Jun 17, 2010
I am staggered by multiple universes. What? More than one universe? Isn’t the universe everything?
According to current cosmology, we live in an immense “multiverse”—a limitless ensemble of disconnected regions of space-time, each alone a “universe,” each alone exponentially larger than all we see with our largest telescopes, each alone with different laws of physics. And all together, unimaginably vast.
I am dizzy. What would multiple universes mean?
Max Tegmark, the scientific director of the Foundational Questions Institute (FQXi), which explores frontiers of physics and cosmology, explains that “our universe is just a finite region of space, so it’s not that crazy to imagine that there would be more. The simplest space is just the one that goes on forever, and that’s also what our simplest theory produces.”
In that theory, there are a vast number of different universes, perhaps an infinite number of different universes, each one formed from an earlier universe by being squeezed out in some way. “If one piece of space can generate more, then those are going to go on and do their own thing and, much like bacteria, just keep doubling, doubling, and doubling,” Tegmark says.
Space like bacteria, doubling without end? Nice metaphor, but is this poetry or reality?
“I really believe it’s real,” Tegmark says. “I’m amazed by the fact that not only do we have good evidence for some kind of parallel universes existing, but also there are many different kinds of parallel universes. It’s just shockingly difficult to write down a theory that describes everything we see in the universe and nothing more.”
He continues: “We have a very beautiful theory for why the universe is so big. It’s called ‘inflation,’ where a very small amount of space stretches out and produces more volume. The problem is this inflation never stops. Perpetual inflation generates infinite space.”
There are several ways to generate multiple universes, Tegmark says. Quantum mechanics can create multiple universes due to quantum branching of fundamental particles that make “choices” based on the probabilities that lie at the heart of quantum theory. In addition, he says, “modern string theory provides a vast number of possible solutions to its equations so that the best theory we have for what made space so big ends up making different parts of space, which are these other solutions.”
Tegmark goes further still. “Ultimately,” he says, “there might even be an even more extreme kind of parallel universe. Assume we can figure out a set of equations that can describe everything fundamental about this universe—equations you can print on a T-shirt. There’s probably a different universe for every such set of equations, for every kind of T-shirt.”
Multiple universes would change just about everything we thought we knew, and Tegmark poses at least four radically different kinds of multiple universes: cosmic inflation of space; quantum branching; string theory; and, wildly, innumerable sets of mathematic equations.
I stand stunned by the reach of reality. I seek meaning—the meaning of it all. But meaning seems swallowed by interminable spaces. And if there’s no meaning? I mustn’t fake it, or even force it.
Anthony Aguirre, a theoretical cosmologist and FQXi’s associate scientific director, says that if a multiverse really exists, “it would alter the nature of reality in the most fundamental way. The multiverse is not just much bigger, it’s also much more diverse, with each universe having different properties—which is even more exciting. It would change the way we think about almost every question in cosmology and fundamental physics.”
Aguirre relates the multiverse to the profoundly baffling question, “Why does our universe seem so hospitable to life?” He says: “If fundamental parameters were changed just a little—the strength of the electric interaction or of gravity—life as we know it could not happen. So how did we get so lucky? It could have just been that the universe rolled the dice and we landed 30 sixes in a row and here we are. That seems hard to swallow, so you look for other explanations. Could it be that life forms naturally in any sort of universe? That would be pretty exciting. It would mean that, at least in theory, there are wildly different life forms, based on totally different physics.”
Alternatively, he continues, “it could be that there was some element of design, some supernatural agent, that created the universe or some kind of natural beings who traveled back in time to create the universe or who create universes in their labs. That’s another set of options. Or it could be that the multiple universes are real, and they are hugely diverse, so that [it is not at all surprising] we live in just the place where we can live.”
What intrigues me about this question is that it’s hard to imagine additional categories of explanation, and it seems as if the categories we have are universally exhaustive—wild luck, different life forms based on different physics, some kind of design, and multiple universes conspiring with self-selection. In other words, every possibility that can exist we have in one of these categories. And every “ultimate explanation” feels literally unbelievable.
The most accepted mechanism for generating multiple universes is cosmic inflation. Alan Guth is its originator. What meaning does he find in multiple universes?
“One of the lessons that one learns early on when starting to think about cosmology is that the universe is unbelievably large and, by any comparison, we are unbelievably small,” Guth says. “And if this theory called ‘inflation’ is right, there are probably an uncountable number of ‘pocket universes,’ each of which is vastly larger than the universe we observe. In fact, the number is very likely infinite, which would mean that any importance that we have has to be importance that we give to our own lives. We can’t look to the cosmos to find importance of human civilization.”
I say to Guth: What has always astounded me, and what can literally make me quiver, is the fact that all of this knowledge has been achieved in less than 5,000 years of recorded history and in about 500 years of science. That’s less then an eye blink in the totality of universal time.
“I completely agree,” Guth says. “It’s mind-boggling how successful cosmology has been. After I first posed inflation back in 1980, we discovered in 1982 that inflation made definite predictions for the nonuniformities in the cosmic background radiation. At the time we were doing these calculations, we didn’t think there was any chance in the world that these very minute variations would ever be observed experimentally. Here’s why this seemed so hard. The temperature of the cosmic background radiation is 3 kelvins and the walls of this room are 300 kelvins, so it’s 100 times as hot in this room as the temperature of the cosmic background radiation. Now, the intensity of radiation is proportional to the fourth power of the temperature. This means that the intensity of the radiation coming off the wall is 100 million times more than the intensity of the radiation in the cosmic background radiation. Yet astronomers can detect this cosmic background radiation, and they can even detect variations in it that are on the order of one part in 100,000. And then to see that the measurements actually agree with the prediction of inflation theory is just astounding.”
I ask Guth about inflation’s timeframe, going back, not to the first second of the universe 13.7 billion years ago, but to a minuscule fraction of a second, 10-37th to 10-35th seconds to be astonishingly precise.
“When I started this,” he recalls, “it seemed absolutely absurd, but the origin of most of these absurd numbers comes from the grand unified theories of particle physics on which this cosmology is based.”
Another incredible fact: To understand the origin and structure of the entire universe, we need to understand the quantum mechanics of the smallest things in the universe, and vice versa! And these two ends of the size spectrum are separated by more than 60 orders of magnitude.
To me, Guth’s insight of cosmic inflation is one of humanity’s greatest achievements. Ever! I’m stupefied by what one ordinary human being has discovered. It’s exhilarating to appreciate the power of human thought.
But how to get from cosmic inflation to multiple universes?
Andrei Linde devised eternal, chaotic inflation, showing how myriads of universes are generated without end. And he, too, wonders what’s it all about.
Linde explains how two dominant theories—multiple universes in cosmology and string theory in particle physics—work together. String theorists no longer expect a single, unique solution to their equations, he says: “In the string theory ‘landscape’ (meaning many, many different possibilities), there are at least 10-500 possibilities or ‘vacua’—each of which could generate universes” (based on the different ways of “compactification” of the 11 or so dimensions of string theory).
Whereas most physicists believe that multiple universes cannot be verified, Linde points to what he considers to be experimental evidence: the correlation of our existence with the exquisitely specific requirements of the constants of physics, such as the mass of the electron. “If the electron mass would be two times larger or smaller, we would be dead,” he says. “Our life is correlated with this particular value. So then why is it so that we have all of these unexplained numbers with very strong correlations with our existence? The only theory that as of now explains this experimental fact is the multiverse theory.” Each universe has different values for the constants of physics, he explains, so that “you can try them out: You can try to live here, you can try to live there.” And whichever works, apparently, works.
To Linde, the deep meaning of multiple universes is that they explain the incredible fine-tuning of our single universe, the so-called “anthropic principle.” Yet innumerable universes seem a hefty price to pay for explaining the one universe in which we find ourselves.
And not every cosmologist is a convert. Paul Davies equates the multiverse theory with the “God theory”—which for him is not a compliment—because, he says, both theories account for this universe “by going outside of it.”
He says “the simplest thing is to try to explain the universe we see from entirely within it, without appealing to hypothetical entities that exist outside of it. The problem about multiple universes is not that such things are scientifically unreasonable. They’re very reasonable. But how on earth are we going to know about them?” Eternally expanding universes would be branching off and expanding faster than the speed of light, so even in principle, they could never be seen.
“The main objection to a multiverse is philosophical, not scientific, in that what you’re doing is trying to explain the universe we see by appealing to an infinite number of universes that we don’t see,” he says. To him, that “is no better than traditional theology, which simply states that there is an unexplained God outside of the universe that is necessary to explain what we see within the universe.”
It may be the case, he says, that “a proper mathematics analysis would find that the complexity of the explanation of the multiverse, which is an infinite number of universes we don’t see, is about the same as the complexity of the explanation of traditional theology, which is an infinitely complex God outside the universe that we don’t see. Multiverse and God are really the same thing in different languages. And so my point of view is ‘a plague on both your houses’; we need to try to find the explanation for the universe from within it, from what we see. We should not appeal to anything external; we should not multiply these unseen entities.”
Davies rejects the idea that “any universe you like is out there somewhere. I think such an idea is just ridiculous and it explains nothing. Having all possible universes is not an explanation because by invoking everything, you explain nothing.”
So no multiverse, no God. OK, Paul, then what?
If multiple universes are real, an infinite number of universes, everything changes. Whatever you believe—no God, God—nothing‘s the same. If only the material world exists, the material world is inconceivably larger. If an infinite God exists, God’s infinity is amplified by astounding new meaning.
If multiple universes are real, Guth and Linde will be lauded as discoverers for all future history. Yet they are normal people. Normal people on an ordinary planet. Normal people envisioning multiple universes. Normal people seeing shadows of infinity.
I can’t imagine anything closer to truth.
Robert Lawrence Kuhn speaks with Max Tegmark, Anthony Aguirre, Alan Guth, Andre Linde, and Paul Davies in “What Do Multiple Universes Mean?”—the 20th episode in the new season of the Closer To Truth: Cosmos, Consciousness, God TV series (59th in total).
The series airs on PBS World (often Thursdays, twice) and many other PBS and noncommercial stations. Every Thursday, participants will discuss the current episode.
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