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.
“Fluctuations, in this equilibrated Universe, could come in countless forms. Renowned physicist Ludwig Boltzmann staggered out onto the Ringstrasse, knowing that he had only moments before his brain dissolved once more into formless Chaos. . . .”
No question yet, but I thank you for this excellent book 🙂
Time being a Lorentzian complimentary coordinate to space emerges from the second derivatives of time that appear in gauge-invariant vacuum solutions to Maxwell’s Equations. So, is the comparable lack of a temporal observable in QM due to the fact that solutions to Schrodinger’s Equation are linear in time?
I developed an interest in cosmology late in life. I’m now 64. Feeling I don’t have time to learn from the basics up, I use another method. I start with the new and most interesting, “good stuff” and the I learn down just far enough to understand the theory. It may take reading many books to “get it” or it may be just one word I need defined. This is working well for me overall, and who cares if I know more about generalativity than chemestry, or that I never took a physics class. It does however set me up for some embarassing misconceptions. I wasn’t sure what a “field theory” was for a long time. I would be going along understanding the material and then it would talk about some famous scientist’s field theory, and I would wonder why do they call it that! The notion that these folk were out measuring things in the woods didn’t fit the material at all. I tried to find out what it mean many times but just couldn’t. It is hard to look up a phrase, and if it isn’t on TV with cool pictures, my friends don’t know. Finally I just made up my own definition. I decided it meant any work or experiment that wasn’t done in a lab or collider etc. and let it go. It wasn’t until I was thinking about Bosons being force particles that it came clear. “Forces and fields”, or maybe it was “forcefield” that brought it home. I am still laughing at that one! Now I think I know what “as a funtion of time” means, but I have been wrong before. Please indulge me and clarify it.
PS. I bet I could understand what Josh just said if I worked at it, but I think I’ll pass, and continue reading “Chapter Two”.
Josh– not really. Time is just treated completely differently from space in quantum mechanics. The are treated very similarly in relativity, which seems to suggest some kind of tension, but in fact the tension is easy to resolve, until you get to quantum gravity.
Susan– hooray for getting interested in science of any sort late in life! “As a function of time” simply means that something is changing as time passes. At any one moment, quantum mechanics tells us that we describe the state of the world by a “wave function,” which can be used to calculate the probability of obtaining any particular result for an observation. But that wave function changes as time passes. So the history of the world is described by a series of wave functions, one at each time, which together we call “the wave function as a function of time.” If that makes sense.
It tells me what I needed to know, Thanks.
This might be beyond the scope of chapter 1, but — is there a Plank time? The time cousin to 10^-33 centimeters?
Susan, ‘function’ is a math term, maybe you remember it from precalc or algebra. simply stated: It is an equation with variables (x and y) and y will change with x: 3+x=y … if I let x be 5 then y will be 8. If I let x be 1 then y will be 4. If something is a function of time then it will change with time (or will time change when that ‘something’ changes?!)
“In relativity, there’s no such thing as “at the same time,” at least when we’re talking about two truly distinct events at different points in space. If something happens very far away, we can’t say it happens at the same time as something that happens right next to us, because that depends on the reference frame we are using.”
From http://www.newscientist.com/blogs/culturelab/2010/01/about-time-too-your-questions-answered.php This answer leads me to a paradox.
Doesn’t the collapse of the wavefunction of the universe happen everywhere at once? If you say no then my follow up question will be: split the distance between the two far away events, if they still don’t happen at same time, split distance again, repeat until you find a point where they both occur at same time as collapse of wavefunction of the universe. Now, explain how come that distance is different from step n-1?
If you say yes, then all events can be related unequivocally to the moment of the collapse of the wavefunction of the universe. We have our universal frame of reference, No?
Andy– Yes, it’s 10^-44 seconds. Given a distance you can always convert into a time, and vice-versa, by dividing or multiplying by the speed of light.
waveforms– That’s bothered a lot of people, including Einstein. The thing is, we can describe the wave function as collapsing instantaneously in any reference frame, and all the observational consequences are exactly the same. So there’s no preferred frame.
Sean, Really am enjoying the book. Your comment #41 in answer to #40 was well worth noting…observers always perceive the direction of the “flow” of time as resulting from a (macroscopic) increase in entropy? Even in dual or yet higher dimensional configurations time could only be identified as it resulted from an upward change in entropy? relates to the irreversibility of time?
Sean, I don’t know why you would target a physics book at Americans. All Anglophones will find it perfectly readable. Honestly, we dont really mind if you spell “colour” wrongly and use American Football metaphores. There was no difficulty or extra cost getting the “American” version here on Amazon.co.uk. They dont even label them as imports anymore. Most of the marketing seems to be web-based and UK science magazines have already reviewed it, so that does not make any difference either. I remember one of Smolin’s books having a UK version released 6 months after the US version. I doubt it sold well because anyone like me who had an interest had already bought the US version without noticing the difference. If your publisher tells you that popular physics books dont sell well in the UK ask them if they are counting sales of the US versions here.
I dont think two time dimensions stops quantum mechanics being fundamental, otherwise what kind of theory is F-theory? (The answer may depend on exactly what you mean by “quantum mechanics is fundamental.”) Of course two time dimensions is problematic for causality, but as you say, it is open to empirical test and if evidence of two time dimensions is found it will certainly change our view of time. That was the original point.
The core idea of the book is the concept “entropy.” What does that mean?
Entropie, which means “the measure of the disorder of a system,” was coined in 1865 by physicist Rudolph Clausius (1822-1888) based on the German word “Energie” by using the Greek word entropia “a turning toward” (en- “in” + trope “a turning”).
Look at Wikipedia. It now has at least four different definitions:
– Entropy is a measure of the number of ways in which a system may be arranged, often taken to be a measure of “disorder” (the higher the entropy, the higher the disorder).
– Entropy is a measure of a system’s tendency towards spontaneous change.
– Entropy is a measure of certain aspects of energy in relation to absolute temperature.
– Entropy is a measure of the uniformity of the distribution of energy.
It means disorder, change, energy, and distribution? That’s four different ideas. And you can easily find more definitions by reading about entropy.
This explains the problem with entropy. Writers shift back and forth between various definitions when they talk about entropy.
Sean, can you give us a clear definition of entropy? Or does this word have multiple shades of meaning?
Is it that the early universe was low entropy or just lower than presently?
If it is just low-er then it doesn’t seem quite the same puzzle.
And if it was low in some absolute sense, relative to what?
Sorry, that was probably not very clear. Maybe my problem is this: If the early universe was a fog of photons and particles, why is that considered low entropy? How was it different from my mix of coffee and cream?
Andreas– There are many definitions of entropy. We’ll talk a little about them in Chapter 2, and in more detail in Chapter 8.
rww– We’ll get to that, in Chapter 3 and again in great detail in Part Four, especially Chapter 13.
Just got started reading chapter 1. This is going to be a fun book.
Sean, on page 10 you imply that John Wheeler is the source of the statement “Time is Nature’s way of keeping everything from happening at once”. Although Wheeler might have been fond of this quote, he was not the originator. On page 351 of Wheeler’s book Geons, Black Holes, and Quantum Foam, Wheeler writes that he found the quote as a graffito in the men’s bathroom at the Pecan Street Café in Austin.
On page 323 of the April, 1978 issue of The American Journal of Physics you can find essentially the same quote attributed to the physicist C. J. Overbeck. No reference is given. Using the internet I was able to find an article by Overbeck in the August 1973 issue of The Rotarian Magazine in which he writes “What is time? As a physicist I have on occasion answered that question by saying, quite seriously, ‘Time is that great gift of nature which keeps everything from happening at once’.” Of course, Overbeck might have been repeating or rephrasing something that he had heard or read somewhere else!
Most hits on the internet appear to attribute the quote to Wheeler, so he might very well end up owning it.
Thanks for the catch. I definitely have seen it attributed to Wheeler, but it’s easy to imagine the Matthew effect at work.
Also, quite a few internet hits attribute the quote to Woody Allen. I guess we’ll never know for sure.
I think your book is written for people like me. That is those who are happy with concepts and intriguing ideas. It is science, but well explained and not too hard to understand. I know there is understanding, and deeper understanding, and really understanding. To learn enough for personal satisfaction is the goal. I believe folk put physicists, cosmologists etc in with “brain surgeons and rocket scientists” all very smart people. This is of course is completely true, but by doing so they put themselves in the category of dumb. They are likely “smart enough”. It is the intriguing ideas that may get them to give it a try. I think it is testimony to how far the knowledge of the universe has come that we can ask seriously “whats outside the universe”. Up to now it has been sort of “I’m still trying to figure out what is inside the universe, so I am not going to think about that!” As you point out, some of these ideas have been around for awhile, but thinking about time in terms of natural laws and physics, is all new to most of us. Thanks for putting it out there.
PS. to Frank and Sean. I haven’t taken any math since Algebra I in highscool, thanks for adding to Seans answer. Who knew I would be buying math learning DVD’s about 37 years later. When I implied I could learn hard technical things, I should have added, if I live long enough! The waveform information makes me want to know more.
Let me change the above “outside the universe” to “before the low entropy state of the universe”, or something along that line. (I knew I should have read ahead a little).
It “seems’ to me that C itself determines time’s existence and also our perception of it. Were there no speed limit on light, the unfolding of the Universe would be but a wink, over in a flash. BUT, limiting C (but what exactly limits C ?) allows the unfolding of process and events, ie. what we call time. (I am NOT a physicist, just a curiopus stranger.)
It would further “seem” to me that it is fabric of space itself which puts the brakes on C, and that by delving into that, we will discover a technique for “Warp Drive”, etc. We have been looking at all the stuff that is just along for the ride, as if there answer were there. I think, not! (Now there’s an ambiguous statement.)
I will buy the book from Amazon and delve in… working through Robert Laughlin right now.
stuck here….. out of entrophy…. delete
No, Buffalo Bob, it’s the other way around: you have TOO MUCH entropy!
In the news this morning. The universe contains 30 times more entropy than earlier estimates.
http://www.sciencedaily.com/releases/2010/01/100126104844.htm
Okay, I have an important (to me!) question about chapter 10. Surely you won’t make me wait 8 more weeks (2 months!) to get an answer! (I hope!)
BUT, I’ll ask it back here on the Chapter 1 discussion from last week, so as not to disrupt the active Chapter 2 thread that just started this week.
I promise I’ll ask again in March when we get to chapter 10!
Okay, that’s my groveling. Now the question:
So, in chapter 10 you rule out the possibility of the eternal recurrence scenario based on the low probability of an observer of our type (human) being surrounded by a non-equilibrium visible universe compared to the probability being a “boltzmann brain” human observer who pops into existence to find himself surrounded by chaos.
As you say, in the eternal recurrence scenario there should be far far more of the later than of the former.
Okay. So, my question:
If the recurrences are really eternal, then shouldn’t there be infinitely many of BOTH types of observers? Countably infinite?
And aren’t all countably infinite sets of equal size?
So in an infinite amount of time we would accumulate one countably infinite set of our type of observer. And over that same amount of time we’d could also accumulate another countably infinite set of the “Boltzmann Brain” type of observer.
The two sets would be of the same size…countably infinite. Right?
So probabilistic reasoning wouldn’t apply here, would it?
Especially not in a “block” universe where we don’t even have to wait for an infinite amount of time to pass.