What of Current Mysteries in Physics and Cosmology?
If my view of the future is correct, it means that the world of physics and astronomy is inexhaustible; no matter how far we go into the future, there will always be new things happening, new information coming in, new worlds to explore, a constantly expanding domain of life, consciousness, and memory.
—Freeman Dyson
Consider next the problems at the edge of science today: are they all solvable, or are some genuine mysteries? Not every interesting problem that scientists encounter is a Big Question. Those of profound significance to human beings qualify as philosophical mysteries, but some other problems still qualify as scientific “how” mysteries. There are many such problems. Consider first some in particle physics and cosmology: How did the universe begin (if it did)? How did the universe’s present state evolve? How will the universe end (if it will)? Why is the universe made of matter and not just energy? What are the smallest components of matter, and how do they relate to fields of energy? Is space infinite and eternal? Why does the universe have the forces and constants it has? Is the flow of time a component to reality or merely an illusion that our mind creates? Are there other “universes” beyond our possible range of observation? Why does the universe have multiple levels of organization, and how did the higher levels appear? What is the role of randomness in the development of the universe? Or is everything in some sense necessary, so that if the universe evolved again we would end up exactly as we already have? If some of these problems remain standing, they will be classified as philosophical mysteries. Other scientific puzzles may remain scientific mysteries—for example, why some particles have no mass, or why matter has an effect on space. So, do we have reasons to believe today that some of these problems will end up being unanswered or unanswerable and thus will end up being intractable mysteries?
Particle physics is one of the greatest achievements in science. A hundred years ago we knew almost nothing of the nature of an atom; now we know its nature and an incredible amount about levels below it. Particle physics’ very precise mathematics and experimental results have been established since the 1920s, and the Standard Model of subatomic particles and forces explained in terms of quarks, leptons, and bosons was set in the 1970s. But it is old news that understanding particle physics has not advanced since then. When a physicist of the stature of Richard Feynman says, “I think it is safe to say that no one understands quantum mechanics. … Nobody knows how it be can like that,” we know we are in strange territory. There currently are a number of different ontic interpretations of the mathematics—from the Copenhagen Interpretation favored by antirealists that eschews all attempts to understand how the physics works to a realism involving indeterminacy to realisms involving determinacy (either by each possible experimental outcome being realized in different universes in Hugh Everett and Bryce DeWitt’s “many worlds” solution or by David Bohm’s inelegant interpretation involving hidden variables and faster than light signals) to Eugene Wigner’s interpretation that gives consciousness a role in experiments. So far, all models have produced the same experimental predictions. And no other progress has been made on other grounds for forming a reasoned consensus. It may well be that all existing interpretations are wrong.
Many aspects of particle physics are certainly so bizarre as to be an affront to our everyday commonsense—for example, entanglement of particles resulting in connected “nonlocal” effects, or theorizing a possible backward flow of time. But some aspects are presented to the general public as being more mysterious than they really are. For example, the claims “There is no reality in the quantum world,” “Nothing exists until observed,” and “The Heisenberg Uncertainty Principle shows that physics can no longer provide reliable information about the physical world and that the physical world has lost its claim to objectivity.” Those claims are wrong. Even antirealists admit that something exists that causes the observed effects, even though we cannot know anything about it—the mixture of the unseen reality and our measuring procedures produce what is observed, but that is not to deny that that unseen reality exists. That reality exists independently of our observations and is “nothing” only in the mistaken sense that Stephen Hawking says that the world came from “nothing” (as discussed in chapter 5). Nor does the Uncertainty Principle mean that there is no objective knowledge of particles: physicists can gain very precise knowledge of what is really there—they simply cannot measure momentum and location at the same time. The act of observation does affect what is there, but on submicroscopic scales it is not surprising that the light used to measure properties affects what is there. Nor is the “wave/particle duality” usually presented properly: an electron is not both a wave and a particle—it is always observed as a particle. However, groups of particles exhibit some wave properties—that is, wave properties are properties of groups of particles but never the properties of a single particle. What is actually there—the reality-in-itself—is something “we know not what” that can produce either the wave or particle effect when we mix different actions with it in different experimental setups. All that is ever observed are particles, never waves or fields. The only “duality” is that we cannot observe an individual particle and a group of particles at the same time. It is also worth noting that the “wave-function” is only a mathematical construct within quantum theory that shows the probabilities of arrangements of particles—it is not a feature of space controlling those arrangements.
One of the new mysteries in particle physics involves “supersymmetry.” This is the assumption that particles of matter may be converted into particles of force and vice versa. Why and how this should happen is a mystery. Is some unknown force responsible for breaking symmetries? There is no empirical evidence yet for such symmetry. There is also the issue of why some particles are massless and why particles in the Standard Model have different masses: why do different particles “feel” the presence of a Higgs particle or field that gives some particles mass differently? The nature of “dark matter” that is not made up of quarks or other parts of visible matter is currently a mystery, as is the nature of the “dark energy” that is hypothesized to explain the accelerating rate of the universe’s expansion. Thus, what we can observe may constitute less than 5 percent of the mass of our universe. And to what degree theories about these matters will be testable is an issue.
The bizarre effects described in the theory of relativity are well known—the twin paradox, the contraction of length of objects moving near the speed of light, the absence of a universal “now” (and consequently of simultaneity), and so forth. The loss of simultaneity wreaks havoc with the notion of causation and thus with the very idea of “natural laws.” Scientists question whether time exists. Is matter continuous or digital—is it, to use Bertrand Russell’s metaphor, a bowl of jelly or a bucket of shot? And why? Space is no longer seen as a big empty box but as the reality out of which matter arises, and yet matter can bend space. Thus, matter loses its status as the primary category for what is physically real to a space-time field. Is matter just an excited state of space-time—the surface fluctuations on an ocean of energy? But to see matter metaphorically as “condensed energy” or “condensed space-time” only pushes the mystery of beingness back one step to “what is space-time?” It also adds the mystery of how matter arises from it. That space itself, and not merely its contents, is expanding is a mystery: the galaxies are not expanding “into” space but are being carried along as space itself expands—space is not expanding into anything and yet is somehow still getting larger. And recent theorizing about “atoms of space-time” with literally nothing in between tightly meshed atoms only adds to this model the mystery of nothingness in between particles of space.
Both general relativity and the Standard Model in particle physics are extremely well confirmed—most recently in relativity by reportedly finding the gravity waves that Einstein predicted. They also are complete enough that they leave few puzzles pointing in the direction of where possible new theories may lie. But this leads to a big problem: the two fundamental and well-confirmed theories are incompatible. The physics of the very large and the very small simply conflict. Relativity is deterministic, while particle physics appears indeterministic. More basically, gravity requires a continuity that particle physics cannot provide. Thus, there is something basically wrong in our theory of things—we cannot conceive that both theories can be correct. We believe that one or both theories must be revised, but attempts to reconcile them (such as “quantum gravity”) have failed for decades. Nor has any attempt to reconcile them in terms of the emergence of space-time out of quantum realities been attempted. No one wants to accept that there is no reconciliation, but the lack of headway may indicate that we have not yet reached the fundamental laws in one or both fields.
This brings up attempts to find a single theory for all the known physical forces—that is, devising a “Theory of Everything.” If devised, we would end up with an equation that would fit on a T-shirt that encompasses all of basic physics, or at least the shortest possible computer program whose output is the laws of our universe. It would show that our universe could not be ordered otherwise than it is—it would give a necessity to all that is since there would be no contingent posits, and we would have a certainty and completeness that many crave. It would show that the laws of our universe are not arbitrary. It would answer Einstein’s question: God had no choice in creating the world as it is. But a “Theory of Everything” embraces all phenomena only if reductionism is correct: only if reality is organized reductively would a physical TOE be the foundation of all chains of explanations—if reality is organized antireductively, then a TOE would be only a “Theory of One Level of Everything.” Alternatively, if antireductionism is true, a TOE would have to incorporate all biological and psychological structures. In the end, all structures would be different manifestations of one underlying structure.
Also consider what a TOE must explain. A true TOE must explain why there is both visible and dark matter and energy, why there are six types of quarks and not more or less, why there are the number of different particles there are and why they have their particular masses and properties, the strengths of different physical constants, and so forth.1 Why did four forces disentangle from the primal force—why these and not others? Why weren’t matter and antimatter created in equal amount (and so destroy each other)? Why, as Paul Davies asks, are there a set of laws that drove the featureless gases of the Big Bang toward life and consciousness? Why is the universe set up to gain more and more levels of complexity? How do different levels of organization appear? Why didn’t the universe remain simpler—for instance, having nothing more complex than quarks? Indeed, why was the universe so unstable that it could not remain in its initial state of symmetry? Why wasn’t the universe governed by something like Newtonian laws rather than relativity and quantum laws? In sum, why does the universe have all the fundamental features it has and not others, and why is the universe as creative and complex as it is? In addition, there are the questions of the initial conditions of the Big Bang, why the stuff of our universe was set up to “bang,” why inflation can happen, and what happened before the Big Bang? Indeed, why is there any space-time at all? Answering these questions is obviously a tall order, but nothing less constitutes a truly total explanation. And this is not to mention the philosophical issues of why anything exists for the TOE to operate on, why there is order in nature, and why any TOE exists at all. The contingent events of history would not have to be explained, but no fundamental scientific laws and constants could be left as unexplained brute facts for a theory actually to be a “Theory of Everything.”
Theories of superstrings—one-dimensional lines of energy that wiggle in different ways—are one candidate for a TOE. They unify general relativity and quantum physics in a consistent way. They also would bring order to the current hodgepodge of subatomic particles. One version—Edward Witten’s M-theory—predicts the existence of particles carrying gravitational forces. However, this theory has problems: it requires more than half a dozen more dimensions to the universe that are not “unfurled,” and there are a mind-boggling number of alternative types of universes in the model (at least 10500). More importantly, it runs up against a major roadblock: it is not yet empirically checkable—it does make predictions, but ones that cannot be tested with the energies available with our current accelerators. It does encompass all the discoveries that preceded it, but it is based on no more than the mathematics of the theory of our universe’s initial inflation and its own elegance. Thirty-five years ago, Richard Feynman quipped that superstring theorists do not make predictions but excuses, and the same is still true today. “M-theory” has become “Mystery-theory.”
Alternatives to string theory that might be testable today are being proposed. So too the recent discovery of dark matter and dark energy—if they in fact exist and are not merely epicycles of theory—raises the question of whether we are in a position to believe that we know all the basic features of our universe. When scientists claim that dark matter and dark energy constitute more than 95 percent of the mass of our universe, one has to wonder whether anything else of such a magnitude has been missed. The same for undiscovered items on the smallest scale: scientists at the Large Hadron Collider in Switzerland recently reported possible traces of a new particle that does not fit in the Standard Model. Evidence of a fifth physical force (possibly connected to dark matter) has also just been reported. Computer simulations of a universe without the weak nuclear force have also worked fine, suggesting that we do not really know what the true fundamental forces of the universe are. In addition, mathematicians may not have yet devised the proper math to summarize the patterns that are being observed.
Thus, today we may not be anywhere near ready to devise a true TOE, and it is arrogant to think otherwise—indeed, all of the current relevant theories may be in a relatively primitive state. Perhaps a conceptual revolution unifying general relativity and particle physics would so alter how we see things that any TOE proposed now would then look silly. Nor can we be confident that there are no forces on the smallest and largest scales that simply lie beyond our capacities to know. Even if we could reach the level of superstrings with some new accelerator, we can never be confident that there is no further level explaining them. So too, we cannot rule out that there may be a rational structure to all of the cosmos that is simply permanently mysterious to beings such as ourselves.
There is also the entire issue of how science could show that there is only one consistent set of physical laws. Perhaps there are many possible TOEs that could produce viable universes, and this raises the issue of why our particular TOE is embodied in our universe—perhaps a creator god would still have had a choice even if there is a TOE. Any necessity to a TOE would be lost. For Steven Weinberg, the possibility that the world could have been operated by another TOE is an “irreducible mystery” that cannot be eliminated. Thus, our TOE would require an explanation for why it was instantiated in reality: something would be needed to explain why that equation is in force and not another. A multiverse theory would be one explanation: if each “miniverse” has its own TOE and is causally unrelated to the other miniverses, one with our features is only to be expected. But in that case, the laws of our miniverse are accidental and not universal. Moreover, no law can explain itself—gravity cannot explain why the universe is set up to allow gravity to operate in the first place. Nothing can be self-explanatory—it is either explained by something else or is simply an unexplained brute fact.
Or perhaps no TOE is possible. There may be no one fundamental underlying order but only local ones. Perhaps there are some arbitrary constants or laws in our universe. Perhaps the idea of unified cosmos—a “uni-verse”—is, as Bertrand Russell suggested, only a relic of pre-Copernican astronomy. Perhaps, as Freeman Dyson hopes, the world of physics and astronomy is inexhaustible, infinite in all directions, and that a TOE is an illusion: just as Gödel’s theorems show that axioms in mathematics leave unanswered questions, so too no set of axioms in physics produces answers to everything—otherwise, “the Creator had been uncharacteristically lacking in imagination.” Certainly, Stephen Hawking’s declaration in 1980 that the goal of theoretical physics might be achieved by the end of the twentieth century did not pan out.
In any case, enthusiasm for TOEs has greatly waned in the last twenty-five years.
Also consider the old and new mysteries in cosmology. One bit of old news is the “fine tuning” controversy. Various physical constants seem perfectly suited to an amazing degree for producing life (even if there turns out to be comparatively little life in the universe).2 It looks as if conscious beings are built into the universe. As Freeman Dyson said: “I do not feel like an alien in this universe. The more I examine the universe and study the details of its architecture, the more evidence I find that the universe must in a sense have known that we were coming.” And it is hard to accept this as simply a brute fact—most of us feel that it demands an explanation. So far there have been three responses. First, many scientists say that, despite appearances, “fine tuning” is an illusion, just an effect of the early inflation of the universe—the variables are interconnected and by this interconnection necessarily produce a stable universe with many features, only one of which is life. Others offer one of two deeper explanations: either a designer god set things up for conscious beings to appear, or a multiverse theory explains it. In a multiverse scenario, as long as there are a sufficient number of miniverses, and the laws and constants vary from one miniverse to another, then of course a world like ours should exist—many may be without laws or otherwise sterile, but some producing life would occur. But many theists fervently resist any multiverse scenario since it would be an alternative explanation to God: a creator god could, of course, create a multiverse as easily as one miniverse, but the order of our world could no longer be used as evidence of a god. To Richard Swinburne, it is the “height of irrationality” to posit trillions of other worlds simply to explain the features of our one world. But multiple miniverses were not posited to explain fine tuning. They are the consequence of other generally accepted theories—in particular, the idea of the inflation of our world, an idea well supported by both observational data and established theories. That multiple miniverses would explain the apparent fine tuning is only a bonus.3
In fact, multiverse models are becoming increasingly popular among scientists. The idea of an eternal multiverse was first hypothesized by Alexander Vilenkin in 1983. Various models have been inferred from various theories in physics and cosmology. Many agree with Paul Davies that some form of multiverse theory is “probably an unavoidable consequence of modern physics and cosmology.” The idea of countless worlds arising and dissolving goes back to the pre-Socratic Greek Anaximander’s idea of the Boundless (aperion), but the contemporary theories result only from spinning out the consequences of the math of other theories (such as superstring models) and are currently only theoretically testable. They add a whole new dimension to the question of whether the cosmos is infinite and eternal since other miniverses would not merely be hidden dimensions of our own miniverse. These theories expand the universe in a way not comparable to any theories in the past—that the stars are far from our solar system, that there are other galaxies, and that our universe is expanding. Each miniverse is distinct from ours, and the “mother universe” or even each miniverse may be propagating new miniverses forever, each possibly with its own set of laws and constants. Finding evidence of, in effect, other entire universes would have an existential impact on us second only to finding intelligent life on other planets.
Philosophers David Lewis and Robert Nozick go to the extreme of advancing an all-worlds hypothesis: every logically conceivable world exists. But any of the models would not only explain why our miniverse has the structure to produce life, we no longer have to ask what an eternal creator god was doing prior to 13 to 14 billion years ago before our Big Bang occurred. It also introduces the issue of whether the universe is eternal and offers different options for the ultimate fate of our miniverse. If what occurred prior to the Big Bang is cut off by the heat of the Big Bang, science is precluded from empirically addressing what may have come before or the nature of any other miniverses or of the multiverse of all the miniverses and their source (the “mother universe”). In addition, we could never tell how many miniverses remain undetectable or what their laws are. So too, the whole question of the origin of the entire cluster of miniverses becomes unanswerable. Physics and cosmology become at best only sciences of our local observable miniverse, not truly universal of all of reality. We would have an explanation for why our miniverse is the way it is, but only as a random result of a far larger incomprehensible universe. Mysteries within our miniverse may be dampened, but the mystery of the total universe only vastly increases.
But again, the drawback to multiverse models is testing for the presence of other miniverses unconnected to our own. To John Wheeler, Hugh Everett’s “many worlds” solution to problems in particle physics has to be rejected because “its infinitely many unobservable worlds make a heavy load of metaphysical baggage.” Observations may actually be possible to detect a past collision of our miniverse with another miniverse, but critics contend that until such evidence is found the entire multiverse scenario is only a matter of metaphysical speculation—elegant metaphysics that is guided by mathematics, but metaphysics nonetheless.
The general lack of testability and observational support in multiverse and string theories has generated a dispute among physicists about the nature of science itself. Some physicists such as Sean Carroll claim that “empirical checking” is now an outdated notion (at least for these Big Questions in physics and cosmology). They want to change the rules of science: in “post-empirical science,” what matters is elegance, consistency, and the mathematics of a model. As Helge Kragh puts it, this would be an “epistemic shift,” a redefinition of science, not by philosophers but by a minority of active scientists. Leonard Susskind labels advocates of Karl Popper’s falsification requirement “the Popperazi” for trying to impose unrealistic and irrelevant methodological restrictions on science.
Disparagers of this view respond that this redefinition spells the end of science in these fields: when we abandon checking, what we have is no more than speculative metaphysics, not scientific theories at all. (Of course, experimental physicists, as opposed to theoretical physicists, have always had a great disdain for philosophizing.) If a theory makes no checkable predictions, it is worse than useless from a scientific point of view—it leads to just concocting fairy tales. Such speculation reflects the age-old human need to have creation stories, but ideas that predict nothing produce no testable claims and no fruitful research—they are not science but no different than theology or astrology. Advocates of the standard view readily admit that all theories begin with speculation, but they see no reason to end the demand that at some point observable consequences are required for a theory to be science—the speculation must become empirically useful at some point down the road. For them, to drop the need for some empirically confirmable or refutable claims would be the end of science. As Einstein said in the first half of the twentieth century, “Time and again the passion for understanding has led to the illusion that man is able to comprehend the objective world rationally by pure thought without any empirical foundations—in short, by metaphysics.” He added (and Kant would agree): “Concepts are simply empty when they stop being firmly linked to experience.”
Advocates of the new view of science point out that problems with these theories have persisted for decades with little progress: competing theories interpreting quantum physics have remained intact since the 1930s; the Standard Model has only gotten more and more complex since the 1970s; and theories such as cosmic inflation and superstrings have been around since the 1970s with little or no advancement. This stagnation is sufficient, they argue, to redefine science: the new theories may be one step beyond empirical science, but they are not unbridled speculation or groundless fairy tales, as critics assert—it is not “anything goes.” Mathematics develops along with science, and perhaps developments in math can take the lead here. (That we do not know the nature of math adds to the problem. Advocates of the new physics would have to be Platonists: math must structure reality and not merely be our invention to summarize data if it is to be the basis of a new speculative science.) But critics still insist that this makes “particle physics” into “particle aesthetics” and theories become grounded only in our sense of beauty and our untrustworthy intuitions of what is real—we cannot call a theory “science” unless it takes the risk of making some confirmable or disconfirmable predictions.
Must a theory predict novel phenomena, or can it merely make sense of existing data and still be called “scientific”? Can a theory remain testable only “in principle” indefinitely and still be called “scientific”? Can such a speculative theory be the basis for further research? Or is “scientific research” reduced to speculation alone? Do the new “post-empiricists” simply want to keep the honorific name “science” rather than admit that they are doing metaphysics? How will this dispute be resolved? Certainly, philosophers cannot dictate to scientists how to practice their craft. Perhaps this is a case where physicist Max Planck is correct: “a scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”
However, whether we label these edges of science “science” or “metaphysics” is not important: if the theories never become checkable, it would mean either way that science is hitting a wall. How do we know a theory is true and not just a groundless overextension of a theory into metaphysical illusion, no matter how elegant it is? How could a theory accepted solely on grounds of elegance be the basis for further speculation? In old-fashioned “empirical science,” elegance and consistency are part of the set of criteria utilized for selecting one theory from among the available (but empirically equal) options, but they never become the sole grounds for acceptance when testing is impossible. And remember that Ptolemaic cosmology and Newtonian physics were once considered the most elegant options.
This points to another issue: are we approaching an era when the only “revolutions” on the Big Questions in particle physics and cosmology will be on the conceptual side, with multiple theories all explaining all of the available data? Could scientists reconceptualize nature around another root-metaphor (e.g., the universe as the output of a computer program) with other idealized conditions in a way that not only does not need certain hypothesized entities (e.g., dark matter or black holes) but also rejects what are now considered basic laws such as the law of conservation of energy or the invariance of the speed of light? (And there is a cottage industry of scientists who reject the Big Bang, the expansion of the universe, relativity, or the Higgs particle.) This in turn leads to such issues as whether there is a genuine question of whether space-time is flat or curved: do we mathematize nature, and could we come up with another mathematics for the geometry of space-time? If computer programs come to dominate physics, will we see space and particles as digital? Does such a prospect render the whole question of the “real” nature of reality moot, as antirealists argue? Or would the end of “empirical science” mean the end of antirealism in philosophy of science since science would no longer be able to make predictions? Are laws not “objectively real” but just the way we currently happen to describe things? Are they, as Victor Stenger puts it, “simply restrictions on the ways physicists may draw the models they use to represent the behavior of matter”? Arthur Eddington thought that the laws of nature were subjectively chosen by us: they are the rules for recurrent patterns that scientists observe, but the footprint we find in nature is only our own. If any of this is so, what does this say about science in general?
We always like to believe that we are living at the dawn of a new era, but if testable alternatives to the currently untestable theories are not devisable today, any new research on these Big Questions may have to lie dormant until sufficient technology is developed, if ever. If not, these questions in physics and cosmology may come to an end, not because the quest to find final answers has been completed, but because there are limits to what we can know about these matters. Interest in these Big Questions may fade away, as with past efforts to confront them in creation myths. A sense of ennui may engulf them as new scientists turn to what they find to be more productive areas of study. Many scientists may become as depressed as Sheldon Cooper was on The Big Bang Theory when he realized that the field he had devoted his professional life to—string theory—was untestable and that in his mid-thirties he would have to start over in another area.
In any case, today the science of these Big Questions seems to have hit an impasse. Since relativity and particle physics cannot be reconciled at present, we have no reason to believe that fundamental physics is approaching finality. Perhaps all of today’s models are in fact only poor approximations of future ones and will have to be discarded. And as the historian Daniel Boorstin noted: “The greatest obstacle to discovery is not ignorance, but the illusion of knowledge.” Old ways of thinking may interfere with devising new ways of conceiving things. We have to rely on intuitions, and our intuitions are shaped by our everyday world, and these may very well not only be useless when dealing with the more exotic realms but warp our thinking—especially when they are no longer guided by new research data. But human beings being what we are, we may be satisfied by our guesses. All this means that asking the right questions in our situation may prove to be even harder than finding any answers.
But as discussed, we must face that at some point particle physicists will have theorized the smallest components or the most basic fields that human beings are capable of exploring empirically or even conceiving, and that will be the final frontier in this field. But whether this means that scientists will then have reached the most fundamental physical level of organization to reality is still an open question: Are there levels of scale beyond our reach or beyond our comprehension even through mathematics? Are there also other fundamental forces at work on these levels that we cannot know? Indeed, we may in fact be vastly ignorant of the true workings of nature. Current particle physics may be like Ptolemaic cosmology—great on predictions, but fundamentally wrong on theory. At the least, the problem of modeling what is further and further from the everyday realm will only get worse—any reality that physicists strike will no doubt remain highly counterintuitive.
So too with the opposite scale of things: we may have only an inkling of the true nature of the universe as a whole—it may remain fundamentally incomprehensible. Many agree with astronomer John Barrow’s conclusion that the astronomer’s desire to understand the structure of the universe is doomed—we can merely scratch the surface of what is out there. “All the great questions about the nature of the Universe—from its beginning to its end—turn out to be unanswerable. There is a fundamental divide between the part of the Universe we can observe and the entire, possibly infinite, whole.” We can expect, he adds, the universe to be endlessly diverse both throughout space and historically—it is most unlikely to be even roughly the same everywhere. We most likely “inhabit a little island of temperate tranquility amid a vast sea of cosmic complexity, forever beyond our power to observe.” So too, we should “regard with a Copernican suspicion any idea that our human mental powers should be adequate to handle an understanding of Nature at its ultimate level.”
In such circumstances, accepting mystery and remaining agnostic about the theories is mandatory. Indeed, it may be most reasonable to withhold even tentative assent to any of the untestable theories. In addition, we have to accept the prospect that scientists may never be able to answer the big “why” and “how” questions here. However, we are a species that wants answers to these questions, and so we may continue to speculate—these questions affect us existentially in a way most questions in science do not. But we have good reason to believe that we will reach the limits of our knowledge in these areas and no good reason to believe that nature is transparent in all its scales to beings like us. Thus, there are matters that are permanently unknowable. We will have to accept with humility some physical and cosmological realities simply as brute facts incapable of further explanation.
1.A change in one theory can wipe out problems in other theories. Here, adopting a multiverse hypothesis makes the stubborn problem of why elementary particles have the particular masses they have simply vanish: each miniverse may have its own set of values for the elementary particles—there is a randomness and arbitrariness to such values in any given miniverse, and no further explanation is needed for the values in ours. Thus, physicists may have been struggling over what is really a nonproblem, and no TOE needs to explain such values. Of course, we do not know how future theorizing may change the whole landscape of physics.
2.“Fine tuning” can be expanded to include other things. For example, if water contracted when frozen like most liquids do, the oceans would have much more ice, and life as we know it probably would not exist. Or would life have adapted to this and taken another route around this problem? Why are quarks and leptons related to each other in simple ratio? Why do electrons and protons have the same electric charge value?
3.How Occam’s razor applies here depends on your point of view: ontologically, a multiverse is obviously immensely larger, but it is actually simpler from a theoretical point of view—it is simpler for a theory to posit the entire range of logically possible miniverses than only one since for there to be only one miniverse, a new ad hoc rule would have to be added to the theory explaining why only one of the possibilities is realized (e.g., perhaps our universe is the only miniverse because it is the best for producing diversity from limited natural laws, and some unknown force destroyed all other miniverse).