Until the End of Time (2020)
Brian Greene (1963)
428 pages
Late in his deeply engaging and thought-provoking book Until the End of Time, physicist Brian Greene recalls being asked a question that would turn out to have a profound impact on his thinking: “Which news would affect you more … being told you have a year to live or that in a year earth will be destroyed?” (318) Reflecting on it, he came to recognize that although knowledge of his own death might trigger a range of intense reactions, “contemplating the end of the entire species seemed to do the opposite, yielding a sense of futility.” (319) For what we do and what we value to have meaning, he concluded, we must believe that there will be future generations to receive it; death may give an individual life meaning, but the death of the species thoroughly destroys that meaning.
The inflationary model arises out of Einstein’s general theory of relativity, from which, in the late 1970’s, the physicist Alan Guth demonstrated the mathematical possibility “that if a region of space was filled with a particular kind of substance … and if the energy contained … was spread evenly throughout the region … then the resulting gravitational force would … be repulsive.” (47) As happens through the book, this fascinating, if relatively prosaic, description leads to a bewildering conclusion:
Guth’s calculations revealed that if a tiny region, perhaps as small as a billionth of a billionth of a billionth of a meter across, was suffused with a certain type of energy … distributed uniformly, ... the repulsive gravitational push would be so forceful that the speck of space would inflate explosively, almost instantaneously [within a billionth of a billionth of a billionth of a second] stretching to as large as the observable universe, if not far larger. (47)
That is, the universe would inflate from a size unimaginably small, to one unimaginably large, over a time scale unimaginably small.
Already in the first 50 pages we discover that we need to buckle up for a wild ride that will, at nearly every turn, challenge our natural intuitions and understandings about the physical world.
So it is with Greene’s description of the development of stars and galaxies. The basic processes of stellar formation seem, if wondrously complex in their details, relatively straight-forward at a high level: gravity pulls clouds of matter together until the resulting body becomes so dense that nuclear forces cause the fusion of hydrogen into helium, creating a counter force, and so a balancing act leading to stars that burn for billions of years.
But then some troubling questions arise!
For one, if the leading theory for the big bang requires an extremely uniform initial distribution – as any non-uniformity would have led to the gravitational force being attractive – then where did the variability come from that allowed gravity to no longer be repulsive, and instead act to build up increasingly dense clumps of mass? The answer seems to lie in the presence of quantum uncertainty according to Greene: physicists theorize that at the quantum level, in the very early period after the big bang, there were tiny, quantum variations in energy that led to temperature differences on the order of “one part in a hundred thousand.” (51) Unimaginably tiny non-uniformities, but, over a time scale of millions of years, sufficient to initiate the clumping of matter that has led to stars and galaxies.
Another important question about the development of stars and galaxies arises from the second law of thermodynamics, which “declares that over time there is an overwhelming tendency of entropy to increase” (31); how, then, can a star be born, given that a star represents a relatively low entropy condition? The answer, according to Greene, is what he refers to as the entropic two-step: entropy can decrease in a portion of space (a star, or a life form), as long as such low entropy configurations raise the entropy of the surrounding environment. Thus, for example, the human body continually “dispens[es] entropy to the environment through waste and heat.” (108)
This requirement that heat be expelled to the environment by a lower entropy, ordered configuration like a star, a body or a brain, so that the overall entropy increases, becomes central to Greene’s pursuit of the ultimate future for thought, and whether it will continue to be possible in the distant future of our universe.
With molecular Darwinism and the entropic two-step as a basis, Greene describes how succeeding generations of stars provided the crucibles for the creation of the heavier elements. These elements end up a part of the formation of the planets, including earth, and play a fundamental role in the path to life. While Greene provides a concise introduction to these processes, a more detailed exploration can be found in the book Stardust, by astrophysicist John Gribben, who notes:
[although] we still don’t know exactly how life began … we do know, very precisely, what mixture of chemicals is required for the existence of life as we know it. And we know exactly where those chemicals come from --- as a natural by-product of the processes of star formation and evolution. (17, Stardust)
Gribben provides an engrossing portrait of the build up from a universe filled nearly exclusively with hydrogen to one in which the elements necessary for life emerge.
Greene turns in the middle section of his book to the current theories about how the combination of the entropic two-step and evolution that supported the creation of the solar system also collaborated on the development of life on earth. Over several chapters, he traces the path from the origins of the earliest individual cells to more complex forms that over several billion years came to develop mind and consciousness, and then examines the distinctively human characteristics of imagination, storytelling, the concept of the sacred, and ultimately the appearance of creativity.
Exploring each of these steps in some detail, he introduces readers to a sample of the competing theories proposed for how these features might have arisen. Some of these explanations, such as the biochemical theories for the development of cells with an ability to reproduce, can be analyzed and evaluated through experimentation. Others, he notes, such as hypotheses attempting to explain the origin of language, myth-making and the importance of the sacred, rely only on interpretation of an extremely limited and spotty historical record.
Throughout his review of these topics, Greene personalizes and enlivens the discussion by bringing in his impressions and opinions regarding the various theories. He describes his thinking as based on what he refers to as his reductionist approach to understanding phenomena, which he defines one in which it is considered at least theoretically possible to understand how any phenomenon works by breaking it down to the fundamental physical particles of the universe and the laws that govern them.
Then, during his discussion of consciousness, he introduces a related term, physicalists, which he defines as referring to those who believe that consciousness can be explained by “traditional scientific methods, solely invoking physical properties of matter.” (127) Not surprisingly, given his preference for reductionist approaches of understanding, he also takes on the mantel of physicalist, convinced that consciousness arises out of the complexity of the brain, and not due to some extra-physical property. Along those lines, he argues that we humans do not have free will, and, as opposed to finding this unacceptable and unthinkable, that we should celebrate that the feeling we do have free will has arisen out of the complexity of our minds. (In a public interview with Krista Tippett for her program On Being he has an entertaining exchange on free will with a doubting audience member, the transcript of which can be at the end of my review of Edward O. Wilson's The Meaning of Human Existence.)
Greene places a high level of significance on the human development of language and then storytelling. This recalls the wonderful book on this topic by historian Yuval Noah Harari, Sapiens, in which Harari describes the creation and telling of stories as having been central to the social development of Homo sapiens: “There are no gods in the universe, no nations, no money, no human rights, no laws, and no justice outside the common imagination of human beings.” (28, Sapiens) And, Harari argues, this ability to create shared myths and fictions gave us a decisive advantage over other human species. (My review of Sapiens is linked to at the right.)
Different from Harari’s focus in Sapiens on the implications of story-telling, however, Greene examines in detail various of the proposals of how language and eventually storytelling may have developed. He provides a fascinating introduction to these theories – and the uncertainty that surrounds them, given the difficulty of evaluating or demonstrating them through experimental techniques.
Having traced the path from the big bang to current day humankind, Greene then pivots in the final part of the book to explore potential futures for our universe, not only for the matter and energy in it, but also particularly for the possibility of thought being possible given what is theorized about the universe of the far future. And if the timeframe over which the entropic two-step and evolution have operated since the microbes came into existence on the earth of four billion years ago is challenging to grasp, know that that period becomes the merest blink of an eye in Greene’s push into what the future may hold.
In order to provide some small handhold for grasping the timeframes he considers, Greene asks us to picture the Empire State building. He defines street level as when the big bang occurs, the first floor as 10 years of the universe after the big bang, and then every subsequent floor as representing the passage of 10 times as many years as the previous one. Thus, the second floor is a hundred years after the big bang, the third floor a thousand years after, and so on. The effect of that increasing rate first truly sinks in when Greene notes that the time from the birth of our sun to its eventual death as a collapsed “dense ball of carbon and oxygen … ultimately transitioning to a dark frozen orb” (253) will be the short distance from a few steps below the 10th floor to a few steps above it. And yet, before his exploration of the future ends, he will have gone past the top, 102nd floor, 10120 years after the big bang. Far beyond it.
Although he bases his considerations of the future of the universe on the current understanding of its physical properties and laws, substantial uncertainty exists. This is reflected already in the first possibility he considers – that the energy that is thought to be causing the current expansion of the universe may not be constant, and so could increase. Currently, this repulsive force is extremely small, overwhelmed by the other forces in regions of space where matter is present – thus the extreme uniformity requirement for the big bang. Indeed, it is only in the huge, empty regions of space between groups of galaxies that the repulsive force dominates and so drives expansion. Some physicists, however, have modeled a scenario in which an increase in that repulsive force could overwhelm the other forces in the universe, shattering all matter apart in a so-called big rip, already around the 11th floor.
Comfortingly, Greene finds that scenario “unlikely,” and proceeds up the stairwell.
A fascinating event plays out just another floor higher, however, assuming the current expansion continues. By around the 12th floor, galaxies beyond our local group will have redshifted to the point of no longer being visible, due to the expansion of space having them moving away from our region of space faster than the speed of light. (Greene points out that this doesn’t violate Einstein’s theories, because these galaxies are not actually moving faster than the speed of light; it’s the fabric of space that is expanding ever faster, while the light coming to us from those galaxies is constrained by the speed of light.) By that point, the cosmic background radiation will also have dissipated to the point of becoming undetectable. Thus, astronomers of that future time will lack the two key experimental indictors that demonstrated to current day scientists that the universe is expanding, and they will thus find the observable universe to appear static!
Farther out, beyond the era when the stars begin winking out and the available matter for forming new stars becomes scarce, Greene considers the kinds of events that have low probability, but, when the time frames become long enough, can no longer be discounted. To demonstrate this idea based on a simple example he uses elsewhere in the book: one might dump a bag of pennies on a table once per minute, and not expect to get all heads for weeks, months and even years; but, do it for 10 million or ten billion years, and that very unlikely occurrence can no longer so readily be ruled out.
Some such events are not so surprising. For example, stars passing close enough to disrupt each other’s orbits around the galaxy, or their planets’ orbits, may be a once in a million years occurrence. Consider timescales of many billions of years, however, and the disruption of solar systems and even galaxies becomes likely. More dramatically, Greene points out that at the timescales represented by going to still higher floors, matter itself will decay.
Eventually, then, Greene arrives at his central question: at what point will thought become impossible? Clearly, having reached an epoch characterized by an “absence of complex atoms and molecules” (269), he is not considering thought in the sense of something performed by the human mind. Instead, he considers the broadest possible view: “our only constraint … being that the process of thought fully conforms to the laws of physics, can thought persist indefinitely?” (269)
What follows is a fascinating examination of the basic physical function of a human brain: take in energy, carry out processes related to thought, and release waste heat. And here again, entropy rears its head, as Greene focuses on the requirement that for thought to occur, there must be the ability to expel waste heat. The question then becomes, at what point might it no longer be possible to expel that waste heat, thus making thought impossible. Putting aside the possibility of intelligent life interceding in unimaginable ways in the future to counter the dissipation of the universe, and uncertainty over the future evolution of the physical laws and constants of the universe, he demonstrates that “the far future of thought is precarious” (278), at timescales well before we reach even the top floor of the Empire State Building.
At time scales far beyond the top of his tower to time, however, come truly mind-bending possibilities, again arising out of the current mathematical models of the universe and timescales that allow even highly unlikely events to occur. Among these oddities comes into play “that the second law’s decree is probabilistic. Entropy can decrease.” (269) A theoretical consequence of this are Boltzmann brains: spontaneous accumulations of particles which come together to form the exact configuration of a thinking brain – say, your brain as it exists at this very moment, or this next one, with all the “thoughts, memories, and sensations that currently reside in your brain.” (297) The implications, including whether I at this moment writing this, or you reading this, might in fact be a Boltzmann brain, are unsettling to consider.
And he has yet to come to his discussion of the possibilities of the multiverse…
In the concluding chapter, Greene returns to the question of the meaning of our lives in the face of the likelihood that thought will at some point come to an end in the universe: “even though we can contemplate eternity, and even though we can reach for eternity, apparently we cannot touch eternity.” (309) He argues that it makes no fundamental difference whether we know that the earth will be destroyed in 100 years, with all humankind lost, or that the universe will end in 10100 years, extinguishing all thought. In either case, eternity is lost to us, to all we think and do and learn. But, far from despairing over this conclusion, he finds it a reason to value and cherish our lives all the more, and proposes that “in our quest to fathom the human condition, the … direction to look is inward. … It is a direction that forgoes ready-made answers and turns to the highly personal journey of construction our own meaning.” (325)
In Until the End of Time Greene takes readers on a fascinating tour of the history and possible futures of our universe, as well as humankind’s place in that story, from the origin of the first cells to the development and ramifications of consciousness and thought. Where there are competing theories about a topic, he gives a sample of the different directions in thought on a topic, while still personalizing the account with his take on it. By including references throughout his narrative from pop culture, as well as classical literature and thought, he enlivens his presentation; his writing style transmitting the wonder he himself clearly feels as he engages on these topics.
Late in the book he touches briefly on the human longing for immortality. After summarizing the concerns many philosophers have expressed about how boring immortal life would likely turn out to be, he sounds a more optimistic note:
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 … to conclude that we would necessarily grow bored suggests an unduly parochial vision of the immoral mind. (317)
Greene turns the immortality question on its head, arguing that the significance immortality has for us makes clear how important we must take each day of our mortal lives.
In a sense, Greene’s conclusion echoes a writer who comes from a completely different tradition, the Christian philosopher Miguel de Unamuno. Unamuno argues in his essay Tragic Sense of Life that to see death as
a beatific vision, a loving contemplation in which the soul is absorbed in God and, as it were, lost in him” is misguided, and that, indeed: “man’s highest pleasure consists in acquiring and intensifying consciousness. Not the pleasure of knowing, exactly, but rather that of learning. In knowing a thing we tend to forget it, to convert it, if the expression may be allowed, into unconscious knowledge. Man’s pleasure, his purest delight, is allied with the act of learning, of getting at the truth of things, of acquiring knowledge with differentiation. (201, Tragic Sense of Life)
It is this passionate pursuit of learning that seems to drive Greene’s life and work, and that he imparts to readers on each and every page of his writings.
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Have you read this book, others by this author, or even similar ones by other authors? I’d enjoy hearing your thoughts.
Other of my book reviews: FICTION Bookshelf and NON-FICTION Bookshelf
