What is Many worlds interpretation: Definition and 57 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.

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  1. bushmonk

    I How many worlds is Many Worlds talking about?

    For clarity, consider a very orderly crystal with a single radioactive atom at a specific location. It decays by alpha emission. When the alpha particle is emitted, it disrupts the location of nearby atoms and then comes to rest and forms a stray helium atom. It would seem that there is a...
  2. P

    B Need help with understanding time travel

    Ridiculous! I know. But as a 9th grader, there are a few things that have been bugging me. I had a conceptualisation of how 'time travel' could work. However, it's based on the presumption ( a very large one at that) that the many-worlds interpretation of quantum mechanics is correct...
  3. S

    I Many worlds interpretation with unequal probabilities

    Let's pay a visit to one of Schrodinger's cats. In the classical statement of the case, we have to decide if the cat is alive or dead when the probability of the radio-active decay mechanism has a 50/50 chance of releasing the cyanide, most often posed as 60 minutes. If I understand the MW...
  4. S

    Nima Arkani-Hamed's opinion on Many Worlds?

    I was wondering what was the opinion of the physicist Nima Arkani-Hamed towards the Many Worlds interpretation. Is he open to the possibility of it being true? Does he support it?
  5. S

    I Many Worlds as Many Histories?

    I was reading this paper from George Smoot (https://arxiv.org/abs/1003.5952) where he assumes the holographic principle as true and conjectures that our universe would be encoded on the "surface" of an apparent horizon as the weighted average of all possible histories. In that way, there would...
  6. Bob Walance

    I Many Worlds, EPR and ER=EPR

    This question is not intended to invoke arguments about whether Hugh Everett's theory, now referred to as the Many Worlds Interpretation of Quantum Mechanics, is feasible or not. When I heard David Wallace say that Many Worlds does away with the so-called 'spooky action at a distance' referred...
  7. M

    I David Deutsch's Many Worlds Interpretation and the Double Slit Experiment

    David Deutsch is a well known proponent of the Many Worlds Interpretation. His argument seems to be that a single photon in the double slit experiment must be interfering with one from another world. It is commonly held by physicists that the the photon, as a wave going through double slits, can...
  8. EclogiteFacies

    A Does Everettian QM imply solipsism according to Travis Norsen and Sean Carroll?

    Travis Norsen in his paper Quantum Solipsism and Non-Locality seems to believe that Everettian QM implies some sort of solipsism. He falls it FAPP (for all present purposes) solipsism. (I must say that as a geologist this goes over my head a bit!) However I have recently read Sean Carrolls...
  9. 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...
  10. G

    I How to envision particles in superposition in Many Worlds presplitting

    Should particles in superposition before quantum decoherence (many worlds) be envisioned in the same exact way as they are envisioned before wave function collapse (Copenhagen)? Clearly, the particle in Many Worlds is in a sort of superposition, but with all of the talk about one universal wave...
  11. Lunct

    How can the many worlds interpretation be deterministic?

    So the many worlds interpretation describes every quantum events as a branch point, where in which all events happen. I'll use the example of a coin toss to illustrate my question. If I flip a coin, I create a branch point in my universe from which two universes emerge, where both heads and...
  12. A. Neumaier

    A Many Worlds versus Thermal interpretation

    The two volume treatise Bryce DeWitt, The global approach to quantum field theory, Oxford Univ. Press 2003. which discusses the canonical approach to dynamical quantum gravity, is probably responsible for the fact that the many worlds interpretation (MWI) of quantum mechanics has a sizable...
  13. M

    I Schrodinger’s cat and the Many Worlds interpretation

    Schrodinger’s Cat and the many worlds interpretation states that the wave function collapse doesn’t happen at all; every possible outcome of an observation actually comes to pass in its own separate universe. We are presented with a binary (discrete) outcome (dead or alive) but what if there...
  14. S

    A What is von Neumann's branching of possible worlds?

    In the Many Worlds Interpretation's wikipedia article (https://en.wikipedia.org/wiki/Many-worlds_interpretation), it says, at the "Reception" part: "(...) On the other hand, the same derogatory qualification "many words" is often applied to MWI by its critics, who see it as a word game which...
  15. Quantum Alchemy

    I A question about Many Worlds and my Remote Control

    I get so many different answers to this question so maybe here someone can pin this down. When I get up in the morning and I turn on my TV, I have over 3,000 channels so is there a universe with a version of me going to each channel? If not, how do I go to one channel over the other? Can my...
  16. pinball1970

    I Sean Carroll podcast on many worlds interpretation

    Interpretation of quantum mechanics is something that is discussed at length on pf so it would be interesting to get views of the quantum guys on this short (30 mins) podcast. Thanks...
  17. S

    A Does Feynman's path integral ignore alternative histories?

    Summary: Does Richard Feynman's multiple histories ignore alternative histories? Did Richard Feynman's multiple histories (https://en.wikipedia.org/wiki/Multiple_histories) ignore the existence of other alternarive histories or paths? I ask this referring to this comment from this page...
  18. S

    Could MWI create universes with fundamentally different physical laws?

    Summary: Could MWI (Many Worlds Interpretation) create universes with fundamentally different physical laws? Physicist John Wheeler proposed along with Hugh Everett and Bryce DeWitt the 'Many Worlds' Interpretation of Quantum Mechanics (although he expressed some doubts about its validity) I...
  19. J

    I David Deutsch (1985) attempt to solve the incoherence problem

    Can anyone elaborate on Deutsch's attempt to solve the incoherence problem? He postulates a continuously infinite set of universes, together with a preferred measure on that set. And so when a measurement occurs, the proportion of universes in the original branch that end up on a given branch...
  20. 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...
  21. P

    Stargazing What is the best Dobsonian telescope with a goto feature?

    My interests include; Large telescopes & Astrophotography Sub-atomic particles The Copenhagen Interpretation Black Holes Bubble universes and the Multiverse Many Worlds Theory The Holographic Proposal Quantum entanglement Causality, determinism and free will
  22. J

    I Can the Many Worlds interpretation state the Born Rule as a postulate?

    Every derivation from the MWI of the born rule is circular. http://fmoldove.blogspot.com/search?q=MWI So my question is, can the MWI state the born rule as a postulate (without deriving) and still be a coherent interpretation of probability? The most famous argument against this notion is by...
  23. J

    I Is this derivation of the Born rule circular in any way?

    https://arxiv.org/abs/1411.6992 They derive the born rule from the MWI. Is this circular?
  24. B

    I Quantum eraser in Bohmian Mechanics and many worlds theory

    All the literature on the quantum eraser that I've seen is grounded in the Copenhagen interpretation of quantum mechanics. It's very easy to understand the experiment in those terms. Do you know how quantum eraser experiments are interpreted by the de Broglie–Bohm theory? What is erased in this...
  25. J

    A Does the Frauchiger-Renner Theorem prove only MWI is correct

    Hello all, I have only seen this paper brought up here once before based on the search function 2 years ago, and the thread devolved into something off topic within the first page. I am asking in reference to this paper: https://arxiv.org/pdf/1604.07422.pdf Which claims to show that single...
  26. N

    I Many Worlds Interpretation existence

    I have a few questions about the Many Worlds Interpretation. I read the article https://plato.stanford.edu/entries/qm-manyworlds/ but was having trouble understanding what the "measure of existence" is supposed to represent in the theory, and why a believer in the idea should adhere to either...
  27. S

    How can Many Worlds be reconciled with unequal probabilities

    If I understand the many worlds QM interpretation correctly, for every quantum event the universe divides. However not all quantum events have a 50/50 probability. How does the many worlds interpretation deal with quantum events that have,say a 1/3 2/3 probability split?
  28. J

    I MWI proven wrong by penning trap experiments?

    Just a reminder to you all, I am just a layman... These experiments were both done is what is called a penning trap. I think this only proves the version of MWI where the universe doesn't actually split. The "bare" theory, where no new matter is created. According to MWI an electrons...
  29. 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...
  30. durant35

    I Many Worlds vs Classical Mechanics

    I have a question regarding the ontology of the many-worlds interpretation which by my assumption shows some deficiencies in this way of thinking. When many worlders describe branching and effects giving rise to multiple worlds they typically invoke Schrodinger cat-type experiments where from a...
  31. N

    I How does MWI deal with the destruction of interference?

    How does MWI deal with the destruction of interference in the double slit experiment when a detector is placed at the slits? Since the wave function never collapses, and the universe doesn't actually split in MWI, how does the interference go away? Does the measuring device at the slits reshape...
  32. N

    Doesn't MWI violate Lorentz Invariance?

    Doesn't the Many Worlds Interpretation violate Lorentz symmetry when the universe splits?
  33. N

    I Problem of quantum tunneling and Many Worlds interpretation?

    On wikipedia it says that MWI doesn't explain quantum tunneling well. "A tunnelling particle would have more energy than what is actually measured in experiments." What do you guys think?
  34. N

    A Many worlds interpretation incompatible with quantum gravity

    On wikipedia, I found one of the objections to MWI. "We cannot be sure that the universe is a quantum multiverse until we have a theory of everything and, in particular, a successful theory of quantum gravity.[73] If the final theory of everything is non-linear with respect to wavefunctions then...
  35. I

    Is anything possible in the many worlds interpretation?

    In the many worlds interpretation of Qm, is there one universe in which I am a horrible murderer, for example?
  36. C

    A Refutation of physics in _The Beginning of Infinity_?

    Does anyone know of a written refutation of the quantum physics David Deutsch presents in his book _The Beginning of Infinity_? PS I have no intention of summarizing the material. If you aren't familiar with it, I don't want you to try to argue with a summary.
  37. J

    I Questions on exact details of the many worlds interpretation

    I have hard time thinking the many worlds interpretation is correct. I also find its description imprecise. Here are some questions I would like someone to answer about the interpretation. 1. When a wave form photon hits a screen and become a particle form photon, this event splits the world...
  38. J

    The Higgs Mass and the Many worlds interpretation

    I have a question about the Many worlds interpretation. Does the observed mass of the Higgs boson suggest that the many worlds interpretation is incorrect, as the mass falls smack in the middle of the predicted values of both supersymmetry and multiverse interpretations of the standard model of...
  39. phillovix

    I Many Worlds Interpretation and Coffee

    Hey there. Based on the many worlds interpretation, is: Everyone simultaneously having coffee with everyone else? Has everyone already had coffee with everyone else? Are these possibilities occurring 'somewhere' continuously? Do these possibilities only occur one at a time, or does the...
  40. J

    Understanding the many worlds interpretation

    I have a question regarding the quantum event when a wave live photon transforms into a particle like photon. In the many worlds interpretation there is a split into multiple worlds. My question is this: Do all the multiple worlds supposed to see the photon transform into a particle like photon...
  41. Adam LeTrexane

    A Addresses of Parallel Universes

    Hi there! Alright, so let me start off by saying I'm a biochemist by trade, but have an extreme (and possibly unhealthy) interest in the more bizarre aspects of modern physics. Admittedly, I don't understand the mathematical formalisms associated with the theories I know of, so bear with me if...
  42. R

    Measurement problem and many worlds

    Hello, sorry if I created new thread that is already open, but I did not find answer. I would like to ask you about measurement problem (double slit experiment) and many worlds. When interference pattern is created, the dot on screen just show us in which branch or world we are. But if we...
  43. Rodrigo Cesar

    Many Worlds Interpretation and act of measuring

    "We can’t make a measurement without influencing what we measure. before we look, there are only probabilities. When we open the box, they give way to a single actuality" It would be more like this, all the time, Until we look...
  44. T

    Exploring the Many Worlds Interpretation of Quantum Theory

    I have a question regarding the Many Worlds Interpretation(MWI) of quantum theory. Is there any proposed thought experiment that can/does provide some kind of solid/good proof for the MWI? I have an idea, an experiment and I am very curious about it's validity/soundness and the...
  45. C

    Many worlds interpretation, probability distribution

    Where exactly do the probability distributions we observe come from under the many worlds interpretation? I know it has something to do with being the only stable configurations in Hilbert space but I don't understand why. This is my attempt to explain it in my own way, please tell me if it...
  46. T

    Problems with Many Worlds Interpretation

    Hello, While the majority of physicists embrace the Many Worlds interpretation of quantum decoherence, I am holding out hope for the Copenhagen interpretation or better yet, a undiscovered interpretation. Please allow me to pose three problems I have with the MW interpretation. 1) There...
  47. C

    Which book explores Many-worlds interpretation and Hugh Everett's ideas?

    What is a good book that I could read about Many-worlds interpretation and what Hugh Everett was thinking.
  48. B

    How is the many worlds interpretation of QM related to the multiverse theory?

    To my understanding you can believe in the multiverse theory without subscribing to many-worlds interpretation of quantum mechanics. But can you subscribe to the many-worlds interpretation while also believing there is only this one universe (and that it just has hidden dimensions). Can...
  49. I

    Possible argument in favor of many worlds interpretation

    Please forgive me if I am hideously wrong in any of my points. I am not terribly well-versed in quantum physics. Alright. This all began when I was thinking of a somewhat speculative and arguably philosophical idea that probably wouldn't have much of a place on this forum. My train of...
  50. rrw4rusty

    Questions on Many Worlds Interpretation

    Hi! I've seen videos depicting the ‘Many Worlds Interpretation’ of quantum physics which show T-Rex stomping through your living room because the K2 Event didn’t take place in that parallel universe, you know the hype you see on the MWI. While probably, no one ‘really’ thinks this is...