Bruno Marchal wrote: > > 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.
This is what I've suggested before. There may be a smallest non-zero probability, so quantum evolution is not strictly unitary and after sufficient decoherence the off diagonal terms of the reduced density matrix become strictly zero. Brent >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 -~----------~----~----~----~------~----~------~--~---
