Many World Interpretations – MWI

Is it useful for science? or for people?

This page (by Craig Rusbult, PhD) explains why I think a Many Worlds Interpretation — proposing that our Universe is constantly “splitting into alternate histories” to produce Many Worlds with a zillion versions of you, each making different decisions, doing everything possible — isn't useful for science, and isn't beneficial for people.  But... in making this claim, there are reasons to be appropriately humble.   /   iou:  I began making the page in March 2023, and eventually (maybe late 2024?) it will become more fully developed.  /   more:  For a wider context, Multiverse Science & Theology and Interpretations of Quantum Physics.

My intuitions-about-reality (similar to those of most people) are that the reality of our universe isn't the Many Worlds of MWI.  Although I enjoy the creatively imaginative speculations about time travel & alternative realities when they're in drama fiction — in fact, my favorite movie is "It's a Wonderful Life" and my short list includes "Groundhog Day" — these movie fictions are imaginary science fiction, rather than claims for science reality, such as those made by MWI.  Unfortunately an MWI-view-of-reality can be psychologically reified – made to “seem real” in our thinking-and-feeling worldviews – due to the societal prestige of science, when MWI is declared to be “an accepted view of scientists” even though non-MWI also is an accepted view.  Also, Many Worlds has a fascinating appeal (similar to the movies I enjoy) that leads to some people wanting to believe it's how reality is.

MWI is uniquely strange:  Another page explains how, by acknowledging the rational perspective of Here-and-Now, we can understand that if we live in a Universe within an immense Cosmological Multiverse, everything would appear normal and would be normal.  But...

There would be major differences between an MWI “Multiverse” and a regular (non-MWI) Cosmological Multiverse, IF either exists in reality.  They would differ in many ways, including (especially important) personal identity, because only MWI claims a sharing of exact-histories that occur in the same here-and-now body.  How?  After an MWI branching the near-duplicate-of-me (in the other future immediately after branching) was (in the instant before branching) an exact-duplicate-of-me, with a totally shared history of everything that ever happened to me/us while we shared the same body, thinking-and-feeling exactly the same things, being exactly the same person.  Even IF there are near-duplicates in a Cosmological Multiverse* — if it exists, and if the universe-types are exactly matched in all ways, and if the immensity is close enough to infinity — the kind of intimate total-sharing-of-history in MWI (between exact-duplicates) would never occur, and any near-duplicating would never have the “personal identity” connections of MWI in which immensely numerous versions-of-me (in our futures) previously were (in our pasts) exactly-me, because there would never be any here-and-now sharing of experiences.

* This "IF" requires an if-if-if, and I would bet against all of these happening, due to the extreme improbability.  One reason is that if we live in a multiverse, it's only immensely-large, not infinitely-large.  But the impossibility of physical infinity isn't an obstacle with MWI, because even with a finite number of me/us at any point in our shared history, in each future instant EVERYTHING that is possible will happen in some history-branch;  therefore even though infinite size isn't possible, it isn't necessary, because I nevertheless will make every possible decision and do every possible action, in each instant.  Because it's personal this is very strange, is much stranger than the speculative events that would be impersonal — because they would happen independently in separate here-and-now realities, so there are no bodily-shared experiences & memories — when we creatively imagine strange things with near-duplicates in a Cosmological Multiverse, where all of our experiences would appear normal and would be normal.  With MWI, all experiences would appear normal, but the total reality actually would be un-normal, by violating our normal perceptions of what is happening in reality.

Probably this personal strangeness is part of MWI's appeal for some people, who use it to rationalize their behavior, to reduce personal responsibility by thinking “well, I'm behaving badly in this history-branch but I can't avoid it, and I'm behaving better in other branches.”   /    a question to consider:  What are the associations between MWI and postmodernism? and atheism?  I don't know for sure, but think there might be strong influences because MWI can be used to question the importance of rationality (for postmodernism) and (for atheism) to rationalize behavior by decreasing personal responsibility.  This would be appealing for postmodernists and atheists, providing a motive to prefer MWI – to propose it and defend it – even though the empirical support for non-MWI is equally strong.

Due to the consistent empirical success of Quantum Physics (using the Schrodinger Wave-Equation to calculate the Quantum Mechanics of the many kinds of wave-particles that together form nature), I'm very confident that Quantum Physics is an excellent theory;  it's the best we have, for what it does;  it seems to be a correct description (although it's incomplete) of what's happening in nature.  I'm questioning only the Many Worlds Interpretation of Quantum Physics.  Instead I think a Modern Copenhagen Interpretation of Quantum Physics — modernized because it's updated so it views decoherence (not consciousness, as in some interpretations of Copenhagen Interpretation) as an essential part of trying to understand the WHY-HOW-WHAT of “wave-function collapse” when Quantum Physics becomes the Classical Physics we commonly observe in everyday life, to satisfy one aspect of an equivalence principle between quantum & classical — is a better description of reality, compared with MWI.   /   note: Currently I'm putting “wave-function collapse” or “collapse” in “...” quotations as a reminder that this isn't a physical collapse (ontological collapse), but instead is a non-physical change that we call a “collapse” of the wave-function, in an uncertainty-of-knowledge collapse (epistemological collapse) when uncertainty becomes certainty, when what-we-know abruptly changes (to match an abrupt physical change) when a quantum system converts from potentiality (with many possible results that might happen) to actuality (of a specific result that did happen).

different perspectives:  It's important to recognize the difference between perspectives of scientists in different areas.  The area of science that is my favorite (and is where I'm most expert) is chemistry, especially its logical explanations of “how things behave” at levels involving many interactions between many atoms.  In chemistry the common level (multiple particles) differs from a common level (single particles) in quantum physics.  In this way, chemistry is closer to the multi-particle levels of biology or cosmology.

philosophically productive experiments:  When our goal is to develop accurate theories about what's happening in nature, now and in the past, it's useful to observe nature “in the wild” with field-study experiments like those of cosmologists (to study the universe) and biologists (to study living organisms).

philosophically confusing descriptions of experiments:  By contrast, physicists usually do lab experiments using equipment (e.g. wave-particle generators & detectors, slits or filters, etc) that produces measurements (noun);  often this process is described as “measuring” (verb) that is done by a conscious “observer” (noun), even though the “measuring” actually is done by a lifeless detector with no consciousness.  When describing quantum-level events, scientists & non-scientists typically say “there was no definite result until the result was measured (or was observed)” – implying the significant actions of an observing person who did the measuring (or observing) – instead of just saying “there was no definite result until the physical interaction that produced physical decoherence, thus actualizing the definite result,” which basically means “there was no definite result until the result happened.”  When we're thinking about wave-particles, a common custom (by scientists & non-scientists) is refusing to acknowledge the central role of physical interactions (instead of human consciousness) when there is a transition from potential-results into an actual-result.  This error is the cause of much confusion in philosophy of physics.     {note: Some quantum events – e.g. radioactive decay of a nucleus, or transition-between-states in an electron within an atom – don't involve a physical interaction, and [iou] I'll try to learn more about these, re: how they occur;  but for these events, and others, consciousness doesn't play an ontologically-causal role in the change from potential to actual.}

In the history of nature humans are mostly irrelevant,

so in quantum physics we should be mostly irrelevant.

In the overall history of nature, the actions of humans have minimal relevance.  One of my sections about the role of "observation" in quantum interactions calls attention to a historical fact that – for everyone except solipsists who believe “nothing exists except me” – should be accepted as being obviously true:

Almost all events in the history of nature (99.99999...%) have not been observed by humans, because we are limited by a Here-and-Now Principle. [i.e. we can produce effects only Here-in-location and Now-in-time.]   If nothing “really” happens until a human observes it, how did nature operate – with nuclear reactions in stars, biochemistry in organisms, and more – during the 14 billion years before we began making quantum observations?  And even now, almost all quantum processes – occurring in distant galaxies, on earth, and in our own bodies – are unobserved.

In the overall grand story of nature, we are not very important.  This fact should be seriously considered (but often isn't) when we're interpreting quantum physics, because any General Theory about Reality should be consistent with the fact of our general irrelevance.  When we consider this fact, it's one aspect of an equivalence principle stating that quantum physics (for things that are small or large) should correspond to our observations (of things that are large, and to our knowledge of history that includes history before human observers existed) in classical physics, and in cosmology & biology.  {it's analogous to another equivalence principle stating that relativistic physics should correspond to classical physics, at slow speeds.}   i.e. Our theories of quantum physics should correspond to our observations that almost all phenomena during the past 14 billion years, and at the present time, occur without any interaction with humans.  In the overall history of nature, past & present, we're extremely non-important.  Despite this, I'm frequently disappointed when quantum physics is described with bad words – i.e. words that often are misunderstood, that many users-of-words know will be misunderstood – of “observers” who “make measurements,” because this leads to distorted misunderstandings, as outlined near the beginning of my page about Schrodinger's Cat and Quantum Mysticism:

Much confusion occurs because “oops, they used a bad word” in the early history of quantum physics.  How?  The confusion is caused by common misunderstandings of what observation means in quantum physics.  Let's look at what this word does and doesn't mean, in common language and in quantum physics. .....  {this paragraph then continues with explanations of the does-and-doesn't}

Due to this unfortunate habit when describing a Copenhagen Interpretation — by over-emphasizing our epistemology (re: what we can know) in ways that affect our ontology (re: what exists & what is happening) — our beliefs about “what is happening in the world, and why” can become distorted, as in the Mystical Physics claimed by proponents of New Age Worldviews.  {what Mystical Physics is and why it's not supported by Quantum Physics}   These distortions produce...

effects that are direct and indirect:  Claims for “consciousness creating reality” can be connected with Copenhagen, can be used to construct a distorted “Copenhagen Strawman” that's a weak Copenhagen-with-consciousness, instead of a strong Copenhagen-with-decoherence.  Then this weak strawman can be argued-against by some proponents of MWI, who explain how MWI avoids these distortions.  In this way, even though a criterion of equivalence with history is not directly relevant for MWI (which works equally well for all kinds of history), it's indirectly relevant for MWI because it's directly relevant for perceptions of Copenhagen (due to its associations with “consciousness claims” that do occur even though they're scientifically unwarranted, that allow the construction of weak strawmen) so it's directly relevant for comparative evaluations of Copenhagen-vs-MWI.

MWI – a Many Worlds Interpretation of Quantum Mechanics – proposes that our world is constantly “splitting” into Many Branches-of-History that are Many Worlds.

But are these Real Physical Worlds, or is MWI just the Real Conceptual Worlds of mathematical imagining?  When physicists discuss MWI they typically use a lot of mathematical jargon, making it difficult to understand “what MWI claims that a branch-of-MWI really IS” so it's refreshing to get a simple answer, like that of PeroK in this thread:  "In MWI there is only ever one universe, eternally evolving unitarily. All your measurements and worlds and branches are just part of this. Your mistake, perhaps, is to imagine separating them [the history-branches of MWI] all out into physically different systems. They are only really logically separate."  So is MWI just a mathematical fantasy?  Maybe its overall effect is (like a postmodern prank, a metaphysical practical joke) implying “everything you think-and-feel is wrong” or something similar?   /   An example of mathematical jargon is later in the thread (in which nobody told PeroK “you're wrong”) when PeterDonis said "Strictly speaking, this [conservation of energy with MWI] is only true if the universal wave function is an eigenstate of the universal Hamiltonian. Otherwise there is no well-defined notion of ‘total energy’ at all, so there's no ‘energy’ that can be conserved."  OK.  But in our everyday thinking about reality, most people (including scientists) want to know “where does the immense amount of mass-energy come from, to form the Many Worlds of MWI?”  But if the Many Worlds do not physically exist in reality – instead they're only "logically separate" worlds in mathematical imaginings, or in the abstract non-physical Hilbert Space of Quantum Math – do the Many Worlds have any claim-to-reality that we should seriously consider?   /   More detail is in Stanford Encyclopedia of Philosophy, explaining MWI proposals for "What is A World?" and "Who am I?"

conservation of energy:  I think mainstream proponents of MWI propose a “thinning of energy” with the total energy being fractionalized when splitting occurs, in a probabilistic way, e.g. if a result is 80% probable it will occur in a new branch that gets 80% of the currently-available total energy of the old branch.  Due to the immense number of branches, if each branch has only a tiny fraction of the original energy (in the mass-etc at the instant of Big Banging), how is this consistent with our observations of mass-etc that is normal (is not tiny) in galaxies & humans & everything else?  I've heard this described as energy-within-a-branch (as defined by a limited observer in that branch) versus total-energy-of-the-universe (as it would be defined by an unlimited super-observer of all branches).  I don't know how this distinction (within-energy vs total-energy) is viewed by physics experts who are critics of MWI, whether they think it's a satisfactory explanation.  AFAIK there are no objections by experts.  And I don't know how this view of energy(s) “fits” with the statement by PeroK that the Many Worlds are logically-separate instead of physically-separate.   ??

a scientifically productive experiment:  If we want to learn essential concepts-about-reality from a lab experiment, one of the most useful is the basic double-slit experiment that's described below.  It's very useful due to its simplicity, showing us that physical interaction (not human consciousness) causes each individual wave-particle to make an abrupt transition from an entity with potential characteristics (described by its wave-function) into an entity with actual characteristics, when there is a “collapse” of its wave-function.  However, instead of emphasizing the obvious fact of WHAT (i.e. something physically-significant happens due to the abrupt transition), typically there is philosophical agonizing over the WHY-and-HOW (and even WHO, somewhat strangely) of the transition.  This discomfort — because physicists don't fully understand the WHY-HOW of “collapse” and maybe are bothered by claims for “consciousness creating reality” by a few scientists and many non-scientists — seems to be a central motive for scientists who accept the Many Worlds Interpretation, MWI.*  But if we simply acknowledge that human consciousness is not part of the WHY-HOW it would be easier to just accept the WHAT (of “wave-function collapse”) as a foundation for understanding what has been happening in nature for 14 billion years, without any human consciousness.

explaining it away:  MWI copes with this by saying “the abrupt change is just an illusion, because in this history-branch you/we are experiencing this particular result (instead of another result), but there is nothing unique about this history-branch, and other versions of you (in other history-branches) experienced other results.”  And they pose a challenge: “unless you can prove MWI is wrong, we can claim it's correct.”

* A stronger motive for MWI is related.  It's wanting a theory that is more-complete, that (unlike a Quantum Theory plus Copenhagen Interpretation) doesn't admit “we don't know the WHY-HOW of collapse” but instead claims “collapse never happens” so “our Quantum Theory plus Many Worlds Interpretation is less-incomplete because it doesn't need the missing explanation (for HOW-WHY collapse occurs), instead it explains why the missing explanation isn't missing because it isn't needed.”  But this benefit of MWI (in having a theory that is more complete) helps us understand only if it's correct.  If it's incorrect, it leads to misunderstanding.  I agree with the many scientists (although not all) who have evaluated MWI and don't think it's correct, who think an incomplete explanation (with Copenhagen) is better than an incorrect explanation (with Many Worlds).  But we can only say "think" because currently there is no way to empirically compare these interpretations, so they're empirically equivalent and personal preferences can “swing the balance” toward one or the other.   /   also:  For some scientists (and non-scientists) another appeal of MWI is that it's deterministic, by contrast with the possible non-determinism of Copenhagen that claims there is no specific result for a quantum system (only probabilities for different specific results, calculated by the Wave-Equation) before a quantum event “happens” when “a collapse-into-specificity” happens, when probabilistic predictions are converted into a specific result.  Although I prefer non-determinism, some people don't.     { In many ways the conversion for a small quantum-level event is analogous to a large classical-level basketball game when probabilistic predictions are converted into a specific result at the end of actually playing the game. }

double-slit experiments with single wave-particles

There are empirical reasons to prefer a theory that proposes “collapse” because this corresponds to our observations of physical reality.  A simple fact — that quantum-level interactions do seem to produce “collapse” due to interactions between physical entities (not due to human observations with human consciousness) — is clearly illustrated by double-slit experiments with single photons.  This was done in 1909 (and refined in 1986), showing that each electron self-interferes (while it's behaving-as-a-wave for awhile) before it physically interacts with a detector (when it behaves-as-a-particle).

In the short time period after the physical interactions begin, SOMETHING SIGNIFICANT HAPPENS.  This leads to “collapse of the mental wave-function [being used to make predictions]” and it does occur, even if we don't fully understand the WHY-and-HOW, and even if proponents of MWI don't like this fact because it spoils the beautiful simplicity of the universe's wave function.  We should recognize the “significant happening” and incorporate it into our view of "what is happening" so there is a correspondence between theory & observation, as in a Copenhagen Interpretation that's modified by updating-revising it with modern knowledge (developed in the 1970s-80s) about decoherence.  I think this correspondence is more important than the mathematical elegance of MWI.

the characteristics of MWI Theory

For physicists (and other scientists) the major scientific-philosophical appeal of MWI is its mathematical elegance as a theory with beautiful simplicity:  a Many Worlds Interpretation of Quantum Mechanics postulates that a single wave-function for the universe (Schrodinger's Wave Equation) develops continuously through the universe's entire history.  Simple.  Although some people criticize MWI based on Occam's Razor, because MWI predicts the existence of many world-histories (aka many worlds), it's more useful to think about Ockham's Razor as a way to evaluate theory simplicity.*  This criterion for theory evaluation actually favors MWI — because it's difficult to imagine a theory with broader scope (claiming the ability to predict EVERYTHING at every time) and greater simplicity (with one equation for everything) — when it's compared with theories that propose a “collapse” of the wave-function, as in a Copenhagen Interpretation. {or should we think “non-MWI proposes collapse” and “MWI proposes no-collapse” so both are equally simple?}   But...

There are empirical reasons to prefer a theory that proposes "collapse" because this corresponds to physical reality, as explained above.

* This link for "theory simplicity" goes to part of a page that summarizes part of my PhD Dissertation about Scientific Methods.

criteria for evaluating theories

For interpreting Wave Function of Quantum Mechanics, currently there is empirical equivalence between Copenhagen (with “collapse” of Wave Function to produce one Real History) and Many Worlds (with “no collapse” instead “all possibilities occur” with many Real Histories);  but IMO the philosophical & theological implications favor the non-MWI of Modern Copenhagen (supplemented with decoherence) when interactions – not “observation by a human” – produces collapse.  And with analogous logic,...

For theory-explaining The History of Our Universe, there is empirical equivalence (AFAIK) between Actual History (in an Old Universe) and Apparent History (in a Young Universe);  but IMO theological implications favor Actual History in Old Universe.   {my page about this}

comments:  Later I'll describe ways to evaluate when there is empirical equivalence, but with theological implications dis-favoring one:  for example, young-earth apparent age (with false history),  Copenhagen (I think it's ok if we reject New Age speculations about “observers creating reality” that lead to unscientific Mystical Physics) versus MWI (with no “me” to be judged, plus no character-stability in heaven unless it becomes non-MWI).

Here I'll try to distinguish between personal preferences (merely “I don't like MWI” while “some others do like MWI”) and criteria (scientific based on evidence-and-logic, plus philosophical & theological) that are more general, to supplement personal, to provide stronger support for arguments and counter-arguments.

IOU – Above are "essential ideas" about MWI.  Below are "extra ideas" about theology and science; 

[[ iou:  The page-title asks if MWI is useful for science (this now is examined above, in ways that will be expanded & revised, but are roughly what they will be later) and is useful for people (this is examined below, but eventually it will be much more thorough than now, when only one biolife-and-afterlife aspect is examined with any depth [and later this will be deeper-and-wider];  one afterlife aspect is just a quick outline;  and other biolife aspects are totally missing now, but will be developed in the future).   /   I'll continue trying to imagine a way for materialistic MWI to be theologically acceptable (re: personal identity & personal accountability), and to discover if anyone else claims to have found a way.  I'll think about possibilities for a divinely-regulated MWI, and in what ways (and to what degrees) these might be theologically satisfactory, for biblical worldviews that range from hyper-Calvinistic divine sovereignty to the other end that heavily emphasizes the libertarian free will of people.  Currently I cannot imagine these ways and how they could be theologically satisfactory, am wondering if this is possible.   /   This process will include the ideas below, which originally were part of a section (in my Main FAQ for Origins) asking Was our “just right” universe intelligently designed by God? ]]

Divine Judgment with Normal Accountability & No Accountability, as in 2a & 2b:

An essential characteristic of conventional MWI (i.e. materialistic MWI that assumes “it occurs naturally” means “it occurs without God”) can lead to challenging theological questions for someone who believes the Bible.  Why?  Below, the first two graphs show “total scores” for Faith and for Actions, with these two aspects of life rated (by God) on a 10-point scale.  Of course, representing a person's entire life with a Faith-and-Actions “life score” that's a single graph-point is extremely oversimplified — because these aspects of life (Faith & Actions) are multi-dimensionally complex — but the graph-points let us recognize a theological problem of MWI, when we logically conclude that either a life-score does exist (with non-MWI) or doesn't exist (with MWI).

one “life score” for each person:		ONE “life score” for one person:		NO “life score” for this person:

Later, when each person will be judged by God based on our Faith & Actions – so “what we sow in Life, we will reap in Afterlife” – it seems possible for God to judge fairly if there is normal non-MWI, but not with strange MWI.   /   With non-MWI, each person makes choices that matter, that make a difference in reality, about what they think-and-do in every instant of their lives.   /   But with MWI a person thinks-and-does “everything possible” in every instant, so they never make any choices.  They have no responsibility for what they think-and-do, thus there can be no accountability.  They have ALL life-scores, which means they have NO life-score that can be judged by God.  This absence of personal accountability (if MWI happens) is biblically questionable, so MWI seems theologically questionable.    {there are reasons for humility in our theological claims about MWI}    {could the "no accountability" of MWI provide a motivation for it to be embraced by non-theists?}

probabilistic splitting of branches:

Does MWI eliminate the possibility of "meaningful" decisions?  Maybe.  Or maybe not.  MWI proposes that the number of history-branches containing a particular decision depends on its probability, so if a person has an 80% chance of doing a certain decision-and-action, this will occur in 80% of the branches.  Is this “80% decision” meaningful?  It's impossible to know, and difficult to even speculate.   /   And how might God evaluate a person if there is MWI?  Here are some speculations:   • Maybe... all “percent decisions” will be considered, to produce a single “average you” if God somehow evaluates your life in a way that considers all of the history-branches.   • Or maybe... at each instant God uses His knowledge-and-power to metaphysically reify one particular outcome that becomes The Reality because God defines it to be The Reality and causes it to be The Reality;  if He does this, The Real You would have one Real Life that is made from the total sequence of all your divinely defined Realities.   • But maybe... instead of one life, you have a zillion lives.  If a lifetime of branching produces a zillion variations-of-you, maybe God will evaluate each “you” so each is separately accountable, with each having Normal Accountability for their Here-and-Now Responses.  But if this occurs, will our afterlife be extremely crowded, with zillions of you-versions (exponentially multiplied) existing?   /   Here is another factor.  With any speculative scenario (my ••• and others) the complexity would increase in two ways, because in addition to the you-life now being experienced by you, every other person would have zillions of them-lives.  When these are combined, there would now be zillions of additional you-lives, produced by the branchings-of-you that occurred before this point in your life, due to the diverse responses of them-lives that was produced by their branchings, thereby increasing your branched-life(s).  Due to their branchings combined with your branching, the variations-of-you would multiply super-exponentially, and the you-lives would be so immensely numerous that it's difficult to imagine the complexity of “your life(s)” and the evaluation(s) by God.

Some Theological Speculations about MWI:  If there is a “probabilistic splitting” of branches, could a theist propose a “probabilistic personal accountability” that would make MWI more theologically acceptable?  For example, imagine that Joe has a 5% probability of deciding-and-doing a Stupid And Sinful Action “SASA” and in 5% of the MWI-splitting worlds he does SASA, but in 95% he doesn't.*  Would this produce any kind of personal accountability that could be consistent with the Bible?  I can't imagine how it would, although (of course) this could be due to my lack of creative yet biblically-based imagination.

* This kind of splitting (with “probability weightings”) is proposed in common versions of MWI, at the microscopic level of quantum events;  and maybe (but I'm not certain) it's proposed that probabilities of quantum-level events would get “scaled up” to the macroscopic level of Joe's decision, thus producing a 5%-and-95% splitting into different worlds, just for this one decision? (it's "?" because I haven't yet checked this.}

MWI in Heaven:  In the Bible we see that a final Kingdom of Heaven will be physical, and we can reasonably assume it will be based on quantum physics.  IF this involves materialistic-MWI, would every person in Heaven do everything possible (including many sinful thoughts-decisions-actions), and if “yes” would this hinder the perfect joy of Heaven?  Maybe.  Or maybe not, because a theist can claim that after Total Sanctification (to remove personal sinfulness) a person will have 0% probability of having sinful thoughts-and-actions, so even with MWI there could be a sinless Heaven.    [[ iou – Obviously, this idea needs to be developed more thoroughly & carefully.  {a speculation about one possible solution if MWI will happen then}

an important difference:  In a Regular (non-MWI) Multiverse, in your Here-and-Now you would have Zero Interaction with any near-duplicates who might (if the immensity is almost-infinity) occur elsewhere in the There-and-Then of another universe.  By contrast, with MWI your near-duplicates (in the future) were (in the past, until a branching) exact-duplicates because you had an exactly-shared history of everything that happened to you/them (it was a Total Interaction) until one of the numerous branchings then produced future variations-of-you;  and each of them would consider you to be a variation-of-themself.     {a more thorough explanation of this difference}

the extremely-immense number of MWI Histories

IF splitting occurs for every quantum interaction that is significant (re: decoherence) during the past 14 billion years {and during the lifetime of a person beginning with conception}, this would produce an IMMENSE number of histories for the universe, {and for each person}.  Here are some descriptions:

Philip Ball says "This picture [with MWI] gets really extravagant when you appreciate what a measurement is.  In one view [and I think it's the most reasonable view], any interaction between one quantum entity and another photon of light bouncing off an atom — can produce alternative outcomes, and so demands parallel universes.  As DeWitt [pro-MWI] puts it, “Every quantum transition taking place on every star, in every galaxy, in every remote corner of the universe is splitting our local world on earth into myriads of copies.”  In this “multiverse,” says the physicist and many-worlds proponent Max Tegmark, “all possible states exist at every instant” — meaning, at least in the popular view, that everything that is physically possible is (or will be) realized in one of the parallel universes."

Emily Quresh-Hurst quotes pro-MWI Sean Carroll:  "We don't know how often branching happens, or even whether that's a sensible question to ask… but we do know that there is a lot of branching going on;  it happens every time a quantum system in a superposition becomes entangled with the environment.  In a typical human body, about 5,000 atoms undergo radioactive decay every second. If decay branches the wavefunction in two, that's 2⁵⁰⁰⁰ new branches every second."  And this radioactivity is only one kind interaction, among MANY others, that occurs inside a human body.  And these would be combined (if MWI) with the much-more-numerous interactions that occur outside a human body.

a question:  If a certain result has 5% probability, will it occur in 5% of the history-branches?  If instead of 5% there is a 4.999% chance, would there be 4999 MWI-Branches with SASA, versus 95001 without it?  i.e. what "fine grain" precision would the probabilities have?  should we use 5% or 4.999% or (if it's predicted by the wave-equation) 4.9999999999% in our analysis of MWI-Branchings?  Why does this matter?  If it's 4.999% instead of 5% (i.e. it's 4999-out-of-100000 instead of 1-out-of-19) this increased precision would lead to a huge increase in the number of branches.   /   also:  What is the proposed mechanism for actualizing this kind of probabilistic splitting?  I assume the answer is that none is needed, because "the splitting will happen naturally if there is no wave-function collapse."

iou – Soon, these sections (and others) will be developed-and-revised, to describe key concepts, to logically examine arguments & counter-arguments.  This will be mainly "new writing" but also will include quotations from other pages written by me and by others — e.g. Philip Ball (basically anti-MWI), Sean Carroll (very pro-MWI), Emily Qureshi-Hurst (re: theological implications of MWI) — plus links for youtube videos.

other sources (in my writing) that I will cite:

• Regarding “collapse” of the quantum wave function (i.e. connections between Schrodinger's Equation & Cat), Interpretations of Quantum Observation showing why it does not involve consciousness in ordinary everyday situations, or in sophisticated lab experiments.    {plus other pages about quantum physics & philosophy}

• An overview of how a multiverse could “beat the odds” for intelligent design, before history and/or during history — Fine Tuning in a Multiverse: Science & Theology — is Part 5B in my FAQ about Creation, Evolution, and Intelligent Design.

This page is https://asa3.org/ASA/education/views/mwi.htm