On 05 Mar 2009, at 12:43, Stathis Papaioannou wrote:
> > 2009/3/5 Bruno Marchal <[email protected]>: > >> Sure. But note that "a lot of things happens", including the white >> rabbits and aberrant histories. Quantum intefrence and decoherence >> explains why those aberrant histories are relatively rare. > > Could it be that some things which seem physically possible, like the > matter in my keyboard spontaneously rearranging itself into a > miniature fire-breathing dragon, are actually impossible under MWI, > i.e. don't occur in any branch of the multiverse? If we take seriously *classical* quantum mechanics into account, or even *special relativistic quantum mechanics* into account, I don't see how we could prevent such happening (your keyboard becoming a dragon) in the multiverse. It just follows from the math. Of course the probability that your keyboard become a firing dragon in your branch is much little than winning the big lottery every nanosecond during 100^100 millennia. The main reason is that in such theories position and momentum are described by continuous variables, and the quantum splitting or observers differentiation operate on the continuum. They are even a continuum of variant among your possible dragons, but this remains relatively rare. Of course we have good reason to dismiss both classical quantum mechanics and special relativistic mechanics as the "real theory", given that they "forget" the unavoidable problem of quantization of gravitation, and thus of space-time. If we take into account gravitation, we have a choice of theories on which physicists are still debating a lot. I would say that with the "superstring" sort of theories, the multiverse generates still a continuum of differentiation of stories, and that keyboard-dragon transformation will still happen in many branches (but will still be very rare, for the same reason as above). If we take the Loop-Gravity kind of theories, then gravitation (which curves space-time) is properly quantized, and we get eventually a discrete space-time. In that case, if we add the assumption that the physical universe is sufficiently little, it may be that the keyboard-dragon transformation does not occur, in the resulting finite or enumerable multiverse. Now, *this* would be a problem for comp, because comp implies indeed that everything consistent happens somewhere indeed (unless Günther is right and that some comp super-selection rule applies, but I don't see where such super-selection could come from). Of course keyboard-dragon types of transformations are utterly NOT verifiable, even in the ironical first person way of quantum or comp suicide. If you decide to kill yourself until your keyboard transforms itself into a firing dragon, a "simple" evaluation of the probabilities will show that you have 99,9999... % of chance of surviving only with a brain making you believing that such a transformation has occurred, when it has not. It is the general practical weakness of comp or quantum suicide: if you ask for something *near-impossible", suicide will send you in dreamland (1 person view), and probably in a asylum (3 person view). Bruno http://iridia.ulb.ac.be/~marchal/ --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/everything-list?hl=en -~----------~----~----~----~------~----~------~--~---
