|
book reviews
physics and philosophy of timereviewed by T. Nelson |
|
|
book reviews
physics and philosophy of timereviewed by T. Nelson |
Reviewed by T. Nelson
Suppose you’re an editor who wants your authors to go off into the weeds and discuss their most outlandish theories. How to do it? Easy: pose an unanswerable question and turn them loose.
Take ‘timelessness.’ It evidently makes as little sense to the authors of Time and Timelessness as it does to the reader, but they all give it a try. It’s a testament to their ingenuity that they provide interesting and sometimes insightful discussions of topics related in one way or another to cosmology—if not necessarily to ‘timelessness.’
The first few chapters are scholarly historical philosophy discussing ancient Greek cosmology, Hegel, and Kant.
Laura Follesa says that Hegel did not like science or mathematics. He also didn’t understand it. He made numerous calculation errors in his doctoral dissertation De orbitis planetarum. Hegel wrote: “True philosophy repudiates the principle of experimental philosophy,” which should be ‘cast aside.’ Hegel got this idea from Plato’s Timaeus and thought science produces “fragmented, detached, unnecessary and finite parts of knowledge that have nothing to do with ‘true’ philosophy.” Yet Hegel later also threw Plato under the bus—a pretty crowded place in philosophy these days, with Hegel now down there as well—saying Plato mixed myths and philosophy and produced an impotence of thought.
As for ‘timelessness,’ Hegel said the world was eternal and had no beginning, but also that whether the world has a beginning or not was an either-or question and thus was badly posed: “If we are talking about the finite, then we have both a beginning and a non-beginning.” He could have condensed his whole argument into four words by saying he had no clue.
Silvia De Bianchi says Kurt Gödel’s rotating model of the universe came from Kant, who rejected absolute time in cosmology. But, De Bianchi says, Gödel didn’t consider Kant’s later work where Kant said the ether is hypostatized space.
Moving right along . . . .
After chapters describing spacetime functionalism and relationalism, we get a thoughtful philosophical discussion by Marco Forgione of causal set theory (CST), which is based on the Hawking-Malament Recovery Theorem (MRT). This theory said that the causal structure of relativistic spacetime determines its metric structure. As Rafael Sorkin put it, order plus number equals geometry.
CST thus portrays spacetime as a network of causal relationships. In CST, time is portrayed as an ascending directed graph. Lines connecting the nodes represent the probability of interaction. This could give a false impression: these nodes don’t represent objects, only events, so it wouldn’t make sense to demand that CST account for cancellation of past histories. There are other objections, like “causal indolence,” where it is claimed that there could be events that are causally unconnected. The author says is a severe problem, but this assumes that causally unconnected things are real, which is debatable. What CST is actually saying is that causation is more fundamental than spacetime.
The beauty of CST is that it’s a way of viewing time as an emergent property. The main weakness is that CST doesn’t yet show how these ‘events’ could have independent existence apart from specific particles and points in space. The author finally settles on an ‘interventionist’ approach.
Probably the most interesting chapter is the article by Enrico Cinti and Marco Sanchioni on F-theory.
F-theory is a non-perturbative extension of Type IIB string theory that has two temporal dimensions, compared to only one in all the others. ‘Non-perturbative’ means that F-theory reduces to IIB in an asymptotic limit. Its advocates see F-theory in the same way that Special Relativity reduces to Newtonian physics.
The authors try not to drown the reader in advanced physics, but it is still necessary to write a few sentences like this one:
An M-theory vacuum on the space R1,2k×CY5-k, where CY5-k→K4-k is an elliptic Calabi-Yau manifold (with a section), is dual to an F-theory vacuum with a 10-dimensional gravitational manifold R1,2k+1×K4-k.
What the heck does that mean? R, CY, and K are various theoretical constructs that describe space. The superscripts are simply the numbers of dimensions. It is physicist talk for saying the two theories (M- and F-theory) are ‘dual.’ This is a very strong statement that means the reality underlying the formulas is exactly the same—if certain conditions are met.
F-theory's reformulation of Type IIB string theory is done using elliptic fibration. The authors say an elliptic fibration is a fiber-like structure—an elliptic curve that resembles a torus over each point in space, but existing in the next two higher dimensions, sort of a multidimensional halo.
But what would it mean to say there are two time dimensions? The authors say it is “conceptually challenging” because two dimensions of time would cast doubt on the Second Law of Thermodynamics and of causality. Even Max Tegmark, with his affinity for speculative ideas, had trouble with it. Indeed, one could argue that since nothing beyond the first four dimensions has ever been observed, all these higher-dimensional theories are purely abstract, maybe serving the same purpose as hidden variables in quantum mechanics.
The authors are aware of this and cite Nick Huggett’s 2017 article Target space ≠ space. Huggett wrote that the space in string theory is not the same space we ordinarily experience, but something else.
And so the authors turn to philosophy to decide what exactly we would need for something to be a spacetime dimension. Maybe, they say, something is only a dimension if gravitons propagate in it. This would mean that the ‘fiber’ isn’t really spacetime and the graviton only ‘lives’ there. The metric of space doesn’t propagate in the fiber, so distances are all zero and there is only one time dimension. So, the fiber is just some weird brane. But they certainly had us going for a while with that extra dimension of time.
The chapters start out with historical philosophy and gradually become more technical and scientific, with the last chapter on Noether symmetries being the most mathematical and abstract. Daniele Oriti’s chapter hypothesizing that the universe is a type of quantum fluid and that its evolution follows the same hydrodynamic principles as Bose-Einstein condensates is a good example of a far-fetched idea that might prove useful. He proposes using the BEC as a model for gravity, though this faces obvious challenges, the biggest one being that a BEC can’t reproduce gravitational dynamics.
The chapter by Marco de Cesare, discussing whether time reverses during the Big Bounce, suggests that the arrow of time might point in different directions in different spacetime regions. A question to keep in mind in this and other chapters is: If time changes directions, doesn’t that mean there’s a point when there’s no time? If there’s no time, how can something happen?
Anyway, this book is unique: unlike many other books that start out dull and get more and more interesting, all the chapters are rich in original imaginative ideas, some of which are highly speculative. Asking whether any of them is correct isn’t the point of science. The goal is to keep theorizing creatively. If so, they’ll eventually get to the answer.
No index. The authors assume that many technical details are already known to the reader. Most of the authors are Italians but their English is excellent.
oct 21 2026