Lee Smolin’s new book, Time Reborn, is out today. For more about the ideas in the book, see video of a talk here, and an interview here.
While I mostly vehemently agreed with what Smolin had to say in his last book, The Trouble With Physics, I find myself equally vehemently in disagreement with this one. On some of the topics covered, I’m indifferent to his arguments mostly as a matter of taste. While my views on human society are likely similar to Smolin’s, I’ve never found the scientific insights of fundamental mathematics or physics to have anything significant to tell me about this part of life. Similarly, while I’ve spent some time studying philosophy, I’ve mostly found this of little help in gaining deeper understanding of math or physics. Others though have a very different experience than me, and I’m not about to argue against people looking for enlightenment wherever they happen to find it.
On some of the scientific issues dealt with in the book, again I’m mostly just indifferent. Smolin accurately explains how the lack of predictivity makes typical multiverse models empty, but I’m not convinced that his favored alternative (“cosmological natural selection”) does much better. While I understand well the human appeal of wondering about what came before the big bang, I’ve yet to see any specific models of this that carry enough explanatory power about anything to make them particularly attractive or interesting.
Many of the ideas Smolin is arguing for are clearly labeled as what they are: speculative challenges from a very much minority point of view to some of the received wisdom of this kind of science. Unfortunately, parts of his argument that are most problematic are ones which are in danger of becoming the new received wisdom of the subject. The refusal to admit the failure of the idea of string/M-theory unification has left many of our most prominent theorists pushing the idea that fundamental physics is based on some new and very different degrees of freedom, with dynamics that just happens to be too complicated to allow them to find vindication by seeing how the Standard Model emerges at low energies. For his own reasons, Smolin signs on to a version of this point of view, writing:
I’m inclined to believe that just about everything we now think is fundamental will also eventually be understood as approximate and emergent: gravity and the laws of Newton and Einstein that govern it, the laws of quantum mechanics, even space itself…
A large part of the elegance of general relativity and the Standard Model is explained by understanding them as effective theories. The beauty is a consequence of their being effective and approximate. Simplicity and beauty, then, are the signs not of truth, but of a well-constructed approximate model of a limited domain of phenomena.
The notion of an effective theory represents a maturing of the profession of elementary-particle theory. Our young, romantic selves dreamed we had the fundamental laws of nature in our hands. After working with the Standard Model for several decades, we are now simultaneously more confident that it’s correct within the limited domain in which it has been tested and less confident of its extendability outside that domain.
This notion that the SM is “just an effective theory”, with its fascinating and deep mathematical structures nothing but an artifact of low-energy approximation has become the reigning ideology of the last few decades. One impetus for this has been string/M-theory, with its conjectured very different physics at short distances. This has been put together with our modern understanding of renormalization, according to which non-renormalizable theories make perfect sense as effective theories. The argument is then made that this is all there is to the SM, neglecting to note that to a large degree the SM couplings are asymptotically free, meaning that (most of) the quantized geometric degrees of freedom make perfectly good sense at all energy scales.
Smolin’s view that the recent history of particle physics makes us “less confident of its [the SM’s] extendability outside that domain [where it has been tested]” is one I strongly disagree with. Despite endless “naturalness” and “fine-tuning” predictions based on the “nothing but an effective theory” argument, the SM has not only been vindicated at the LHC over a large new energy range, but the discovery of the Higgs has shown it to have just the right characteristics to make perfectly good sense up to extremely high energies, far beyond anything we can test.
I’ve been teaching a course this past year on quantum mechanics for mathematicians, emphasizing the role of Lie groups, unitary representations and symmetries in providing not only useful calculational methods, but governing the underlying structure of the theory. Smolin argues instead that, based on Leibniz’s “identity of the indiscernibles”, symmetries cannot be fundamental (although a footnote says this doesn’t apply to gauge symmetries):
Symmetries are common in all the physical theories we know. Several of the most useful tools in the physicist’s toolbox exploit the presence of symmetries. Yet if Leibniz’s principles are right, they must not be fundamental.
This applies to the very structure of quantum mechanics:
Quantum mechanics, too, is likely an approximation to a more fundamental theory.
since it is linear, and he bets thus just a linear approximation to some fundamentally non-linear theory. Again, mathematical simplicity is seen as an artifact of approximation, not indication of something fundamental.
Smolin ends with a vision that is pretty much the exact opposite of mine, one with a vastly diminished role for mathematics in understanding the nature of reality:
The most radical suggestion arising from this direction of thought is the insistence on the reality of the present moment and, beyond that, the principle that all that is real is so in the present moment. To the extent that this is a fruitful idea, physics can no longer be understood as the search for a precisely identical mathematical double of the universe. That dream must be seen now as a metaphysical fantasy that may have inspired generations of theorists but is now blocking the path to further progress. Mathematics will continue to be a handmaiden to science, but she can no longer be the Queen.
Unfortunately it seems possible that Smolin’s arguments about mathematics will resonate well with the current backlash against sophisticated mathematics that one sees at many physics departments in the wake of the failure of string theory. In a footnote he explicitly argues that the problem with string theory was too much symmetry:
Indeed, we see from the example of string theory that the more symmetry a theory has, the less its explanatory power.
I don’t understand this argument at all. The problems with string theory are something I’ve written about endlessly here, but too much symmetry is not one of these problems.
Smolin has been quite right to point out in recent years that fundamental physical theory is in a state of crisis, but I think his diagnosis in this book is the wrong one. Abandoning the search for a more powerful mathematical understanding of the world because the huge success of this in the past has made further progress more difficult is the wrong lesson to draw from recent failures (the nature of which he lucidly described in his previous book).
My own interpretation of the history of the Standard Model is that progress came not from finding more, larger symmetries, but from a deeper appreciation of the various ways in which gauge symmetry could be realized (spontaneous symmetry breaking, confinement, asymptotic freedom). The arrival of string theory pushed the study of gauge symmetry into the background, and these days one often hears arguments against its fundamental nature, such as this one from Arkani-Hamed
What’s as a misnomer called gauge symmetry, whose beauty is extolled at length in all the textbooks on the subject, is completely garbage. It’s completely content free, there’s nothing to it.
Smolin’s arguments against the fundamental nature of symmetries, even if gauge symmetry is let off the hook in a footnote, just reinforce some of the attitudes at the root of our present-day crisis. The problems that remain in fundamental theory are difficult, but denigrating now the powerful ideas that have led to success in the past won’t help find a way forward.
Update: For more about this, there’s a review in the NYRB, and a piece at edge.org (with responses).
Peter, could you elaborate about why you see a “current backlash against sophisticated mathematics that one sees at many physics departments”?
Thanks Peter, very interesting review. FYI, there seem to be several forthcoming books of interest to this blog’s readers, including “String Theory and the Scientific Method” by Dawid, “Farewell to Reality” by Baggott, and “Bankrupting Physics” by Unzicker.
Gauge symmetry is an absolutely central concept in string theory.
Why don’t you like what Nima says? What do you think he means?
I am surprised that you so vehemently agreed with Smolin’s earlier book. He subscribes to an extreme philosophy of science. I won’t try to summarize it here, but I think that it is one that not many scientists would agree to.
I read a draft of the book half a year ago or so. Now reading your review makes me think I read a different book altogether! The one I read basically argued that emergence in time cannot be accurately described by mathematics and therefore there is a limit to what can be described by (eternally true) mathematical laws. It’s a mistake, he says, to attempt a time-less understanding of the world, and with some good will you can extend this line of thought to less fundamental problems that plague the world today.
I don’t think this has so much to do with philosophy, it’s more a matter of contemporary thinking. It is typically the case that insights from science reflect in sociology and politics. Just consider how much Darwin has shaped our thinking of adaptive systems, of trial and error, of selection of the fittest. Just think how much we’ve had to rethink our own space in this universe with the realization that ours is not the only planet, not the only galaxy, and that the universe isn’t static but evolves. Don’t you think that influences the way we perceive of our environment and how we interact with it? I find it quite plausible that the way we model and develop theories of nature today does influence how we attempt to manage our planet.
Now I disagree on pretty much every step in his argument, but I agree that there are probably limits to what we can learn about nature using mathematics. (For reasons I elaborated on here.)
All this now makes me think I should probably read the final copy.
Wow, Peter. I watched the talk, expecting some philosophical disagreement, but I am absolutely flabbergasted by how totally nonsensical so many of these statements are. “Speculative” is way too kind an adjective .
You’re wrong about string theory, but if this heap of nonsense can get some of the Not Even Wrong treatment for its manifest scientific irrelevance and logical absurdity I could come to appreciate that. (I mostly come here for your links which are sometimes pretty good 😉
P: I agree that string theory would also fall into the category of new “ways for gauge symmetry to be realized”, and it subsumes all the other ways, so I would also object to that statement. And I’ve heard Nima make this point, that we shouldn’t use the word “symmetry” when talking about gauge redundancy because it doesn’t correspond to an operation we can physically perform, but a redundancy in the description. Thats fine, as far as that point goes, but the key observation is that symmetry and redundancy are two sides of the same coin. So I’ve never understood the impetus to emphasize the distinction in that way. All available physical evidence indicates that symmetry is a fundamental, organizing principle – the exact opposite of what Smolin claims on purely philosophical grounds.
I shall read the book. From what you mention in the review, I salute the appeal to Leibniz (who seems to more and more relevant to today’s science, like in CS) and I totally agree with Smolin “That dream must be seen now as a metaphysical fantasy that may have inspired generations of theorists but is now blocking the path to further progress.”
As for “Mathematics will continue to be a handmaiden to science, but she can no longer be the Queen”, it simply ignores that mathematics currently used in physics is the late bloom of 19th century math and not the 21st century hottie.
What is rather strange and self-contradictory w.r.t The Trouble of Physics in this Leibniz’s “identity of the indiscernibles” argument of Smolin is that in that book he quite convincingly discussed the failure of using “beauty” arguments to build successful physical theories discussing the example of SU(5) and the absence of observation of proton decay.
Now he is questioning the fact that symmetries are fundamental based not on science, but by subscribing to Leibniz’s philosophical principle that we have no scientific reason whatsoever to believe it is correct (not yet at least).
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Just received my Kindle copy of Lee Smolin’s new book yesterday. Read your and Lubos Motl’s reviews this morning. When you two agree, I’m all the more convinced that I will find Lee’s book as enjoyable and thought provoking as his past works.
Chorasimilarity’s reference to Leibniz is on point. No less a light than Hermann Weyl — who lived in some world intersecting mathematics, philosophy and science and who synthesized the best of all three — took Leibniz at his word that the universe is best understood in the behavior of the infinitely small. Considering Weyl’s further insights into the Continuum, it is no leap of faith or logic to extend the principle to the infinitely small and continuous.
T. H. Ray,
Being inspired by philosophy to do physics is all good if you use the physics and not the philosophical inspiration itself to convince your fellow scientists. Beyond Weyl there are many other examples of scientists using philosophical guidance that led to correct physics, the most striking one being perhaps Heisenberg and his positivist views that inspired him on writing the foundations of quantum mechanics. However, it was experimental predictions and confirmations that convinced the scientific community, not some philosophical debate. There are also good examples of inspirations that led to incorrect physics and Lee Smolin himself points to good examples in The Trouble of Physics.
Smolin could even be right about Leinibz, the “identity of the indiscernibles” and symmetries, but on what science is concerned is not enough to have the inspiration, you have to do the work.
“Lubos Motl’s reviews this morning”
I doubt that Motl even read the book.
I had thought that if you take all the symmetries that you can think of and the physical priciples we think should hold true and try to build a model, what you end up with is superstring theory. If superstring theory does not work, then one or more physical principle is approximate or symmetry is not applicable. Is Peter saying that no, we need to dream up of new ways the same principles can manifest themselves?
Many thanks for your review, which is mainly a statement of disagreement on points off the book’s main argument. Disagreement is fine, of course, but you don’t even mention the main ideas, nor do you critique the actual arguments the book presents for them. As a result you take the main claims out of context.
Very briefly the book focuses on a single question: How are we to make theories of the whole universe, rather than isolated systems? The main novelty of the book is the claim that this cannot be done by scaling up the theories we have; to make a successful cosmological theory requires new principles.
There are two main contentions: First that the standard form of physical theories of fixed laws acting on fixed spaces of states breaks down when we try to extend them from theories of isolated systems (where they work fine-hence I have no issue with the standard model) to theories of the whole universe.
Second that to address issues which arise when making a cosmological theory, time must play a more central role. In particular, the book argues that laws must evolve in time if we are to explain how the laws and initial conditions are selected.
The book embraces the relational philosophy of Leibniz, Mach and Einstein, which means it is very friendly to local gauge invariances as the main way we have to express relational theories. This is hardly a radical point of view given the successes of general relativity and Yang-Mills theory.
There is an argument that global, non gauge symmetries cannot be fundamental on a cosmological scale, nor can they be realized operationally in a cosmological context. I have no issue with the central role of global symmetries in the physics of isolated systems and, indeed explain why they arise in these cases, thus no disagreement with their use in quantum mechanics or quantum field theory. The issues I have arise only in the context of attempts to make theories of the whole universe.
General relativity provides an example of this. When applied to closed universes it has no global symmetries, but when boundary conditions are imposed appropriate to the description of isolated systems, global symmetries appear.
Can I suggest that if you consider the actual argument of the book, rather than take the conclusions out of context, you and your readers might find yourselves in agreement with more of it,
Your point is well taken. However, I have never found Lee Smolin’s research overly philosophical. As Lee himself says above, “The book embraces the relational philosophy of Leibniz, Mach and Einstein, which means it is very friendly to local gauge invariances as the main way we have to express relational theories. This is hardly a radical point of view given the successes of general relativity and Yang-Mills theory. ”
Or as Einstein put it, in a simple but meaningful way: “All physics is local.”
Lee is also right that without boundary conditions, general relativity is restricted not by anything *physical,* only by the special relativity limit.
Personally, I have found that general relativity suffers no loss of meaning when being described as “finite but unbounded” — usually taken to be finite in time (bounded at the singularity of creation) and unbounded in space (a geodesic returns to its starting point) — when converted to a theory finite in space and unbounded in time.
Which of course supports Lee’s concept of the enhanced physical role of time.
Thanks for the reply. I agree with most of what you say, but when people make this point regarding redundancy vs. symmetry, the point is precisely that they are not the same thing.
When people like Nima (or Seiberg) say things like this, or something to the effect of “gauge symmetry is not a symmetry”, what they really mean is to remind people that gauge “symmetry” generators map states in the Hilbert to totally equivalent quantum states. With global symmetries this is not the case, and you know it well: in the path integral you divide out by the gauge orbits to avoid an overcounting of physical states, but this is not true of global symmetries! This is an important distinction, and it’s the distinction Nima is probably trying to make. Cosmologists make it all the time. It’s also the reason why anomalies in gauge “symmetries” are theoretically unsound, but anomalies in global symmetries are just fine.
Thanks for writing. You’re right that it would have been a good idea for me to address the main point of your book, since you’re arguing from that to the conclusions I disagree with.
The problem I see with the argument for laws that evolve in time is one that you yourself identify in the book: what you call the “meta-laws dilemma”. You speculate a bit in the book on ways to resolve this, but I don’t see a convincing answer to the criticism that whatever explanation you come up with for what determines how laws evolve, I’m free to characterize that as just another law. And based on experience with the entire history of physics, new, more fundamental laws come together with deep connections to mathematics. One problem here of course is words, we may not agree on what I’m allowed to call a “law” (a word I’ve always disliked in this context anyway…)
About global vs. local symmetries there is much to say, but a specific question would be about global internal symmetries. Is electric charge conservation (global U(1) symmetry) just an approximation? I’m willing to believe that such global internal symmetries are replaced by something else in regimes where gravity gets quantized, but the replacement requires an insight we don’t now have into how space-time and internal symmetries unify. This insight seems to me likely to require more mathematics and deeper use of symmetry arguments, not less.
P: this (gauge symmetries are a redundancy of description) is a standard point of graduate quantum field theory – I don’t see the need for big names, this is not some special profound insight.
That said, I have no idea what is meant by the statement that gauge symmetry is content free. That the coloured particles of the Standard Models organise into colour SU(3) representations, with associated multiplicities, is anything but content free, with profound experimental implications.
Maybe in the end the Lorentz symmetry isn’t fundamental- I can’t imagine that, but it certainly is a logical possibility. Still, the constraints are formidable and certainly whatever conception of time emerges it won’t be a return to the one held by Newton.
I’ve always followed quite closely what goes on at the intersection of math and physics departments especially in the US, and, while I’ve no solid numbers, my observation is just that on the whole there’s now quite a lot less interest in math coming from typical physics departments than there was say 20 years ago (Witten was discovering remarkable things at the math/physics boundary, drawing interest from both sides). One big counterexample is the Simons Center, but except for that, it’s hard to find examples of anywhere in the US where physics departments are showing much of an interest (for example in their hiring) in mathematics.
If you’re referring to Smolin’s interest in Feyerabend, that’s something on which I would mostly agree with Smolin.
Arkani-Hamed’s was speaking in the context of certain work on scattering amplitudes, where there’s a serious issue. The over-the-top comments on gauge symmetry I don’t think were sensible, and reflect an attitude I think is problematic. But gauge symmetry is a huge, huge subject, and a serious discussion of it is best left for another day.
You’re pretty much right. When people make this distinction, they define symmetry to mean something that isn’t a redundancy — which global symmetries are not — and hence gauge symmetries do not fit into this category. Contrary to what you say, this is not always stated correctly in QFT courses, hence Nima’s (and Seiberg’s, and others . . .) reason for complaint.
But as Peter would say, we’re getting too far afield 😉
I think the problem with theoretical physics today is that many of the theorists are divergent thinkers–the trade space keeps getting larger and larger. If you have an optical system with all divergent lenses, then you never converge. You need people that are like converging lenses, such as Einstein, who simplified things, so that gravity was just geometry. The truly gifted simplify, the less gifted complicate.
Dear Peter and Lee,
While I haven’t yet had a chance to read Lee’s book, I wanted to point out that questioning the fundamental physical role of symmetry, understood in the specific sense of Lie groups and Lie representation theory, need not entail a general rejection of mathematical sophistication in modeling nature. Rather, such an approach may reflect an effort to understand these central concepts in a broader context, by relaxing some hypotheses on underlying structure.
As an example, one might try to generalize representation theory in an order-theoretic context. A not-totally-unheard-of setting for such an idea is causal set theory, though I personally believe causal sets to be somewhat deficient. At any rate, such an approach might be based on the following rather obvious statements:
1) An important instance of Lie group symmetry is given by symmetry groups and local symmetry groups of spacetime continuum geometries, such as the Poincare symmetry group of Minkowski space; 2) breakdown of continuum geometry often arises in quantum-theoretic approaches to fundamental spacetime structure; 3) in this context, one may expect modification of spacetime symmetry groups into mathematical structures more general than Lie groups; 4) causal structure encodes much of the structure of classical spacetime, while extending to much more general order-theoretic settings; 5) it is then natural to ask what are the analogues of symmetry groups for causal structures, and to examine their “representation theory.”
One might expect this to lead merely to the study of order automorphisms of partially ordered sets, which still form a group, but this is only the “active” view, corresponding to diffeomorphisms of classical spacetime. The other half of the story is the “passive” view, given by refinements of partial orders, which has nothing to do with group theory in general; this corresponds to changes of coordinates in classical spacetime. For those unfamiliar with this point of view, a good example is the relativity of simultaneity, which illustrates how the causal order on relativistic spacetime admits different refinements, which may order causally unrelated events in different ways. A few such refinements are coordinate systems in the usual sense, but most are not. The moral of all this is that important applications of group symmetry in conventional contexts can bifurcate into multiple points of view in more general settings, some still involving symmetry, others completely different.
My personal hunch is that the next experimentally verifiable progress we will see in elementary particle physics will probably come from the same old well of gauge theory that has produced so much over the last fifty years. In a thousand years, however, I doubt that fundamental physics will still be based almost exclusively on continuum geometry, which was already established as the cornerstone of still-current theory in the days of the Gruppenpest, when no one knew anything about modern algebra, information theory, or computer science. Most people with a real passion for understanding nature and no personal stake in the outcome of current or pending experiments are probably more interested in the thousand-year view. Take care,
I think the problem is, in principle, that symmetries have both a
“physical dimension” (there should be a physical understanding of what it
means to have a symmetry, and to “change point of view” wrt a symmetric object),
and a mathematical dimension (mathematicians came up with great ways to
see symmetries, and tools to manipulate them).
For relativity, our understanding of both physical and mathematical aspects is
complete: We know what “symmetry w.r.t. reference frames” means
in physical terms, and can directly relate this symmetry to experimental
Similarly, in General Relativity the “Gauge transformations”
have a ready physical
interpretation as changes to non-inertial reference frames.
Mathematically, this symmetry is extraordinarily subtle, but the physical
interpretation of the symmetry is apparent even when, from a mathematical point
of view, the geometry is not really “symmetric” in the usual sense (for example
the closed universes Lee Smolin cites).
Gauge theory is very different in that the symmetry is defined mathematically
but lacks a ready physical interpretation. We know that
theories which have lots of symmetries have fewer infinities, and
infinities are typically less observable (technically, theories with symmetries
are more anomaly-free and renormalizeable).
We know the consequences of such symmetries (there is such a thing as “charge”), and they can even be used to get predictions out (the Higgs, as a manifestation
of the fact that Gauge symmetry “has to be there in the UV”).
Nevertheless, we do not know what it really
means to “change the Gauge”, its something the theorist does to make
calculations easier. For relativity, or for that matter angular momentum invariance or translational invariance, “changing the Gauge” is
something experimentalists can readily connect to their apparatuses.
And string theory (post 2nd revolution) has not really
helped this point, the justifications given
for Gauge symmetry are really not that convincing.
It is “experimentally evident” that more and more clever ways to mathematically
manipulate symmetries is not adding to physical understanding: Very very smart
people did this for decades, and we came up with either proposals which seem not to hold up to experiment, like GUTS and Supersymmetrical models, or
really profound insights about theories which are
phenomenologically unviable, like N=4 Super Yang Mills. But perhaps rather than
“abandoning symmetry”, a good start would be “explaining what symmetries mean”.
If your comment is not about the book, it’s off-topic.
We are living in the age of grandiose speculations in physics and Smolin has become one of its most visible actors. His talk at Perimeter was vague and loaded with self-contradictions. I found it very disturbing that a scientist would give such a talk to a general audience. What did they get out of it?
Until the near end of the talk it was all blah, blah, blah, as he said himself – he was attacking others all along and when he was finished with that there was little time left for him to describe his own ideas.
As an example he criticized the laws of physics for being deterministic whereby the future is predictable and there is no place for the free will. But then quantum mechanics tell us that these deterministic laws often lead to a multitude of possible outcomes, each with its own future. He attacked mathematical formulas of physics because they don’t allow the laws to change with time. I would say, go ahead and propose your model, compute its “observables” and let the results be tested by experiments. Before having done so it is wise to shut up. He says “Every application of physics to parts of the universe is an approximation, it can’t be exact.” So what! What a vague statement! What has the word exact got to do with physics? We never measure any quantity with infinite precision. As physicists we understand that we will never be able to make “exact” statements. A concept such as TOE (Theory of Everything) is of course unphysical as it can never be tested but that should not stop us from making progress by refining our theories or inventing new ones.
I am also very much in favor of the invention and use of new and deeper mathematics to describe nature. I only argue that it is unreasonable to motivate this by the mystical fantasy that the mathematical description is truer than our experience of the present moment and its passage in time. There are sufficient reasons to believe that mathematics is useful in nature without believing there is some mathematical object isomorphic to nature in all aspects.
A metalaw may evade the infinite regress problem if it doesn’t have the form I call the Newtonian paradigm, which involved fixed timeless dynamical laws operating on a fixed timeless space of states. Such a metalaw would be different in important ways than our present laws. I do give several examples in the book of ideas under development, some of them in papers. I agree these need much more development but the examples I give show how the metalaw problem may be solvable.
I am sorry you didn’t like the talk, it is hard to present this argument in an hour to a mixed audience. That is one reason I wrote a book. But, please note that I didn’t attack anyone personally, I gave a critique of certain issues blocking the progress of science and proposed alternative solutions. I agree the time was too short to give details, but those are described in the book and in scientific papers going back to 1992. It is exactly because I have, proposed …” models, computed “observables” and let the results be tested by experiments” that I feel it is OK to describe them in a public forum. One model, cosmological natural selection, made two predictions, both published in 1992, that have stood up to test since then. One, that the heaviest neutron star be less than two solar masses was confirmed again in a paper just published in science (Antoniadis et al.,Science,Vol 340). The other, that inflation, if true, is governed by a single field moving in a potential determined by a single parameter, is confirmed by the recent Planck observations.
In the book I describe these in detail as well as newer models of evolving laws and how they might be tested.
I thought time and the measure of time were different. So is Lee Smolin talking about the measure of time reborn or time reborn? The measure of time as represented mathematically is reversible but time as described in thermodynamics or as we experience it has an arrow and is not reversible.
What I think I see going on with these type of books is more of a slow-motion meta-argument and academic positioning about where to focus your collective brainpower, because perhaps we have reached some sort of collective limit in what we (er, you) can figure out, and it will take every learned neuron to acheive some breakthrough. So if it’s one of those “fellow scientists, we need to study this novel idea as the way forward” book, I will pass.
Oh, and Hawkings has gone “full sci-fi” in my opinion.
“I only argue that it is unreasonable to motivate this by the mystical fantasy that the mathematical description is truer than our experience of the present moment and its passage in time.”
FWIW, I couldn’t agree less. Nothing could be LESS true than our “experience of the present moment”. That “experience” which no-one can even grasp (witness the endless fruitless discussion about qualia) is a second-hand, unconsistent, faked-up, stitched together, event-reshuffling and event-inventing narrative of “what happened a bit earlier”, a datastructure thrown barfulously together by a cognitive apparatus made to acquire food, sleep, safety and sex with least energy expense. Which is why Penrose’s ideas about the human mind as a self-consistent theorem prover are ludicrous.
If you want to do and think consistently however (using the amazing capacity of the human cognitive apparatus to use external physical machinery and memory to remember things and keep on track), you need consistent models.
Mathematics *is* the setting up of consistent models. Those that do not give you a kilo of gold when you turn clockwise once.
As the universe *is* consistent (axiom #0), a (infinite set of) mathematical model of it exist.
Whether that model can be discovered, approximated or whether “time” has any part in it is another question entirely
Lee Smolin has just published an article in New Scientist titled “It’s Time Physics Recognised That Time Is Real“. You will, however, have to register with New Scientist to read the article, and the article will only be viewable (using that “for free” registration) for about another ten days, or so.
The only book on Time worth reading is Indian polymath C. K. Raju’s “The Eleven Pictures of Time”
A ‘lay’ perspective- I have a doctorate in molecular quantum mechanics, so not the really hard stuff.
I welcome Lee’s book because it challenges us to think in new scientific directions. Having followed cosmology and particle physics for 30 years, I believe the field has reached an impasse; since the mid 1980s we’ve been confirming existing theory with no new breakthrough ideas or unexpected results.
I believe we’re in a time similar to that just before Einstein, and when Special Relativity was published it was initially ignored- similar to Lee’s ideas, not well received but necessary to move thinking on to a new position with radically new insights. Is Lee he next Einstein? Maybe, maybe not- but he is prompting the challenges that create the space for the next Einstein.
A paragraph I omitted:
Dark matter, dark energy and the accelerating expansion, plus the ‘axis of evil’ in the CMB. Aren’t these the ‘aether’ and michelson-morley experiments of our day?
“when Special Relativity was published it was initially ignored”
no it wasn’t
Dear Lee Smolin,
In your reply to my comment you say “please note that I didn’t attack anyone personally”. It is true that except for Max Tegmark you didn’t specify the names of those you were criticizing but that makes the situation even worse. In addressing a general audience, you made statements such as “Physicists claim that they know the answers to these questions” and that the theories by those physicists were false. Because the audience doesn’t know who these physicists of yours are, they must have thought that you mean the entire physics community while the majority of physicists, for example, those working on graphene or on fractional quantum hall effect have hardly been involved in the process you were describing. Your “physicists” make up a tiny fraction of the physics community – those who love to speculate.
By the way the reference you gave (Antoniadis et al., Science, Vol 340) does not refer to your work. Neither can the authors test your theory, at least not yet. They make observations in a nonlinear regime – a “previously untested regime, qualitatively very different from what was accessible in the past.“ I am afraid you have to wait to see what such observations in the nonlinear regime have to say about your theory.
Because I am not familiar with your theory, I hope someone else will check your statement that the recent Planck observations confirm it.
You are right “ignored” was too strong. But recognition of its implications did take some time, and Einstein certainly didn’t gain instant acclaim.
I listened to the talk carefully. It is just horrible. I hope the audience does not think everybody in physics is so shallow and trivial. I am a little encouraged by the reviews on Amazon, the public is not that stupid it seems.
The prediction of cosmological natural selection that was tested in the paper in Science was that the upper mass limit of neutron stars is at most two solar masses. This is tested each time a neutron star mass is measured. The paper doesn’t have to reference the prediction to confirm the prediction, it is enough that the measurement they report confirms it, which it did.
All physicists, whether working on graphene or condensed matter physics, employ the framework of fixed laws acting on fixed state spaces-the framework I call the Newtonian paradigm. As I explain in the book, this is exactly what they should be doing. My criticism is not of the usual practice of physics, it is confined to the extrapolation of the usual practice to cosmological theories. ie the only thing I criticize is attempts to apply the Newtonian paradigm to theories of the whole universe.
This point-that the methodology which succeeds so well when applied to laboratory systems fails when applied to the universe as a whole-is the first step of an argument that was sketched in the talk and is described in detail in the book. So my intention was hardly to criticize anyone, it was to make an argument about whether the Newtonian paradigm can be applied to answer cosmological questions. Does this make it clearer?
I’m up to p. 202 and so far I think the book is excellent.
Dear Lee Smolin,
In order to make a convincing case for your model you need to have predictions that are significantly different from the standard ones. The measured neutron mass (2.04 in the units of the solar mass), listed in table 1 of the paper by Antoniades et al., falls in the expected range in general relativity. No big deal as far as I can see.
“Simplicity and beauty, then, are the signs not of truth, but of a well-constructed approximate model of a limited domain of phenomena.”
Peter, I fear you are being so protective of what you love (the beautiful mathematics) that you are missing the point here — that this beauty doesn’t mean it’s physically relevant.
It is a historical fact, which I’m sure you know as much as anyone, that not only does beautiful mathematics not imply that physics works that way, but ALSO (and just as relevant) it’s possible to get so hooked up on one aspect of the mathematics that you actually MISS the larger structure behind the scenes.
The poster child for this (a good example because it’s easy enough to understand) is quaternions and the whole foolish battle of the 19th C between those who did and did not support their use in physics. And what was the ultimate resolution? Both sides were so obsessed with one aspect of the issue (algebra) that they got the geometrical interpretation wrong, and ultimately missed out on the huge wider world of Lie groups, spinors and the rest of it.
One could argue the same thing for pre-Minkowsi EM, where incredible ingenuity going into solving Maxwell’s equations missed out on the more significant issue of understanding them in full geometric consequence.
If I were to make a modern analogy I’d ask (at the risk of appearing foolish, because I haven’t studied this enough to be sure I’m correct) whether Clifford Algebras fall in the same sort of pattern. They meet all the mathematical desiderata: they unify a lot, they’re conceptually extensible to all dimensions, they result in a non-obvious large-scal pattern across dimensions; and they’re a neat practical tool for calculating certain entities. BUT I’d argue that what physics really needs is a better geometric understanding of simple Dirac spinors in 3+1D, that Clifford Algebras have not delivered that, and that it doesn’t seem likely that they will. Beautiful math, yes, but shining a powerful light in the wrong direction for physics.
Since at least GR and Dirac physics have operated on a kind of “if the math is beautiful enough it has to be right” autopilot, and this is what has brought us to supersymmetric strings. It is THIS against which Smolin is reacting, not a generic dislike of sophisticated math.
(It may be easier to understand the sentiment by imagining applied to a different field. Economics is another science where appreciation of beautiful math has proved immensely destructive to the task of understanding the actual world in which we live, as opposed to the better world of our minds.)
You miss the point. The point is that CNS predicts the upper mass limit is 2 solar masses which is substantially lower than predicted by the conventional picture of neutron stars. Had the NS mass been 2.5 solar masses or more it would have been a clear refutation of the prediction of CNS. Please look at arXiv:1202.3373, which is a recent review article about cosmological natural selection, or read the book before making further incorrect claims.
I’m an atheist, but this stuff makes me hope to God we see something new in the LHC before it’s shut down.
The talk Peter linked to was Lee’s April lecture for wide audience
there is also one given 26 February in the quantum foundations seminar
clear, cogent, efficient presentation, with interested questions from audience e.g. Rob Myers, Neil Turok
I would recommend anyone interested to watch the February talk.
It seems to me that the idea of law-like regularities emerging in a process of past events generating a new layer does not at all depend on CNS, which is just one example of an evolutionary process. However the highest mass estimate for neutron star I have been able to find appeared in October 2012, and was for the pulsar
It’s newly discovered and the authors cautiously say “if confirmed”. They say that “all viable solutions” to their data give a mass > 2.1 solar. But they seem to think a considerably higher mass than that is likely.
Before that, the highest mass estimate was for a longer-period pulsar and ( I gather) less precisely determined: PSR B1957+20
van Kerkwijk, M. H., Breton, R. P., & Kulkarni, S. R. 2011, ApJ, 728, 95
They said 2.4±0.12
but also acknowledged some systematic uncertainties and but the minimum at 1.66 solar.
There’s the very recent estimate of 2.01 that I think Lee referred to already:
Really two topics here: CNS hypothesis and the neutron star mass limit prediction, on the one hand, which has been around for some 20 years(!)
And on the other hand this new, rather beautiful, idea of a meta-law process which explains both the flow of time itself and the appearance of seemingly timeless regularities we think of as natural laws.
Again, check out the quantum foundations seminar talk of 26 Feb!
My advice is not to get sidetracked arguing about the wide-audience public lecture.
**Smolin’s arguments against the fundamental nature of symmetries, even if gauge symmetry is let off the hook in a footnote, just reinforce some of the attitudes …**
Symmetry is something that needs to be explained and it doesn’t make it less important or beautiful to have an explanation for how it arose. To take an analogy, the bilateral symmetry of many animals can be explained by digging into evolutionary history, and having an explanation doesn’t diminish it’s importance as a fact of biology.
Thank you for the references on neutron star masses. What an exciting and rapidly developing field of research!
You give us the advice “not to get sidetracked arguing about the wide-audience public lecture.”
Actually, the major point of my comments concerned the wide-audience public lecture aspects of Smolin’s talk.
When we scientists talk to each other and at our seminars we can say almost whatever we like. Under such circumstances the audience, usually equipped with healthy skepticism and sufficient amounts of grains of salt, has the capacity to understand and analyze what the speaker is talking about. The general public doesn’t and can easily be misled.
Smolin is a leading figure at an Institute with a very high academic reputation. The general public will tend to consider him as an authority and believe in what he says. Therefore he, as well as other speakers at such occasions, should not mislead the audience by making sweeping statements of the kind Smolin did – attacking mathematics, saying all physicists were wrong and so on.
It is just fine that someone like Smolin takes an alternative approach to physics. But it remains to be seen if his approach will teach us anything new about the world we live in.
I beg your pardon, if my use of english language is not that good I’d want.
I’m very interested on what consequence has and will have in the near future (say 10 to 15 year) “sophistication” of mathematical ideas, theories, physicists will take advantage of for improving predictability power without exiting SM framework.
Does Lee Smolin’s book also deal with this topic?
I’m a physic teacher, sometimes students fond of math and phys ask me about.
I thank you!
This is a great, much needed book that will hopefully spark discussion in areas of physics that are largely ignored. (I just gave it a 5 star review on Amazon a little while ago.) For the sake of brevity however, I will get right to my criticisms:
Although several times you examine time theories and their possible consequences on the relativity of simultaneity, you didn’t specifically explore how time dilation (during relative motion and proximity to mass) fit in with a real, global theory of time. I think this was a mistake since, in my opinion: only through a better understanding of what makes clocks speed up or slow down, will we be able to understand what makes them run at all.
Also – would you consider all time theories described as “emergent” to be illusory? And if so, why would they have less of a chance of being time-arrow asymmetric than real global time? For example – my starting point is the question: Do all of the fundamental behaviors expressed among particles, forces and fields exist in time, or are those behaviors themselves the actual expression of time? It is my contention that the behaviors actually are time (each atom is its own clock). If we suppose that is true for a moment, I can’t think of any scenario where all behaviors in the universe would spontaneously and simultaneously run in the reverse direction.
Personally, I think the time reversibility concept is bizarre in general. We assume that why everything different about today than yesterday is due to probabilities given certain rules among all of the particles, forces and fields in the universe. If time were to start running backward, then either all of the above would have to miraculously run in reverse with a sudden opposite cause & effect for each set of forces or “reverse time” would externally drive them on some sort of auto pilot. The former is highly improbable and the latter is not logically consistent. Why would the forward direction of time be driven by the behaviors of various forces while the reverse would be driven simply by reverse time itself? Please let me know if I have misunderstood something here?
I watched the video Marcus recommended. The model Smolin proposed seems to have momentum traveling backward in time from “child” events to their “parents” as part of a momentum balancing process. I’m not sure how that makes sense, but maybe it’s just some sort of convention that physicists are used to.