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50 Years of the Multiverse Interpretation
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.'
Wasn't it proven that the multiverse interpretation is mathematically equivalent to the other more traditional approaches like wavefunction collapse and decoherence?
I like SF as much as probably most people here, but I can't see the scientific significance.
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Greg Egan wrote a book 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.
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When something is measured, it collapses it... What causes the collapse? Perhaps consciousness? No. It's just that once you've measured where something is, the probability of it being somewhere else is drastically reduced for a while. What's the probability that I left my keys in the kitchen instead of the bedroom? Let's say 50%. "Oh," a friend says, "I just saw them in the bedroom." so what does that probability become? 0%. It was measurement, not some mystic force, which reduced the area in which my keys are most likely to be found. It's no different with quantum mechanics.
Fnord.
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.
In the many worlds interpretation of quantum mechanics the wavefunction does not collapse (that is the copenhagen interpretation).
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.
The multiverse hypothesis is an ancient idea. I remember reading about a poetic image used in Hinduism to describe it: that of "Shiva's Necklace". It's said that the god Shiva, which together with Vishnu and Brahma form the (main) Hinduist Trinity, the Trimurti, wears around his neck an infinitely long necklace with an infinite number of beads. Each bead is a full universe, ours being just one among them, and Earth with us just an infinitesimal aspect of that single bead.
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.
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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.
You are mistaken.
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.