But with no way to estimate how likely it is, you're blowing money on mere possibility.
There isn't no way to estimate it. We can make reasonable estimations of probability based on the data we have (what we know about nanotech, what we know about brain function, what we know about chemical activity at very low temperatures, etc.).
Moreover, it is always possible to estimate something's likelyhood, and one cannot simply say "oh, this is difficult to estimate accurately, so I'll assign it a low probability." For any statement A that is difficult to estimate, I could just as easily make the same argument for ~A. Obviously, both A and ~A can't both have low probabilities.
That's true; uncertainty about A doesn't make A less likely. It does, however, make me less likely to spend money on A, because I'm risk-averse.
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July Part 1