Does the Multiverse Explain Cosmological Fine-Tuning?
- Jason Pluebell
- Oct 1
- 18 min read
Updated: Oct 2
In the first three articles, we have covered the idea that the universe had an absolute beginning some time in the past. We covered the philosophical issues that arise from accepting the idea of a past-eternal universe, as well as the Kalam Cosmological Argument, which posits three premises that, if proven true, will confirm the idea of a cosmic beginning. We then examined the scientific and mathematical developments that led to the most accepted cosmological origins model, the Big Bang. This theory posits that the universe has been expanding, and extrapolating back in time results in the universe converging on one single point of infinite density, corresponding to zero volume, implying a beginning. We also looked at the BGV Theorem, which states that any expanding universe will have a temporal beginning and must be past incomplete. For further discussion about the BGV Theorem, see Did the Universe have a Beginning. We also examined an area of physics called the fine-tuning parameters of the universe.
We discovered that our universe exhibits extremely low and ordered entropy in the present, and must have been even more ordered at the beginning. The universe has a very specific initial arrangement of mass-energy, aswell as containing physical laws that, in themselves, are fine-tuned, and the constants within them are exquisitely fine-tuned with improbable values. We looked at a few naturalistic interpretations, such as the Strong and Weak Anthropic Principles, and how they fail to explain the existence of rare fine-tuning without invoking a transcendent intelligence. Indeed, naturalism posits that the only thing that exists, from which everything comes, is solely matter and energy. Proponents of this worldview presuppose that nothing outside of the natural world can exist, and many hold forms of naturalism that try to expand its explanatory power by postulating an infinite array of other separated universes.
Thus, the Multiverse Theories were created in order to explain the fine-tuning problem that is posed to naturalists. This fine-tuning they attempt to explain away was present from the very beginning, which suggests more of a fine-tuner external to the universe, rather than an internal one. X cannot cause X; something like Y must act to cause X. Even though the interpretations of the SAP and WAP were thrown out the door, nonetheless, some still tried to explain away the fine-tuning issue by increasing the likelihood of a life-permitting universe being created by chance; by positing an infinite amount of universes, by which a life-permitting one is bound to emerge at some point.
The Inflationary Multiverse
When the fine-tuning features of our universe were discovered, many naturalists were introduced to a massive problem: a cosmic beginning, one with implications of an eternal fine-tuner, some may even call God. To get around the bush of an intelligent fine-tuner, theorists postulated an infinite number of causally separated universes existing within a further expansion of space, no matter how unlikely or irrational it may be. And unlike popular belief, these theories did not only posit multiple universes, but an entire ensemble of mechanisms and agents that make this infinite array possible. Proponents of these theories envision our universe as the winner of a cosmic lottery game with an endless number of players, which is rather convenient when explaining fine-tuning.
Vacuum Energy: The energy of space, caused by the minimal energy level a quantum system can exhibit due to fluctuations, derived from the Heisenberg uncertainty Principle.
But the other universes in these theories are causally separated from one another; in other words, one event in one universe cannot affect events in another. Thus, positing a universe-generating mechanism lowers the rarity of a life-permitting universe and shifts the fine-tuning issue to the result of random chance; moreover, there would need to be a mechanism, otherwise, from where would these universes be coming from? Thus, we come to the first type of Multiverse Theory, the Eternal Chaotic Inflationary Model. This model posits an outward pushing, expanding field that has vacuum energy, causing further expansion of space in which universes can be born. This expanding field is called the Inflaton Field.
Created by Adrei Linde, Aland Guth, and Paul Steinhardt to explain a few issues found in the universe. It was created to explain the universe's relative homogeneity of temperature in the Cosmic Background Radiation, the flatness of the universe, as well as the absence of predicted monopoles, all mentioned in Did the Universe have a Beginning. Proponents posit that shortly after the beginning of the universe, space experienced a sudden, rapid expansion that smoothed out the mass-energy and stopped a fraction of a second later to a more modest expansion rate. The most accepted version of this theory is the above-mentioned Eternal Chaotic Inflation model.
As the inflaton field continues to expand, it decays in random locations due to quantum fluctuations in its vacuum energy, causing low-energy pockets to form, called bubble universes. The continuous expansion of the field causes bubble universes to slowly expand with it, away from each other, practically never making causal contact. This model's mathematics explained away the fine-tuning of initial conditions only, not even touching the laws of physics, as the universes generated exhibit the same laws as the field is subject to. Inflationary proponents claim that since there is an infinite array of other universes, every single event that has occurred, and will occur in this universe, is bound to happen in another universe, an infinite number of times. This, in turn, makes the extremely implausible features probable.
String-Theory Multiverse
Since Inflationary Cosmology wasn't adequate to explain both the initial conditions and laws of physics, theorists looked for another theory. This motivation led to the creation of String Theory. This theory, originally made to describe the Strong Nuclear Force, posits that the fundamental units of matter are not particles, but one-dimensional strings of energy. Each string exhibits a different vibration pattern that can be either in an open or closed string form. All elementary particles are simply manifestations of these vibrations. The theory found its roots in the 1960s and was made for the sole purpose of describing the Strong Nuclear Force. Despite another method, Quantum Chromodynamics, proving to be more reliable for this purpose, John Shwartz revisited the theory in the 70s in an attempt to unify General Relativity and Quantum Physics (Meyer, Return of the God Hypothesis, Pg 501, note 11).
Boson: Particles that transmit and carry their corresponding force, for example, the Gluon is the boson that carries the Strong Nuclear Force.
Fermion: Material Elementary Particles, such as nucleons and electrons.
The first version of String Theory described particles called bosons, thought to carry the Strong Nuclear Force, and required a 26-dimensional spacetime, 22 of which were unobservable. More modern versions have found that about seven dimensions are enough to include both fermions and bosons. Remember that dimensions here do not refer to separate worlds or universes, but a physical quantity that describes space, matter, or time.
Where Are these Dimensions?
But where do these extra, unobservable dimensions reside? They are curled up into many different structures on an infinitesimally small degree, smaller than 10-35m, which physicists call the Planck Length. These incredibly tiny compactifications of spacetime dimensions are called Vacua, and theorists envision these vacua containing the vibrating strings, where the 22 or 7 extra dimensions manifest the particles we observe on the macro-scale universe. As the strings in the vacua vibrate, lines of flux form around them that hold the spatial dimensions in a specific shape. These lines of flux can be imagined to be similar to the lines of flux drawn in magnet diagrams (the lines that extend from one pole to another). This theory is a particle-based theory of gravity, rather than a fabric-like warping theory of General Relativity.
It posits the existence of particles called Gravitons: massless, closed strings that transmit gravitational attraction. Since General Relativity is a theory of gravity, and String Theory posits a gravity particle, it was highly expected that the theory would reduce all forces to gravity, and unify General Relativity with Quantum Physics, creating a Grand Unification Theory, or a theory of everything! Specific vibrations of gravitons produce observable gravitational attraction, with other vibrations generating material particles, called Fermions.
String Theory Revised...
Early models only produced universes that contained only bosons, with no fermions. In order to explain the existence of fermions, string theorists posited an arbitrary principle called Supersymmetry. Supersymmetry states that for every bosonic particle, there exists a complementary fermionic particle, and every fermionic particle has a bosonic counterpart. This principle reduced the first proposed 26-dimensional spacetime to just 10 dimensions. Thus, they proclaimed the existence of not only gravitons, but also their supersymmetric counterpart particle, the Gravitino, which gives rise to different fermionic particles. String theorists hoped that by postulating this new form of physics, they would be able to create a single unified theory, one that reduced all four fundamental forces into one mathematical structure (Dimopoulos, Splitting Supersymmetry in String Theory) that accurately described everything.
But... the mathematical structure of the theory didn't produce any solution corresponding to the physics of our universe. This is because the equations for string theory had an infinite number of solutions (different vacua compactifications) that each described different physical laws. It wasn't long before the light of finding a solution that matched our universe began to dim. The number of solutions that have a positive value for their cosmological constant represented anywhere between 10500 and 101,000 different vacua. String Theorists called this vast number of vacua solutions the String Landscape.
Finally Explaining Fine-Tuning... or so it Seems
Despite the extremely large number of solutions, the vast majority not corresponding to our universe, some theorists still attempted to use this to their advantage. They claimed that each solution to the equations represented a different universe with different laws and constants. They postulated that the different shapes of vacua determined the physical laws that manifest in the macro-scale universe, as well as the lines of flux determining the constants within those laws. They then applied this interpretation to the beginning of the universe.
They imagined each universe first as an initially high-energy compactification of space exhibiting one single quantum gravitational field (a quantum field responsible for gravity, stemming from Quantum Field Theory). Then the lines of flux around the universe begin decaying and losing energy, allowing new spatial compactifications of dimensions and strings to occur in the vacua, corresponding to a different universe with different laws. These new shapes would determine the laws of physics, and the size of them (determined by the strength of the line of flux) determines the constants. As this decay continues, a universe would change from one form to another, as each universe cascades down the landscape of possible vacua compactifications represented by the many possible solutions to the equations.
“But this postulation is highly debatable, since there is no way of knowing how much of the string landscape will get explored by such a means.” (Meyer, Return of the God Hypothesis, Pg 501, note 18)
There is no reason whatsoever to expect that the entire landscape will be explored by a cascading universe. If the cascade doesn't cover all possible solutions, there is zero guarantee that the decay of flux would eventually result in a life-permitting universe. Thus, though this theory does explain some fine-tuning, it does so by sacrificing observable entities in favor of purely theoretical ones.
Multi-versal Teamwork that Makes the Confusion Worse
Does String and Inflationary Cosmology provide adequate explanations for the fine-tuning of the laws & constants of physics, and the initial mass-energy distribution at the beginning of the universe? Oxford Philosopher Richard Swinburne applies the principle of Ockham's Razor (read more about the history of Ockham's Razor here: https://www.ptequestionstoeden.com/post/return-of-the-god-hypothesis-part-1-the-judaeo-christian-origins-of-modern-science), which states that when explaining specific phenomena, we should avoid multiplying unobservable, theoretical explanatory entities as much as possible. Positing a transcendent intelligent designer offers only one single explanatory entity: an intelligent, powerful, personal, transcendent causal agent, rather than infinite unobservable universes and multiple theoretical mechanisms.
Accepting the naturalistic multiverse requires the acceptance of two separate universe-generating mechanisms, not just one. Inflationary Multiverse explains the fine-tuning of the initial conditions, but not the laws and constants of physics. This is because the entire inflaton field operates according to the laws of physics of our universe, and each bubble universe thus contains the same laws and constants as the field they are born into; only the mass-energy distributions of these universes are different. On the other hand, String Theory explains the fine-tuning of the laws and constants, but in most models, it never touches the initial distribution. The only String model that explains both is called the Cyclic Ekpyrotic String Theory Model. The only issue is that this theory posits many unobservable entities. It proposes that our universe exists as a thin membrane like fabric of three-dimensional spacetime called a 3-brane that resides in a higher, 11-dimensional spacetime called the "bulk". Some models only posit two 3-branes, while others incorporate other brane pairs.
The different 3-branes collide within the bulk every trillion years to generate new universes. The breaking of Ockham's razor here renders it beyond dull. The unreasonably multiplied entities of this theory include: the 3-branes of spacetime; multiple universes that exist in the bulk; eleven extra dimensions of spacetime, including seven unobservable ones; an eleven-dimensional gravitational field containing other 3-branes; and a process of collisions every trillion years that produces 10500 new universes. Another theory, called M-theory, posits vibrating membranes of energy and unobservable compactifications of extra spacetime dimensions; and lines of flux. As you can see, the extrapolation of the imagination is astonishing.
This means that to create a cosmological theorem that explains both the initial conditions and physical laws and constants would require both an inflationary mechanism operating in conjunction with String Theory vacua. This need for teamwork led to the formulation of a new hybrid theory, the Inflationary String Landscape Model.
The Inflationary String Landscape Model
The theory of the Inflationary String Landscape was coined in the early 2000s by the American Physicist Leonard Susskind, and was later pushed by other physicists like Raphael Bousso and Joseph Polchinski (Meyer, Return of the God Hypothesis, Pg 336). They proposed the decay of lines of flux around an initial vacua universe, just like Standard String Theory, but added the occurrence that in each vacua, inflation would happen. As these vacua begin to expand from their inflaton fields, the fields decay in the local regions from fluctuations to produce bubble universes, each exhibiting different laws and initial conditions. While this theory did seem to explain the fine-tuning based on chance, it sacrificed observability for a massive ontology of causal entities.
Inflationary Absurdities
Now, Inflationary String Theory does explain fine-tuning, but "at the cost of what philosophers of science call a ‘bloated ontology’” (Meyer, Return of the God Hypothesis, Pg 336). A bloated Ontology occurs when a model or theory is unnecessarily complex and contains more entities, categories, or relationships than are required to explain a given phenomenon. The Inflationary String Model does so by positing a very large number of purely theoretical and hypothetical explanatory entities, for which there is no evidence of their existence. The combination of the unobservable mechanisms of inflationary and String Theory affirms the existence of many entities that we cannot observe. This list includes the following:
An Inflaton Field.
The decay of the field creates bubble universes.
Each universe produced has different initial conditions.
The inflaton field will continue to expand forever, and has been doing so eternally into the past. Basically, that actual infinities can exist.
Particles are actually the vibrations of one-dimensional strings.
As these strings vibrate, lines of flux form around them,
The initial universe (vacua) had lines of flux that determined a positive cosmological constant out of the near infinite ones that don't.
The validity of Supersymmetry.
Gravitons and Gravitinos exist that manifest as bosons and fermions.
Each solution to the equations represents a possible universe.
An inflaton field and string landscape universe generating mechanism can produce a cascade that includes enough universes to reach a life-permitting one.
The main issue with these theories is their violation of Ockham's Razor, which is not a law, but a very good and proven method for finding what's responsible for something. The constant speculation about unobservable entities just bashes the edge of the razor. So much so that it seems as if there are almost no observable entities within them, except for those observed in our universe (those things on which the theory is built). Not only do these theories multiply unnecessary explanatory bodies, making one accept obvious absurdities, but they also just push the fine-tuning issue back another layer.
Inflationary/String Theory Fine-Tuning
The universe-generating mechanisms themselves seem to require prior fine-tuning to produce a universe like ours, trampling right over the exact issue they were designed to solve.
Inflationary Fine-Tuning
To explain the homogeneity of the Cosmic Background Radiation, the inflaton field must have a specific energy level at the start of the expansion of the universe, aswell as a specific decay rate to allow a life-permitting universe to result. This precise halt of expansion requires its own fine-tuning to one part in 1053, all the way to 10123. Not only is the halt fine-tuned, but the amount of time that expansion occurs is too. Inflation begins around 10-37 seconds after the beginning and stops exactly at 10-35 seconds, with a size growth of 1026 times the universe's original size.
Moreover, recent research has revealed that the majority of universes that experience inflation will not inflate to a life-permitting universe. The inflaton field generates more universes not suitable for life than those that are, this is because the field is subject to random quantum fluctuations, with no goal for life. The estimated chances of generating a universe compatible with life are no less than 1 part in 1066,000,000 (ten followed by 66 million zeroes), a number that trumps the amount of elementary particles in the observable universe at 1080, multiple times over. This implies that the inflation itself requires prior fine-tuning, begging a cosmic fine-tuner even more than standard Big-Bang models (Sean M. Carroll and Heywood Tam, Unitary Evolution and Cosmological Fine-tuning, referenced in Meyer, Return of the God Hypothesis). But wait! There's more! The massive energy from expansion during the inflation period would increase the total entropy of the universe far more than the normal expansion of the Big Bang. In other words, the surge of expansion energy would increase the disorder of the mass-energy distribution (like dropping a bowling ball on top of a tower of cards, or slamming a heavy object on a table with dominoes standing up on it; the surge of energy from the ball or heavy object would cause the ordered dominoes or cards to decrease in the order they had before and fall over); thus, the distribution before expansion must have exhibited an even finer arrangement to account for the massive increase in disorder caused by inflation to retain the entropy it exhibits today, which is rather highly ordered (for a discussion on the universe's entropy, see here: https://www.ptequestionstoeden.com/post/is-our-universe-fine-tuned-for-the-existence-of-life). Thus, inflation begs for an even lower entropy of the initial homogeneity in the mass-energy distribution to account for the low entropy, ordered structures we observe in our universe today.
Thus, there are multiple layers added onto the already existing multi-layered fine-tuning issue, if inflationary models are entertained. This makes theism a simpler hypothesis than Inflationary Cosmologies.
Them Fine-Tuned Strings
String cosmologists envision a compactification of space that represents a universe that contains a high-energy quantum gravitational field, which begins the process of "exploring the landscape". As the lines of flux decay, different configurations of spacetime arise along with new laws of physics. A universe may experience a phenomenon called Quantum Tunneling, allowing a universe to jump into a new, higher-energy state that produces other bubble universes, but the chances of tunneling occurring are statistically low. This, too, requires prior fine-tuning. Remember that the solutions to String Theory equations that represent a universe with a positive cosmological constant are around 10500 to 101,000 solutions. But there are far, far more solutions that don't meet this single requirement; thus, to ensure a cascade down the landscape through as many low-energy solutions as possible, the universe must have begun at possibly the highest energy level. Think of this like the game of high striker, or ring the bell: where a person must smack a target with a hammer with the goal of transferring enough kenetic energy to make a metal puck slide up a vertical tower to ring a bell. If a person doesn't wack the target with enough energy, the puck will never scale the tower. Similarly, a universe would have to start at the highest energy level possible to ensure a life-permitting universe is within the exploration of the landscape, just like if a person wants the puck to scale the entire tower to reach the bell.
But the BGV Theorem also applies to Standard String Theory models; exploring the string landscape would also require a beginning, along with fine-tuning, the same issue they attempted to kick out of the river. This, in turn, implies the need for exquisite initial conditions because of the rarity of the highest-energy solutions compared to all other solutions at 1 part in 10500 at the least. But there is no guarantee that the entire landscape will be explored, which further implies some sort of fine-tuned mechanism that can guide the process to explore those solutions that are compatible with life. Not only do the standard models invoke fine-tuning, but other models do as well.
The Cyclic Ekpyrotic model that introduces the many 3-branes of spacetime that collide every trillion years requires the 3-branes themselves to be specifically positioned to guarantee the correct collision occurs. The branes of spacetime must be parallel to prevent large inhomogeneities in the resulting universe. The two universes must remain parallel in the multidimensional spacetime they inhabit to 1 part in 1060 across not just their current distance from each other, but a distance 1030 times greater than the distance between them to generate a life-permitting universe, which is fine-tuning on an entirely different level. The energy potential of the colliding branes is also fine-tuned to 1 part in 1050 (Renata Kallosh, Lev Kofman, and Andrei Linde, Pyrotechnic Universe).
The process of attempting to explain one area of fine-tuning seems only to push the issue to a new location, the location intended to explain the very fine-tuning issue it further bloats!
Where's Waldo...
These theories do not just have fine-tuning reasons to doubt them, they also lack a lot of empirical confirmation too. Neither are they the best explanations for what they aim to explain. The Standard Big-Bang Model is able to explain the homogeneity with simple fine-tuning parameters, and physicists can easily account for the relatively uniform temperature of the Cosmic Background Radiation purely on mathematical grounds, without invoking inflation (Meyer, Return of the God Hypothesis, Pg 505, note 41).
“The homogeneity and flatness problems are only considered problems by those who regard the existence of fine tuning as a problem” (Meyers, Return of the God Hypothesis, Page 343).
The other issue these theories attempt to explain, the absence of magnetic monopoles (predicted particles that only exhibit a single magnetic pole), can also be explained by concluding they do not actually exist, and the unification models that predict them, for other reasons as well, not true.
Failed Inflationary Predictions
Not only have inflationary Models taken hits in prior fine-tuning, as well as other absurdities, they have all experienced their fair share of failed predictions, a red flag that a scientific theory or model is not correct. The first failed predictions it the variations in the wavelengths of the Cosmic Background Radiation, mainly that these theories predicted variations far larger than what has been observed. Inflationary models predict larger variations in the temperature; due to fluctuations in the inflaton field, and once the period of inlfation ends, the energy of the inflaton field is converted to standard mass-energy, thus causing the previous variations to enlarge themselves as hot and cold spots in the CMBR. but the Planck Satellite has not detected the predicted variations of most models.
The second failed predictions is the absence of detectable gravity waves from quantum fluctuations in the gravitational field. These models predict that the gravitational quantum field experiences random fluctuations that should be detectable as random warps of space, as the fluctuations would cause gravity to randomly curve in various locations. They predict that when photons interact with these warps, they will polarize in a distinctive, detectable way. To this day, no random warps of space have been found, and no photon has been either.
Scale Invariance: When the scale at which the patterns of an image are observed, I.e. how much the observer zooms in on the image, doesn't affect how the patterns look. Another easier definition are objects that do not change their fundamental properties, no matter how much its scale or size is increased.
The last major failed predictions in the phenomenon known as scale invariance in the imaging of the CMBR variations. Inflationary models predicted a moderate invariance of the variations of the CMBR, but recent imaging of the CMBR shows an almost near perfect scale invariance, more than the theories predicted.
Failed String-Theory Predictions
String theory has, as well, bore some heavy blows when it comes to failed predictions. The prediction of gravitons and gravitinos said they were not going to be detectable, but other supersymmetrical elementary particles should. The Large Hadron Collider in Switzerland has never detected these predicted particles. String theory states that these particles should be detectable under specific high-energy conditions, those of which can be met in the Collider. To date, no supersymmetric particle has ever been detected, despite repeated attempts to do so.
Moreover, the idea of a particle responsible for gravity does not really jive with me personally. This is because, for a graviton to travel and transmit the gravitational force, it would have to move through spacetime. But our most accurate models for gravity are interpreted as the curvature of spacetime itself, and that the curvature is gravity. Thus, how can a particle that travels though spacetime cause spacetime itself to curve? It just doesn't really make sense, unless spacetime and gravity are two distinct and separate entities.
Conclusion
As we have seen in this overview of Inflation and String theories, they do not really offer a simpler and more plausible explanation for fine-tuning. Inflationary theory posits an underlying inflaton field that is eternally expanding with bubble universes, but requires even more exquisite fine-tuning in order to produce a universe that is life-permitting, as well as the sheer probability of one spawning at 1 part in 1066,000,000. String theory posits that the universe began as a tight compacification of spacetime (vacua) that was held together by lines of flux, that when decayed, allowed different spacetimes to arise, and thus different universes; but failed to predict the very thing the theory is grounded upon, as well as prior fine-tuning to guarantee a cascade includes ours. The failed predictions of both theories lowers their credibility as actually being true models.
Moreover, positing a single intelligence offers a simpler explanation to the fine-tuning than does offering a whole host of individually fine-tuned mechanisms that still require a beginning. Richard Swinburne, Oxford philosopher affirms the principle of Ockhams razor, which states that when explaining phenomena we should avoid multiplying theoretical entities as much as possible. The God Hypothesis offers one explanatory entity, an intelligent, powerful, transcendent agent rather than multiple unobserved mechanisms like an infinite array of separated universes and universe generating mechanisms. Thus, we can soberly conclude that the Multiverse just pushed the fine-tuning problem to the very location that is meant to explain it. Theism stands as the best explanation for the beginning, and the fine-tuning parameters of the universe. God bless you, Amen.
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