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

In this book, Sean Carroll aims to connect the most mundane phenomena from the everyday life such as the scrambling of eggs to the most speculative concepts in cosmology such as bubble universes where time runs backwards. Of course, science has shown that no such relationship exists - even though it may be attractive for some really ambitious armchair physicists - so Carroll fails. But it may be interesting to look at this failure in some detail.

To make the book "cooler", Carroll has used various random characters such as Miss Kitty, a cat who hides under its sofa, and Brad Pitt who grows younger with time (as F. Scott Fitzgerald told him to do in "The Curious Case of Benjamin Button"). The storylines were largely absent and they didn't help to shed light on the highly controversial scientific points, either. The same seems to be true for several quotes - such as those from St. Augustine. I suspect that the author only wanted to superficially "connect" with the lay readers and broader audiences. After all, the same thing can be said about the title which is a mutation of the title of a famous novel by James Jones.

Carroll occasionally writes some things about physics of time that are correct. At any rate, the main scientific goal of the book is to argue that the irreversibility of the phenomena around us (e.g. that we get older and never younger) is a consequence of some details in the history of our Universe. We must live in a bubble Universe surrounded by other bubbles where time runs backwards and where many other logically inconsistent phenomena take place.

Carroll never shows why he thinks that the asymmetric scrambling of an egg is linked to any of those crazy speculations about our cosmic pedigree. In fact, we can't blame him for his failure. Nothing like that can be explained because no relation of this sort exists. Even for a good writer, it would be hard to demonstrate something that is so fundamentally untrue.

The irreversibility of time is related to the so-called second law of thermodynamics - to the increasing amount of disorder of any isolated physical object (increasing entropy). And this law can be proven and has been proven more than 100 years ago. The entropy of objects is related to the statistical properties of a large number of atoms (inside the same egg - the rest of the Universe and its history is irrelevant, because of the "locality" of the laws of Nature). Undergraduate students have been correctly learning that thermodynamics (gross observations about the heat, temperature, and irreversibility) may be derived from statistical physics (mathematics applied to many atoms) for a century. Unfortunately, Sean Carroll didn't listen to his teachers because he apparently thinks that thermodynamics is a consequence of some details in cosmology. He has missed the main point of statistical physics.

There is nothing unnatural (or even paradoxical) about the low value of entropy in the past. Quite on the contrary, it is a consequence of the second law that guarantees that the entropy increases. We know that the entropy used to be lower and we know that it agrees with all other laws of physics that have been empirically validated.

The proof of the increasing entropy due to Ludwig Boltzmann (who later committed suicide, being surrounded by people not unsimilar to Carroll himself who were unable to appreciate the depth and validity of his key insights into thermodynamics) also uses a pre-existing logical arrow of time but there is nothing wrong about it. The logical arrow of time - saying that we may remember the past and not the future - belongs to the logic of any conceivable world with "time" that qualitatively resembles ours. No world with "observers" can exist without it.

While the microscopic, exact laws of physics may be time-reversal symmetric (they don't distinguish the past and the future) or at least CPT-symmetric (ignore the acronym if you don't know what it means), the logic how we apply them in the presence of unknown data always "discriminates" the past from the future. For example, if you calculate the probability that a particle decays into a pair of particles and you don't specify the spins, you must sum the probability over the final spins (because you don't "care" about them) but you must average over the initial spins (because you don't "know" them).

Summing is something different than averaging - and the past therefore differs from the future. And this asymmetry - an extra denominator preferring a larger number of states in the future than in the past - automatically implies that the entropy increases. The role of "assumptions" and their "consequences" in logic is asymmetric. And in the same way, whenever there is any incomplete information, the past and the future play an asymmetric role, too - because by the very definition of the words, the past is described by the "assumptions" and the future is about their "consequences". Because there's no symmetry between the assumptions and their consequences, it's also impossible to mix the two arrows of time inside a bigger multiverse.

Also, in a striking contrast with Carroll's text, the methods to retrodict the past are completely different than the methods to predict the future. To predict the future is "straightforward" - quantum mechanics tells us the probabilities. However, to reconstruct the past, we must choose competing hypotheses, assign them with (somewhat arbitrary) priors, and do the logical inference. The answer - our retrodiction - is not unique. But when we do it correctly, we may see that the entropy in the past was lower than today.

Most of the mysterious properties of the bubble Universes discussed by Carroll are even more impossible than the ordinary "time machines" and "wormholes" from some conventional popular books. If there exists a contest looking for a professional physicist who prints and sells a book promoting the most scientifically nonsensical phenomena and relationships between them, Carroll is a new hot candidate.

The science in the book makes no sense and the purpose of the book is for the author to show how he can make science popular. Except that it isn't science and I guess that it won't get too popular, either, because the references to the popular culture are excessively cheap, chaotic, and out-of-touch even for highly undemanding readers. Finally, let me say that you should largely ignore the unhelpful votes under the unfavorable reviews because the author uses his blog to distort the public perception of this very strange book.

After reading Mr. Carroll's book, I am reminded of a conversation that supposedly occurred between an old Indian and a white man in the late 1800s. The white man was trying to impress upon the Indian how much more advanced white civilization was when compared to his. He drew a small circle in the sand and said, "This is what the Indian knows." He then drew a larger circle around the first one and said, "And this is what the white man knows." The old Indian thought about this for a moment and then proceeded to trace a much larger circle around this second circle and said, "And this is what the white man does not know." This is how I feel about the current state of theoretical physics and cosmology. There are more questions than answers. At the end of this book I came away with a feeling of profound futility. I lost count of how many times Carroll said something like, "More research needs to be done." or "We don't know the answer yet." or "It's a complete mystery." Every book of this type that I've read in the last ten years ends at the same place -- we're stuck and none of the current theories we have adequately explain any of the fundamental questions about the nature or origin of the universe. String theory? It could be correct, but there is no way to prove it one way or another. Is the universe comprised of 11 dimensions? Possibly. The jury is still out. Does time exist? Yes, but it may also be an illusion. Parallel universes? Very likely. But, we may never know for sure. Is time travel possible? In theory yes, but the universe doesn't seem to like it, so it may never be technologically feasible. How about quantum entanglement, is this a real effect or does it signify some deeper, hidden property of the universe, or is it more like Bohm's guide wave interpretation? Everybody seems to have a different view. Sometimes things seem to come down to personal likes or dislikes. Did the universe have a beginning or has it always existed? Was there a Big Bang or was there a phase state shift? Bump and grind branes anyone?

I think I've reached the point where I'll just stop reading this sort of book for the next ten years. Carroll and others of his ilk are clearly very bright people with a grasp of advanced mathematics that puts me to shame (college calculus was as far as I got), yet despite their intellectual accomplishments they have nothing new to say on these subjects at the moment. Apart from selling books and making a buck, I really wonder why we need more books like this. Until some new breakthroughs come along I'll bide my time and just hope I live long enough to know what dark matter and dark energy are.

This is a wonderful book that would merit a second reading to understand it more fully. At a fundamental level physics consists of the Standard Model, General Relativity and the Big Bang Inflationary Model of the universe. However, in this model there is something unexplained and it is the Past Hypothesis, that is that the universe started in a low entropy configuration. However the author speculates that perhaps the Big Bang was neither the beginning of time nor a moment of low entropy, but a moment of lowest entropy and the entropy increases in both directions of time, towards the future of the Big Bang and towards its past (from our point of view). This would be the situation in a single connected universe, although string theory predicts a multiverse.

Trying to elucidate the meaning of time (perhaps "an emergent phenomenon rather than a necessary part of our ultimate description of the world") the author reviews special and general relativity, Boltzmann's entropy, black holes and the controversy about conservation of information, life, quantum mechanics, inflation and the multiverse. Generally speaking the book is written in an accessible style (eggs can be broken and turned into omelettes, but not the other way around to describe the Second Law), but you will need to reread some parts to make the most of it.

In the final chapter Sean Carroll faces the "search for meaning in a preposterous universe". I quote: "We find ourselves, not as a central player in the life of the cosmos, but as a tiny epiphenomenon, flourishing for a brief moment as we ride a wave of increasing entropy...Purpose and meaning are not to be found in the laws of nature, or in the plans of any external agent...it is our job to create them. One of those purposes -among many- stems from our urge to explain the world around us the best we can. If our lives are brief and undirected, at least we can take pride in our mutual courage as we struggle to understand things much greater than ourselves". I think he has a point. It is in our human nature to try to find meaning to things. The universe is meaningless. I agree and I think that Woody Allen would also.

...this book was perfect. Much like either of my ex-wives this book repeats and repeats and then repeats the same concepts over and over. This book could easily have been one-third it's size. To summarize this book: time=entropy. That's all you need to know. Now find something worth reading. I could go on but then my review would be as self serving as the book.

I found the style of the book hard to deal with. It's overwritten, with a lot of silly examples thrown into the mix that just confuses the story and delays the reader from the points the author is trying to make. So it's not an elegant discussion we have here. It's the feeling you get when someone takes way too long to tell a joke, embellishing to the point of frustration. I would advise reading part of this before jumping in with a purchase, maybe you'll like it. Wished I had, what a waste and disappointment.

This book did not need to be written. I expected more from Sean Carroll. I have his Teaching Company lecture series on Dark Energy and Dark Matter which is excellent. Frankly this book is a huge disappointment. It is overloaded with wanderings through science history citing off-the-point facts and figures that can already be found in countless other volumes and sources. It gave me the definite impression that Mr. Carroll had a panel of graduate students write this book for him- or at least most of the chapters. It is that off-focus. It never gets to the point. And whether it reminds you of your ex-wife or not, it does keep repeating the same concepts long after the horse is dead. Okay, we got the bit about entropy. There are no original ideas in this book. It introduces no new theories, and draws no interesting conclusions. The only salient concept is that time moves in one direction because entropy moves in one direction. Unless you are completely ignorant about basic science and cosmology you will find this book to be the same as I did - a waste of time (and money). Sean Carroll please don't waste your time writing books that go nowhere and say nothing new.

Roughly the first 3/4 of the book is quite standard physics, and a few related fields, e.g. information theory. The last few chapters, where the author, Sean Carroll, suggests a possible answer to the puzzle, are much more speculative, something he makes very clear.

To me the book was quite interesting. A few equations are displayed, but there is no actual use of mathematics. I have an M.S. in Applied Physics, so I cannot really say how a reader with no technical background would cope with it. Carroll goes through a lot of material, and the sheer quantity of it might be overwhelming. Unfortunately, that is just the way things are. Nobody is going to cope with this without the willingness to do some hard thinking. Carroll does include a lot of pop culture references that readers can relate to, although one of those may not be in any future edition of the book.

A couple interesting (to me) notes:

The complexity of the universe is different from the entropy. Just after the Big Bang the universe was very simple--the same high energy subatomic soup every where. Right now the universe is very complicated: There are lots of galaxies, stars, planets, black holes, people, etc. However, the entropy of the universe has increased: The formation of all those objects is mostly due to gravitation, as matter coalesces together. This gravitational process increases the total entropy, more than offsetting the order in all the structure. Eventually all of this structure will fade away. Even black holes will decay by the Hawking process, leaving a very thin, cold, dark, and simple universe. So while the universe started in a simple state, evolved into a complex state, and will eventually decay into another simple state, the entropy is always increasing. See pages 199-201.

Long ago, as an undergraduate at Carleton, one of my professors talked about the total energy of the universe. The gravitational potential energy V between two bodies decreases as they approach, because gravitation is attractive. For computational purposes we usally set V = 0 when the distance between them is infinite, and he argued that this is the natural thing to do. Then the gravitational energy is always negative. Assuming a finite universe, you can add up all the positive energy of mass, kinetic energy, etc. and then offset it by the negative gravitational energy. Professor Titus suggested the total energy of the universe would be zero. Carroll mentions in passing that you can prove this in general relativity. See p. 358.

Now the universe appears to be infinite (this was not so clear back in 1972), so strictly speaking you cannot speak about its total energy. But the general concept still applies: Gravitational energy is still negative. Something can be created from nothing, if the something is offset by sufficient gravitational energy.

The whole book reminded me of what Sir Arthur Eddington wrote:

"The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations--then so much the worse for Maxwell's equations. If it is found to be contradicted by observation--well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

On a lighter note, all of this talk about time and the universe also made me think of Severn Darden's
_Metaphysics Lecture_, which begins:

"Now, why, you will ask me, have I chosen to speak on the Universe rather than some other topic. Well, it's very simple, heh. There isn't anything else!"

Roughly the first 3/4 of the book is quite standard physics, and a few related fields, e.g. information theory. The last few chapters, where the author, Sean Carroll, suggests a possible answer to the puzzle, are much more speculative, something he makes very clear.

To me the book was quite interesting. A few equations are displayed, but there is no actual use of mathematics. I have an M.S. in Applied Physics, so I cannot really say how a reader with no technical background would cope with it. Carroll goes through a lot of material, and the sheer quantity of it might be overwhelming. Unfortunately, that is just the way things are. Nobody is going to cope with this without the willingness to do some hard thinking. Carroll does include a lot of pop culture references that readers can relate to, although one of those may not be in any future edition of the book.

A couple interesting (to me) notes:

The complexity of the universe is different from the entropy. Just after the Big Bang the universe was very simple--the same high energy subatomic soup every where. Right now the universe is very complicated: There are lots of galaxies, stars, planets, black holes, people, etc. However, the entropy of the universe has increased: The formation of all those objects is mostly due to gravitation, as matter coalesces together. This gravitational process increases the total entropy, more than offsetting the order in all the structure. Eventually all of this structure will fade away. Even black holes will decay by the Hawking process, leaving a very thin, cold, dark, and simple universe. So while the universe started in a simple state, evolved into a complex state, and will eventually decay into another simple state, the entropy is always increasing. See pages 199-201.

Long ago, as an undergraduate at Carleton, one of my professors talked about the total energy of the universe. The gravitational potential energy V between two bodies decreases as they approach, because gravitation is attractive. For computational purposes we usally set V = 0 when the distance between them is infinite, and he argued that this is the natural thing to do. Then the gravitational energy is always negative. Assuming a finite universe, you can add up all the positive energy of mass, kinetic energy, etc. and then offset it by the negative gravitational energy. Professor Titus suggested the total energy of the universe would be zero. Carroll mentions in passing that you can prove this in general relativity. See p. 358.

Now the universe appears to be infinite (this was not so clear back in 1972), so strictly speaking you cannot speak about its total energy. But the general concept still applies: Gravitational energy is still negative. Something can be created from nothing, if the something is offset by sufficient gravitational energy.

The whole book reminded me of what Sir Arthur Eddington wrote:

"The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations--then so much the worse for Maxwell's equations. If it is found to be contradicted by observation--well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

On a lighter note, all of this talk about time and the universe also made me think of Severn Darden's
_Metaphysics Lecture_, which begins:

"Now, why, you will ask me, have I chosen to speak on the Universe rather than some other topic. Well, it's very simple, heh. There isn't anything else!"

The behavior of matter (or energy) in space and time is described by the laws of physics, but the puzzling thing about physical reality is that space and time behave differently. Space is the same in all directions and it never changes, but time has preferred direction; past to future and the cause-effect relationship runs parallel to this. There is no such thing as special place (space) in the universe but there is a special time. This is a mystery because physical laws governing the fundamental particles are mostly time-symmetric (it can function thermodynamically or anti-thermodynamically), but the time-asymmetry observed in many macromolecular processes is thermodynamic and it has an arrow of time. Examples include, a glass bottle breaking into pieces or hot water becoming cold are attributed to the second law of thermodynamics which seem to set this arrow of time. Thus the physical reality is not only governed by laws of quantum physics and relativity, but also by the second law of thermodynamics which requires that the entropy (a measure of disorderliness) of a closed system, such as this universe, increase with time. This implies that the past has more order than future, hence the state of orderliness was probably the highest (or the entropy was the lowest) at the origin of the universe (big bang). The problem of justifying this arrow is not so much showing that the entropy of isolated systems increased, but explaining why there was low entropy in the past. While inflationary theory proposed by Alan Guth explains many key features of the early universe but it doesn't explain low entropy.

In this book, the author looks for clues in several areas such as, properties of black hole; information-loss paradox and Hawking radiation, string theory, inflationary epoch, multiverse cosmology and baby universes. He argues that a classical de Sitter background (mother space-time where vacuum energy is positive) does not fluctuate, but the space would be expanding and quantum fields will be fluctuating in a classical fashion. But if quantum gravity is taken into consideration then de Sitter space is itself susceptible to quantum fluctuations and this result in not only stretching and bending of spacetime as required by general relativity but also they could splice into multiple pieces. These pieces first appear as bubbles of spacetime, and then they grow and splice off to form baby universes. The baby universe created in a background de Sitter space is inclined both towards its past and to the future, but each baby universe starts in a dense low entropy state and exhibits a local arrow of time as it expands and cools. The baby universes born in the past have an arrow of time pointing in the opposite direction to those in the future, but for each universe, the time is directed towards increasing entropy and the multiverse manifests overall time symmetry. The author's hypothesis sharply contrasts the idea that big bang represents the boundary to space and time, and it dispels the notion that space and time were created at this time. He distances himself from other physicists like Larry Schulman who suggests that the universe switched to a highly ordered state at about 380,000 years when the universe became transparent to light (1, 2). The essential features of thermodynamics in the arrow of time are discussed by others which include mathematical physicist Roger Penrose (3), physicists Robert Wald (4), and Larry Schulman (5).

This is an excellent review of the concept of time in terms of physics, cosmology and philosophy. You need to have basic knowledge of physics to understand and appreciate the core ideas of the author. Chapters 12-15 are most interesting and the author discusses certain aspects of cosmology and black holes that are not relevant to physics of time but his discussions are well presented and it is very interesting to read. The main hypothesis of the author, about the arrow of time presented in chapter 15 is largely speculative and it is unlikely that physicists are convinced with his argument, however the debate will continue.

1. Schulman, L.S., Source of the observed thermodynamic arrow. [...], Nov 17, 2008
2. Gold T., Am. J. Phys. 30, 403-410 (1962)
3. [[ASIN:0679776311 The Road to Reality: A Complete Guide to the Laws of the Universe]]
4. Wald, R.M., The arrow of time and the initial conditions of the universe. [...], July 21, 2005
5. [[ASIN:0521561221 Time's Arrows and Quantum Measurement]]

There is, unfortunately, a great deal of false and misleading ideas put out by scientists today. The reason is excessive attention to the process and calculations of science, ignoring fundamental principles. The best example is discussions about the nature of a black hole. The statement, often heard, that a black hole is a region of space with such a large gravitational field that nothing can escape, is simply false. The correct statement is that a black hole is a region of space where the spacetime geometry is so extremely distorted that it takes forever for anything to reach it. It is nonsense to speak about the inside, for there is no inside in this extreme geometry.

Recently Science News had an article about time. Again, we must not forget fundamental principles of physics. Length is defined as that which is measured with a ruler. Time is defined as that which is measured by a clock. The future does not exist, as it did not yet happen. The past does not exist, as one cannot go into the past, for if so, it would not be the past. The only reality is the present, which includes records, such as pictures and memories, of past events. Time does not 'flow', for it does not make sense to measure this flow. The reason for the direction of time is clear ' we have records of past events, not of future events.

A few physicists have written books and articles on this topic, but it seems that these correct ideas have gotten lost with all the other ideas on this topic.

A new book discussing this is [[ASIN:1453818359 Rational Thinking, Government Policies, Science, and Living]].