Science of a Multiverse:

Theories proposing Mechanisms for a Multiverse 

        This page — which is an extension of the multiverse-science in a page about FINE TUNING OF THE UNIVERSE - MULTIVERSE AND/OR INTELLIGENT DESIGN? — will assume some knowledge from the "FINE TUNING..." page, which therefore is a good place to begin.  FINE TUNING examines a wide range of perspectives (scientific, philosophical, and theological) so if you're interested in design questions, you'll find it useful to read all of its first part (Summary, Strong Evidence & Plausible Explanations, Basic Principles) but if you want a streamlined quick education, focusing on the science of a multiverse, I (the editor, Craig Rusbult) recommend reading the sections about:
        Universe-Types and Actualized-Universes (you can find it by scrolling down to halfway through Basic Principles, or add #multiverse to the URL so it's ...multiverse.htm#multiverse), then scroll down to The Science of a Multiverse (or add #science to the URL) and read whatever you want, to fill any gaps in your knowledge.  If you're interested in design questions, you can click one of the links for anthropic reasoning, or just read this summary:

Anthropic Reasoning:
        1. If a multiverse exists, and if it contains enough universe-types, the fine-tuned properties of nature that are “just right for life” and seem highly improbable in a single-universe — and thus leading to claims that our universe was intelligently designed — will become more probable in a multiverse-universe, and all that's needed is for one (or more) of the many universe-types to be fine tuned for life, plus observer-selection by the Anthropic Principle.  It's analogous to getting a royal flush, with 10-J-Q-K-A of the same suit:  in one 5-card deal it's highly improbable;  but in 10 million deals there is a high probability of seeing many royal flushes, due to the increase of probabilistic resources.  Here is the analogy: Almost all hands {universes} will not be a royal flush {will not be fine-tuned for life} but we expect that at least one will be, due to the immense number of hands {universes}.
        2. A multiverse can also affect evaluations of claims for design-directed action during the history of nature — for example, to create the first life or to supplement the natural mechanisms of neo-Darwinian evolution — based on a claim that there are many actualized-universes of our type.
        In cosmology, usually the first kind of claim (#1, for an intelligent design of nature) is the main concern, and is the main context for anthropic reasoning.

        The following sections — imported from the FINE TUNING page, with editing-cuts indicated by ..... — are especially useful for understanding the proposed mechanisms for generating a multiverse:

String Theory Landscape — A Theory of Everything with Many Universe-Types?
        Why is nature fine-tuned for life?  Proposals for explaining this fine tuning by anthropic reasoning (“beating the odds” with a multiverse) require an immense number of universe-types.  According to string/M theory * ..... the basic properties of nature are caused by vibrating strings of energy. ..... With string theory the properties of nature might take MANY different forms (perhaps 10⁵⁰⁰ forms, with common estimates ranging from 10¹⁰⁰ to 10¹⁰⁰⁰) in a string landscape of possibilities that could produce many universe-types within a multiverse.  How?  Even if all strings in all universes were governed by the same fundamental laws of nature, if the characteristics of strings vary from one universe to another — due to differing quantum fluctuations in the early stages of different universes — this variability could produce different observable effective laws of nature in the low-energy conditions that begin within a second after a Big Bang expansion.  How? *
        The transition of conditions from high-energy to low-energy is outlined in a Big Bang Overview: "The early universe was filled... with a very high energy density. ... [then several stages later, but only 10^-12 seconds after the Big Bang beginning] ... the temperature dropped, leading to further symmetry breaking processes that manifested themselves as the known forces of physics, elementary particles, and..."  For details you can click their links, or look at Wikipedia's history of the Big Bang (assuming inflation) in a graphical timeline and (with a caution that "all ideas concerning the very early universe are speculative") verbal timeline. .....
        * terminology:  11-dimensional M-theory (with membranes & strings) was proposed in 1995, elegantly unifying five earlier versions of 10-dimensional string theory (with strings);  usually but not always (so check the context) M-theory and string theory are used as synonyms, and it can also be called string/M theory or M-string theory.
        * DNA and Strings:  Another how-question is answered, by Leonard Susskind, using analogy between a DNA landscape and string landscape, with different sets of DNA-properties {or string-properties} specifying the biological-properties {or nature-properties} in different organisms {or universes}, and letting organisms {or universes} have diversity.

Four Possibilities for a Multiverse
        Max Tegmark asks us to imagine four possible levels of a multiverse:
    Level I Multiverse — our universe is part of a vast mega-universe (produced by inflation) containing many large spatial domains, including the one where we live, that are actualized-universes;  these are all the same universe-type, but with differing initial conditions.
    Level II Multiverse — contains many Level 1 multiverses, and each of these can have differing properties of nature;  possible generating mechanisms (chaotic inflation, colliding string-branes, black holes) are described below.
    Level III Multiverse — a "many worlds" interpretation of quantum physics proposes that each universe is continuously quantum-split into many independent realities with diverging histories;
    Level IV Multiverse — includes universes that differ in their fundamental laws of nature, instead of just differing in their initial conditions (as in Levels 1-2), histories (in 1-2-3), or (in 2) the low-energy observable effective laws of nature for nature's dimensions, equations, physical constants, particle properties,...

Multiverse Levels and Intelligent Design
        If a multiverse exists at any level(s), the implications for design depend on whether the multiverse contains many universe-types and/or many universe-actualizations, which are required for two types of anthropic arguments against intelligent design:
        An odds-beating argument against a design of nature requires a multiverse containing many different universe-types with different laws of nature.  This variability-of-types occurs with Levels 2 (different effective laws) and 4 (different fundamental laws & thus different effective laws) but not with 1 (same effective laws, only initial conditions differ) or 3 (all are in same universe, so nothing differs except the diverging histories).
        An odds-beating argument against design-directed action (during the history of nature) requires a multiverse containing many actualized-universes of the particular universe-type being studied.  This would occur with all four levels of a multiverse, if they exist.  And with Levels 1, 2, and 4 the actualized-universes would have differing initial conditions, which would help produce variability in histories.

..... [ in FINE TUNING the sections above were followed by web-resources describing the four possible levels, and a section about "A Multiverse and/or Intelligent Design: Divine Design of a Multiverse?" that begins, "Below you'll see a variety of proposed mechanisms for generating universes in a multiverse, and for each we can ask if there are reasons to suspect that this mechanism was intelligently designed." ]
 

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Now, building on the foundation from above, here is more about the science of a multiverse:

Possible Physical Mechanisms for Producing a Multiverse:
Some cosmologists extrapolate from our single observed universe to the possibility of many other unobserved universes in a multiverse.  When we ask "how could this happen?", what kind of theories do they propose?

editor's comment:  I'm not confident about some aspects of the descriptions below, so I'll ask some questions that I'm hoping will be answered by those who are more expert in this area of science.  It's been very difficult finding explanations that are clear and thorough at a non-technical level, that can help me (as an intelligent non-expert from outside the field) to understand-and-visualize, so any help you're able to provide will be greatly appreciated.  Craig Rusbult, email-available-soon

question — Are the following two sub-sections (copied from FINE TUNING) accurate?

        Inflation as a Universe-Generating Mechanism for a Multiverse at Levels 1 and 2
        Inflation Model (Level 1) — The basic concepts of inflation (what it is, why it's proposed, evidence for it,...) are explained earlier.  If the process of inflation produced many other spatial domains similar to our own, this would be a Level 1 multiverse.  All of these domains would be “universes” having the same properties of nature, but with different initial conditions and thus different histories.  But if there were enough actualized universe-domains the histories might begin to “repeat” by producing nearly-identical histories, leading to questions (philosophical and theological) about duplicates.
        Chaotic Inflation Model (Level 2) — Although simple inflation is supported by significant indirect evidence, proposals for chaotic inflation are based only on theory.  Some theoretical models of inflation, but not others, predict that during inflation many “big bangs” occur, with each producing a new Level 1 multiverse.  Typically, single-field models of inflation (but not double-field hybrid models) predict a process of chaotic inflation that will be future-eternal, continuing forever, and if the new Level 1 multiverses have differing properties of nature (as in a string landscape) this would be a Level 2 multiverse;  but probably the process could not be past-eternal, so it would have to begin sometime in the past.
        Scientific details about possibilities for generating a multiverse — including more about inflation (which currently is the most popular view among advocates of a multiverse) but also ideas for producing universes by black holes, string-membrane collisions, or in other ways — are in MULTIVERSE SCIENCE - THEORIES ABOUT MECHANISMS.
 

The rest of this page is not in FINE TUNING, it's only here.
 

Level 1:

        Inflation Model (Level 1) — The basic ideas (what it is, evidence for it,...) are explained in FINE TUNING.  A Level 1 multiverse would be produced if at different points in time-and-space during the inflationary phase, different parts of the inflating multiverse stop inflating and — in a reheating that converts the potential energy of a hypothesized inflaton field into the mass/energy of hot radiation & particles, as explained in the Big Bang timelines — become post-inflation universe domains (aka Hubble volumes) such as our own observable universe.  All universe-domains within a particular Level 1 multiverse would have the same properties of nature because they all share the same Big Bang beginning;  but they would have different initial conditions because each universe has a second "beginning" (when it becomes a distinct domain) that occurs at its own distinctive point in time-and-space.
• questions — Is the above description accurate?  Is there only one big bang for the entire Level 1 multiverse, or does each domain have its own big bang? (does a big bang occur before or after inflation? is there just one pre-inflation bang that is shared by all domains, or a post-inflation bang in each domain when after reheating its newly formed radiation/matter energy expands?)  I'm confused because I've seen claims that the size of a Level 1 multiverse is infinite (but does this refer to space or space-with-matter?) and I've also seen descriptions of large-but-finite ratios for expansion during the inflationary phase, such as Wikipedia saying that the inflaton field "drove the portion of the universe that is observable to us today to expand from approximately 10^-50 metres in radius at 10^-35 seconds to almost 1 metre in radius at 10^-34 seconds."  I'm not visualizing how this expansion (from a tiny radius of 10^-50 meter) could occur within many different domains if there was only one Big Bang event, instead of one bang-expansion for each domain.  And if a domain-inflation ends with a radius of 1 meter, how is this consistent with overall inflation that produces infinite space within the multiverse?  Obviously I'm missing something in visualizing the domain-geometry and/or the multiverse-geometry, and how they're related.  /  By the way, my description above, in the pre-questions paragraph, was inspired by a statement of Alan Guth who said "In what I would regard as the conventional version of the inflationary theory, the Big Bang was also not in that theory the origin of everything [does he refer to Level 1 or Level 2?] but rather one had a very long period of this exponential expansion of the universe, which is what inflation means, and, at different points, different pieces of this inflating universe had stopped inflating [with inflaton energy becoming, at this point, energy of radiation or radiation-and-particles in reheating?] and become what I sometimes call pocket universes."  It's very difficult to find good descriptions of "inflationary geometry" so I've extrapolated from this, and very possibly I got it wrong, especially now that I'm re-reading what he says, and I'm wondering what he means by "pocket universe" and whether (when he says "this inflating universe had stopped inflating") he is describing a Level 1 multiverse (this seems to be his definition here) or Level 2 multiverse (which seems to be his definition elsewhere).
• IOU - We'll link to one or more resource-pages explaining the structure and characteristics of an inflationary level 1 multiverse.

 
Level 2:

        Chaotic Inflation Model (Level 2) — This model, which is an extension of inflation, proposes that during inflation many new "inflationary big bangs" occur, with each producing a new Level 1 multiverse.  Proponents claim that this process of chaotic inflation is future-eternal, continuing forever, producing more and more new Level 1 multiverses and thus a Level 2 multiverse;  but probably the process is not past-eternal, so it would have to begin sometime in the past.  A model of eternal chaotic inflation is based on two postulates, from general relativity and quantum physics:  the relativistic self-cloning of space by inflation;  and quantum fluctuations of an inflationary vacuum producing different metastable states (false vacuums that are a lowest-energy local state, but not the lowest-energy global state, not the overall global minimum) which lead to different low-energy forms of a string theory landscape.   /   terminology (multi vs uni): a Level 2 multiverse contains many Level 1 multiverses (Tegmark's term) that also can be called bubble universes (Linde's term) or pocket universes (Guth's term);  and pocket universe also has a literary meaning.
• question:  Is this correct?  I'm uncertain about the geometry of Level 2 (and its relationship with Level 1) and even Guth's definition of pocket universe, whether it refers to a Level 1 multiverse within a Level 2 multiverse [I think this is the meaning] or an isolated spatial domain (universe) within a Level 1 multiverse / also, there seems to be inconsistency (as noted in the "multi vs uni" comment above) with a "Level 1 multiverse" called a "universe" in the context of a Level 2 multiverse
• question:  A main theme of what I wrote for FINE TUNING is that (as stated in inflationary cosmology from Wikipedia) eternal inflation is predicted by some inflationary models but not others — a few screens down from the link's starting place, the section for "non-eternal inflation" says that "unlike most other models of inflation, many versions of hybrid inflation [with 2 or more fields] are not eternal" — so which models (eternal 1-field non-hybrid, or non-eternal 2-field hybrid) seem to be most satisfactory in most ways?  Does this issue now seem settled (not proved, but reasonably certain) or is it uncertain, and might it become more settled in the near future?
• A summary of multiverse-ideas including energy conservation, chaotic inflation, and string theory, from Science Daily News.  {5 k}
• An introductory overview of multiverse ideas by David Bailey, describes basic ideas (terms, inflation and chaotic eternal inflation, string landscape,...) and the wide range of views about these ideas.  {12 k}
• Scott Shakelford tells the story of theories about eternal chaotic inflation from the viewpoint of Andrei Linde.  {18 k}   /   William Orem describes String Theory & Chaotic Inflation and their relationships, in a marriage (of Renata Kallosh with Andrei Linde) and in science.  {11 k}
• Eternal inflation and its implications by Alan Guth, says "it can be proven under reasonable assumptions that the inflating region must be incomplete in past directions, so some physics other than inflation is needed to describe the past boundary of the inflating region" so even though chaotic inflation might continue into the future, it had to begin sometime in the past.  {1 k abstract, plus 41 k paper}
• abstract - http://energy.nobelprize.org/abstracts/linde_050619.pdf - slides - http://energy.nobelprize.org/presentations/linde.pdf - report - http://energy.nobelprize.org/reports/linde_report.pdf

• If you want to wander through audio-video discussions of chaotic inflation and other topics, you can explore the website of Closer to Truth, which is a television series about Cosmos, Consciousness, and God, with prominent scholars interviewed by Robert Lawrence Kuhn.  Their videos about Cosmos — mainly featuring scientists who are advocates of a multiverse — are especially relevant for learning about a multiverse.  And if you explore the video clips from their shows you'll find other interesting topics, including "Arguing God from First Cause" among the discussions about God.

        Black Holes (Level 2) — [this is extremely incomplete and rough-draft] -- Lee Smolin proposes that a black hole singularity can produce a big bang singularity, and there is cosmological natural selection for properties of nature that increase the production of black holes within universes, analogous to Darwinian biological natural selection.   /   questions:  As with the Cyclic Model below, one of my questions is about the extent of Smolin's anthropic reasoning;  he claims that the cosmological constant is modified by natural selection (to maximize the production of black holes) but what about all of the other types of fine tuning?  What varies from one universe to another? and how much? which properties vary randomly (as in a string landscape) and which are constant (or have minor variations between mother and daughter universes)?  I haven't begun researching this yet, but I'm worried that it might be just as tough to find good information for this as it is with other types of multiverse proposals.  Sigh.

        The Distant Past and Distant Future?
        When we ask, based on current scientific knowledge, "what happened before the Big Bang?" and "what will happen in the faraway future?", we find some principles and many speculations.
        In the distant past, the Planck era (aka Planck epoch) of the early Universe, from zero to 10^-43 seconds after its beginning, probably was extremely hot and dense, with a large amount of energy in a tiny volume.  Whatever the conditions were — maybe a unique singularity where the familiar laws of physics break down, with infinite density and spacetime curvature? * — they differ from later conditions, and this unfamiliarity makes it difficult to be confident about knowing the physics of what the earliest universe was, and why.   {* But maybe a singularity-breakdown can be avoided with physics based on string theory.}
        Regarding the distant future, we have more data and more scientific principles.  Will the universe continue expanding forever, or will it eventually begin contracting to produce a Big Crunch when everything comes back together in a small volume?  The answer, according to the current consensus of scientists, depends on matter density and dark energy.  If in our universe the density of matter (symbolized by a Greek capital omega, Ω) equals its critical density (defined as 1) the universe-geometry will be flat as in Euclidean geometry;  or the geometry could be closed (if Ω > 1) and positively curved like a sphere with elliptical geometry, or open (if Ω < 1) and negatively curved like a saddle with hyperbolic geometry.  A universe with open geometry will expand forever.  If we consider only the effects of mass and gravity, a universe with closed geometry will continue expanding for awhile but with a decreasing rate, and will then begin contracting to eventually produce a Big Crunch.  But the repulsive effects of a positive cosmological constant (due to dark energy) can overcome the attraction of gravity, and thus prevent the contraction-and-collapse of a universe with open geometry;  and it will certainly tip the balance, from neutral to contractive, in a universe with flat geometry.
        What does the data show?  It seems to indicate that Ω is either 1 or slightly larger than 1, and dark energy is causing the Universe to expand at an increasingly fast rate.  But if the characteristics of dark energy change in the future, causing it to behave in an unexpected way (and we currently don't know much about dark energy, so a change is possible although speculative), an eventual contraction is possible, even though it currently seems improbable.
        • Wikipedia's summary of ideas about the ultimate fate of the universe includes proposals that the Big Bang will become a Big Freeze (if expansion is never followed by contraction), Big Rip (if expansion becomes extremely fast), Big Crunch (due to contraction), and Big Bounce (after a Big Crunch).  Some of these ideas are outlined below.

        Oscillating Universe Model was developed in the 1930s, and is now considered obsolete;  it proposed that our universe has oscillated repeatedly by going through Bang-and-Crunch cycles: Bang-Crunch-Bang-Crunch-Bang-etc.  Its most serious problem is a result of the Second Law of Thermodynamics, which predicts an increase of entropy during each cycle that would be passed on to the next cycle, leading to increasingly longer Bang-Crunch cycles.
• Some web-sources, including Wikipedia, describe new thinking (in 2007) about a Big Bounce Model that seems to be a modern variation of the old Oscillating Universe Model.  [IOU — I need to look at this, to learn what it is and decide what to say about it here.]
• Wikipedia describes three cyclic models: outdated original, plus Steinhardt–Turok and Baum–Frampton.  The original model failed due to the problem of increasing entropy during each cycle, but in the early 21st century "recently discovered dark energy component provided new hope for a consistent cyclic cosmology," inspiring the newer models described below.  {6 k}

        Cyclic Model (Level 2) was originally constructed by Paul Steinhardt and Neil Turok.  This model proposes that many universes, including our own, arise from collisions of two 3-dimensional branes (proposed in string theory) in a 4-dimensional space.  When collisions do happen, they can occur in a huge number of places along the branes, with each collision producing a big bang and a universe like our own, but with different properties of nature.  The branes then recoil from the collisions and separate, but they continue attracting each other and a long time later (after about a trillion years) the branes have another set of collisions, to produce new universes, and this cycle continues forever into the future.  This model mainly agrees with the Big Bang model, except for what happened before the beginning, but it disagrees with an Inflationary Big Bang.   [question: How much diversity in nature-properties, from one cycle to the next, is proposed? I think they propose a continual decrease in the cosmological constant, which decreases quickly in early cycles when its value was high, and more slowly now that its value is much lower;  the authors seem to dislike anthropic reasoning as with a string landscape, but how do they explain the many other types of fine tuning besides the cosmological constant?]  [question: I've seen descriptions of collisions occurring in a huge number of "bumps" along colliding branes, each producing a big bang universe, and Steinhardt/Turok's book Endless Universe describes exponentially increasing numbers of universes during each successive cycle, but I haven't seen a multi-collision scenario described in their book (they describe brane-surface irregularities but these produce structures, such as galaxies/etc, within a universe) or in any web-pages about the Cyclic Model.]
• Steinhardt and Turok describe their model in a book, Endless Universe: Beyond the Big Bang, that has its own website with information About the Book plus links (for Reviews, an Excerpt,...) to explore.
• The basic ideas from Word-IQ: Branes & Brane Cosmology & Ekpyrotic Model & Cyclic Model.  {8 k total}
• video: You can hear-and-see Brian Greene's explanation of the Ekpyrotic Cyclic Model in The Elegant Universe (in Hour 3, chapters 4, 5, and especially 6) and the string theory "context" is explained earlier in the 3-hour series.
• Before the Big Bang by Michael Lemonick, in Discover, has excellent writing and illustrations.  {23 k}
• Bruce Gordon outlines the Cyclic Ekpyrotic Model and scientific criticisms.  {4 k for slides 63-67}
• A critical review of Endless Universe by Peter Woit, who likes (and agrees with) their criticisms of inflationary cosmology, but wishes the authors were more critical about string theory and their own cyclic model.   {5 k}
• Paul Steinhardt has written an Introduction to the Cyclic Universe {8 k} and other summaries, explaining an ekpyrotic universe model that led to a cyclic universe model.  {8 k, 6 k}
• video: A Talk with Neil Turok about the history and content of his cyclic model.  {28 k transcript, xx video}
• audio: The Big Rumble over the Big Bang was an NPR "On Point" radio discussion between Neil Turok (pro-cyclic), Alan Guth (pro-inflationary), and Janna Levin, with host Tom Ashbrook.  {4 k text, 43:44 audio}
• A Briefing on the Ekpyrotic/Cyclic Universe by Justin Khourya, is "a short overview of the ekpyrotic/cyclic model of the universe, an alternative to the standard big bang inflationary paradigm."  The paper's structure is like a sandwich, with clearly written summaries {6 k} in Sections 1 and 6 serving as non-mathematical bookends for the technical treatment {9 k} in Sections 2-3-4-5.

        Another type of Cyclic Model, from Baum & Frampton, is one of Wikipedia's three cyclic models and is summarized in two pages from UNC,  #1  #2 .  {4 k, 4 k}   /   question:  How seriously is this considered among scientists?  I haven't seen much about it.

 
Level 3:

        A Many Worlds Interpretation of Quantum Physics (Level 3)
        note: This section is identical to the section in FINE TUNING.
        This speculative interpretation of Quantum Physics (aka Quantum Mechanics) claims that the wave function never “collapses” during a physical interaction that converts a range of possible results (whose probabilities can be calculated using the math of quantum physics) into one result that actually occurs (and therefore now has a probability of 100%) as proposed in the conventional Copenhagen Interpretation.  Instead, with a Many Worlds Interpretation (MWI) during every physical interaction of every wave-particle in the universe, every possible result actually occurs in its own separate branch of history.  Thus, with MWI during each instant of time an immense number of history-branches are produced, and during the next instant each of these branches split into many more branches, and this has continued since the beginning.  This process would produce an unimaginably huge number of history-branches where EVERYTHING happens, including each of us doing every possible thought and action, which raises difficult theological questions about MWI that are described in FINE TUNING.
        Some scientists are fascinated by the mathematical elegance of MWI, but this mental convenience requires paying a high cost in physical extravagance.
        In MWI the history-branches are probabilistic because, in order to avoid an immense violation of energy conservation, they cannot all be “real” in the usual way we define reality.  It's difficult to understand exactly what is being proposed.  But whatever the proposal is, a Level 3 “multiverse” is definitely different than Levels 1, 2, and 4, so there are reasons to think Level 3 should not be considered an authentic multiverse.
        With MWI all of the imagined history-branches would occur in the same universe, so there is only one universe-type and one set of initial conditions.  But anthropic reasoning requires many universe-types, so an MWI-universe is not useful for a non-design explanation of fine tuning in our universe.  But MWI could be used to challenge claims for design-directed action during the history of nature, because with MWI everything that could happen (including a natural origin of life and all of its possible evolutionary developments) would happen in some branches of history if the only question is probability, if no laws of nature are being violated.
• A 5-page series by Andrew Thomas is a good overview of Quantum Mechanics including Quantum Decoherence which explains why "I believe far too much is read into the so-called ‘collapse of the wavefunction’. ... the Many Worlds interpretation seems very much a product of the fifties [when we knew less than now]. Recent results in quantum decoherence have given us new insights into the quantum measurement problem, and there is no longer any need to propose parallel universes to explain the process."
• How would Christian Theology deal with MWI? is an article followed by comments, beginning with the best.  {18 k total}
• I.O.U. — Eventually, but probably not until at least early 2011, there will be more about quantum physics in the links-page for INTERPRETATIONS OF QUANTUM MECHANICS.

Energy Conservation in Many Worlds
    This part of my page about theological interpretations of a multiverse (asking “are duplicates a problem” and so on) ends with a humble comment:  "This section is in the appendix because I haven't yet checked it with quantum experts, so maybe I've misunderstood something about relationships between the mathematics and claims for physical existence, about the science-and-interpretation of MWI, and the claims made by MWI."  This question is included here because I'm hoping for insightful responses.
    If many universes (each with a huge mass/energy) are being produced by the process claimed by MWI many times each second, does this violate a conservation of energy?  The MWI-Everett FAQ (by Price) says NO because "the energy of the total wavefunction... involves summing over each world, weighted with its probability measure."  Similarly, Wikipedia says "the energy of each branch has to be weighted by its probability, according to the standard formula for the conservation of energy in quantum theory. This results in the total energy of the multiverse being conserved."
    Although this is mathematically correct according to the quantum-math used to calculate probabilities, MWI claims that every MWI-world actually does physically exist in reality (with 100% probability) so every instant a near-infinite amount of mass/energy is being produced. (unless the universe being split by MWI has exactly-flat geometry and its total energy is exactly zero, as proposed in “free lunch” theories)  Even though all of this new mass/energy cannot be observed (due to decoherence) with MWI the new mass/energy does physically exist, because every possibility in the quantum wave-function of our universe does physically exist.  Although MWI is called "many worlds" the MWI claim is that all history-branches actually occur within our own universe, but they are hidden from our observation by decoherence.  Can this vast increase of actual physical mass/energy be explained, or are MWI advocates hiding behind mathematical formalism instead of coping with the physical implications of MWI?  This defense of MWI (with energy “weighted by its probability”) seems to assume that mathematical description = physical reality, that the quantum-equation is physical reality because it correctly describes probabilities for what will occur in physical reality;  but this interpretation-assumption is the central claim of MWI, so the defense uses circular reasoning and therefore is logically questionable.

 
Level 4:

        Level 4 Multiverse — Different Fundamental Laws of Nature
        note: This section is identical to the section in FINE TUNING.
        The essence of this imagined multiverse is the possibility of universes with different fundamental laws of nature.
        Max Tegmark goes far beyond this concept in his appeal for mathematical democracy, which is "a form of radical Platonism" claiming that "mathematical existence and physical existence are equivalent, so that all mathematical structures exist physically as well. (quoting page 118 of the multi-author book, Universe or Multiverse)"  This view is an extreme minority view among scientists and everyone else.  For example, Leonard Susskind, who proposes a multiverse (which he calls a megaverse) with many universe-types that include all string-landscape possibilities, says "It's one thing to argue that theory gives rise to many possibilities for the Laws of Physics, but it's quite another to say that nature actually takes advantage of all the possibilities.  Which of the many possible environments materialized as real worlds? ... Mathematical existence is not the same as physical existence, obviously. (pg 293 of The Cosmic Landscape)"
        Tegmark says (p 118 of U or M) that his mathematical democracy "casts the so-called modal realism theory of David Lewis in mathematical terms."  Modal Realism proposes that everything we can imagine (and more) actually does happen physically, somewhere in an infinity of worlds.  Wikipedia says "the theory was widely considered to be too implausible to be taken literally, as Lewis urged it should be ... [and a typical response was] what Lewis calls the ‘incredulous stare’."  And regarding human motivations, "While people are concerned with what they could have done [in our world], they are not concerned with what some people in other worlds, no matter how similar to them, do."
 

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As explained in the introduction for this page, the links-page for FINE TUNING has additonal educational information about "a wide range of perspectives (scientific, philosophical, and theological) so if you're interested in design questions" you'll find it useful to read FINE TUNING.
 

 

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