Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

Much as mature Great Danes are large and mild while shih tzu puppies are small and manic, large black holes are calm and cool while small black holes are frenzied and hot.

As a black hole radiates, its mass decreases and, in turn, its temperature increases. What happens when the black hole is almost gone, when its mass nears zero and its temperature soars toward infinity? Does it explode? Does it fizzle? Something else? We don’t know.

According to general relativity, the recipe for building a black hole is dead simple: gather any amount of mass and form it into a ball of a sufficiently small size.11 Of course, even a passing familiarity with black holes leads you to expect that “sufficiently small” means really small, spectacularly small, ludicrously small. And in some cases your expectation is right on the mark. To turn a grapefruit into a black hole, you’d need to squeeze it down to about 10−25 centimeters across; to turn the earth into a black hole you’d need to squeeze it down to about two centimeters across;

Atoms and molecules and the structures they build depend intimately on the properties of their particulate constituents. The sun shines because of the physics and chemistry of hydrogen and helium, which depend on the properties of protons, neutrons, electrons, neutrinos, and photons. Cells do what cells do mostly because of the physics and chemistry of the molecular constituents, which again depend on the properties of the fundamental particles. If you change the masses of the fundamental particles you change how they behave, and so you change more or less everything.

Being swept away by a light-speed wall of doom, while swift and painless, is something most of us would rather avoid.

From a staunchly physicalist perspective, all of that is in your head right now because of the particular arrangement of the particles that are in your head right now. Which means that if a random spray of particles flitting through the void of a structureless, high-entropy universe should, by chance, spontaneously dip to a lower-entropy configuration that just happens to match that of the particles currently constituting your brain, that collection of particles would have the same memories, thoughts, and sensations that you do. Whether in honor or reproach, I don’t know which, such hypothetical, free-floating, untethered minds formed by the rare but possible spontaneous coming together of particles into a special, highly ordered configuration have become known as Boltzmann brains.20

A survey of a long-enough stretch on the timeline would thus reveal that the total population of Boltzmann brains far exceeds the total population of traditional ones. The same is true even if we focus on only those Boltzmann brains whose particulate configurations imprint the erroneous belief that they arose in the traditional biological manner. Once again, however rare a process, over arbitrarily long durations it will happen arbitrarily many times.

If you then ask yourself for the most likely way that you acquired the beliefs, memories, knowledge, and understanding that you currently hold, the dispassionate answer based on sheer population size is clear: your brain just spontaneously formed from particles in the void, with all of its memories and other neuropsychological qualities imprinted through the particular configuration of the particles. The story you told of how you came to be is touching but false. Your memories and the various chains of reasoning that have led to your knowledge and your beliefs are all fictitious. You do not have a past. You have just come into existence as a disembodied brain endowed with thoughts and memories of things that never happened.25

If a brain, yours or mine or anyone’s, can’t trust that its memories and beliefs are an accurate reflection of events that happened, then no brain can trust the supposed measurements and observations and calculations that constitute the basis of scientific understanding.

For the kicker, among such conclusions, now rendered untrustworthy, is the likelihood that I’m a spontaneously created brain floating in the void.

In short, rare spontaneous drops in entropy, which are entailed by the laws of physics, can shake our confidence in the laws themselves and all they supposedly entail. By considering the laws operating over arbitrarily long durations, we are plunged into a skeptical nightmare, rattling our trust in everything.

The quantum jitters that result in one history being different from another are random and hence they sample every possible configuration. No history is left behind. The infinite collection of universes thus realizes every possible history, and each such history is realized infinitely often.

This entails a peculiar conclusion: the reality that you and I and everyone else experiences is happening out there in other regions—in other universes—over and over again. Modify that reality in any manner that is not strictly forbidden by the laws of physics (you can’t violate the conservation of energy or electric charge, for example) and it is also out there, over and over again. It tickles the mind to fathom realms where alternate realities play out—Lee Harvey Oswald misfires, Claus von Stauffenberg succeeds, James Earl Ray doesn’t. Quantum aficionados will recognize a similarity to the so-called Many Worlds interpretation of quantum physics, which envisions that every possible outcome allowed by the quantum laws takes place in its own separate universe.

Physicists have debated for more than half a century whether this approach to quantum mechanics is mathematically sensible and whether, if it is, the other universes are real or merely useful mathematical fictions. The essential difference in the cosmological theory we are now recounting is that the other worlds—the other regions—ar...

Against this backdrop, Garriga and Vilenkin offer a curious sort of optimism. They note that because every history plays out across the infinite collection of universes, some will necessarily enjoy rare but fortuitous drops in entropy that keep particular stars and planets intact, or yield new environments containing sources of high-quality energy, or any of a wide array of unlikely developments that will allow life and thought to persist far longer than otherwise expected. Indeed, as Garriga and Vilenkin argue, if you select any finite duration, however long, there will be universes among the infinite collection in which unlikely processes swim against the entropic stream to keep life alive for at least that duration. And so, among the infinity of universes, some will host life and mind arbitrarily far into the future.

Life and thought here in our universe, in what we have long considered the universe, will likely draw to a close. Perhaps there is consolation in knowing that somewhere in the vast reaches of infinite space, well beyond the boundary of our realm, life and thought may persist, conceivably indefinitely. Still, even though we can contemplate eternity, and even though we can reach for eternity, apparently we cannot touch eternity.

Sensitivity to pattern is, in part, how we’ve prevailed. We look for connections. We take note of coincidences. We mark regularities. We assign significance. But only some of these assignments result from considered analyses delineating demonstrable features of reality. Many emerge from an emotional preference for imposing a semblance of order on the chaos of experience.

often speak as if our mathematical equations are out there in the world, relentlessly controlling all physical processes, quarks to the cosmos. That may be the case. Perhaps we will one day establish that mathematics is fundamentally stitched into the tapestry of reality. When you work with the equations day in and day out it surely feels that way. However, I am more confident in asserting that nature is lawful—that the universe is made of ingredients whose behaviors follow a lawful progression—the very basis of the journey we have taken in this book.

Although I consider it unlikely, I allow for the possibility that in the future, when we proudly show alien visitors our equations, they will politely smile, tell us that they too started with math but then discovered the real language of reality.

Historically, the physical intuition of our ancestors was informed by the patterns evident in familiar encounters, from falling rocks to snapping branches to rushing streams; there is manifest survival value in having an innate sense of everyday mechanics.

I hold to a version of this perspective when we shift focus to qualities that guide our evaluation of human experience. Right and wrong, good and evil, destiny and purpose, value and meaning are all profoundly useful concepts, but I am not among those who believe that moral judgments and assignments of significance transcend the human mind. We invent these qualities. Not from whole cloth. Our Darwinian-selected minds are predisposed to be attracted to or repulsed by or scared of various ideas and behaviors.

Some 13.8 billion years ago, within ferociously swelling space, the energy contained in a tiny but ordered cloud of inflaton field disintegrated, shutting off repulsive gravity, filling space with a bath of particles, and seeding the synthesis of the simplest atomic nuclei. Where quantum uncertainty rendered the density of the bath slightly higher, the gravitational pull was slightly stronger, enticing particles to fall together in ever-growing clumps, forming stars, planets, moons, and other heavenly bodies. Fusion within stars, as well as rare but powerful stellar collisions, melded simple nuclei into more complex atomic species, which, upon raining down on at least one planet in the making, were coaxed by molecular Darwinism to assemble into arrangements capable of self-replication. Random variations of the arrangements that happened to abet molecular fecundity spread widely. And among these were molecular pathways for extracting, storing, and dispersing information and energy—the rudimentary processes of life—which, through the long haul of Darwinian evolution, became increasingly refined. In time, complex, self-directed, living beings emerged.

Particles and fields. Physical laws and initial conditions. To the depth of reality we have so far plumbed, there is no evidence for anything else. Particles and fields are the elementary ingredients. The physical laws prompted by the initial conditions dictate progression. Because reality is quantum mechanical, the pronouncements of the laws are probabilistic, but even so the probabilities are rigidly determined by mathematics. Particles and fields do what they do without concern for meaning or value or significance. Even when their indifferent mathematical progression yields life, physical laws maintain complete control. Life has no capacity to intercede or overrule or influence the laws.

Through the force of selection, evolution takes a hand in shaping life’s behavioral repertoire, favoring activities that advance survival and reproduction. Among these, ultimately, is thought. The capacity to form memories, analyze situations, and extrapolate from experience provides potent artillery in the arms race for survival.

Add in language, and one such self-aware species rises above the needs of the moment to see itself as part of an unfolding from past to future. With that, winning the battle is no longer the only concern.

And so we develop explanations of how the universe came to be and how it might end. We tell and retell stories of minds making their way through worlds, real and fanciful. We imagine realms populated by departed ancestors or semi-powerful or all-powerful beings that reduce death to a stepping-stone in an ongoing existence. We paint and carve and etch and sing and dance to touch these other realms, or to pay homage to them, or simply to imprint the future with something that attests to our brief time in the sun.

But even with their evolutionary origin still fodder for debate, these aspects of human behavior manifest a widespread need to step beyond the mere eking out of transitory survival. They reveal a pervasive longing to be part of something larger, something lasting. Value and meaning, decidedly absent from the bedrock of reality, become intrinsic to a restless urge that elevates us above indifferent nature.

Whereas Gottfried Leibniz wondered why there is something rather than nothing, the deeply personal dilemma is that self-aware somethings, like us, subsequently dissolve into nothing. To acquire a temporal perspective is to realize that the vibrant activity animating one’s own mind will one day cease.

A frequent if fraught expectation, lightly entertained by many and intensely pursued by some, is that we would be entirely better off if death would bow out of human proceedings altogether. From ancient myth to modern fiction, thinkers have pondered the possibility. Perhaps it’s telling that in these excursions things don’t always turn out so well.

Notwithstanding these concerns, I suspect that we are sufficiently resourceful—and endowed with endless time we would become all the more so—to grow into thoroughly well-adjusted immortals. Our needs and capacities would likely transform beyond recognition, rendering assessments based on what keeps us engaged and motivated in the here and now of little or no relevance.

The imagined fate of value and significance in an immortal world makes clear that in a mortal one understanding a great many of our decisions, choices, experiences, and reactions requires seeing them in the context of limited opportunity and finite duration.

Most of us deal quietly with the need to lift ourselves beyond the everyday. Most of us allow civilization to shield us from the realization that we are part of a world that, when we’re gone, will hum along, barely missing a beat. We focus our energy on what we can control.

Through it all, we grow accustomed to looking out to the world to find something to excite or soothe, to hold our attention or whisk us to someplace new. Yet the scientific journey we’ve taken suggests strongly that the universe does not exist to provide an arena for life and mind to flourish. Life and mind are simply a couple of things that happen to happen. Until they don’t.

Even so, to see our moment in context is to realize that our existence is astonishing. Rerun the big bang but slightly shift this particle’s position or that field’s value, and for virtually any fiddling the new cosmic unfolding will not include you or me or the human species or planet earth or anything else we value deeply.

Accompanying these breathtaking insights are deep and persistent questions. Why is there something rather than nothing? What sparked the onset of life? How did conscious awareness emerge? We have explored a range of speculations, but definitive answers remain elusive. Perhaps our brains, well adapted for survival on planet earth, are just not structured for resolving these mysteries. Or perhaps, as our intelligence continues to evolve, our engagement with reality will acquire a wholly different character, with the result that today’s towering questions become irrelevant. While either is possible, the fact that the world as we now understand it, remaining mysteries and all, holds together with such a tight mathematical and logical coherence, and the fact that we have been able to decipher so much of that coherence, suggests to me that neither is the case.

As we hurtle toward a cold and barren cosmos, we must accept that there is no grand design. Particles are not endowed with purpose. There is no final answer hovering in the depths of space awaiting discovery. Instead, certain special collections of particles can think and feel and reflect, and within these subjective worlds they can create purpose. And so, in our quest to fathom the human condition, the only direction to look is inward.