Words

Welcome to this week’s installment of the From Eternity to Here book club. Today we look at Chapter Two, “The Heavy Hand of Entropy.”

[By the way: are we going too slowly? If there is overwhelming sentiment to move to two chapters per week, that would be no problem. But if sentiment is non-overwhelming, we’ll stick to the original plan.]

Excerpt:

While it’s true that the presence of the Earth beneath our feet picks out an “arrow of space” by distinguishing up from down, it’s pretty clear that this is a local, parochial phenomenon, rather than a reflection of the underlying laws of nature. We can easily imagine ourselves out in space where there is no preferred direction. But the underlying laws of nature do not pick out a preferred direction of time, any more than they pick out a preferred direction in space. If we confine our attention to very simple systems with just a few moving parts, whose motion reflects the basic laws of physics rather than our messy local conditions, there is no arrow of time—we can’t tell when a movie is being run backward…

The arrow of time, therefore, is not a feature of the underlying laws of physics, at least as far as we know. Rather, like the up/down orientation space picked out by the Earth, the preferred direction of time is also a consequence of features of our environment. In the case of time, it’s not that we live in the spatial vicinity of an influential object, it’s that we live in the temporal vicinity of an influential event: the birth of the universe. The beginning of our observable universe, the hot dense state known as the Big Bang, had a very low entropy. The influence of that event orients us in time, just as the presence of the Earth orients us in space.

This chapter serves an obvious purpose — it explains in basic terms the ideas of irreversibility, entropy, and the arrow of time. It’s a whirlwind overview of concepts that will be developed in greater detail in the rest of the book, especially in Part Three. As a consequence, there are a few statements that may seem like bald assertions that really deserve more careful justification — hopefully that justification will come later.

Here’s where I got to use those “incompatible arrows” stories I blogged about some time back (I, II, III, IV). The fact that the arrow of time is so strongly ingrained in the way we think about the world makes it an interesting target for fiction — what would happen if the arrow of time ran backwards? The straightforward answer, of course, is “absolutely nothing” — there is no prior notion of “backwards” or “forwards.” As long as there is an arrow of time that is consistent for everyone, things would appear normal to us; there is one direction of time we all remember, which we call “the past,” when the entropy was lower. It’s when different interacting subsystems of the universe have different arrows of time that things get interesting. So we look briefly at stories by Lewis Carroll, F. Scott Fitzgerald, and Martin Amis, all of which use that trick. (Does anyone know of a reversed-arrow story that predates Through the Looking Glass?) Of course these are all fantasies, because it can’t happen in the real world, but that’s part of the speculative fun.

Then we go into entropy and the Second Law, from Sadi Carnot and Rudolf Clausius to Ludwig Boltzmann, followed by some discussion of different manifestations of time’s arrow. All at lightning speed, I’m afraid — there’s a tremendous amount of fascinating history here that I don’t cover in anywhere near the detail it deserves. But the real point of the chapter isn’t to tell the historical stories, it’s to emphasize the ubiquity of the arrow of time. It’s not just about stirring eggs to make omelets — it has to do with metabolism and the structure of life, why we remember the past and not the future, and why we think we have free will. Man, someone should write a book about this stuff!

Welcome to the first installment of the From Eternity to Here book club. We’re starting at the beginning, with Chapter One, “The Past is Present Memory.”

Excerpt:

The world does not present us with abstract concepts wrapped up with pretty bows, which we then must work to understand and reconcile with other concepts. Rather, the world presents us with phenomena, things that we observe and make note of, from which we must then work to derive concepts that help us understand how those phenomena relate to the rest of our experience. For subtle concepts such as entropy, this is pretty clear. You don’t walk down the street and bump into some entropy; you have to observe a variety of phenomena in nature and discern a pattern that is best thought of in terms of a new concept you label “entropy.” Armed with this helpful new concept, you observe even more phenomena, and you are inspired to refine and improve upon your original notion of what entropy really is.

For an idea as primitive and indispensable as “time,” the fact that we invent the concept rather than having it handed to us by the universe is less obvious—time is something we literally don’t know how to live without. Nevertheless, part of the task of science (and philosophy) is to take our intuitive notion of a basic concept such as “time” and turn it into something rigorous. What we find along the way is that we haven’t been using this word in a single unambiguous fashion; it has a few different meanings, each of which merits its own careful elucidation.

The book is divided into four major parts — Part One gives an overview of the issues, Part Two discusses relativity and time travel, Part Three (the longest and best part of the book) is about reversibility, entropy, and the arrow of time proper, and Part Four puts it all into a cosmological context. So Part One is somewhat out of logical order — it’s an attempt to survey the terrain and raise some ideas that will come to fruition later in the book.

The basic point of Chapter One is to examine the ways in which we use the concept of “time.” I’ll readily admit that this doesn’t sound like the sexiest idea for an opening chapter. (In my next book, an important character will be murdered within the first few pages, after which his beautiful daughter will be compelled to search for his killer in various exotic locales.) The first chapter has to serve multiple purposes — it obviously needs to provide some background for the rest of the book, but this is not a classroom where you can assume the audience will necessarily follow you to the end. So the first chapter also has to be fun and engaging, hinting at some of the mysteries to come.

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From Eternity to Book Club: Chapter OneRead More »

As promised, we’re going to have a book club to talk about From Eternity to Here. Roughly speaking, every Tuesday I’ll post about another chapter, and we’ll talk about it. Easy enough, right? (Chapters 4 and 5, about relativity, are pretty short and will be combined into one week.)

For the most part I won’t be summarizing each chapter — because you’ll all have read the book, so that would be boring. Instead, I want to give some behind-the-scenes insight about what was going through my mind when I put each chapter together — a little exclusive for readers of the blog. Of course, in the comments I hope we can discuss the substance of the chapters in as much detail as we like. I’m going to try to participate actively in all the discussions, so I hope to answer questions when I can — and certainly expect to learn something myself along the way.

The book is divided into four parts: an overview, spacetime and relativity, entropy and the Second Law, and a discussion of how it all fits into cosmology. You can find a more detailed table of contents here, and here is the prologue to get you in the mood. Part Three is definitely the high point of the book, so be sure to stick around for that.

So see you next Tuesday! Get reading!

Part One: Overview

• January 19: Chapter One (What is time?)
• January 26: Chapter Two (Entropy and the Second Law)
• February 2: Chapter Three (The expanding universe)

Part Two: Relativity

• February 9: Chapters Four and Five (Special and general relativity)
• February 16: Chapter Six (Time travel)

Part Three: Entropy and the Arrow of Time

• February 23: Chapter Seven (Determinism and reversibility)
• March 2: Chapter Eight (Entropy according to Boltzmann)
• March 9: Chapter Nine (Information, memory, life…)
• March 16: Chapter Ten (Recurrence and Boltzmann brains)
• March 23: Chapter Eleven (Quantum mechanics)

Part Four: Time and the Universe

• March 30: Chapter Twelve (Black holes)
• April 6: Chapter Thirteen (Evolution of the universe)
• April 13: Chapter Fourteen (Inflation)
• April 20: Chapter Fifteen and Epilogue (Explaining the arrow of time)

The book ended up with a pretty fun collection of epigraphs for each chapter. But there are a lot more good quotes about time than chapters in the book. Here are some of the quotes I did not end up using. Further examples are hereby solicited — who knows when they might turn out to be useful?

“Everything happens to everybody sooner or later if there is time enough.” — George Bernard Shaw, Back to Methuselah

“Time is the longest distance between two places.” — Tennessee Williams, The Glass Menagerie

“The future’s not ours to see.” — Doris Day

“Time rushes toward us with its hospital tray of infinitely varied narcotics, even while it is preparing us for its inevitably fatal operation.” — Tennessee Williams, The Rose Tattoo

“Time, you old gypsy man,
Will you not stay,
Put up your caravan
Just for one day?”
— Ralph Hodgeson

“Time present and time past
Are both perhaps present in time future,
And time future contained in time past.
If all time is eternally present
All time is unredeemable.”
— T.S. Eliot, “Burnt Norton” (Four Quartets)

“Time is the substance from which I am made. Time is a river that carries me along, but I am the river; it is a tiger that devours me, but I am the tiger; it is a fire that consumes me, but I am the fire.” — Jorge Luis Borges, Labyrinths.

Apparently you have to be extremely careful when it comes to poetry; fair use doesn’t necessarily extend very far.