The boundary between science and mere scientific speculation can be elusive. Albert Einstein famously performed only thought experiments, but those mere ideas yielded counterintuitive predictions leading to experiments conclusively confirming his revolutionary theory. Other thought experiments imagined by Einstein and his colleagues meant to demonstrate the impossibility of quantum theory actually turned out to be conductible. When performed, those experiments refuted Einstein’s arguments and help confirm the quantum.
I think I can safely say that nobody understands quantum mechanics. —Richard Feynman
Recently, however, some much more troublesome (and troubling) ideas have been advanced by some astrophysicists and cosmologists: string theory and the multiverse. The motivation and justification of string theory is to bring order to the menagerie of subatomic particles. String theory posits that we live not in a four-dimensional universe of space-time (once a highly counterintuitive notion, but now firmly established) but in a universe of many more dimensions (10 or 11, at last count), most of which we ordinary humans fail to notice simply because we’re unable to move in or through them (and because they’re very, very small relative to the more familiar ones). The usual analogy is that of two-dimensional creatures living in a flatland—on a surface (either a plane extending infinitely in two dimensions or a bounded one such as the surface of a sphere)—who would be unable to perceive a third dimension (and perhaps even to conceive of it). With 10 or more spatial dimensions, we’re told, we can conceive of subatomic particles not as point-like entities but as string-like ones vibrating in modes that can account for the variety of particles actually observed. However, no testable predictions have yet been advanced to confirm or disprove the idea.
At several stages in the history of science, some theories and entities were posited only because they were useful, although many scientists working at the time doubted their physical reality. The heliocentric model of the solar system, for example, was initially accepted not as physically true but simply because its mathematics made it simpler to account for the apparent motion of the planets. Similarly, the atomic nucleus, the electron, and the photon were all at first considered useful concepts having no physical reality. It was sometimes not even clear that the theories could ever lead to experimentally testable predictions.
Of course, not all theories are successful, and not all hypothesized entities (for example, phlogiston and the élan vital) prove themselves to be real. As experiments (and, eventually, practical applications) proved the usefulness of some ideas, the concepts they embodied became accepted as part of physical reality. Right now, we’re at the familiar stage in which we can’t even conceive of a way to experimentally test the theory of hypermultidimensionality. However, if the history of science is any guide, scientists will eventually think of some observable implications and will perform the appropriate experiments. If the experiments succeed, the theory will become part of our scientific reality, and the previously paradoxical concepts will somehow become familiar and workable, even if not understandable; if those predictions fail, the theory will be rejected. However, if no one ever devises experimentally testable hypotheses, the theory will simply fade away as scientifically unproductive. (Or a competing theory without the extra dimensions will be devised that gives a better account of reality.)
The theory—or theories—of the multiverse, however, seems even more problematic than hypermultidimensionality. String theory hasn’t led to any testable predictions yet, but such predictions don’t seem to be intrinsically impossible. The notion of the multiverse, on the other hand, appears to be untestable in principle.
The notion of the multiverse, masquerading as scientific speculation, is equally entertaining and equally fictitious.
The notion that there can be more than one universe at first seems oxymoronic—after all, the word universe, with its prefix uni-, mean the whole of reality, all that exists. However, there is at least one striking parallel to this evolution of meaning: the word atom means, essentially, indivisible. Although we now know that what we still refer to as atoms are indeed further divisible and contain smaller entities, we now use the word to refer to the smallest unit of an element. Similarly, the word universe may be retained to point to its more-or-less original referent but with different implications: an entity that consists of everything that exists, of which there may be several.
Not all multiverses are created equal. One brand of multiverse, even if it may be untestable is, at least, scientifically unobjectionable. Our universe is currently understood to have originated in a Big Bang some 13.8 billion years ago. Given the limits of the speed of light, if some of the universe is already further away than 13.8 billion light-years (due to a period of hyperinflation), it is forever isolated from us. There may, then, be any number of island universes—initially parts of the same universe originating in a single Big Bang—each forever isolated from one another. Although this notion is in principle untestable, it appears at least consistent with our current understanding of reality.
The much more problematic notion of a multiverse arises from a highly speculative interpretation of quantum mechanics. At that level, we’re told, the universe is in principle indeterminate. Certain properties of a subatomic particle (for example, whether the spin of a particle is up or down) have no reality—only relative probabilities—until a measurement is taken. One interpretation of quantum theory is that, at the moment of measurement the indeterminacy collapses and the spin is determined one way or the other.
However, another interpretation is not that a quantum collapse simply takes the one path or the other, but that the universe actually bifurcates at that moment, taking both paths at once, each in a separate universe cleaved from the original one, and henceforth and forever isolated from all others.
Not being able to understand one aspect of reality however is no justification for an entertaining but equally incomprehensible one.
It is awe-inspiring to imagine that a simple experiment in subatomic physics performed in our little corner of the universe could have such a powerful effect as to cleave it into two separate realities. Has the universe been innocently going along all this time without bifurcating until quantum physics was discovered and these experiments were performed? (This is not entirely without precedent: after all, no nuclear explosion ever occurred on Earth until scientists discovered how to set one off.) Does it all depend on a physicist daring to disturb the universe? Or is it that quantum collapse intrinsically causes universe bifurcation? Since there are an awful lot of particles in the universe (and, under some interpretations, all particles are quantum particles), they’re presumably collapsing all the time, leading to an awful lot of universes.
In some interpretations, quantum collapse eventually leads to all possible universes. We’re invited to imagine universes in which the asteroid that caused the extinction of the dinosaurs and so led to the evolution of Homo sapiens never hits Earth; in which Abraham Lincoln recovers from John Wilkes Booth’s bullet; in which Adolf Hitler was a successful painter and never becomes Führer; and of course a great many universes—in fact, almost all of them—in which nothing of interest to us happens at all. It’s like Borges’ near-infinite library of all possible books, The Library of Babel. Borges’ story, of course, is a thought experiment not meant to be taken literally. The notion of the multiverse, masquerading as scientific speculation, is equally entertaining and equally fictitious.
In its recent usage, the notion of the multiverse was motivated not by any compelling and inescapable implication of quantum mechanics itself but only by our difficulty making sense of it. This concept of the multiverse is entirely unlike, for example, the fact that light behaves sometimes like a wave and sometimes like a particle. We have been compelled to accept that duality as a demonstrated reality, even though it makes no intuitive sense. We don’t understand duality because we can think only in humanlevel terms: light isn’t really much like an ocean wave or a BB pellet—these are just the best we can do.
This article appeared in Skeptic magazine 22.1 (2017).
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The multiverse, on the other hand, is an idea some people apparently believe makes intuitive sense—perhaps because it’s such a familiar and appealing staple of science fiction—but we’re not being forced to accept it by experimental results. We may be permanently at the stage in which we accept the mathematical accuracy and usefulness of the theory of quantum mechanics without ever being able to digest and accept its physical reality—all interpretations may forever seem counterintuitive and paradoxical. Not being able to understand one aspect of reality however is no justification for an entertaining but equally incomprehensible one. The wonder of the human mind is not that we can’t understand all of reality—it’s that we can understand any of it.
This limitless proliferation of universes seems to violate the laws of the conservation of matter and energy. Worse, it violates William of Ockham’s Razor: Entia non sunt multiplicanda praeter necessitate—that is, Entities should not be multiplied unnecessarily. Nor should universes be.
About the Author
Peter Kassan, over the course of his long career in software, was a programer, a software technical writer, a manager of technical writers and programmers, and an executive at a software products company. He’s the author or co-author of several software patents. He’s been a skeptical observer of the pursuit of artificial intelligence for some time. His last piece for Skeptic was “I Am Not Living in a Computer Simulation, and Neither Are You,” in issue 21.4.
About the image at the top
Universum by Heikenwaelder Hugo, Austria [CC BY-SA 2.5], via Wikimedia Commons is a colorized version of The Flammarion (by Anonymous [Public domain], via Wikimedia Commons) — a wood engraving by an unknown artist that first appeared in Camille Flammarion’s L’atmosphère: météorologie populaire (1888). The image depicts a man crawling under the edge of the sky (as if it were a solid hemisphere) to look at the mysterious Empyrean beyond. The caption underneath the engraving (not shown here) translates to “A medieval missionary tells that he has found the point where heaven and Earth meet…”
Source: Trouble in the Multiverse