What is Many worlds: Definition and 133 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. durant35

    I Many worlds and cosmological evolution

    Hello guys, I have a question that came up to my mind while thinking about the evolution of our universe and quantum mechanics. It involves cosmology so maybe that was the right spot to post it, and of course the moderators can do it if they feel it's more adequate for the thread, but my...
  2. N

    Many Worlds Interpretations and probabilities

    This probably has been asked before but I didn't find it. As I understand it with the Many Worlds Interpretation of quantum mechanics, a different "world" exists for each outcome. I have read about the an issue regarding probability outcomes within a world but cannot remember the answer. The...
  3. 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...
  4. durant35

    I Born rule for macroscopic objects

    There is one thing that I don't understand when considering quantum mechanics for macroscopic bodies. It is said that classical mechanics is a valid approximation and that macroscopic bodies that we encounter on everyday basis have a small uncertainty in position and momentum. So far, so good...
  5. 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?
  6. 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...
  7. 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?
  8. D

    A Sean Carroll's Talk about Everett Many Worlds

    What do you think of Sean Carroll's talk about the Everett Many Worlds Principle?
  9. Quotidian

    B LHC findings -- 'Naturalness' and Many Worlds

    In December 2015, scientists at the Large Hadron Collider (LHC) thought they may have seen a hint of a brand-new particle. This appeared by way of a couple of 'bumps' in the data, which triggered such an avalanche of interest that 500 papers followed. But, alas, subsequent research has shown...
  10. durant35

    I How does the concept of determinism apply to the branching of many worlds?

    I am having a hard time understanding the evolution of many worlds in the context of determinism. If each branch evolves deterministically what can be said about a branch that splits into two branches? I will try to give an example so the question can be understood better. For instance if my...
  11. 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...
  12. 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...
  13. 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...
  14. D

    Exploring the Possibilities of Parallel Universes: Seeking Help

    Hi, I will not claim extensive knowledge of physics which is exactly why i need honest help from you all.. Writing a story based on the idea that with every single decision being made that a new time line is created.. I want it to be logical and possible even if its only theoretically...
  15. entropy1

    Do CI and MWI Interpret Quantum Probabilities Differently?

    Suppose we fire a photon P at a polarisation filter F1, and it passes the filter, thus forcing the polarisation of P in an eigenstate M1. Subsequently, the photon falls through a polarisation filter F2, forcing P in eigenstate M2. Now, if I understand correctly, the probability of P passing F2...
  16. 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...
  17. Cynthesis

    Many Worlds - What drives the parallel branching?

    There is one segment of this interpretation that has always nagged at my mind. It's the part where a separate branch splits off at each individual choice. For a simple example; I have a choice to turn left or right, I choose to turn right, so now according to this interpretation another version...
  18. Erik Ayer

    How does the Many-Worlds Interpretation handle the measurement problem?

    How does many worlds reconcile with entanglement? Is it just that in one world the particles were up/down, and in another world they were down/up?
  19. 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...
  20. Hybrid

    I Many Worlds - Superdeterministic?

    Forgive me if this question has been asked previously on this board, but I cannot seem to find anything similar having searched around earlier. I suppose this blog entry written by the Physicist Robert Oerter linked below has accurately reflected how I feel about Many Worlds: "But now you see...
  21. N

    What is a universal wavefunction in MWI?

    I'm alittle confused, is it saying that all the fundamental particles in the universe are really just one wave function?
  22. bhobba

    Many Worlds and Quantum Field Theory

    I have been meaning to ask this one for a while - but never seem to get around to it. In MW its sometimes said it's simply the working out of the universal wave-function via Schroedinger's Equation. Of course Schroedinger's Equation is only valid non-relativistically. Wallace doesn't really...
  23. 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...
  24. B

    How would MWI explain delayed choice quantum eraser?

    How would MWI explain the delayed choice quantum eraser? http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser#The_experiment_of_Kim_et_al._.282000.29 I don't see how this can be explained with MWI. If the idler photon hits detector 1 or 2, an interference pattern can be seen on the...
  25. Q

    New Many Worlds objections, right/wrong ?

    I came across these objections in a paper about the status of Interpretations: Why Current Interpretations of Quantum Mechanics are Deficient arxiv.org/abs/1408.2093 In it the author raises 2 objections that he calls: The Observer energy problem and Initial entropy problem. This is way past my...
  26. DrClaude

    Exploring Quantum Phenomena: Many Interacting Worlds Approach

    What do you guys think about this? Quantum Phenomena Modeled by Interactions between Many Classical Worlds Michael J. W. Hall, Dirk-André Deckert, and Howard M. Wiseman Phys. Rev X 4, 041013 (2014) We investigate whether quantum theory can be understood as the continuum limit of a mechanical...
  27. Demystifier

    Many Worlds proved inconsistent?

    In a paper entitled "Nothing happens in the Universe of the Everett Interpretation": http://arxiv.org/abs/1210.8447 Jan-Markus Schwindt has presented an impressive argument against the many-world interpretation of quantum mechanics. The argument he presents is not new, but, in my opinion...
  28. nomadreid

    How do Feynman's many paths and Many-worlds interpretation differ?

    I get a bit confused seeing where Feynman's many paths fits into the Many-worlds interpretation. Both start off with the fact that there are many possible paths for a particle to take. Then, crudely paraphrasing Feynman's schema, each path will be given a probability amplitude according to the...
  29. craigi

    Many Worlds, Indistinguishability, Pascal's Triangle and the Gaussian

    Suppose we have a quantity which can take discrete equally spaced values. Iteratively, we can increase or decrease this quantity by one quantum, splitting into two new worlds each time. After multiple iterations we have some indistinguishable worlds, as described by Pascal's triangle. As the...
  30. tom.stoer

    Many Worlds and conservation of energy

    I would like to re-start the discussion regarding conservation of energy in the many worlds interpretation. Kith did not agree with my example, so hopefully it becomes clearer now where I see problems regarding the interpretation. Let's prepare a particle in a state like ##|\psi\rangle =...
  31. S

    How does the double slit experiment prove many worlds?

    Hi, I`ve been reading and watching videos about the double slit experiement, and when scientist fire one electron at a time through the double slits, and the do not interfere, how does that prove that there are more dimensions and that sub atomic particles are in a superstate. How does that...
  32. J

    Experiment to test if many worlds is the correct interpretation

    hi there. I studied physics for years, even went as far as getting a PhD. but that was 13 years ago, since then rusty. Anyway something occurred to me and I wondered what you all would think about it. My question is, can anyone think of an experiment you could do to check if the "many...
  33. S

    A problem with probabilites in many worlds

    In many worlds, all the results with probability>0 happens. But the predictive power of a theory is based in that events with very low probabilities no matter ( the possible ocurrence is `[but a constant]) around the averaged valued by the exponential of shannon entropy, that in the case of...
  34. I

    Proof of Many Worlds: Decoherence and Hidden Variables Explained

    http://www.ipod.org.uk/reality/reality_nist.asp they have proof that a macroscopic object can exist in two distinct locations at once and decoherence just hides the many worlds? They even separate the states by pushing them apart. This must mean they were seperate? If we ignore...
  35. I

    Does superpostion imply many worlds?

    The fact that objects exist in superpostion which means they exist in multiple postions(proven fact), doesn't this automatically imply many worlds? ignoring collapse interpretations, can there be any single world interpretations of quantum superpostion?
  36. K

    Many Worlds + Anthropic Principle

    This might be interpreted by some to border on the fringes on pseudo-science, but I feel logic dictates that conclusion must be one of many possibilities according to the theories. Has anyone ever considered that the many worlds interpretation combined with the anthropic principle has some...
  37. S.Daedalus

    How Many Worlds are in a Universe?

    So, this is a simple question that's been bugging me for a while. Let's consider a particularly simple universe (and its wavefunction): a single qubit. This might be in a superposed state, wrt the computational basis (\lbrace |0\rangle, |1\rangle\rbrace), such as |\psi\rangle =...
  38. 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...
  39. 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...
  40. T

    Is there a difference between Many Worlds Interpretation and Relational QM?

    Whats the difference between Many Worlds Interpretation and Relational QM. Here is what I understand in few words: MWI: The whole universe system evolves with Schrodinger Equation without Quantum Collapse, but when a subsystem interacts with other subsystem, it seems like Quantum Collapse...
  41. A

    Engage in Many-Worlds Quantum Theory Debate

    Hello, I am new to this forum. This is an excellent, informative forum; therefore, I felt compelled to join. I would be interested to engage in dialogue with individuals who support the Many-Worlds interpretation of Quantum Theory. Personally, I despise this interpretation as I believe it is...
  42. A

    Many Worlds based on the observer effect

    Hi, I understand that some people believe in the many worlds interpretation because of the probabilistic nature of quantum mechanics but couldn't another many worlds exist under the observer effect. I'll give a thought experiment using the double slit. When bob measures the measures electrons...
  43. G

    Infinities and the Many Worlds theory

    Can anyone help me understand a feature of the Many Worlds interpretation of quantum theory, please? Many people (on this forum and elsewhere) say that the Many World's theory implies infinity parallel universes. I can understand why people think so. For example: Suppose a photon is sent...
  44. J

    I Science Lay Person Question about Many Worlds Theory

    The logical objection that the 'science layperson' has (in my opinion) to the many worlds theory of quantum mechanics is the 'artificial' solution the construction of a new universe based on two possible options appears to present. The example of flipping a coin, and in one universe a heads...
  45. M

    Many Worlds interpretations and Groundhog Day

    I'm hoping that this is considered on topic, as (for me) it might help me to understand some of the implications of the Many Worlds interpretation of quantum mechanics. And, an interesting movie. Probably some of you remember "Groundhog Day" (1993) staring Bill Murray as Phil Connors. He...
  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. K

    Many worlds in a single infinite universe

    First of all I want to apologize for any incorrect/non-physical terminology. Theoretical physics is not my field (which is neuroscience) and I only have some very basic knowledge in the mathematics of modern physics. Recently I read a couple of popular physics books by Brain Greene and Leonard...
  49. 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...
  50. R

    QM interpretation like Many Worlds but with 'real' particles?

    Hello Forum, I've been reading about MWI, the Bohm interpretation, and Feynman QED. Combining elements from these interpretations, I've been building up my own simple mental model of 'how to picture the state of affairs', and I've been speculating about the feasibility of interpretations...
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