# Talk:Many-worlds interpretation

Breitbart posted an interesting headline entitled "Parallel universes exist - study". I wonder if that is connected at all. --Remi 06:51, 25 September 2007 (UTC)

"According to quantum mechanics, nothing at the subatomic scale can really be said to exist until it is observed." <-- I think this should be, "According to some interpretations of quantum mechanics, nothing at the subatomic scale can really be said to exist until it is observed." Murray Gell-Mann discussed this in his book, "The quark and the jaguar". Gell-Mann explained his view that the universe works just fine without "observers". Gell-Mann does not like the "many worlds" interpretation. Gell-Mann prefers to speak in terms of "histories" and probabilities of alternative histories. Various physical processes (such as particle interactions with physical systems that function as particle detectors) result in decoherence independent of there being a human observer involved. When a detected particle causes a physical change in a particle detector, that physical interaction reduces the probabilities of most alternative histories (alternative paths of the detected particle) to zero and leaves one history with probability of 1. Gell-Mann calls this "pruning branches" in the tree of alternative histories, describes such "pruning" as resulting from non-remarkable physical events and contrasts it with other views of "collapse of the wave function" that are "often presented as if it were a mysterious phenomenon". I cannot find the new article by David Deutsch. I find it interesting that so many physicists are still struggling to explain how our observable universe could have come into being, while at the same time other physicists assume that an infinite number of universes are continually being created, with no need to account for how those creations occur. --JWSchmidt 18:38, 25 September 2007 (UTC)

- I wonder if there are many physicists who
*like*the many-worlds interpretation (apart for those for which it is the specialization). Parallel universes are experimentally unreachable (unless they fuse with the observed universe after branching - we would then have multiple possible histories of which only one has been observed). The MWI is therefore unfalsifiable and unverifiable (Question 1A). A headline "Parallel universes exist - study" will then meet some circumspection. The header in*New Scientist*is more prudent: Parallel universes make quantum sense. Arjen Dijksman 20:21, 1 October 2007 (UTC)- "David Deutsch at the University of Oxford and colleagues have shown that key equations of quantum mechanics arise from the mathematics of parallel universes." <-- I have to question the "arise from". I still have not seen what Deutsch published (is it published?), but I suspect at best he could have shown that some mathematical treatment of "parallel universes" is consistent with some other mathematical treatment of quantum mechanics. I'm skeptical about the Platonic thinking that leads some physicists to imagine that physical reality "arise from" mathematics. I prefer the idea that we invent mathematical tools that can be useful in our efforts to understand physical reality. --JWSchmidt 20:40, 1 October 2007 (UTC)

- Some Deutsch's writings can be found there: http://www.qubit.org/people/david/.

I also read, in an essay by him, that the "proof" for multiple universes would be building a quantum computer. A quantum computer would "communicate" with other universes (other instances of itself in parallel worlds) to make the calculations. According to him, for certain algorithms designed for a quantum computer, the number of calculations and space needed to accomplish them could exceed the number of particles in our own universe. Thus, if the quantum computer can make the calculations and gives a result, then that computer made its calculation with the help of other universes' calculations and data space. Also, there is the many worlds interpretation of photons interference by saying that the photons interact with themselves. This later is not provable, some scientists think. Davichito 17:17, 29 September 2008 (UTC)