What is Many-worlds: Definition and 37 Discussions

The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wavefunction is objectively real, and that there is no wavefunction collapse. This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe. In contrast to some other interpretations, such as the Copenhagen interpretation, the evolution of reality as a whole in MWI is rigidly deterministic. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957. Bryce DeWitt popularized the formulation and named it many-worlds in the 1960s and 1970s.In many-worlds, the subjective appearance of wavefunction collapse is explained by the mechanism of quantum decoherence. Decoherence approaches to interpreting quantum theory have been widely explored and developed since the 1970s, and have become quite popular. MWI is now considered a mainstream interpretation along with the other decoherence interpretations, collapse theories (including the Copenhagen interpretation), and hidden variable theories such as Bohmian mechanics.
The many-worlds interpretation implies that there are very many universes, perhaps infinitely many. It is one of many multiverse hypotheses in physics and philosophy. MWI views time as a many-branched tree, wherein every possible quantum outcome is realised. This is intended to resolve some paradoxes of quantum theory, such as the EPR paradox and Schrödinger's cat, since every possible outcome of a quantum event exists in its own universe.

View More On Wikipedia.org
  1. P

    Everett and Gell-Mann at the notable Massagon(?) meeting

    While discussing at https://www.physicsforums.com/threads/why-is-there-no-consensus-about-the-meaning-of-probability-in-mwi.1059618/post-7054892 somebody posted this video: where Gell-Mann in a interview with Geoffrey West discusses the contributions of Everett. He says in the transcript...
  2. J

    I Many-worlds implies computers are not conscious?

    Consider the following thought-experiment in the many-worlds interpretation. Suppose that I have a reversible conscious observer AI and a particle with +1/2 spin in the z direction. Next the observer measures the spin in the x-direction and therefore spits into a version that measures +1/2 and...
  3. S

    I Do all mental states really exist in some universe in Many-Minds?

    According to the Many Minds interpretation of quantum mechanics (https://en.wikipedia.org/wiki/Many-minds_interpretation), the distinction between worlds in the Many Worlds interpretation should be made at the level of the mind of an individual observer. I have read that, in this case, each...
  4. ShadownightPrograms

    I Many-Worlds Theory: Simulation Program in C#

    Here is the Code File in an txt. I can on request provied the whole Program, which includes the PSE, AtomFunctions and many useful but not all implemented Funtions to solve the Many Worlds Problem in C#. Please feel free to ask questions via here or email [e-mail address deleted by Mentors] I...
  5. T

    I Danger for the Many-Worlds Interpretation?

    Sabine Hossenfelder claims: This, of course, is not what we observe. We observe only one measurement outcome. The many worlds people explain this as follows. Of course you are not supposed to calculate the probability for each branch of the detector. Because when we say detector, we don’t mean...
  6. J

    I Energy in Everett's Many-worlds Interpretation

    Hi, Is anybody able to explain how energy is "distributed" in the many-worlds interpretation. I'm using scare quotes as I think this may be the wrong line of thought. It's tempting to imagine energy being distributed amongst subsequent branches as the wave function evolves but I'm not certain...
  7. T

    I Question regarding the Many-Worlds Formulation

    As Sean Carroll states here superpositions "come into being" due to "the magic of decoherence". Please criticize the following reasoning: He decides to measure "a spinning particle that can have spin-up or spin-down." He' measures spin-up and he'' measures spin-down. The day before his sister...
  8. durant35

    I Many worlds and high-amplitude anomaly branches

    A question came up to my mind while thinking about probabilities and Born rule in the context of the Everettian approach. It is often said that anomalies/maverick branches where the experiments go horribly wrong and crazy stuff happens have a negligible amplitude/measure so they really don't...
  9. CynicusRex

    Improbability of the Many-Worlds Interpretation?

    If the MWI would be true, wouldn't there be at least one reality where human civilization advanced much faster than we did and therefore: contacted all other universes; destroyed all the universes; colonized all other universes; etc. Since, as far as we know, this has not happened, doesn't this...
  10. T

    Many-Worlds with no other choice

    Are there certain events that must inevitably occur in all of the possible branches the wave function could split into? For example, if a black hole forms in our ''branch,'' what other possibility is there for that collapsing configuration of matter other than to turn into a black hole? Unless...
  11. B

    Can the "many-worlds" in QM inter-communicate?

    My layman understanding of the many-worlds interpretation of QM is that if a person had to make a decision between A and B and he chose A, then the universe splits into 2 branches, one where A was chosen and another where B was chosen. First of all, is this correct? Secondly, regarding the...
  12. G

    Basic questions about decoherence

    Hi, I've been reading some (very) basic texts on decoherence and have some questions about it: 1. What is the difference between decoherence and dephasing? 2. Assuming decoherence, can we completely do away with collapse theories (i.e. theories in which wavefunction collapse must be...
  13. T

    Many-Worlds, Inflation & Dark Energy

    Are there any predictions made by the Many-Worlds interpretation of QM that could be ascribed to inflation and or dark energy? In other words, could the hypothetical branching cause our universe to expand?
  14. stevendaryl

    The Born Rule in Many-Worlds

    I'm not 100% sure that this is the right forum to post this, but I think that the people who read the Quantum Physics forum might be interested: Sean Carroll has written a paper explaining how it is possible to derive the Born Rule in the Many Worlds Interpretation of Quantum Mechanics. I'm...
  15. atyy

    Many-worlds, Schroedinger, Heisenberg pictures

    I've usually heard the many-worlds interpretation described in the Schroedinger picture, in which the wave function evolves unitarily. Does a Heisenberg picture exist for many-worlds, or is the Schroedinger picture more fundamental in that interpretation?
  16. C

    Big Rip Cosmology and Many-Worlds Quantum Mechanics

    My question is based on two theoretical assumptions. 1) The universe continues with its expansion resulting in an eventual "Big Rip". 2)The many-worlds interpretation of quantum mechanics is correct. In this scenario will all the "branches of reality" in the many-worlds undergo the "Big Rip"...
  17. M

    Many-Worlds, Deriving the Born Rule?

    Lately I have been interested in the many-worlds interpretation, and in particular the way it is described by Wallace in his latest book The Emergent Multiverse. In the book he tries (or succeeds) to derive the Born rule from unitary dynamics by using game-theoretic arguments. But for this he...
  18. G

    Many-worlds: When does the universe split?

    Hi, I don't quite understand some central points of the many-world interpretation: When does the splitting happen, and is there superposition in a single universe? I see two alternatives: 1. There is superposition in a single, and this universe splits when we measure. This means we can...
  19. G

    Quantum Zeno effect rules out many-worlds?

    Hi, I've read somewhere that the Quantum Zeno effect, should it really exist, rules out the many-worlds interpretation. However I did not understand the argument (actually there was no argument, seems the author considered it obvious). Could someone please elaborate on this? BTW, what's...
  20. P

    Questions/Problems with Many-Worlds Theory.

    So I've been skimming about the Many-Worlds hypothesis and I just have a few questions as a curious student who is at the very beginning of learning physics. So pardon if my knowledge is limited compared to you guys: 1. It talks about wave function not collapsing. But how is this so if wave...
  21. tom.stoer

    Question regarding the Many-Worlds interpretation

    Let's prepare and experiment with individual photons moving along the z-axis and polarization in the xy-plane such that a detector registers - polarization along the x-axis with 90% and - polarization along the y-axis with 10% According to the MWI for each registered photon there's a...
  22. P

    The Many-Worlds Interpretation: how far does it go?

    The Schrodinger's cat thought experiment provides two possible outcomes in the many worlds interpretation; it is dead in one universe, and alive in the other. There are however many other possibilities of what could happen; there are wave functions concerning the positions which the cat may...
  23. C

    Question about the Many-Worlds Interpretation

    I get the basics of the interpretation, but I don't understand one specific element. If there are parallel worlds, where is this parallel world? Is it like a stack of newspapers, each page being a different world, where the entire, connected newspaper is the universe? What I'm asking is if this...
  24. Quotidian

    The Many-Worlds Interpretation of QM

    Greetings all. I'm a new poster here but have spent some time on philosophy forums previously. I subscribe to New Scientist and try and stay reasonably current with science, on the popular level at least. This week they have had a feature about physical cosmologies and 'theories of...
  25. F

    Interaction across many-worlds

    I was reading a description of the many-worlds interpretation and it stated that the separate universes cannot interact with each other. But in the double slit experiment isn't the interference pattern that is seen when both slits are open, specifically caused by this interference? How can...
  26. J

    Simplified Afshar experiment: many-worlds interpretation

    Hi, I would be interested in what people think of the following experiment. Imagine a laser beam is split into two coherent beams A and B that are made to cross each other at right-angles. Beyond the point of intersection let us assume that there is a detector A in the path of beam A and...
  27. M

    EPR & Many-Worlds: Understanding the Basics

    I am in the process of trying to understand, in basic terms, how the many-worlds interpretation (MWI) might explain the EPR experiment. In this context it is hoped that the scope for what appears to be almost unlimited speculation might be reduced. It seems that the original EPR experiment of...
  28. R

    Many-worlds true quantum event generator

    Hi, what cheap device is available where a quantum choice can be made.. for example.. particle that goes to left or right path or other similar? I'd like to experience what it is like to split myself between going to work or stay at home. According to Many World Interpretation, when I observe...
  29. Y

    Quantum Gravity & the Many-Worlds Interpretation

    I have read that MWI predicts that gravity is quantised. Is this prediction unique to MWI? If for example, someone discovered a quantum theory of gravity that was correct, that MWI would be declared the only valid interpretation of QM and that interpretations such the Copenhagen interpretation...
  30. nomadreid

    Is the Many-Worlds Interpretation Symmetrical?

    The Many-Worlds interpretation tells us where the information “goes” at a measurement. Does it also tell us where the information “comes from” afterward to create the new undetermined state? If it is symmetrical, then does that mean that a measurement is the result of confluence or interference...
  31. N

    Exploring Quantum Theory: Schrödinger's Cat & the Many-Worlds Interpretation

    Hi I was wondering if someone could better explain this. I do not quite understand the implications. Thanks for any input. "Unlike the Schrödinger's cat thought experiment which used poison gas and a radioactive decay trigger, this version involves a lethal weapon and a device that...
  32. F

    On the many-worlds interpretation

    I've read mostly non-mathematical accounts of this interpretation so forgive me if I'm not making any sense. I have the impression that a many worlds theory is an application of our laws of the universe, to the multiverse. To make a simple analogy, it would be conceivable (?) that in one...
  33. E

    Many-Worlds Theory: Existence of Multiple Universes

    I'm not a huge fan of many-worlds theory, but I do think that multiple Universes can exist. My only problem is that if there's an infinite number of Universes, why hasn't a Universe collided with our own yet? Are there other Universes somehow keeping that Universe from colliding with ours? And...
  34. A

    Many-Worlds of Hugh Everett - a Sci Am reference

    Just a Sci Am reference: http://www.relativitycalculator.com/articles/multiple_universes_hugh_everett/page_98.html
  35. R

    Superposition or Many-worlds interpretation?

    Just wondering what you guys think about the results of the double slit experiment...
  36. M

    Many-worlds interpretation: Worlds joining instead of splitting?

    If two branches of the tree eventually came to be identical would they join or would they continue to exist as separate worlds? If they joined, observers in each would remember a different history. Any connection between this and relativity where people observe the same event happening in...
  37. Q

    Many-Worlds Interpretation Issue

    OK, I have a problem with the many-world interpretation, namely the quantum suicide experiment. My problem: How exactly does your consciousness transfer over? When you die in your current "reality," do you just swap randomly to one of the parallel worlds? Or are each of the conscious entities...