The Number of the Heavens: A History of the Multiverse and the Quest to Understand the Cosmos

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Release Date: 
September 16, 2019
Harvard University Press
Reviewed by: 

“The most readable tour of cosmology from the perspective of the multiverse to date.”

Author Tom Siegfried is a contributing correspondent at Science News, and his work has been included in the Best American Science Writing. The title The Number of the Heavens, comes from mystic Gnostic system called Abraxsas. Siegfried’s The Number of the Heavens is not a mystic system but a tour of the debate on the possibility of multiple universes. This is not an in-depth survey on today’s research, so much as an historical survey of the idea of multiple universes. Siegfried believes such a study matters, “because the existence of a multiverse may be essential for understanding the universe we live in.”

The possibility of a multiverse goes pretty far back in history. Where Siegfried’s story starts is in medieval cosmology. Siegfried tells us, “In the year 1277, the bishop of Paris loosened Aristotle’s grip on the science of the Universe . . . Tempier [the bishop of Paris] freed religious scholars in Paris and elsewhere to profess that God could create as many universes as he darn well pleased.”

Siegfried’s narrative zigs and zags, from medieval times, Siegfried jumps ahead to more recent cosmology. That we know the universe is expanding is not a new discovery, but the current discussion is a question of the expansion rate and whether that rate is constant or increasing. The question of expansion rate goes back to Einstein and the equation for the theory of general relativity, first set down in 1917, which included the rate as something called the cosmological constant, lambda. It was Einstein’s belief the universe was neither expanding nor contracting. In 1929, Edwin Hubble determined the universe was expanding, and in 1998 it was determined that the expansion rate is accelerating.

Much of the science covering the early part of the big bang is conjecture, and not everything about the expansion is understood. Cosmologists imagine how the big bang could have occurred, and then try to get the math and physics to line up. There have been many successes by using this method. Using conjecture on top of conjecture has lea to better understanding several long-standing problems in the areas of expansion, flatness, the need for closeness early-on to explain distant relations, and the conditions necessary for life.

For example, calculations show the universe to be too large to have the structure that it has now with respect to the speed of light (which governs the speed of gravity) which forces the rate of expansion to have changed over time. Another question is as to the universe’s “flatness,” as massive objects acting through gravity warp space. And yet another question, is the average density, omega, which happens to be just right for the conditions for life to exist, not just just right but exactly just right, that is, right to one part in a quadrillion.

The problem of how expansion first stopped or slowed is called the “graceful exit,” and cosmologists have created parameters to make it work out for modeling. One of the side effects of this model is the creation of independent bubbles in space-time that when resolved to have occurred once, appear to have occurred many times. A model of inflation, proposed by Andrei Linde 1982, introduces new problems that have been solved by any number of inflationary theories, including “chaotic” inflation where the principles of physics are different in each universe, and where we live in a “bubble” where the constraints are suitable for life.

And so ends Chapter One.

Chapter Two begins with a tour of modern philosophers, historians, and biographers identifying the earliest depictions of the multiverse in ancient writing. Due to the greatest availability of sources in medieval records, Siegfried starts with the medieval view of the multiverse. The medieval cognoscenti though capable in mathematics were beholden to scripture. Reality took a back seat to religion. That is, the philosophy of how things should be according to scripture, is more true than evidence and discovery in-the-world. The consequence of such a world view twists mathematics to match religious doctrine.

Siegfried writes, “Science was theology’s handmaiden, a tool for discovering the glory of God’s creation.” The takeaway for readers will be an extensively detailed view of a broken way of thinking and will find educated and imaginative minds having very little to do with reality. And mathematics applied to nonsense, is still nonsense. That is, a world where calculating the number of angels that can dance on a pin, or calculating how the universe revolved around the Earth, an Earth that is spherical and motionless, is considered the righteous, and not just the right, thing to do.  In this world, whether there is, or is not a multiverse, depended on considering what the Catholic Church believed.

Siegfried next goes back in history to the Greeks, and what the Greeks thought of the multiverse. A few Greek philosophers did believe in infinite worlds, but not Aristotle, and much of Siegfried’s discourse is on Aristotle as much of Aristotle’s work was translated and taught in the medieval era. Aristotle, having died 300 years before Christ, held sway in medieval minds even though he had a philosophy that did not always line up with Christian teachings.

Though attempts to ban Aristotle’s works in their entirety was not successful, but banning the teaching of a few of Aristotle’s specific propositions was successful, for example, claiming God could not have made multiple worlds, where, as noted earlier, in the year 1277, Christian doctrine was revised to allow God to do anything, including create multiple universes.

Chapter Three provides the Greek view of the atom and here Siegfried offers a reasoned connection between the very, very small, and the very, very huge; the atom to the cosmos. However, Siegfried also tries too hard in putting the “popular” into popular science, proverbially “jumping the shark” when he claims, “Epicurus was an advocate of happiness. He would have appreciated the line “happiness is truth” from the 2013 Pharrell Williams song ‘Happy.’”

Chapter Four considers the evolution of the idea of the universe over time. Once, the word “world” was equivalent to “universe”—there was no concept of the universe as we understand it today, and the meaning of “world” evolved from what our eyes could see to the extent of what could be measured, if not seen. Siegfried tells us that Roger Bacon, a 13th century scholar, addressed the possibility of the multiverse in detail, only to end up agreeing with Aristotle that it was impossible. William of Ockham, of the eponymous razor, too disbelieved of the possibility of the multiverse, stating, “I say God can make a better world than this one.” One might very well counter, “perhaps He did.”

Though in one instance, countervailing religious thought, medieval logicians and mathematicians in their attempt to cope with the concept of infinity, let their logic to get ahead of doctrine when they considered that if the universe were infinite, then the Earth could not be the center of the universe, because infinity does have a center. Boom! Medieval mind blown.

The historical tipping point from religious doctrine to science occurred when philosophers begab to consider the question as to why God would choose to act by miracle when He could also work his way by natural law. I.e. if God could do anything, then why not act by the laws of physics?

Centuries pass. Writing in 1543, Copernicus still had to worry about the Church and considered not putting his name on De Revolutionibus, his book that proposed that the Earth orbited the Sun. He did end up putting his name on the cover but, in its introduction, there was a disclaimer that Copernicus had no clear-cut memory of from where he got his idea. The story, as relayed by Siegfried, gets better. De Revolutionibus’ publication was overseen by a theologian, who might have on his own, put Copernicus’ name on the cover and may have written the introduction. The story is, Copernicus died soon after publication from the shock of betrayal.

It took one hundred years after De Revolutionibus for the Earth to orbit the Sun to be taken as true. But by the Renaissance, though philosophers and astronomers may have believed in an infinite cosmos with infinite universes holding infinite worlds, they also believed in magic, astrology, and angels. Polymath Sir Isaac Newton, who made personal astrology charts for pay, was not concerned with the multiverse, confining his attention to the solar system. Galileo claimed to be uninterested in the idea of the multiverse, believing that arguments both pro and con were inconclusive. Yet what Galileo did believe, had to be recanted. Siegfried tells us of the astronomer Johannes Kepler, who “managed to modernize the Copernican solar system by establishing that the planets’ orbits are ellipses . . .” Kepler too, was pressured by dictates of religion, and he also denied the possibility of a multiverse.

In the 18th century, the structure of the Milky Way, the galaxy that hosts our Sun, had not yet been resolved, though astronomer Thomas Wright considered the Sun to be no different from other star, and not at the center of the Milky Way, but at the edge. As for the possibility of other galaxies, resolving what were imagined at that time as “island universes” had to wait for larger telescopes. And though nebulae or fuzzy patches had yet been resolved, they began to be cataloged.

With better telescopes, the idea of the island universe gave way with the discovery of more and different strange objects such as spiral nebulae and supernova, and a new idea, there is only one universe comprised of a “complicated menagerie of objects.” The view of the existence of a solitary universe with billions of galaxies held sway, but not without argument, through the 19th century. In the early 1920s when Edwin Hubble was able to use the Cepheid starts as a “standard candle” to calculate the distance to the most distant stars, he showed that the universe was not just big, but also getting bigger.

Siegfried explains that the modern idea of the multiverse comes from quantum mechanics, and to illustrate his description, uses references from science fiction, including Star Trek and Dr. Who, TV shows that sometimes use plot lines based on real science. There is, however, an earlier, but still modern, concept of the multiverse that goes back to the 1950s with physics graduate student Hugh Everett III. Everett’s thesis advisor, Archibald Wheeler, who described his advisee’s theory as “barely comprehensible.” Published in 1952, Everett’s thesis became known to popular physics journals in the 1960s but missing its technical parts. Everett’s thesis became known as the many-worlds theory in 1970s and is believed by at a few physicists today. Siegfried interviews physicists both for and against the multiverse.

The largest following among physicists for the multiverse appears to be based on anthropic principles, that is, as the conditions for life come from arbitrary fundamental properties of atoms and forces that have to be just right, this is incredibly unlikely unless God designed it to be so. Such a thought can make non-religious physicists uncomfortable, however, if there were billions of multiple universes, each with arbitrary fundamental properties, that would change what is an unlikely special case into a mathematically probable case.

The explanation of how a multiverse can make our universe a probable one, comes from the trying to explain the accelerating expansion of the universe, which calls for new theories for the big bang—and here Siegfried neatly ties up loose threads from the first chapter. One model of the big bang, proposed by Andrei Linde in the early 1980s, implies that there were multiple or an infinite number of big bangs where it would be impossible to not have an infinite number of multiple universes, and each different as to its laws of physics. Though the math indicates there might be a multiverse, the physics, that is, the reality says there is only one.

There are different categories of multiverses, identified by Max Tegmark, book Our Mathematical Universe previously reviewed on this website. There is a more comprehensive list created by Brian Greene, in his book The Hidden Reality, which has its own Wikipedia page. Greene identifies nine different kinds of multiverses, though the more relevant point is not what kind of multiverse we have, but “whether they exist at all.”

Where we sit today on the idea of the multiverse, is that it is an unproven theory, as is string theory also, which according to Siegfried, also requires a multiverse. The match between what mathematicians can calculate, and what reality is, is debated today in the questions:

If you can imagine it, does it exist?

If you can calculate it, does it exist?

Does math describe reality, or is math reality itself?

The most readable tour of cosmology from the perspective of the multiverse to date.