Physicist Alan Lightman has a fascinating piece on the “multiverse” in the latest issue of Harper’s (“The Accidental Universe,” Dec. 2011).
Multiverse theories posit that what we have long thought of as the Universe, all the galaxies we can observe, is just one of many universes—perhaps an infinite or endlessly growing number of them, or perhaps a fixed but large number like 10500. (The number of atoms in the observable universe is only about 1080, so 10500 is a lot, as in 10420 universes per atom. For comparison, a trillion is only 1012.) In my crude mental picture, the multiverse is a big ball of foam in which each bubble is a Universe. This image is almost certainly nonsense, but since the human mind is constitutionally incapable of accurately picturing even an electron, that’s probably OK.
(Image by Fir0002/Flagstaffotos, released under GFDL.)
In each bubble Universe, according to various multiverse theories, the laws of Nature are different. Gravity is different, the forces that glue atomic nuclei together are different, the mass of an electron is different, and so on. All these basic constants, the theories say, are randomly set in each universe. In our own, these random settings happen to have produced conditions where life—and therefore observers, like us—can arise. In fact, the settings of our cosmos are notoriously “fine-tuned” for life. If even one of the physical laws we observe were even slightly different—and no reason has been found, yet, why they shouldn’t be—there would be no atoms, or no stars, or some other life-defeating condition.
Some people have cited cosmic fine-tuning as evidence for a God. Lightman quotes Francis Collins, the evangelical Christian and first-rate biologist who presently heads the National Institutes of Health (an evolution-affirmer, by the way), as follows:
To get our universe, with all its potential for complexities or any kind of potential for any kind of life-form, everything has to be precisely defined on this knife edge of improbability . . . [Y]ou have to see the hands of a creator who set the parameters to be just so because the creator was interested in something a little more complicated than random particles.
Multiverse theory explains fine-tuning without dragging in God. If it is true, most universes are not livable, so they contain no observers: observers can only arise in livable universes. Given the very large number of universes in the multiverse, there is no “knife-edge of improbability” but rather a near-certainty that some universes will, by pure chance, turn out life-friendly. We, inevitably, live in one (this is the “anthropic principle”). A close parallel is the fact that within our own universe, all observers must evolve on habitable planets like Earth, even though planets form in a scattershot way and most are lifeless. Not all planets or universes are habitable; but all inhabited planets or universes are habitable.
Theists who have rushed to cite the fine-tuning problem as evidence for God may well find multiverse theory dismaying, but according to Lightman, some physicists are also dismayed. For centuries, theoretical physicists have been hoping to derive everything from a single, fundamental law or force, an equation you could wear on a T-shirt: but multiverse theory, Lightman says, kills that hope. The “laws” we observe, though fixed, are random in origin. The multiverse is therefore a bitter blow to “the idea,” as physicist Alan Guth puts it, “that we could understand everything—i.e., the universe—in terms of mathematics and logic.”
Worse, we can never observe the multiverse, because every bubble but our own is out of reach, over the horizon. “[W]e have no conceivable way of observing these other universes and cannot prove their existence,” Lightman writes: “Thus, to explain what we see in the world and in our mental deductions, we must believe in what we cannot prove.” He compares this to how theologians take “some beliefs on faith.” Heavy irony alert: Although the multiverse saves physicists from the fine-tuning argument for God, it does so only by demanding faith in something else, namely the multiverse. Hence Lightman subtitles his essay “Science’s crisis of faith.” The crisis is that science may have to resort to faith.
Remarks:
• Religious believers should never look to scientific mysteries for evidence of God: this is always a “God of the gaps” error. Francis Collins is canny enough to refuse such thinking in his own field, biology, but falls for it in astrophysics, where his fine-tuning argument is dead on arrival thanks to the multiverse. Even if multiverse theory someday falls from scientific favor, restoring the fine-tuning problem to its original vigor, we should count on some other scientific solution eventually being found. It almost certainly will be.
• The fine-tuning problem has been overrated as good news for religion. On the other hand, multiverse theory has been overrated as bad news for religion: Lightman quotes physicist Steven Weinberg as saying that “if correct [it] will leave still less support for religion.” But many religious believers have completely given up on God-of-the-gaps thinking and will not turn a theistic hair if the multiverse turns out to be good science. Nor is this the first time we have found out that the world is much bigger than we thought. Not until the 1920s did astronomers prove that the spiral nebulae, those thousands of bright little vortices our telescopes reveal, are other Milky Ways, other “galaxies” each containing billions of stars. For a while they were called “island universes” (a phrase coined by Immanuel Kant in 1755). So, the multiverse is fascinating science. But will it weaken religion? Don’t bet it on it.
• Multiverse theory is also, I believe, being oversold as a “crisis of faith” for science, a game-changing category-buster that is forcing reluctant scientists into quasi-religious affirmations of fundamentally untestable claims. On the contrary—scientists are already proposing observational tests of multiverse theory. In 2011, a group of astronomers described a method of searching the skies for evidence of collisions between our universe and others:
Many of the theories giving rise to eternal inflation [a species of multiverse theory] predict that we have causal access to collisions with other bubble universes, providing an opportunity to confront these theories with observation. (Feeney et al., 2011)
Compare that to Lightman’s “we have no conceivable way of observing these other universes and cannot prove their existence.” Moreover, astronomers with NASA have claimed to observe flowing movements of hundreds of galaxy clusters that, they say, are best explained by gravity from another universe (Kashlinsky et al. 2008, Mersini-Houghton et al. 2009). None of this is settled science, but it at least shows that observational tests of the multiverse are conceivable. We’ll presumably never be able to image another universe, but so what? Black holes cannot be directly observed either—they swallow light—but astronomers are nevertheless convinced that they exist because some phenomena that we can observe (e.g., movements of stars near the center of our galaxy) cannot be explained any other way (Feeney et al. 2011). That the multiverse might be no more directly observable than a black hole does not, then, seem to place it in a uniquely science-disturbing class. Even if we conceive “faith” simplistically as “believ[ing] in what we cannot prove,” scientists are not being forced by multiverse theory into anything resembling faith. Plus, philosophers of science almost universally agree that nothing is ever absolutely proved in science: science only approximates the truth more and more closely, and that’s fine. Working belief without absolute proof is only science as usual, not a revolution. Nevertheless, I hereby officially predict that someone, somewhere, will soon quote Lightman to support the creationist view that science is just another form of faith.
• I do not see how the quest for fundamental physical law is scotched by multiverse theory—a major theme of Lightman’s article. Judging by his own account, if multiverse theory is validated, our concept of what is “fundamental” will merely be clicked down a level. Those physical theories (e.g., string theory) that describe the arising of numerous universes with idiosyncratic local laws will be those whose terms are truly fundamental, or closer to fundamental, not those (like relativity and quantum mechanics) that include the specific, randomly-fixed knob-settings for gravity, electron mass, and so forth that obtain within our own bubble. As the physical laws of our own universe churn out diverse planets, the physical laws of the multiverse churn out diverse universes. How is that a defeat for theoretical physics?
Physicists love drama as much as any of us, which is how the elusive Higgs boson (a still-undetected subatomic particle) got nicknamed, ridiculously, the “God particle.” Although Lightman writes well, and I don’t doubt that some people, including some physicists, are engaging in exactly the sort of theological speculation and science-is-dead chest-beating that he describes, I think he is, ultimately, spinning a tempest in the cosmic teacup. The multiverse is just our old pal the Universe, everything-that-exists, turning out (yet again) to be much bigger than we thought: but we already knew it to be bigger than we can grasp.
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REFERENCES
S. Feeney, M. Johnson, D. Mortlock, H. Peiris, First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results, Phys.Rev.D84:043507, 2011.
T. M. Heckman, et al., The Coevolution of Galaxies and Supermassive Black Holes: A Local Perspective, Science 333, 182 (2011).
A. Kashlinsky, F. Atrio-Barandela, D. Kocevski and H. Ebeling, A measurement of large-scale peculiar velocities of clusters of galaxies: results and cosmological implications, Astrophys. J. Lett. 686 (2008)
L. Mersini-Houghton, R. Holman, “Tilting” the universe with the landscape multiverse: the dark flow, Journal of Cosmology and Astroparticle Physics, 006 (2009).