions of earth-like planets in the milky way, or there could be only one, or earth could even be the only life-supporting planet in the universe. There is no mechanism given only the existence of earth to reason statistically about the distribution of earth-like planets. Whereas finding a second one tells us a lot. So that's why I say we are in more like the N=0 case, and that finding a second earth-like planet puts us in the N=1 case.