From Eternity to Here: The Quest for the Ultimate Theory of Time

By Sean Carroll | January 14, 2009 10:24 am

You know what the world really needs? A good book about time. Google tells me there are only about one and a half million such books right now, but I think you’ll agree that one more really good one is called for.

So I’m writing one. From Eternity to Here: The Quest for the Ultimate Theory of Time is a popular-level book on time, entropy, and their connections to cosmology, to be published by Dutton. Hopefully before the end of this year! I’ve been plugging away at it, and have shifted almost into full-time book-writing mode now. (Note to collaborators: I promise not to abandon you entirely.)

I have my own idiosyncratic ideas about how to account for the arrow of time in cosmology, but those are going to be confined to passing mentions in the last chapter. Mostly I’ll be discussing basic ideas that most experts agree are true, or true ideas that everyone should agree on even if perhaps they don’t quite yet, or the implications of those ideas for knotty questions in cosmology. Hopefully we can at least shift the conventional wisdom a little bit.

Naturally there is a web page with some details. Here is the tentative table of contents, although I’ve been cutting and pasting pretty vigorously, so who knows how it will end up looking once all is said and done. One thing is for sure, some of these chapter titles need sprucing up.

  1. Prologue

Part One: Time, Experience, and the Universe

  1. The Heavy Hand of Entropy
  2. The Beginning and End of Time
  3. The Past is Present Memory

Part Two: Einstein’s Universe

  1. Time is Personal
  2. Time is Flexible
  3. Looping Through Time

Part Three: Distinguishing the Past from the Future

  1. Running Backwards
  2. Entropy and Disorder
  3. Information and Life
  4. Recurrent Nightmares
  5. Quantum Time

Part Four: Natural and Unnatural Spacetimes

  1. Black Holes
  2. The Life of the Universe
  3. The Past Through Tomorrow
  4. Epilogue: From the Universe to the Kitchen
    Appendix:  Math

If anyone out there is friends with Oprah, maybe drop her a line suggesting that this would make a good book-club choice. I hear that’s helpful when it comes to sales.

Update: And now you can buy it.

CATEGORIZED UNDER: Personal, Science, Time, Words
  • John Kemeny

    Where can I pre-order it?

  • Sean

    You can’t, yet. I think they want evidence it is more than half written before they will put it on sale. Hopefully soon.

    But I like how you’re thinking.

  • rww

    I read the blog, Sean, but it is totally over my head. I love the idea of the book.

  • Otis

    I want this book, Sean, and I want it now. But I’m a little worried when you say that you are working on it “full time”. That is, can you reassure me that you are still devoting the bulk of your intellectual and imaginative powers to conducting original research (I’ve put money on you winning a Nobel prize 30 years from now) and only using your evenings and coffee breaks to compose this wonderful-sounding popular book?

  • moshe

    That looks really excellent, I think I’ll make an exception and read a popular book about theoretical physics when this becomes available. Good luck!

  • kent

    I want to buy one!

  • Peter Coles

    Good luck with the book

    If you’re looking for quotes, try this one:

    “The future becomes the past, presently”

    Well, I like it anyway.

  • Elliot Tarabour

    From the book website…

    “What would Maxwell’s Demon say to a Boltzmann Brain? ”

    Wouldn’t the correct answer be: ” DEWD”


  • Kevin Colagio

    I think that if I read this, my head will explode.

    For just that reason, I can’t wait to get my hands on it.

    *sits down to wait patiently for it to be done.* Is it ready yet?

  • Elliot Tarabour

    Hey I’ve got it. I’ll write the review now and then when the book actually comes out it can refer to the review as an arcane example of time-reversal.


  • Matt

    Yay! There has been a popular-science-book-by-sean-carroll-shaped hole in the universe for far too long.

  • Dave W

    I hope there will be a nod to the discussion thread between Kant and Einstein in which they develop/refute the concept that our minds may simply be so limited as to be incapable of perceiving time more flexibly than we do. Are there any physiological or psychological limitations on the direction of time? If there are, can we even develop language to talk about those limitations?

  • Thor

    Very good! Looking forward to reading the book. Your essay on FQXI was pretty stimulating.

    P.S.: why do the Sean Caroll links at point to your old blog?

  • Random person w/ random thought

    Re ch. 4… [in movie-preview guy’s voice] Newton 2: Einstein: This Time it’s Personal

    Sorry. My will is weak. Couldn’t resist.

  • Low Math, Meekly Interacting

    Looks very interesting, especially if the appendix is something I can hope to comprehend at least a little. Thanks!

  • Neil B

    I don’t think I’ve yet gotten good answers to two points about the arrow of time. One, is the issue of interfering in a “time-reversed world” and how the changes in such a world undermine the credibility of arguing that the AoT is just relative. As I proposed earlier, what if I say, deflect a backwards-happening bullet so it “then” misses the barrel it “came out of” (but not yet in the view of the intruding other world relative to which the intrusion is benchmarked.) If that interference happens, the bullet maybe goes past the gun it should have come out of, runs into a tree etc. and then we have a ridiculous “past” that continues to get more wrecked as time (?) goes on. In principle, our world could be such a time-reversed world if there’s no true physical distinction (or one that matters to showing “legitimacy”, versus some distinctions about nuclear decay etc. that have equal “standing” regarding genuineness.) Yet now many of us can believe that an intervention from another world etc., regardless of what time flow they were in relative to us, could actually change our own past? Such questions are part of the foundational framing and can’t be brushed off from not being more directly operational expressions of what we already know.

    Also, considering how important it is regarding the arrow of time, is entropy rigorously defined? I mean, say I have some material and maybe radioactive (so what the atoms do in statistical mechanics is not all there is to it) is there really, a specific value of “entropy” for that? How could such a rigorous definition be made, and unlike energy or momentum we can’t (?) “put it into” something to measure in a simple way, like using final mass to show change in mass-energy etc. And especially about radioactivity, I mean really – I can have some stuff lying around very cold and lowest “entropy” and if it can radioactively decay, it can change and turn into other stuff etc.

  • Eugene

    Sweet, I can’t wait to see you cross swords with Stephen Colbert!

    Good luck with the book!

  • Andy Lawrence

    I just found a book by Huw Price second hand – Time’s Arrow and Archimedes Point. This is the guy who argued with Hawking in Nature some years back. Its a philosopher’s book but aimed at physicists. In general his book is a plea for taking time symmetry seriously, with all apparent arrows stemming from the Universe having low entropy at one end. As well as the usual stuff about entropy, cosmology, and the radiation arrow, he argues that “advanced action” is just what quantum mechanics needs to make it make sense. So quick opinion Sean – how is his stuff rated by heavyweight cosmologists like yourself ?

  • CW

    If you want Oprah to endorse it, and I don’t think it’s entirely impossible, you really have to use a lot of analogies in your writing. I use an analogy of a deck of cards when describing what entropy is in open/closed systems. Although the milk/coffee analogy is good too. The egg is too simplistic.

    Remember, [b]a lot[/b] of analogies!

  • CW

    Erm, the “a lot” is suppose to be in bold.

    And also, always describe what the possibilities would be if we reach the point of “understanding” (i.e. zero-pollution energy, unlimited food supply, cats and dogs living in harmony, etc.)

  • greg

    Oh, I’m definitely going to look forward to picking this one up.

    As for marketing, I’m sure that this is something you can get all sorts of people to promote, like the folks over at

  • Sean

    Andy, Huw Price is extremely smart and respected. Reading his papers was as important as anything in getting me to think about the arrow of time, and convincing me that there were puzzles conventional cosmology was sweeping under the rug.

    Thanks for all the encouragement, everyone! I will get back to writing now.

  • Blake Stacey

    A popular science book from Sean “the physics one” Carroll? Well, it’s about ti—

    [A hook reaches in and pulls Blake off the blogo-stage]

  • Sam Gralla

    Hi Sean,

    I would suggest including more philosophy. For example, you could discuss the classic argument for God via the impossibility of traversing the infinite. I’m suggesting this not so much because the subject matter begs it, but because the subject matter can accommodate it and you are very good at that sort of thing.

    In general this looks like a great read. One nice thing about entropy, compared to the rest of physics, is that there aren’t that many equations. It’s really a simple physical idea more than anything else. I wonder what the scope of popular books on the topic looks like.


  • randomeda


    Interesting stuff, but one of the mst intersting this i ever read on time was “the end of time”by julian Barbour. He has the fantastic notion that time does not exist. Maybe worth a chapter?

  • lucy

    Sounds great, good enough to briefly abandon normal lurking mode… The Huw Price book is excellent – very, very nearly had me switching to philosophy, though i finally saw the light and am applying to maths PhDs – but a more popular-level book might have more of a chance of getting this stuff more widely known. Price’s veers into some fairly dense philosophy at times.

  • CoffeeCupContrails

    One topic that you could discuss in some detail would be the actual definition of time. How linuguistic barriers limit and shape our understanding of time. You should talk about what the different concepts of time are. There seem to be a many-to-one relationship between the different mental ideas and this one word. There are plenty of references to this.

    Maybe, in the appendix section, you could talk about very real neurological limitations to how much we can grasp concepts like reality and time and other such very abstract things that physicists seem to be talking a lot about the past 20 years.

    I agree with other commenters. You are good at this sort of thing. There needs to be more intelligent discussion by physicists about how we think what we think, and the topic of time and reality falls firmly under that category.

    My two cents


  • Allyson Beatrice

    I think you should have a chapter titled, “Terminator Paradox: Why it was more than just a little creepy for John Connor to send his best friend home to do his mom so he could be born to send his best friend home to do his mom so he could be born…”

  • changcho

    Very nice! Looking forward to it.

  • Pope Maledict XVI

    I think that you should not underestimate the possible effects of such a book on the views of professional physicists. The subject has a very peculiar status: most professionals know that there is some kind of problem about the arrow of time, but they tend to think that it must be somebody else’s business. Apart from those people, there is also a large group who have mistaken notions like “Inflation solved all that long ago…..right?”. And then there are the people with completely crazy elementary misunderstandings, eg the people who deny that cosmology has anything at all to do with the second law of thermodynamics. You have a unique opportunity to straighten all that out, *in addition to* educating the public. So I really hope you will reconsider

    “I have my own idiosyncratic ideas about how to account for the arrow of time in cosmology, but those are going to be confined to passing mentions in the last chapter.”

    If modesty forbids you to emphasise your own ideas, you could survey all approaches, though not in mathematical detail. *Please* give serious thought to this; the subject really needs more attention from experts.

  • Pope Maledict XVI

    Oh yes, and look at this [but don’t read the comments]:

  • JoAnne

    Good luck with the book! I’m sure it will be fantastic!

  • Interested



    Popular level writing- will it be pitched for physicists or non physicists? I just listened to both your audio visual tapes to your links. It is pitched to non physicists. I read some of your writings, it is pitched to physicists. I guess the book will be pitched to physicists, and physics undergraduates. I read a few articles on time from Discover, and I guess in the wake of 30 years from Bing Bang theory, there is a challenge on it, and yours is one of the few very significant contenders, and it might be that evidence could bear out in the next 20-50 years. Though as a non physicist I would appreciate a book in the market pitched for non physicists, I think your book is gearing towards the physics and science community. Maybe you can then do a sequel for non physicists without the necessity of too much complex stuff, and with a kind of talking running commentary of the walk through history, from antiquity to now, and with the now, being the challengers, their ideas and pros and cons, and why your idea is the best or better idea. The contenders I noted from Discovery 03/25/2008 are Steinhart & Turok- endless creations ( so beginningless time) , Sean ( time arrow and eternal time), Barbour no time , and from New Scientist 01/19/2008 is Ravolli (thermal time hypothesis).

    When I was looking to read about time, I find the Discover and New Scientist articles readable, but the articles from Stanford Encyclopedia not readable. If I compare general news article, generally I find the BBC 1 Minute News article easy to read than the Yahoo news article. Maybe the former writers focus on it being understood and read in under 1 minute.
    One question that puzzled me about your symmetry, is why must there be symmetry flowing from your model? Is it the maths that shows there will be symmetry? As a non physicist just trying to understand the way your model unfolds theoretically, I can just as much speculate the new pockets of universes that are created will have the same arrow of time. Is it because your model is drawn with left side and right side, and thus, on 2 directions of the time arrow, that one on the right side has time travelling from now to future, and the one on the left has time travelling from present to past? By your model, does it mean, that if the pockets of universe have time travelling, in the opposite direction of time arrow, that people are born old and grow younger? Or they appear suddenly as old people and start to grow younger? What does “You can evolve the little inflating universes in either direction away from your generic starting point.” Adam Frank in the Discovery article infers you think that “In the super far past of our universe , long before the Big Bang, there could have been other Big Bangs for which the time arrow ran in the opposite direction.” What does it mean by “time arrow ran or runs in the opposite direction?” If our time arrow is one way, forward, to future and not to past, do you mean in the opposite direction, time runs from present to past. How then does reproduction, gestation, child birth, evolution take place? The little universe is born or created, and it expands, and that is like the way, it expands in the other case, where the time arrow ran the other way? But yet, while expansion is same, from low entropy to high entropy and accelerating, the things within that universe that is expanding is running the opposite way?

    Ravolli’s claim that he has evidence to support his thermal time hypothesis by looking at the CMB radiation and that to his surprise, he gets, “a sequence of states describing a small universe expanding in exactly the manner described by standard cosmological equations- matching what physicists refer to as cosmic time” but the New Scientist article did not shed light, what is seen in that CMB radiation or how it is seen, that, the said sequence is obtained, nor why such a sequence, would be so important. Even popular science writers do not think of the ‘gap’ in knowledge of non physicists that prevent them from comprehending what seems so obvious to the science writers.

  • Count Iblis

    An appearance on Larry King Live may also help to sell the book :)

  • Patrick Dennis

    PLEASE hold your ground when your editor demands fewer equations!!!!!

  • Neil B

    “Interested”, read my challenges from January 14th, 2009 at 1:12 pm and see if that sheds light on the weirdness of considering time flow to be relative.

    BTW Patrick, Roger Penrose sure holds his ground against minimizing equations. His semi-popular (?) books like Shadows of the Mind have quite a few equations.

  • Neil B

    Also, here’s a challenge problem about entropy: Consider a muon. Before it decays is structureless and just like a stable particle in terms of properties, but when it decays there is then more complexity in the universe than before etc – how can entropy be coherently defined for such entities, absent a mechanism we can describe inside the way we can for ordinary “heat engines” etc?

  • Interested

    Neil B,

    My first reaction, is this is the sort of science arguments one can expect of scientists to toss at each other as what is time reversal or arrow of time in opposite direction. Your challenging bullets wheeze over my head. But I have been thinking, what is time arrow in opposite direction?

    (a) Whatever we see as present to future, becomes present to past. So, we are born /appear on some planet (earth) old and grow younger…. IMPOSSIBLE. Sorry had to let out my deep response welling inside. .. whatever science or maths calculations say.

    (b) People may have felt at some cross roads there could have taken either path, and if they took one path, it sort of closes the other path. Example, a young man decides whether to marry or be a philosopher. If not mistaken, Soren Kierkegaard, gave up his fiance for that. What if this life on earth he did that, which he did, but in the other parallel symmetrical universe, he took the other path of marrying his fiance. So that’s another time arrow. Why does time arrow have to exact opposite? Who says so and what maths shows so. Whatever can maths show a symmetrical universe where people can be born in different places on earth (different earth in different universes on the other side of the generic point) and lead different lives? Many years ago, I chanced to read a book about this sort of ideas, which displaced idea of linear rebirth. The idea that when one dies, one is reborn, and some are reborn on earth. For instance, the Buddhist order that the Dalai Lama comes from, has this special innovation of finding reincarnations of deceased lineage holders and training them from childhood to reoccupy the position they had held in their past life. Andrew Skilton (p187) says “This practice introduced from India was adopted by other orders most notably the later dGe-lugs (pronounced ge look) order with its lineage entitled Dalai Lama.”

    (c) Why just opposite direction? Why not at an angle direction? Many different angles direction? Opposite but not exactly symmetrical. For that matter, why just symmetry on one axis, the x axis? Why not symmetry all round, so symmetry on y axis and many other , as many other axis? Was it the maths that led to the x axis symmetry? Or was it speculation and then testing it out with the maths? Whichever can testing it out also be done on all other, as many as possible axis?

    (d) I do not really understand entropy, but it seems like less particles, to more. Is a baby just born less entropy than an old aged man at death bed? If yes, then, it would defy the commonly cited entropic 2nd law of T. .. if in the other time arrow earth /universe, where old becomes younger.

    (e) If I go by comparables (and the saying- birds of a feather flock together), that, reality perceived by me is not reality as it truly is, then maybe time is also one of those, perceived by me, but is not as it truly is. Maybe both time and reality are observable phenomena but they are really some thing else.

  • Interested

    Women want to look young. So ageing or decay is important to us. Some men too. So what causes ageing or decay?

    I wonder whether that has anything to with Joan Vaccaro’s ‘negative kaons”. In 11/19/2008 New Scientist, Michael Brooks explained Vaccaro’s point that something like, all particles except negative kaons (“nk”) have it both ways ( arrow of time both ways and not one way). I gather that all except the nk, go up and down and left and right, and look the same, and that is following the respected law of conservation ( parroting here) called CP ( for charge and parity) invariance. This funny nk, do not look the same, if they reverse time arrow, they DECAY!!! According to Vaccaro, this decay is sign of flouting CP invariance. So it is argued that universe has one arrow of time, because of the effect of the nk which mainly has one arrow of time. They came to this view because they found ( how not explained nor clear to me) the present quantum state of the nk is a billion times more similar to the nk of future than nk of past, and so, they conclude the nk on average will move forward in time.

    Now this DECAY stuff, is unclear to me, from this line, “Yet physicists have found that neutral kaons decay in ways that are only possible if they flout CP invariance.”

    I can think of some permutations where decay happens since the writer Michael Brooks did not make it clear or maybe Vaccaro did not make it clear to him or maybe they did not think it was important where the decay took place.

    Did it take place at (1) (a) or 2(b):

    (1) (a) More nk move to future and decay happens
    (b) More nk move to future and no decay happens

    (2) (a) Less nk move back in time and no decay happens
    (b) Less nk move back in time and decay happens

    (3) All other particles move forward and no decay happens

    Movement to future : 1(a) and 2(a) and 3 OR 1(b) and 2(b) and 3 , either of these can fit the bill, “Yet physicists have found that neutral kaons decay in ways that are only possible if they flout CP invariance.”
    So is the neutral kaons causing us to age and decay EVEN AS it causes the arrow of time to move one way to the future?

    If so, we cannot have 2 arrows of time, unless, there is no negative kaons in the other parallel universe/earth on the other side of the generic point.

    There are four truths in Buddhism, first is, all things are not permanent, always changing, and second, is this changing is not satisfying to us ( happiness comes and go, we age and decay), and third, things have no inherent existence as they are in continuous state of flux, and fourth is the prescription through the eight fold path, to address the unsatisfactoriness mentioned. If physicists refer to 2nd law of Thermodynamics, Law of Conservation , CP Invariance, then I shall refer to the Buddhist truths, that, would lend credence to decay, and if that be , time arrow goes one way, then to one arrow of time, unless two arrows of time, also has inbuilt decay mechanism.

    Night Cream , Hand Cream, Face Cream , Body Cream “Anti Kaon” might sell :-))

  • P. C.

    I want the book NOW.
    And translated to Spanish, please.
    And I want icecream.

  • Sean

    When we negotiate foreign rights, I’ll try to insist that every copy of the Spanish version come with a coupon for free ice cream.

  • Sili

    Speaking of books, didn’t you promise signed copies of your opus one to people who gave to Donors Choose? Or did I imagine that?

    I might have, since I seem to recall your offering access to your Trophy Wife(tm) to particularly good givers.

  • Neil B

    Does Noether’s Theorem have something to say about the arrow of time, although it does not deal with entropy ? … Yeah, NT is all about things being constant, but to make the point wouldn’ t you need a progressing time frame to work it out in? And BTW does Noether’s Theorem generalize to universes analogous to ours but with other number of space dimensions? It seems like it should, but I’ve seen various statements that action etc. has special properties in three-D space.

  • andy.s

    I look forward to it Sean. But I bet you’d sell more if you explained it all to your dog.

    Also: re entropy.

    Consider a muon. Before it decays is structureless and just like a stable particle in terms of properties, but when it decays there is then more complexity in the universe than before etc – how can entropy be coherently defined for such entities

    Not sure if entropy would increase in this reaction. Muon decay goes like $latex mu^- to nu_mu + W^- to nu_mu + e^- + bar{nu_e}$. That reaction should be reversible, and in chemistry, IIRC, a reversible reaction does not increase entropy. I don’t know, maybe it’s different with particles.

  • Neil B

    Andy, it is formally reversible but that has little chance of “just happening” so after decay, isn’t there “more entropy” than before because it is effective disorder?
    Also, do you know the answer to my question about Noether?

  • andy.s

    Well, that’s a-whole-noether question, now isn’t it?

  • Jean Paul B.

    Well, while Uwe Price made a lot of good thinking in his essay, I believe he ended, like most thinking on the arrow of time, by having it chasing its own tail. Resolving the question of the second law of thermodynamics by a very specific low entropy initial condition, seems to me just a tautology. It does not answer why entropy is growing with time, but how it could have been possible. So this kind of answer is about the cosmological non-contradiction of the second law, not its reason why. There are several alternative answers about the reason why. One is the now rather outdated Prigogine’s notion that even at the microscopic level time is not reversible. Another is that time arrow is an illusion in a timeless universe driven by Hamiltonian constraints. Then to get back our perception of time you have to introduce something like the thermal hypothesis of Conne/Rovelli. My belief is that this last approach might be on the right way, while still wanting of more fundamental insights on how we build memory (and partial amnesia). What do you think?

  • Sandy

    That’s great Sean, I love to read books about the arrow of time. I have 2 requests:

    Please don’t use scrambled eggs or breaking tea cups as examples of entropy!! They are not examples of entropy and I wish physicists would stop using them (as such).

    I would really appreciate a good discussion that justifies using the Second Law of Thermodynamics outside of its specific parameters.

  • Sili

    If you do use scrambled eggs, then you do so at <a href="; your own peril (last link possibly NSFW – at least if you have your speakers on (but why would you have so at work?)).


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Cosmic Variance

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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