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The Janus Point
What is time? Why is the past so different from the present and the future?This simple question is in fact one of the deepest, most long-standing problems in physics. None of the known laws of the universe can explain it. In The Janus Point, Julian Barbour presents a bold new thesis and a possible solution, with radical implications for our understanding of the Big Bang and the nature of time itself.His argument rests on two vital insights. The first is that the most common explanation for time – entropy – is firstly, because we have no way of explaining how the concentration of energy that would allow the Big Bang to take place came about, and secondly because none of our understanding of entropy takes into account the fact that the universe is infinitely expanding. In addition, our universe is actually becoming ever more complex and ordered as it expands, not less so. The second is a phenomenon which Barbour labels ‘The Janus Point’: any system of particles in motion will pass through a single moment of smallest size, never to be repeated.Combining these two observations, Barbour argues that the universe, and therefore time itself, may not have begun at the Big Bang, but rather at The Janus Point, thus solving the conundrum of entropy.Monumental in vision and scope, The Janus Point offers a ground-breaking challenge to our understanding of the universe and a brilliant solution of breath-taking elegance and import to this most fundamental of problems.
400 pages, Hardcover
First published December 3, 2020
118 people are currently reading
850 people want to read
About the author
Julian Barbour
8 books89 followersJulian Barbour (1937) is a British physicist with research interests in quantum gravity and the history of science.
Since receiving his PhD degree on the foundations of Einstein's general theory of relativity at the University of Cologne in 1968, Barbour has supported himself and his family without an academic position, working part-time as a translator. He has research interests in quantum gravity and the history of science.
Since receiving his PhD degree on the foundations of Einstein's general theory of relativity at the University of Cologne in 1968, Barbour has supported himself and his family without an academic position, working part-time as a translator. He has research interests in quantum gravity and the history of science.
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Displaying 1 - 30 of 45 reviews
October 22, 2021
Thinking Outside The Box
I have no doubt that Barbour is a polymath of considerable renown for his work in the history and philosophy of science. His insights are thrilling in their originality and import. His ability to make connections not just among diverse areas of science but also with literature, philosophy, myth and religion is remarkable. His aphorisms are memorable. The consequence is that his writing is dense to the point of impenetrable obscurity.
Unless you are prepared to engage with the details of such things as phase space, shape spaces, minimal model, root-mean-square lengths, Poincaré recurrence, the Boltzmann brain, Abelian gauge theory, the N-body problem, Kepler pairs, and invariant variations, you will not find much to linger on in The Janus Point. This is unfortunate since it is a self-proclaimed paean to the universe, a sort of celebration of all that is. But it’s a celebration much like an Oxford commencement, in which the orator gives his often lengthy speech entirely in Latin. Snippets are intelligible to many in the audience but only the experts in ancient rhetoric understand the content.
The snippets that I comprehend in The Janus Point centre on his chief concerns: 1) the apparent reversibility of the laws of physics which is contradicted by all experience, and 2) the necessity within current cosmological theory for postulating inscrutable ‘special conditions’ for the universe at the moment of the Big Bang. Both these issues he perceives as deficiencies in cosmological theory involving a misconception of time and a related mistake in the application of the second law of thermodynamics. In his exposition, Barbour critiques not just the historical ‘greats’ in Physics - Newton, Boltzmann, Leibniz, Thomson, Mach, and Einstein among others - but also more recent ‘heavies’ like Penrose, Feynman, and Hawking. Throw in a bit of Shakespeare, Augustine, and Wagner and the result is density bordering on that of a black hole.
Barbour’s response to his two main concerns is, after considerable discursive detours fore and aft in the text, is literally to “think out of the box.” By this he means to consider the universe as what it is: not an experimental enclosure in which the established laws of thermodynamics reign, but an un constrained, expanding space in which certain concepts like entropy and especially time must be re-defined. He proposes an entropy-like concept which he calls entaxy, and which is measured in terms of ‘shape-complexity.’
If I understand him correctly (and this is questionable), Barbour claims that the inevitable increase in the entropy of the universe, and its consequent heat-death, masks a simultaneous process of increasing shape-entaxy. Such entaxy is a potential for order in an otherwise chaotic universe. It is just such entaxy which allows the structure of galaxies, planets, and biological life, including ourselves to emerge from such background chaos. In a sense we already live in the cosmic end-times since “the total entropy of the black holes known to exist within the observable universe dwarfs the entropy of all the matter outside them.” Yet cosmic structures continue to thrive.
So Barbour wants to define time as the growth in complexity rather than the increase in entropy. And according to him (with such complexity that I do not understand it) this implies that the experience of time ‘emanates’ as it were from the point of the Big Bang. But, crucially, it does so in two directions, thus making the Big Bang a so-called Janus point. The ‘line’ on which the arrow of time travels is thus infinite in the past as well as the future. Only what we consider as the past on our side of the Janus point is future on the other side!
Lest I misrepresent what Barbour has to say, let me use his summary: “... the claim this book makes. It is not just that it proposes a new theory of time and with it a first-principles explanation of its arrows; it also aims to overturn the doctrine that it is entropic disorder on a cosmic scale that puts the direction into time. The claim is this: the direction gets into time not through the growth of disorder but through the growth of structure and complexity.” That much I understand.
But I must say that I don’t understand anything more about time that I did before the agony of reading The Janus Point over the last several days. Barbour claims that time is “... ultimately a measure of the difference of shapes, both on the cosmic scale and within well-isolated emergent subsystems.” Really? And as a human being I perceive this how? I’m sure it’s very important to understand. That I don’t is a burden I must endure.
I have no doubt that Barbour is a polymath of considerable renown for his work in the history and philosophy of science. His insights are thrilling in their originality and import. His ability to make connections not just among diverse areas of science but also with literature, philosophy, myth and religion is remarkable. His aphorisms are memorable. The consequence is that his writing is dense to the point of impenetrable obscurity.
Unless you are prepared to engage with the details of such things as phase space, shape spaces, minimal model, root-mean-square lengths, Poincaré recurrence, the Boltzmann brain, Abelian gauge theory, the N-body problem, Kepler pairs, and invariant variations, you will not find much to linger on in The Janus Point. This is unfortunate since it is a self-proclaimed paean to the universe, a sort of celebration of all that is. But it’s a celebration much like an Oxford commencement, in which the orator gives his often lengthy speech entirely in Latin. Snippets are intelligible to many in the audience but only the experts in ancient rhetoric understand the content.
The snippets that I comprehend in The Janus Point centre on his chief concerns: 1) the apparent reversibility of the laws of physics which is contradicted by all experience, and 2) the necessity within current cosmological theory for postulating inscrutable ‘special conditions’ for the universe at the moment of the Big Bang. Both these issues he perceives as deficiencies in cosmological theory involving a misconception of time and a related mistake in the application of the second law of thermodynamics. In his exposition, Barbour critiques not just the historical ‘greats’ in Physics - Newton, Boltzmann, Leibniz, Thomson, Mach, and Einstein among others - but also more recent ‘heavies’ like Penrose, Feynman, and Hawking. Throw in a bit of Shakespeare, Augustine, and Wagner and the result is density bordering on that of a black hole.
Barbour’s response to his two main concerns is, after considerable discursive detours fore and aft in the text, is literally to “think out of the box.” By this he means to consider the universe as what it is: not an experimental enclosure in which the established laws of thermodynamics reign, but an un constrained, expanding space in which certain concepts like entropy and especially time must be re-defined. He proposes an entropy-like concept which he calls entaxy, and which is measured in terms of ‘shape-complexity.’
If I understand him correctly (and this is questionable), Barbour claims that the inevitable increase in the entropy of the universe, and its consequent heat-death, masks a simultaneous process of increasing shape-entaxy. Such entaxy is a potential for order in an otherwise chaotic universe. It is just such entaxy which allows the structure of galaxies, planets, and biological life, including ourselves to emerge from such background chaos. In a sense we already live in the cosmic end-times since “the total entropy of the black holes known to exist within the observable universe dwarfs the entropy of all the matter outside them.” Yet cosmic structures continue to thrive.
So Barbour wants to define time as the growth in complexity rather than the increase in entropy. And according to him (with such complexity that I do not understand it) this implies that the experience of time ‘emanates’ as it were from the point of the Big Bang. But, crucially, it does so in two directions, thus making the Big Bang a so-called Janus point. The ‘line’ on which the arrow of time travels is thus infinite in the past as well as the future. Only what we consider as the past on our side of the Janus point is future on the other side!
Lest I misrepresent what Barbour has to say, let me use his summary: “... the claim this book makes. It is not just that it proposes a new theory of time and with it a first-principles explanation of its arrows; it also aims to overturn the doctrine that it is entropic disorder on a cosmic scale that puts the direction into time. The claim is this: the direction gets into time not through the growth of disorder but through the growth of structure and complexity.” That much I understand.
But I must say that I don’t understand anything more about time that I did before the agony of reading The Janus Point over the last several days. Barbour claims that time is “... ultimately a measure of the difference of shapes, both on the cosmic scale and within well-isolated emergent subsystems.” Really? And as a human being I perceive this how? I’m sure it’s very important to understand. That I don’t is a burden I must endure.
December 5, 2020
In a universe filled by chaos and disorder, one physicist makes the radical argument that the growth of order drives the passage of time -- and shapes the destiny of the universe. Time is among the universe's greatest mysteries. Why, when most laws of physics allow for it to flow forward and backward, does it only go forward? Physicists have long appealed to the second law of thermodynamics, held to predict the increase of disorder in the universe, to explain this. In The Janus Point, physicist Julian Barbour argues that the second law has been misapplied and that the growth of order determines how we experience time. In his view, the big bang becomes the "Janus point," a moment of minimal order from which time could flow, and order increase, in two directions.
The Janus Point has remarkable implications: while most physicists predict that the universe will become mired in disorder, Barbour sees the possibility that order -- the stuff of life -- can grow without bound. A major new work of physics, The Janus Point will transform our understanding of the nature of existence. This is a fascinating, life-altering and accessible read, which is deeply informative and rich in intricate detail. I've read several books that cover this topic but none were as absorbing and engaging as Barbour manages to make this narrative. It is a book I cannot recommend highly enough to those with an interest in our universe, the concept of time and its impact on the way we live our lives, and our philosophical outlook.
The Janus Point has remarkable implications: while most physicists predict that the universe will become mired in disorder, Barbour sees the possibility that order -- the stuff of life -- can grow without bound. A major new work of physics, The Janus Point will transform our understanding of the nature of existence. This is a fascinating, life-altering and accessible read, which is deeply informative and rich in intricate detail. I've read several books that cover this topic but none were as absorbing and engaging as Barbour manages to make this narrative. It is a book I cannot recommend highly enough to those with an interest in our universe, the concept of time and its impact on the way we live our lives, and our philosophical outlook.
August 10, 2021
Well. This was a passionate and mind-breaking book of which I understood exactly half. I thought I was ready to graduate to the Big Books of physics, but I wasn’t (which led me to start a free physics course to fill in the gaps).
However, it was incomprehensible because the author is making a HUGE claim (the universe started ordered & has evolved into complexity) and needs to write seven million proofs for it (understandably). But ultimately his point is so hopeful and lovely: There will be no heat death. Humanity will live on.
I loved one line where he mentioned that while yes, we might feel claustrophobic because we’re trapped on the earth, variety and complexity will continue to grow and astound and we can never feel stuck in that case. Sometimes I feel trapped on the earth in an anxious way. This made me feel better.
I also had to laugh at one of his caveats where he was worried that “sober scientists” would worry he was being too poetic. Oh buddy. He did sprinkle in some Shakespeare here and there but compared to the super pop physics books out there, this was a math textbook.
BUT. The thesis is incredible and essentially breaks every notion of classical physics. I loved that! You learn the same old stories over and over and to see them challenged was inspiring. I’m going to reread this when I can understand the mucky bits.
However, it was incomprehensible because the author is making a HUGE claim (the universe started ordered & has evolved into complexity) and needs to write seven million proofs for it (understandably). But ultimately his point is so hopeful and lovely: There will be no heat death. Humanity will live on.
I loved one line where he mentioned that while yes, we might feel claustrophobic because we’re trapped on the earth, variety and complexity will continue to grow and astound and we can never feel stuck in that case. Sometimes I feel trapped on the earth in an anxious way. This made me feel better.
I also had to laugh at one of his caveats where he was worried that “sober scientists” would worry he was being too poetic. Oh buddy. He did sprinkle in some Shakespeare here and there but compared to the super pop physics books out there, this was a math textbook.
BUT. The thesis is incredible and essentially breaks every notion of classical physics. I loved that! You learn the same old stories over and over and to see them challenged was inspiring. I’m going to reread this when I can understand the mucky bits.
February 12, 2022
Dnf at 65%
Thanks to NetGalley for an earc of this. I ended up listening to the audiobook.
In short, the book is overly esoteric. It's honestly hard to imagine this is actually intended for the lay reader. The basic idea is fascinating: the big bang as imagine it, actually occurred in both directions of time, but on the other side of the big bang, matter evolves with entropy (i.e., the arrow of time) opposite of our own. I was interested in learning about this, but he spends too much time trying to prove it (I feel like a lot of is better fitting a peer reviewed paper) than actually communicating the basic idea. You can hear my thoughts in a couple vlogs, my Washington trip (pretty much just this first clip) and my moving vlog.
Thanks to NetGalley for an earc of this. I ended up listening to the audiobook.
In short, the book is overly esoteric. It's honestly hard to imagine this is actually intended for the lay reader. The basic idea is fascinating: the big bang as imagine it, actually occurred in both directions of time, but on the other side of the big bang, matter evolves with entropy (i.e., the arrow of time) opposite of our own. I was interested in learning about this, but he spends too much time trying to prove it (I feel like a lot of is better fitting a peer reviewed paper) than actually communicating the basic idea. You can hear my thoughts in a couple vlogs, my Washington trip (pretty much just this first clip) and my moving vlog.
August 26, 2023
I should make it clear that I rate books according to how much I enjoy reading them, not how well I understand them.
The challenge of trying to think using new frames and concepts was enjoyable, as was laughing out loud at times because of how far away I was from understanding what the author was talking about.
If you're someone who worries about how the quantum mechanical Bunch-Davies vacuum, squeezed by inflationary expansion, becomes classical...this is the book for you!
The challenge of trying to think using new frames and concepts was enjoyable, as was laughing out loud at times because of how far away I was from understanding what the author was talking about.
If you're someone who worries about how the quantum mechanical Bunch-Davies vacuum, squeezed by inflationary expansion, becomes classical...this is the book for you!
April 3, 2021
I think I get it!
March 2, 2021
The laws of physics do not specify that time must flow "forward" (from our perspective). Then why (as far as we know) does it always do so? Barbour attempts to answer that question by a substituting for the big bang a "janus point," from which time flows in both directions simultaneously (and we happen to be on the past-to-present trip, not the other one). He does not posit that they are mirror images of each other, as if everything that happens in this universe is happening exactly the same (but backwards) in another.
That is a very very simple explanation of this book. It was on the cusp of going over my head more than once (and, let's be honest, probably did so). But it was interesting to think about and enlivened by Barbour's strong appreciation of history and the long line of thinkers in the realm of astrophysics that has led us to where we are today. Certainly a minority position offered here in the book, but one that will require grappling with and answering my folks 5.75 times smarter than I.
That is a very very simple explanation of this book. It was on the cusp of going over my head more than once (and, let's be honest, probably did so). But it was interesting to think about and enlivened by Barbour's strong appreciation of history and the long line of thinkers in the realm of astrophysics that has led us to where we are today. Certainly a minority position offered here in the book, but one that will require grappling with and answering my folks 5.75 times smarter than I.
Want to read
March 23, 2021Here's a thoughtful review at Science: https://blogs.sciencemag.org/books/20...
The review itself is confusing, and since the reception here is mixed, I'm putting this one at the bottom of my TBR. Likely never to be seen again (by me). I've had problems with confusing pop-physics books. Not all due to me....
The review itself is confusing, and since the reception here is mixed, I'm putting this one at the bottom of my TBR. Likely never to be seen again (by me). I've had problems with confusing pop-physics books. Not all due to me....
April 6, 2021
The Janus Point is a provocative, new take on the origins of time and the fate of the universe. Today, most physics believe that the universe as we know it began with the Big Bang, but there may be a different possibility - that the Big Bang wasn't the beginning of time, but merely a very special point in the history of our cosmos. The author calls it the Janus point. If true, it would mean that the universe is driven not by the increase of entropy, but rather by the growth of structure and order.
This book is not an easy read, to be honest, but I still managed to find some interesting, worth-thinking points as follow:
1) The laws of nature don't distinguish between past and future.
2) Time may have split off into 2 directions after the Big Bang.
3) The universe may be increasing in complexity rather than entropy.
4) The three-body problem illustrates how time splits at the Janus point.
5) According to the Janus point theory, entaxy in the universe is decreasing.
6) The Janus point occurs at a moment of total collision.
This theory remains unproven, for now. But it sits firmly at the forefront of current scientific research - and if the Janus point model proves true, we may finally understand the time and its arrows.
This book is not an easy read, to be honest, but I still managed to find some interesting, worth-thinking points as follow:
1) The laws of nature don't distinguish between past and future.
2) Time may have split off into 2 directions after the Big Bang.
3) The universe may be increasing in complexity rather than entropy.
4) The three-body problem illustrates how time splits at the Janus point.
5) According to the Janus point theory, entaxy in the universe is decreasing.
6) The Janus point occurs at a moment of total collision.
This theory remains unproven, for now. But it sits firmly at the forefront of current scientific research - and if the Janus point model proves true, we may finally understand the time and its arrows.
This entire review has been hidden because of spoilers.
September 21, 2025
Finally finished. This book was kind of a mess. It's a popular science book but it was definitely 60% a math book for people who were experts at math. I thought about quitting it many times and just powered through where I couldn't understand what he was saying. I took a few things from the book, a deeper dive into relativity and ratios, and how they relate to cosmology and time, but from my perspective the same conclusions for a reader of my ilk could have been had in 100-150 pages.
Do not recommend for anyone who is not PhD in Mathematics or Physics
Do not recommend for anyone who is not PhD in Mathematics or Physics
August 19, 2020
Intriguing Theoretical Astrophysics. If it wasn't clear from the description of this book, this book is *all about* theoretical astrophysics and the author's new theory of the origins and nature of time. If words like Newtonian and General Relativity and Leibniz and thermodynamics are part of your every day lexicon, you'll probably enjoy reading this. For the rest of us... at least there isn't much math involved in the actual text here? Specifically of the Calculus variety, which gives even many math-oriented people the heebie jeebies? Truly an intriguing work, but I'll be the first to say that I didn't fully follow or comprehend all of it - it is simply that high level. Even though Barbour tries to use narrative examples and structures designed to allow most anyone to have some idea of what is going on, at the end of the day this is still advanced theoretical astrophysics, of the kind that even Stephen Hawking wrestled with. While others more learned in the actual science may find fault here, for what it is I could find none. Very much recommended.
May 8, 2022
One of the worst books on physics that I have ever read and I have read a lot of them. Regardless the complexity of the matter (R. Penrose "Emperor's Mind type of complexity), the Author should have avoided so many auto cross references in his own book, that made the reading insufferable. It's simply badly written; pity, since the topic is really fascinating
March 6, 2021
This book is largely about an attempt to reenvisage the concept of entropy to fit it into a view of the universe as, due to the constant expansion, being more like an open system, rather than a closed system like a box with walls that particles can bounce off. Entropy is normally viewed in relation to this latter view of things. Now this can work well for localised thermodynamic systems, but is misapplied to the universe as a whole, according to Barbour.
As a result this allows him to think more positively about how entropy may apply to the universe overall, in which the arrow of time does not lead us to a heat death style conclusion to the universe, of things becoming more disorganised and equilibrating, like in an isolated thermodynamic system, but instead the arrow of time means continual expansion as in the big bang, but locally also it leads to perpetual complexification of island like entities within that expanse, such as planets, galaxies etc. It suggests this local internal complexification can continue without end into the future.
Part of the way he shows this is through viewing space and time in a purely relational manner, true to Leibniz' insight and concern all those years ago in his argument with Newton over the fact that absolute space and time disobeys the principle of sufficient reason and the principle of identity of indistinguishables. Barbour aims to work in line with these principles to try and provide a different way of envisaging what the big bang means, and what an origin to the universe could mean. This is what the Janus point is meant to represent.
He tries to work in line with these principles, to provide a background independent understanding of the basic "being" of the cosmos, as opposed to the at times ad hoc "past hypothesis", relied upon by many in the standard interpretation of times arrows in line with typical closed-box entropy, and the work of those in string theory that is not background independent and relies only on the principle of non-contradiction, allowing them to end up with many different consistent and mutually exclusive interpretations of what basic reality may be, making it seem more like a mathematical game or model, rather than dealing with fundamental reality of the cosmos.
Part of the way he goes about it all, gets into complex mathematics in relation to N-body and 3-body problems, and kepler pairs, in which out of basic triangular relational snapshots of what he calls shape space, a system can develop to allow our regular notions of time and space to emerge. I couldn't comment much on this more purely mathematical aspect. Only to say it would be something of importance to see more experts in this field look into and check over and verify or falsify some of his results.
In the larger philosophical picture and physical picture, I find this idea of returning to certain basic principles of reason very attractive in our envisaging of the cosmos. As opposed to relying on arbitrary starting points of something from nothing, or ad hoc postulation of principles to fill gaps in the reasoning, like with the standard account of the big bang and the past hypothesis. However, there are some issues remaining, such as quite what he means by this "law of the universe", preceding the more regular and emergent laws of nature and physics we commonly see, that he evokes often to defend his position, and what experimental proofs or falsifications of his theory there could be, because not many are supplied.
Unlike Roger Penrose, who suggests a more clear empirical test of this kind in relation to his conformal cyclic cosmology. I was also surprised that he did not contrast his view with the view of Penrose, for all he says is that he sees Penrose's "closed box" account of entropy and thermodynamics as misguided in line with the standard model. But does not talk of his CCC at all. At times, he seems to be taking some digs at Roger Penrose in general, without himself offering something much clearer. And really it seems to me these two should be finding much common ground in their views of reality and of mathematics.
It would be interesting to see Roger Penrose's response to this cosmological perspective of Julian Barbour and the Janus point, however, given he does not seem much taken by the idea of going for a purely relational view of space and time, it may be hard to reconcile their approaches from the very foundations.
A lot to ponder, and certainly it addressed some of the concerns I have always had with the standard account of the big bang, past hypothesis and heat death of the universe, where, aside from the negative consequences for our future being, it seemed to rely on arbitrary and unproven elements and misguided extrapolations from localised phenomena.
As a result this allows him to think more positively about how entropy may apply to the universe overall, in which the arrow of time does not lead us to a heat death style conclusion to the universe, of things becoming more disorganised and equilibrating, like in an isolated thermodynamic system, but instead the arrow of time means continual expansion as in the big bang, but locally also it leads to perpetual complexification of island like entities within that expanse, such as planets, galaxies etc. It suggests this local internal complexification can continue without end into the future.
Part of the way he shows this is through viewing space and time in a purely relational manner, true to Leibniz' insight and concern all those years ago in his argument with Newton over the fact that absolute space and time disobeys the principle of sufficient reason and the principle of identity of indistinguishables. Barbour aims to work in line with these principles to try and provide a different way of envisaging what the big bang means, and what an origin to the universe could mean. This is what the Janus point is meant to represent.
He tries to work in line with these principles, to provide a background independent understanding of the basic "being" of the cosmos, as opposed to the at times ad hoc "past hypothesis", relied upon by many in the standard interpretation of times arrows in line with typical closed-box entropy, and the work of those in string theory that is not background independent and relies only on the principle of non-contradiction, allowing them to end up with many different consistent and mutually exclusive interpretations of what basic reality may be, making it seem more like a mathematical game or model, rather than dealing with fundamental reality of the cosmos.
Part of the way he goes about it all, gets into complex mathematics in relation to N-body and 3-body problems, and kepler pairs, in which out of basic triangular relational snapshots of what he calls shape space, a system can develop to allow our regular notions of time and space to emerge. I couldn't comment much on this more purely mathematical aspect. Only to say it would be something of importance to see more experts in this field look into and check over and verify or falsify some of his results.
In the larger philosophical picture and physical picture, I find this idea of returning to certain basic principles of reason very attractive in our envisaging of the cosmos. As opposed to relying on arbitrary starting points of something from nothing, or ad hoc postulation of principles to fill gaps in the reasoning, like with the standard account of the big bang and the past hypothesis. However, there are some issues remaining, such as quite what he means by this "law of the universe", preceding the more regular and emergent laws of nature and physics we commonly see, that he evokes often to defend his position, and what experimental proofs or falsifications of his theory there could be, because not many are supplied.
Unlike Roger Penrose, who suggests a more clear empirical test of this kind in relation to his conformal cyclic cosmology. I was also surprised that he did not contrast his view with the view of Penrose, for all he says is that he sees Penrose's "closed box" account of entropy and thermodynamics as misguided in line with the standard model. But does not talk of his CCC at all. At times, he seems to be taking some digs at Roger Penrose in general, without himself offering something much clearer. And really it seems to me these two should be finding much common ground in their views of reality and of mathematics.
It would be interesting to see Roger Penrose's response to this cosmological perspective of Julian Barbour and the Janus point, however, given he does not seem much taken by the idea of going for a purely relational view of space and time, it may be hard to reconcile their approaches from the very foundations.
A lot to ponder, and certainly it addressed some of the concerns I have always had with the standard account of the big bang, past hypothesis and heat death of the universe, where, aside from the negative consequences for our future being, it seemed to rely on arbitrary and unproven elements and misguided extrapolations from localised phenomena.
December 22, 2023
The Publisher Says: In a universe filled by chaos and disorder, one physicist makes the radical argument that the growth of order drives the passage of time — and shapes the destiny of the universe.
Time is among the universe's greatest mysteries. Why, when most laws of physics allow for it to flow forward and backward, does it only go forward? Physicists have long appealed to the second law of thermodynamics, held to predict the increase of disorder in the universe, to explain this.
In The Janus Point, physicist Julian Barbour argues that the second law has been misapplied and that the growth of order determines how we experience time. In his view, the big bang becomes the "Janus point," a moment of minimal order from which time could flow, and order increase, in two directions. The Janus Point has remarkable implications: while most physicists predict that the universe will become mired in disorder, Barbour sees the possibility that order — the stuff of life — can grow without bound.
A major new work of physics, The Janus Point will transform our understanding of the nature of existence.
I RECEIVED A DRC FROM THE PUBLISHER VIA NETGALLEY. THANK YOU.
My Review: On the Solstice, I think a lot about time. Why time's arrow only points in one direction, for example. I am always bothered by the implication inherent in the laws of physics that we presently understand that this is an observational artifact, not part of the structure of physics.
While I sit and ponder the strange dichotomies between what we observe and what theory tells us is possible, Author Barbour sets himself the task of learning the why, and questioning the how, of all the factors in physics that determine this issue's boundaries. That is an immense task.
It is also one well beyond most people's educational, vocational, and experiential capacities. The author isn't writing an academic paper in this book. He is, however, presupposing a lot of knowledge on the reader's part...if you don't know what a Boltzmann brain is, for example, this book will be lost on you...and even for those with the requisite grounding in at least the people who created the outlines of the Standard Model of particle physics, the need for frequent research breaks, aka "fallings down the many rabbit holes", is ever-present.
Very much not a Wikipedia-level treatment of an immensely important topic being argued, studied, researched, and pondered by some of the best-furnished minds in the field of physics today; yet it does not repel boarders with its case-shot loaded cannons of erudition. Author Barbour is quippy and quotable. The problem is quoting him won't help. This is someone with a very broad grasp of physics, history, cultural anthropology, etc. He lays out arguments that I suspect I only dimly grasp for his new model of endlessly repeatable order, ie creation of matter instead of its inevitable and complete decay, grounded in all the currents of thought there are.
Not, as you'd expect, a mere bagatelle to be consumed of an evening. Took me two years to read it, and I regret not a page or a minute of it. I was rewarded with a greatly expanded idea of what the science of physics is reaching for in its quest for a unified theory.
At this #Booksgiving moment, self-gifting this immensely challenging and deeply absorbing book is a great way to invest in your brain's expansion in entirely new ways and directions. It will be a Project. It is also well worth your eyeblinks.
Time is among the universe's greatest mysteries. Why, when most laws of physics allow for it to flow forward and backward, does it only go forward? Physicists have long appealed to the second law of thermodynamics, held to predict the increase of disorder in the universe, to explain this.
In The Janus Point, physicist Julian Barbour argues that the second law has been misapplied and that the growth of order determines how we experience time. In his view, the big bang becomes the "Janus point," a moment of minimal order from which time could flow, and order increase, in two directions. The Janus Point has remarkable implications: while most physicists predict that the universe will become mired in disorder, Barbour sees the possibility that order — the stuff of life — can grow without bound.
A major new work of physics, The Janus Point will transform our understanding of the nature of existence.
I RECEIVED A DRC FROM THE PUBLISHER VIA NETGALLEY. THANK YOU.
My Review: On the Solstice, I think a lot about time. Why time's arrow only points in one direction, for example. I am always bothered by the implication inherent in the laws of physics that we presently understand that this is an observational artifact, not part of the structure of physics.
While I sit and ponder the strange dichotomies between what we observe and what theory tells us is possible, Author Barbour sets himself the task of learning the why, and questioning the how, of all the factors in physics that determine this issue's boundaries. That is an immense task.
It is also one well beyond most people's educational, vocational, and experiential capacities. The author isn't writing an academic paper in this book. He is, however, presupposing a lot of knowledge on the reader's part...if you don't know what a Boltzmann brain is, for example, this book will be lost on you...and even for those with the requisite grounding in at least the people who created the outlines of the Standard Model of particle physics, the need for frequent research breaks, aka "fallings down the many rabbit holes", is ever-present.
Very much not a Wikipedia-level treatment of an immensely important topic being argued, studied, researched, and pondered by some of the best-furnished minds in the field of physics today; yet it does not repel boarders with its case-shot loaded cannons of erudition. Author Barbour is quippy and quotable. The problem is quoting him won't help. This is someone with a very broad grasp of physics, history, cultural anthropology, etc. He lays out arguments that I suspect I only dimly grasp for his new model of endlessly repeatable order, ie creation of matter instead of its inevitable and complete decay, grounded in all the currents of thought there are.
Not, as you'd expect, a mere bagatelle to be consumed of an evening. Took me two years to read it, and I regret not a page or a minute of it. I was rewarded with a greatly expanded idea of what the science of physics is reaching for in its quest for a unified theory.
At this #Booksgiving moment, self-gifting this immensely challenging and deeply absorbing book is a great way to invest in your brain's expansion in entirely new ways and directions. It will be a Project. It is also well worth your eyeblinks.
November 12, 2022
illuminating
Great book. A deep conceptual look at the nature of Time. And Time’s supposed arrow. And the proposed Janus point. By someone working in the field. (Theoretical physics, and you can look up his specific interests).
The author starts out with considerations of entropy and thermodynamics, but then broadens his scope to motion in general, ideas about shape space, relativity and quantum theory. The need for theories to be relational and background independent. String Theory is well known not be background independent. But I was stunned when the author points out that even basic quantum mechanics isn’t. Well of course it isn’t. In hindsight. Making the unification of quantum mechanics and general relativity just that much harder. As he points out some really new fundamental ideas are needed and sorely lacking.
He makes a valiant effort to keep it all readable without assuming too much background, but you have to know something. This isn’t pop science.
That effort falters in the last few chapters. Where he takes a look at the implications for Cosmology in particular for the Big Bang and Inflation. Not an easy read here but a fascinating account of some actual research in progress. Recent papers. One as recently as 2018. So you can get a glimpse of the ideas being worked on. The kinds of constructions being considered.
He doesn’t go much into quantum theory but what’s there is succinct and to the point. He is keenly aware of the need for a quantum gravity theory and points out some ideas. He is not a fan of cosmic inflation and proposes an alternative.
So all in all a fascinating account of some current ideas actively being worked on by one of the researchers actually doing it.
As I like to say ‘Those bears sure know how to have a good time’. If you catch the reference, which admittedly is a bit obscure.
Great book. A deep conceptual look at the nature of Time. And Time’s supposed arrow. And the proposed Janus point. By someone working in the field. (Theoretical physics, and you can look up his specific interests).
The author starts out with considerations of entropy and thermodynamics, but then broadens his scope to motion in general, ideas about shape space, relativity and quantum theory. The need for theories to be relational and background independent. String Theory is well known not be background independent. But I was stunned when the author points out that even basic quantum mechanics isn’t. Well of course it isn’t. In hindsight. Making the unification of quantum mechanics and general relativity just that much harder. As he points out some really new fundamental ideas are needed and sorely lacking.
He makes a valiant effort to keep it all readable without assuming too much background, but you have to know something. This isn’t pop science.
That effort falters in the last few chapters. Where he takes a look at the implications for Cosmology in particular for the Big Bang and Inflation. Not an easy read here but a fascinating account of some actual research in progress. Recent papers. One as recently as 2018. So you can get a glimpse of the ideas being worked on. The kinds of constructions being considered.
He doesn’t go much into quantum theory but what’s there is succinct and to the point. He is keenly aware of the need for a quantum gravity theory and points out some ideas. He is not a fan of cosmic inflation and proposes an alternative.
So all in all a fascinating account of some current ideas actively being worked on by one of the researchers actually doing it.
As I like to say ‘Those bears sure know how to have a good time’. If you catch the reference, which admittedly is a bit obscure.
March 20, 2025
Excellent erudition throughout once more, as expected from our days' Mach, though not rarely in the way of the clarity of the message. By means of splendid prose filled with literary allusions and even quotes, Barbour proposes a solution to the problem of the universe's past hypothesis in the form of what he calls the Janus point, supposed to replace the big bang as time-symmetric spring well of the universe in both forward and backward directions of time. While in his previous book the author collected and refined his critical revision of the concepts of time and space, which he inherited from Mach indeed, here, while continuing the same tread, the best part lies possibly in the history and criticism of thermodynamics, in particular its formulation within confined volumes or rather phase space. Removing this constraint, of largely historical tradition only, Barbour claims that several criticisms and paradoxes on the origin of time's arrow dissolve, and the universe appears as a constant source of creation of complexity, which he ends up equaling to time itself. What strikes as amusing is that Barbour keeps believing time is an illusion and real space must be replaced by visualization of timeless shape space to develop mechanics, but at the same time takes pain in writing the history of physics, it being mechanics or thermodynamics, and acknowledging the contributions of all scientists in the right order and context. Nevertheless, Barbour's ideas are refreshing, provoking, and might even contain prolific seeds of future theories.
August 25, 2022
In this book, the author describes an unorthodox and compelling cosmogonic theory, while providing an explanation (hypothesis) of the arrow of time, which has proven to be a thorny topic in physics: the fundamental equations are - sort of - invariant while inverting the “flow” of time … thus, where does the time come from?! Some authors put forward an hypothesis of a time-free basic physics; the time being recovered as “emergent feature”, if/when needed, but no consensus has been reached on what a sound hypothesis could look like, yet.
The author’s hypothesis is compelling and a lot of effort is poured to explain the ideas without the “un-needed complexities” of mathematics.
Unfortunately, to me, maths is the worst form of explanations - except for all the others that have been tried. As a result, it is difficult to follow the author into the subtleties of the argument and its ramifications.
This said, if you content yourself of an overall description of a compelling, unusual and fascinating hypothesis, this book is worth considering and reading!
I was looking for something more, and because of difficulties in reading, it’s only 3 star to me.
The author’s hypothesis is compelling and a lot of effort is poured to explain the ideas without the “un-needed complexities” of mathematics.
Unfortunately, to me, maths is the worst form of explanations - except for all the others that have been tried. As a result, it is difficult to follow the author into the subtleties of the argument and its ramifications.
This said, if you content yourself of an overall description of a compelling, unusual and fascinating hypothesis, this book is worth considering and reading!
I was looking for something more, and because of difficulties in reading, it’s only 3 star to me.
May 21, 2024
I honestly tried hard to get through this book, but I gave up about 75% of the way through. The ideas are interesting, but in the end I simply couldn't see the point of recasting existing physics into this format. I may have missed something, but what is the hypothesis saying that is different from classical physics, since the 3-body model used throughout seems to have been derived directly from Newtonian mechanics?
The book is full of novel definitions & jargon, specifically coined by the author and his coworkers in the field, so that one eventually gets tired of trying to understand what one is reading - like it was written in a foreign language that needs translating at each sentence. I wanted to see some real calculations and formulae, some hard physical quantities that can be measured, but instead there are just qualitative descriptions and abstractions that become increasingly obscure.
On the other hand, the author's explanation of entropy in the context of disorder and information is one of the best I've seen.
The book is full of novel definitions & jargon, specifically coined by the author and his coworkers in the field, so that one eventually gets tired of trying to understand what one is reading - like it was written in a foreign language that needs translating at each sentence. I wanted to see some real calculations and formulae, some hard physical quantities that can be measured, but instead there are just qualitative descriptions and abstractions that become increasingly obscure.
On the other hand, the author's explanation of entropy in the context of disorder and information is one of the best I've seen.
January 2, 2021
"The Janus Point" by Julian Barbour posits that there is a point at which time runs in reverse for the universe. We think as time as running forward from the Big Bang on, but Barbour believes that time also runs in reverse from that point, although we cannot experience that.
Barbour knows his stuff, but throws a lot of less-comprehensible material at the reader. Richard Feynman, a famous physicist, after trying to explain a topic, once said, "“I couldn’t do it. I couldn’t reduce it to the freshman level. That means we don’t really understand it.” I think Barbour understands the high points of his theory, but has difficulty translating it for non-physicists. The general reader will struggle with the concepts and math, and also with Barbour's general verbosity. It's a fascinating topic and a great theory about which I'd like to know more, but it was a slog to get through.
Slightly recommended.
Barbour knows his stuff, but throws a lot of less-comprehensible material at the reader. Richard Feynman, a famous physicist, after trying to explain a topic, once said, "“I couldn’t do it. I couldn’t reduce it to the freshman level. That means we don’t really understand it.” I think Barbour understands the high points of his theory, but has difficulty translating it for non-physicists. The general reader will struggle with the concepts and math, and also with Barbour's general verbosity. It's a fascinating topic and a great theory about which I'd like to know more, but it was a slog to get through.
Slightly recommended.
August 4, 2022
The Janus Point is a point where objects collide. It defines a past and a future, where the future reflects the past, although imperfectly.
Newton's Laws make it easy to figure out what happens when two objects in free space collide. But adding a third object adds a level of confusion that gave Newton (and still gives many students) headaches.
What emerges from that confusion is often two of the objects revolving around each other and a third flying off to infinity.
In this new theory, the revolving objects provide an origin point by the center of their revolution, a distance scale by the space between them, a time scale by the period of their revolution, and an angle reference by the direction the third object flies off at. All for free. No arbitrary scales need be defined.
The rest of the story is about how this approach may be applied to developing a new (and better) understanding of our universe. Expand the number of objects from 3 to N (any number). It works.
There's a lot of mathy detail later on, but it's worth the trouble. If you're not sure about that, read the last chapter first.
Newton's Laws make it easy to figure out what happens when two objects in free space collide. But adding a third object adds a level of confusion that gave Newton (and still gives many students) headaches.
What emerges from that confusion is often two of the objects revolving around each other and a third flying off to infinity.
In this new theory, the revolving objects provide an origin point by the center of their revolution, a distance scale by the space between them, a time scale by the period of their revolution, and an angle reference by the direction the third object flies off at. All for free. No arbitrary scales need be defined.
The rest of the story is about how this approach may be applied to developing a new (and better) understanding of our universe. Expand the number of objects from 3 to N (any number). It works.
There's a lot of mathy detail later on, but it's worth the trouble. If you're not sure about that, read the last chapter first.
December 26, 2021
Too technical for a layman like me, gave up around 33% in. Also thought the structure of the arguments were a bit incoherent - the author mentioned that some new ideas made it late into the book, maybe they were not integrated very well.
The hypothesis is respectable but not mainstream in physics/cosmology, which means that after struggling through all the maths and geometry you may end up understanding something only a minority in the community accepts. Buyer beware I guess.
But if you're versed in modern physics and looking for an interesting alternative to the current (problematic) entropy oriented framework of cosmology and are up for a challenge in detailed technical arguments and math, this could be worth a look.
The hypothesis is respectable but not mainstream in physics/cosmology, which means that after struggling through all the maths and geometry you may end up understanding something only a minority in the community accepts. Buyer beware I guess.
But if you're versed in modern physics and looking for an interesting alternative to the current (problematic) entropy oriented framework of cosmology and are up for a challenge in detailed technical arguments and math, this could be worth a look.
Read
April 6, 2021The current consensus in physics is that the Big Bang was a very special initial configuration of the universe, from which all the arrows of time now flow. The author proposes that instead, the Big Bang was merely a Janus point – a special location through which time passed and then branched off in two different directions. If true, it would mean that the universe is driven not by the increase of entropy, but rather by the growth of structure and order.
February 19, 2024
as someone who has devoured stephen hawking, carl sagan, and brian greene books, this author could not keep me interested to save his life. the writing was too dense and dry and the importance of what he was saying was not clear. i think he could have made this a little more accessible to the general public while not sacrificing the mathematical integrity of this theory. props to you mr. barbour for all your hard work, but it wasn't for me.
March 31, 2024
Barbour tackles entropy (and other concepts). After 'The End of Time', it is clear that Barbour tries to think differently than anybody else: a free lance scientist. I have no idea if his new theory is correct or not but it is thought-provocating and in science that is very important as it generates other thoughts. There are many references and it is a pleasure to read as there are some historical anecdotes.
December 14, 2024
I adored this.
Definitely not always an easy read, but with a bit of patience everything becomes clearer.
The book presents a very fascinating new theory of time (although you could gather that much from the title alone) and with humourous passages. I would not recommend it for the average lay reader, maybe someone with a bit of a background in any maths-oriented stem field (to have a better grasp of the concepts presented, especially Shape Space).
Definitely not always an easy read, but with a bit of patience everything becomes clearer.
The book presents a very fascinating new theory of time (although you could gather that much from the title alone) and with humourous passages. I would not recommend it for the average lay reader, maybe someone with a bit of a background in any maths-oriented stem field (to have a better grasp of the concepts presented, especially Shape Space).
November 9, 2025
Un apziņa ir vissarežģītākā no problēmām.
Un māksla ir viens maģisks veids, kā ķermeņa "laika kapsulā" ieslodzītā apziņa vismaz uz brīdi spēj savienoties ar apziņu, kas apņem mūs visus it visur un vienmēr.
Un fizika, matemātika - vien intuītivi, ne zināšanu vai dziļas izpratnes līmenī spēju tvert grāmatā klāstīto. Un Laiks - ir ilūzija. Tas mierina. Pat ja savas laika kapsulā (proti, ķermenī) ieslodzītās apziņas daļiņas ierobežojumu dēļ jāpiedzīvo sēras un ilgošanās.
Un māksla ir viens maģisks veids, kā ķermeņa "laika kapsulā" ieslodzītā apziņa vismaz uz brīdi spēj savienoties ar apziņu, kas apņem mūs visus it visur un vienmēr.
Un fizika, matemātika - vien intuītivi, ne zināšanu vai dziļas izpratnes līmenī spēju tvert grāmatā klāstīto. Un Laiks - ir ilūzija. Tas mierina. Pat ja savas laika kapsulā (proti, ķermenī) ieslodzītās apziņas daļiņas ierobežojumu dēļ jāpiedzīvo sēras un ilgošanās.
December 31, 2020
As usual, Barbour does not disappoint. I admit to having a hard time following this one. It has some strands of his other book on time, but uses two different examples of shape space to describe time. The conversational approach he takes in writing is terrific, and unlike a lot of popular science authors, does not talk down to his readers or denigrate those who disagree with him.
April 6, 2021
The Janus Point (2020) is a provocative, new take on the origins of time and the fate of the universe.
Today, most physicists believe that the universe as we know it began with the Big Bang.
But there may be a different possibility – that the Big Bang wasn’t the beginning of time, but merely a very special point in the history of our cosmos.
Today, most physicists believe that the universe as we know it began with the Big Bang.
But there may be a different possibility – that the Big Bang wasn’t the beginning of time, but merely a very special point in the history of our cosmos.
December 20, 2021
A really beautiful book, filled with physics alongside quotes from Shakespeare.
Besides, any book that is formatted around tea/coffee breaks (along with occasional prompts to the reader to make a cup of tea before continuing) gets bonus points from me!
Barbour concludes this triumphant book by asking "could it be that the best guide to the true nature of the universe is to be sought in art? Should we look to Shakespeare rather than Newton and Einstein?"
As a disclaimer, I am a student of physics so I was able to understand the prerequisite physics. Julian Barbour is a master of his field, and so it is a privilege to be able to read his theories that are based on a lifetime of deep study. Julian Barbour is well-known as a revolutionary thinker in physics. I think someone who hasn't studied physics will still enjoy this book, as Barbour's explanations of concepts are excellent. However, this is not necessarily a "popular science" book where scientific accuracy is sacrificed for simplicity. No, this book retains scientific accuracy and deals with deep concepts of physics, perhaps at the risk of estranging some readers who are not so familiar with the underlying physics.
The book contains references and recommended reading for those wishing to take things further.
To quote Lee Smolin's apt review of the book:
"With a rare humanity and a perspective based on a lifetime of study, Barbour writes a book that is both a work of literature and a masterpiece of scientific thought."
In the final section of the book Barbour states that the book is "a song of thanks to the cosmos and the fact that I, like you, am a participant in whatever it does".
He then goes on to include the poem 'Pied Beauty' by Gerald Manley Hopkins:
Glory be to God for dappled things –
For skies of couple-colour as a brinded cow;
For rose-moles all in stipple upon trout that swim;
Fresh-firecoal chestnut-falls; finches’ wings;
Landscape plotted and pieced – fold, fallow, and plough;
And áll trádes, their gear and tackle and trim.
All things counter, original, spare, strange;
Whatever is fickle, freckled (who knows how?)
With swift, slow; sweet, sour; adazzle, dim;
He fathers-forth whose beauty is past change:
Praise him.
Besides, any book that is formatted around tea/coffee breaks (along with occasional prompts to the reader to make a cup of tea before continuing) gets bonus points from me!
Barbour concludes this triumphant book by asking "could it be that the best guide to the true nature of the universe is to be sought in art? Should we look to Shakespeare rather than Newton and Einstein?"
As a disclaimer, I am a student of physics so I was able to understand the prerequisite physics. Julian Barbour is a master of his field, and so it is a privilege to be able to read his theories that are based on a lifetime of deep study. Julian Barbour is well-known as a revolutionary thinker in physics. I think someone who hasn't studied physics will still enjoy this book, as Barbour's explanations of concepts are excellent. However, this is not necessarily a "popular science" book where scientific accuracy is sacrificed for simplicity. No, this book retains scientific accuracy and deals with deep concepts of physics, perhaps at the risk of estranging some readers who are not so familiar with the underlying physics.
The book contains references and recommended reading for those wishing to take things further.
To quote Lee Smolin's apt review of the book:
"With a rare humanity and a perspective based on a lifetime of study, Barbour writes a book that is both a work of literature and a masterpiece of scientific thought."
In the final section of the book Barbour states that the book is "a song of thanks to the cosmos and the fact that I, like you, am a participant in whatever it does".
He then goes on to include the poem 'Pied Beauty' by Gerald Manley Hopkins:
Glory be to God for dappled things –
For skies of couple-colour as a brinded cow;
For rose-moles all in stipple upon trout that swim;
Fresh-firecoal chestnut-falls; finches’ wings;
Landscape plotted and pieced – fold, fallow, and plough;
And áll trádes, their gear and tackle and trim.
All things counter, original, spare, strange;
Whatever is fickle, freckled (who knows how?)
With swift, slow; sweet, sour; adazzle, dim;
He fathers-forth whose beauty is past change:
Praise him.
Read
June 3, 2022This book is beautiful in the sense that the author explains every term that he uses in a very plain and layman approach. Of course, there is no doubt about the originality of the ideas, especially starting from a simple argument (three body motion in Newtonian mechanics) and building up with a history of "entropy" and finally concluding the idea of Janus point. Worth reading.
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