Stathis Papaioannou writes: > That is the basic idea behind these thought experiments with copies: as a > more easily understood analogy for what happens in the multiverse/plenitude.
I don't agree, and in fact I think the use of copies as an analog for what happens in the multiverse is fundamentally misleading. If it were not, you could create the same thought experiments just by talking about flipping coins and such. What is the analog, in the multiverse, of pushing a button to make a copy? When faced with the chance of torture, you are going to push a button to make a copy. What does that correspond to in the multiverse? The closest I can suggest is flipping a coin such that you don't get tortured if it comes up heads. Well, that destroys the whole point of the thought experiment, doesn't it? Of course you'll flip the coin. Anyone would. Pushing a button to make a copy is completely different. That's why we have so much disagreement about what to do in that case, while there would be no disagreement about what to do if you could flip a coin to avoid being tortured. That in itself should be a give-away that the situations are not as analogous as some are suggesting. I would suggest going back over these thought experiments and substitute flipping coins for making copies, and see if the paradoxes don't go away. I believe that many of the paradoxes in the copy experiments are because people do not grasp the full meaning of what copying implies. They are thinking very much in the lines Stathis suggests, that it is a variant on flipping a coin. But it's not. Copying is fundamentally different from flipping a coin, because copying increases measure while coin flipping does not. Measure is crucially important in multiverse models because it is the only foundation for whatever predictive or explanatory ability they possess. Choosing to overlook measure differences in analyzing thought experiments inevitably leads to error. Treating copying like coin flipping is just such an error. If you would instead think through the full implications of copying you would see that it is completely different from flipping a coin. The increase of measure that occurs in copying manifests in the world in tangible and obvious ways. Its phenomenological consequences are no less important. These considerations must be included when analyzing thought experiments involving copies, otherwise you are led into paradox and confusion. Hal Finney