50 Years of the Multiverse Interpretation 198
chinmay7 writes "There is an excellent selection of articles (and quite a few related scientific papers) in a special edition of Nature magazine on interpretations of the multiverse theory. 'Fifty years ago this month Hugh Everett III published his paper proposing a "relative-state formulation of quantum mechanics" — the idea subsequently described as the 'many worlds' or 'multiverse' interpretation. Its impact on science and culture continues. In celebration, a science fiction special edition of Nature on 5 July 2007 explores the symbiosis of science and sf, as exemplified by Everett's hypothesis, its birth, evolution, champions and opponents, in biology, physics, literature and beyond.'
*Interpretation* (Score:3, Informative)
I like SF as much as probably most people here, but I can't see the scientific significance.
Re:MWI is cool and all.... (Score:3, Informative)
Greg Egan wrote a book [wikipedia.org] on that topic. Aliens were relying on non-collapsed wave functions as a part of their normal life. New instruments like the Hubble Telescope were causing mass genocide in the observable universe, which got some aliens pretty pissed off.
Re:MWI is cool and all.... (Score:5, Informative)
Re:MWI is cool and all.... (Score:3, Informative)
It's similar to how you see things. Light bounces off of a thing, and that light bouncing into your eye is how to observe and measure things. Just lower the scale to a single photon of light (or even a smaller particle) and youre set.
The reason you can't measure all the details of a particle at this level is because when the photon you bounce off it actually hits the particle youre measuring, the photon will disturb what you are measuring and thus changes it.
Similar how if you rolled one pool ball on the table to hit another.. It disturbs the other ball and moves it too, so any data you can draw from your reflected ball is no longer accurate since it modified what you just measured after the fact.
Re:MWI is cool and all.... (Score:3, Informative)
Rather, all the *possible* outcomes of a quantum measurement do happen: each one in a different universe.
When you measure one particular outcome, that means that you are in the particular universe where you measure that outcome: by definition.
A measurement consists in an event that translates "quantum information" into "classical information": quantum information is very complex as essentially it means that you are keeping track of what happens in ALL the universes, at some point, you stop doing that, and you become concerned with only what happens in you particular universe: that action constitutes a measurement. And it is from that action that you find out in which universe you happen to be.
Old (Score:5, Informative)
It would be nice if scientists, when talking to non-scientists, drafted lively images like this one. IMHO, it would go a long way in bridging the gap between them and "normal" people, who don't think in terms of numbers and mathematical concepts.
Re:MWI is cool and all.... (Score:5, Informative)
No in the MWI the wavefunction does NOT collpse. This is the whole point of the MWI, in the Copenhagen interpretation the wave function collapses on a measurement to a single state. In the MWI a measurement splits the world into two different states there is no collpse of the wavefunction.
The Copenhagen interpretation abolishes physical reality and brings in the idealist concept of a conscious observer collapsing the wavefunction. The MWI restores physical reality in quantum mechanics.
Let's take the Schrodinger cat thought experiment: <cat alive|cat dead>
This gives rise to the density matrix:
cat alive ...................... cat alive + cat dead
cat alive - cat dead ..... cat dead
The CI supporters would say the MWI didn't explain why we don't see the off diagonal mixed states. But the modern approach to the measurement problems in MWI uses the concept of decoherence which is the interaction of the isolated quantum states with the macro environment. It has been shown that the mixed states are destroyed by interference when decoherence from interaction with the environment occurs. Thus in this experiment the world is split into two, one where the cat is alive and one where it is dead.
The decoherence approach in conjunction with the MWI abolishes the necessity of observers and restores the independent physical reality abolished the the CI. The proliferation of many worlds is the price we have to pay for physical reality and the unitary evolution of the wavefunction.
Re:MWI is cool and all.... (Score:4, Informative)
The reason you can't measure all the details of a particle at the same time is NOT because photons bounce off of it and disturb it. The reason you can't measure all of the details of a particle at the same time is because that is JUST THE WAY IT IS. It has nothing to do with interference from other particles. There is no "reason" for it. No one knows why it works that way. It's called "complementarity", and it's the fundamental quantum mystery.