Why Earth’s History Appears So Miraculous
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Though the end of the universe is typically thought of as a slow unraveling in the far future—the eternal dissipation into darkness after our brief springtime, leading to a cold, empty epoch that will stretch into forever—the universe could also end violently, Aguirre says, and at any time.
“So there are various fields that permeate space,” he began. “The electromagnetic field is a common one. The electron field, the proton field, the Higgs field—these are all fields that exist everywhere. And when we have empty space what we really mean by that is that there are no excitations of these fields. So an electron is like an excitation of the electron field, and when we take all the electrons away, the field is still there. We say that it’s in its vacuum state. But a vacuum state is not necessarily completely stable. It’s the state that you get if you take away all the electrons, but it might still have some energy associated with it. And that energy level could, in principle, be different, or lower. In fact, there’s no particularly good reason to think that the vacuum that we’re in now is the lowest-possible vacuum state in terms of energy. And there are actually pretty good reasons to think that it’s not.”
He started laughing nervously. I didn’t understand why, but would go on to learn that if the vacuum state spontaneously dropped to some new energy level the laws of physics would go berserk and the universe as we know it would be over.
“It would start out as some sort of point-like event somewhere in the universe that would then expand at the speed of light and just kind of destroy everything in a sphere,” Aguirre said. “So as soon as that bubble passed over us we would then be in some other state of the laws of physics that was totally incompatible with us.”
This outrageous disaster isn’t just some academic flight of fancy, the product of coffee-addled fugues at a chalkboard. Just such a psychedelic transition might have happened in our universe’s infancy, as the laws of physics congealed from the primordial fire of the Big Bang, and the fundamental forces we know today crystallized from more exotic forms. In fact, in 2012, when the world celebrated the discovery of the Higgs field (via the Higgs boson)—the thrilling validation of half a century of theory—some physicists quietly averred that the Higgs appeared to be unstable, and may someday destroy the universe.
“So it could be the Higgs field, but it could be any combination of all the other fields in physics that, in principle, could transition to some other vacuum state.”
If it happened it would be the end of everything. And there almost certainly would be no observers afterward.
“But since we’re still here, there’s a reasonable inference that the timescale for this is billions of years, at least. But there’s no particularly good reason to think that it’s—well,” he stopped himself.
“So, there are different arguments you could make,” he said. “You could say that if it’s already been billions of years it could just as easily be trillions or quadrillions or quintillions of years or whatever, so let’s not worry too much, or ...”
Or it could be like those asteroids that kept missing the planet for billions of years before we got here, securing our eventual appearance but blinding us to future peril. Just as observers never show up on worlds that are quickly destroyed, they also don’t appear in universes that quickly unravel. No matter how common they are.
“It may be that ultimately the reason we’re around for so long,” Aguirre said, “is that we’re around.”
The ghosts of innumerable ill-fated universes began to hover over our conversation like skeletons at the feast—or planes at the bottom of the English Channel.
“So,” I started, “there are billions of universes that were hospitable to life but they just—”
“Yeah, they just didn’t last long enough. And we’re one of the universes that lasted long enough ... It may be that we’re kind of living on the edge. Like, we’re sort of the shortest-lived universe that would allow stuff to arise and start thinking about short-lived universes and so on. So that would be a bad scenario.”
Aguirre started laughing again. Just like Sandberg’s mysteriously absent continent-spanning craters, the end of the universe itself might be looming in the anthropic shadows, held at bay—until now—by our very existence. Perhaps it’s only possible to wake up in a universe that has managed an almost impossible cosmic stay of execution lasting billions of years. In the early days of the Large Hadron Collider, when the megamachine kept running into seemingly endless, and increasingly improbable, financial and technical snags, some researchers—calling these mishaps “anti-miracles”—even half-seriously proposed that the universe was censoring us from this sort of destruction of the world occasioned by a successful run of the collider.
There’s something bracing in the sort of license that cosmology grants to its practitioners to think very strange thoughts.
“Do you want to go through the looking glass?” Aguirre asked me.
“I’d love to,” I said, surprised that we hadn’t already done so.
Quantum mechanics, the remarkably successful and remarkably strange physics of the very small, makes predictions whose accuracy can be verified in the real world to an almost arbitrary number of decimal places. In other words, quantum mechanics provides the best description of how the world works at its most fundamental level. One of the most bewildering experimental results of quantum mechanics, and of the 20th century, is that particles seem to exist in a sort of probabilistic purgatory, existing everywhere at once and nowhere in particular, hazily spinning both clockwise and counterclockwise at the same time—that is, until they are observed. Once measured, these many possibilities collapse into one coherent result and the observer measures some specific value for a particle.
One of the leading interpretations of this quantum weirdness is that all of the possible realities for the particle that were winnowed away in this act of observation actually are realized somewhere in branching-off parallel universes, by observers in parallel universes—parallel universes just as real as the one in which we happen to live. Though the universe may be infinite in distance it may also be infinitely divergent in this sort of ontological zoo. This is called the “many-worlds interpretation” of quantum mechanics. Again, this is not an unpopular or esoteric theory. It is one of the most widely subscribed interpretations of the peculiar world of quantum mechanics among physicists. And if a universe-destroying vacuum-decay catastrophe played out, it would take place in this strange, existential arena.
“What’s interesting about the nucleation of these vacuum-decay bubbles is that it’s a quantum-mechanical event,” Aguirre said about the ultimate catastrophe.
That is, the spontaneous initiation of the end of the universe would be probabilistic—like an extremely high-stakes version of Schrödinger’s hapless cat in a box—splitting reality into versions where everything is obliterated and a luckier version that’s spared. And given that we may be creatures of the “many worlds” multiverse, constantly splitting off into different lives, Aguirre wonders whether we could ever actually experience the quantum apocalypse sweeping through the void when it arrived at our doorstep.
“So, do we notice anything? That’s the question.”
If the observer selection bias applies to our own lives, then perhaps we’re constantly being censored to the end of the universe.
“So suppose the many-worlds interpretation of quantum mechanics is right,” he says. “So, one of the two versions of us ceases to exist, but do we actually notice that? So one of us keeps going on just as if nothing happened. Arguably, from moment to moment, I can’t rule out that five minutes ago the other version of us died. There’s no way for me to say that. So there’s an interesting, troubling question as to whether these things could be happening all the time and we just don’t even notice it.”
