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.
In fact, I juggled the first three chapters back and forth. Chapter Two explains the basics of entropy and the arrow of time, while Chapter Three explains the basics of cosmology. At one point I had the current Chapter One placed after these two chapters, on the theory that we could be precise about definitions after we had been exposed to some of the big and exciting ideas. This was a well-intentioned theory, but not an especially good one. Test readers balked, so the current Chapter One was put back in the beginning.
Despite being about definitions and so forth, I think Chapter One turned out to be pretty interesting — indeed, I wonder now whether it shouldn’t have been longer. When you talk to people on the street about “time,” the first questions they ask tend to be along the lines of “what is time, really?” or “is time real, or just an illusion?” This chapter tries to answer those questions, or at least spell out the perspective I’ll be taking for the rest of the book. And they’re important questions, interesting in their own right, even if I breeze through them — lots of philosophical work, not to mention physics, has been addressed to these issues.
We distinguish between three ideas of time — time is a coordinate, time is what clocks measure, and time is the agent of change. These aren’t really “definitions” in any careful sense, so much as “ways we use the notion of time.” And my readers were right — it’s important to set out these different senses right from the start, as I’ve discovered that even physicists tend to blur them together in their minds.
The most important non-obvious stance I take in this chapter is to come down firmly on the side of an “eternalist” or “block universe” conception of time. The past, present, and future are equally real. Philosophers and other deep thinkers have been arguing about this for years, and I kind of dismiss the whole discussion in a couple of paragraphs. Sorry, philosophers! It’s an important issue, but we have other conceptual fish to fry.
So let me know what you thought, and what questions still remain — either about the substance of the chapter, or the stylistic choices made along the way. I’ll try to respond, although I reserve to right to say “hold that thought until we get to Chapter X.” And of course everyone else is encouraged to chime in, too.
I thought it was a good and necessary opener. I’d never really considered just how little I’ve considered what exactly time is. It set the table nicely.
My only quibble with the book so far is I’d have preferred foot notes to end notes. I don’t like having to flip back and forth, but I’m sure the choice wasn’t made haphazardly (maybe footnotes scare people off like equations).
I’m coming at this topic as a layman who hasn’t read much on the topic. Stocked up at Xmas on some Susskind and Feynman as well, but starting off with yours.
Looking forward to your takes on the possibility of “many worlds” (especially), a deterministic universe, Boltzman brains, the anthropic principle and getting hit, I’m sure, with plenty of stuff I’ve never heard of or considered before.
I get tired of hearing/reading concepts that can’t be empirically tested dismissed as out of the realm of science, as if this means they aren’t worth considering. Sounds like this book will take on a lot of those subjects.
Yeah, the footnotes/endnotes debate raged quite a bit. In the end, endnotes aren’t quite as convenient, but they’re much less off-putting for the general reader. And I tried hard not to put anything crucial in there, and make it easy to cross-reference back and forth.
As a layman also, I thought the discussion about “clocks” was very good. I don’t think it’d been brought up before in other physics/philosophical writings that I have read. I thought the “block universe” element was good, and probably necessary for what you present in the later chapters. At this point, I don’t think I grasped the significance of it.
“Time is the agent of change.” I always thought of that the other way around – time emerges from change; when nothing changes – such as when the universe reaches thermal equilibrium – time stands still. Time emerges from the grind of the universe toward thermal equilibrium, doesn’t it? Might be a chicken-and-egg argument (or maybe I misunderstood what you meant by “agent”), but I think time is the emergent property.
When our mind perceives something even if its just 10 feet away it is away from us in space and in time, a fraction of a second that light travels. So for an individual what is the present in time? Is it always the past? Does the concept of past mean different things if you are in different places (Earth or Andromeda Galaxy)? Please comment.
I’m having a bit of trouble understanding the “flow” of time.. Maybe this is tackled later on. While I have no problem accepting that there is a certain unique state, at 10:00am, with Bob and water boiling on the stove, and a mental state of Bob anticipating making coffee, together with a unique state of 10:05am, with a mental state of Bob actively making coffee and so on, I fail to understand the “flow” between them, and why is it that Bob’s mental state feels a forward “flow” of time…
Is this perhaps the whole subject of the book? 🙂 I’m not sure yet, as I am reading a chapter a week…
Metre– I think it is chicken-and-egg, at least with respect to what I had in mind. I wasn’t actively suggesting that time is prior to change, just referring to the role of time as what keeps track of change.
Beltstars– We’ll get into this more in Chapters 4&5. Obviously “the present” is something of an approximation, useful over the scale of meters but less so over the scale of light-years.
Oded– Not sure what to say, this might be more of a psychology question. Time exists as a label that ties all those moments together in a particular order. The increase of entropy allows for a directionality to that set of mental states, so that at each moment we perceive ourselves as having traveled from the past into the future. I don’t have much to say beyond that, I’m afraid.
I agree that it is more practical to see time as a unit of measurement as well as a ubiquitous aspect of our space-time universe. I have always felt that time in a way is akin to gravity. Gravity seems overwhelmed by the other forces sometimes, and only becomes increasingly powerful at the quantum levels, as will be shown even further if the LHC manages to create micro black holes. In the same way, I feel that time may have a further role to play, but that it has more of an effect in extra dimensions, and will not be discovered until we are able to somehow measure the effects of quantum mechanics below the Planck length. Thoughts?
David– I don’t have any specific suspicions that extra dimensions will change the way we view time. Quantum gravity very likely will; I tend to think that time is more fundamental than space, but there’s obviously a lot we don’t know.
I just tried to buy it from my Local Barnes and Noble on my lunch hour and they were sold out. I hate waiting on the Mail. I hope it’s as good as a “Brief History of Time” –I can’t wait for another book to blow my mind away.
There is Nothing better than feeding your baby his nighttime bottle, and reading something, that someday he will read and be blown away as his daddy was. Ahh time…….
I read chapters 1 &2 yesterday. These cover the psychological feel of time (time speeds up, slows down); time of memory (I remember yesterday, etc.); time in physics (entropy, many events can go forwards or backwards), and so on.
Okay, it’s an opening chapter, and I’m willing to let a few pages go by. I hope the book gets down to business.
By the way, I’ve read Brian Greene’s “Fabric of the Cosmos” and Frank Wilczek’s “Lightness of Being” (along with a number of other similar books). Green argues that the key to physics is space: by understanding space, dimensions, string theory, we can understand the world. Wilczek writes that being is based on energy (mass is a form of energy, and thus space is a result of mass and energy). Sean Carroll presents the role of time in physics.
It’s interesting that space, energy, and time are now the leading actors in physics. From a human’s perspective, mass and gravity seem to be the basis of reality, but for physics, mass is a form of energy and gravity is an effect of mass. As all three writers point out, common mass and energy is only about 4% of the universe: it’s mostly dark energy.
This is yet another step away from the human-centric worldview: the Earth is no longer the center of the solar system; Newton’s “mass-centric world” is now only a minor part of the universe.
(By the way, I strongly recommend Greene’s “Fabric of the Cosmos”. Well-written, clearly written, etc. Wilczek’s “Lightness of Being” however… well, he’s not a good writer. Doesn’t explain items, doesn’t position an issue in context, etc.)
Do you see any correspondence to our perceptual arrow of time and the fact that we live “in” time? Compared to the fact that we live in at least 3 dimensions, and yet only perceive space in 2 dimensions? In other words, is the unidirectionality of time a perceptual anomaly (such as space seeming to be two-dimensional)? Also, do you believe that the mechanism of collapsing wave functions is time irreversible, or do we not have enough knowledge in this area yet?
I love philosophy of time stuff so would have been very happy to have more on the block universe/ presentism business, but I can see why you’ve accepted the block universe quickly seeing as you want to go on to relativity, where it’s the natural choice. Oded, that’s a pretty important question I think – the subjective experience of a flow of time is the thing that’s difficult to reconcile with the block time view and (I think) the main reason why some philosophers don’t go along with it. Saying ‘it’s a psychology question’ is how we block time people normally escape at this point!
On the exciting footnotes/endnotes subject, I don’t care which but can I just say thanks for not starting the numbering afresh with each chapter! Normally I really hate having to work out *which* footnote 6 I want every time I flip to the back of the book…
I will buy the book next visit to the book store.
Would it be safe to say that all contents o the book mirror your discussions on the blog format? I know you had dispensed with the philosophical view , but I found your conversation with David Albert an important one.
Assuming this is the case, the thing that flex’s one position on the idea of time is the close association to reverse chronology you presented in your Incompatible Arrows I(Martin Amis),II(Kurt Vonnegut),III( Lewis Carroll ),IV(Scott Fitzgerald). It was a fun exercise.
Also, how far back in time was set in regard to Steven Weinberg’s First three Minutes to have now concluded with the term micro-seconds has helped us push our perspective back toward the beginning of time with The First Few Microseconds, by Michael Riordan and Willaim A. Zajc and as to how particles came to be, served to see that a Supercosmologist who actually thinks outside the box helps to set up what came before the beginning of time.
So the question then might be approached as to the substance of the beginning of this universe and the “continuity expressed inside” some blackhole, while thinking of the quantum gravity issue?
I think this method is a good exercise and I hope I have not gone beyond the boundaries to which time might have been expressed in the book. How it is described from “some horizon” with a conformal field theory approach.
Best,
David– You should hang in there for the rest of the book. The perception of time is ultimately driven by the arrow of time and increasing entropy, although there are many details remaining to be worked out, to say the least.
lk– given that we put the notes at the end of the book, I tried hard to make them as user-friendly as possible. It’s a dilemma! (Until everyone is using electronic readers. By the way, the Kindle edition came out pretty well.)
Plato– some of the book mirrors stuff that appeared on the blog, but there’s much more in the book.
“The most important non-obvious stance I take in this chapter is to come down firmly on the side of an “eternalist” or “block universe” conception of time. The past, present, and future are equally real. Philosophers and other deep thinkers have been arguing about this for years, and I kind of dismiss the whole discussion in a couple of paragraphs. Sorry, philosophers! It’s an important issue, but we have other conceptual fish to fry.”
Do you know whether there’s any consensus on this in the physics community? In any case, the block universe view seems to have direct implications for one common conception of free will, in which the future is thought to be metaphysically open for us to determine, not sitting there in spacetime. I’ll be curious to see if this gets covered in the book. Meanwhile, folks might want to check out the ABC sci-fi series FlashForward which takes up issues of time and free will, which I’ve posted about over at the Garden of Forking Paths.
Love the book club concept, thanks.
So you think the mechanism of wave function collapse is related to the entropic arrow of time?
I am very glad Dr. Carroll gave the philosophical definitions at the end of the chapter: block universe, eternalism, and presentism. I was in desperate need to label these concepts. That being said, I am a PRESENTIST. Time for me is merely a bookeeping variable in physics equations; otherwise, it is an illusion. I believe that there is something in the geometry of the universe which is a “cause” of our emergent experience of linear time, and I cannot believe that there is a block universe where the worldlines of every elementary particle extend indefinitely in two directions. We can move freely in space, but not in time; therefore, I have no evidence of its existence as its very own dimension in space-time.
The keyword here is ‘believe.’ Thus far, I see no means for science to falsify this belief. I am quite surprised that Dr. Carroll would so adamantly take the opposite stance as neither stance appears to contradict physical law.
I’ve seen too many theoretical physics popularizations and far too few on real phenomena, measurements, and experiments.
Tom– I think most physicists are block-universe believers, even if they never lay out that belief explicitly. That seems to be the most natural reading of the differential equations that we think govern fundamental physics.
David– yes, and we’ll get around to that later (Ch. 11). But I don’t think all the details are anywhere near worked out.
Clifford– I didn’t think I was all that adamant.
Jon– those books are certainly there, if you look for them.
I’m here because of your fine lectures on Dark Matter and Energy. As a philosopher I found your analysis and theory clear. Here I’m less comfortable. We can ask ‘What’s supper?’ and when’s supper? We can even say ‘What’s when’? and begin a discussion about time. But When’s what?’ doesn’t compute, which makes time unhandsome, or without a handle.
PS, I’m reading your wife’s useful and friendly book at the same time.
RGG– I’m not sure if you’re looking for a specific response, or exactly what it is that makes you uncomfortable. I tried my best to lay out (very briefly) in Chapter 1 how I thought we should think about time, so that we can spend the rest of the book digging into it more deeply.
I liked how the date and time in some example is January 20, 2010. Hey, that’s tomorrow! A bonus of being an early buyer and reader of the book is its timeliness (er, heheh).
What did you mean by “a straight trajectory between two events in spacetime describes the longest elapsed duration”? is there another way to get from event A to Event B that would be ‘shorter’? I am having a hard time understanding this.
I have other questions regarding the end of the chapter, but I guess I will try to figure them out on my own. Pages 19-25 — do you go into these concept further as the chapters move on, or should a person understand these concepts before going any farther into the book?
Thanks
Bill– Had I known the actual publication date I would have chosen that.
TS– That’s explained more thoroughly in Chapter 4, but yes — the path of shortest duration between two events in spacetime (not points in space!) is one where you zoom out near the speed of light and then zoom back in time to reach the event.
And yes, these are developed in more detail through the rest of the book.