I Time and Space I

Nature Vol. 253 February 6 1975 485

The Physics of Time Asymmetry. By other towards achieving this happy out Part two is concerned with absolute P. C. W. Davies. Pp. xviii+214. (Surrey come, one is lef,t with an uneasy feeling motion and the theory of relativity, University Press; Leighton Buzzard, that something is still missing. The old tracing the controversy between the 1974.) £6.50. problem of the relationship between the substantival view of Newton that space THIS book is about what is popularly indeterministic world of qu.antum is an entity and the relational views of called the 'arrow of time' but the phy!>ics and the fulJy deterministic Leibniz and Mach that it's not there author does not much like the term world of general relativity seems still at all. The special and general theories because the asymmetry is that of the imperfeatly understood. Actually, Dav of relativ~ty are somewhat geaf,ted on world in respect to time, not of time ies exposes the difficullties in his section to this discussion withou,t, of course, itself. The book is a critical study of 6.3, "Quantum measurement theory". solving the problem. Sklar gives a fine the origin of the asymmetry and of its I cannot but conjecture that the place descriptive account of the theories of role in basic physics. Indeed, it could of the observer will somehow have to reIativ'i>ty, which could well be used by serve as the makting of an excellent be recognised more extensively in for physics students wishing simply to course on the foundations of physics. mulating physical theory and that this learn the subject. Even modem ap With the only known exception of will entail the admission of uncertillin proaches such as geometrodynamics properties of K mesons, the laws of ties associated with other physical con get a mention. At the end of this physics are symmetric in regard to stants bes·ides Planck's constant. section the author presents his own time, and so the asymmetry must arise The book most adroitly brings rather unconvincing answer to the from boundary conditions. Davies pro together aU the main relevant lines of problem of the origin of inertial forces. ceeds from that consideration to two thought; whatever remain5 to be done Rejecting Maoh for apparently aes important inferences. First, that irrev must surely start from the ground so thetic reasons and wishing to retain a ersibility in the Universe depends ulti well surveyed by Dr Davies. pure rdationist stance, he proposes that mately on gravita,tion, since any size w. H. McCrea the statement "is absolutely accelera able body in the Universe is held to ted" is not a relational term, giving it gether by its own gravitation and there instead the staltus of a complete as is no permanent equilibrium state for sertion. This may well be a valid such a body. Second, that all important I philosophical contortion, but i,t is un aspects of time asymmetry are trace ITime and space likely that the physicist will be satisfied able to the beginning or end of the with the denial of any explana,tion for Universe. Both bring the subject Space, Time and Spacetime. By inertial forces. naturally into the realm of cosmology. Lawrence Sklar. Pp. xii +423. (Univer Pal1t three of the book deals mainly Appropriately, the chapter in the centre sity of California Press: Berkeley, with time- the usual problems of of the book is on "Thermodynamics Los Angeles and London, 1974.) $15.00; simultaneity, time dilation, twins para and cosmology". Moreover, the fact £7.50. dox and so on in relativity theory that in ordinary electromagne'tism we LA WRENCE SkJ,ar is a philosopher writ and also presents some bold treatment consider only retarded effects is nowa ing about philosophical aspects of space of bizarre topologies, including a days generally explilJined by the 'ah and time, from Newton and Leibniz to discussion of trouser spaces, non sorber' theory of radiation, and so it Einstein and Reichenbach. Neverthe orientable manifolds and closed time again rdates the subject to cosmology. less, his clear grasp of modern mathe like world lines. The discussion is Whether or not the thermodynamic and matics and physics, and his lucid framed in the causal theory of time to electromagnetic properties are inde exposition, make this book eminently which the last part of this section turns, pendent seems to remain an open sui>table for physicists and mathemilltic concluding with the widely held belief question. Davies discusses all that in his ians who wish to explore the philosoph that the theory is implausible. next chapter. Thermodynamic irrev ical background to their subject. The final section summarises briefly ersibility is bound up with probability Although the text is not in any sense the fascinating and controversial sub theory, and a more fund·amental sort mathematical, crucial topological and jeot of time asymmetry. The account of probabil'ity is involved in quantum geometrical concepts are carefully ex suffers somewha,t from superficiality, mechanics, as is then described. plained before they are incorporated and the vital topic of Reichenbach's Finally, Davies discusses the bearing of into the author's thesis. branch systems is not discussed in the whole subject upon the choice of a The book is divided into four main detail. The conclusion given to this sec cosmological model. sections. The first deals with the tion is that we simply 'know' the re Davies skilfully conveys the flavour epistemology of geometry with a his la,tion of temporal priori,ty between of the mathematical treatment without torical development leading up to events. This is a most unsatisfac,tory going into its details. His presentation Minkowskian and Riemannian space esca'pe route, which does nothing to tends to be over-modest, and this in times. Much attention is then devoted dispel the lamenJtable confusion which hibits him somewhat from stCl!ting oate to Poincare's proposition that the geo exists between the phenomenon of the goricaIly the conclusions reached at metrical structure of the world is psychological flow of time and time each stage of the development of the merely a matter of convention and to asymmetry as encountered in the objec topic-the reader has to do a little the exi3tence of different hypotheses tive world, and which is so prevalent searching to find them.. Nevertheless, each equally capable of expla'ining the among scientists and philosophers who "Having completed this book", he same observilltions. The complex web of write about time asymmetry. makes bold to conclude that (Intro argument and counter argument sub This book is a comprehensive, well duction, page 7), "the basic framework divides into many alrtema,tive points of written and authorntative account of for understanding the nature of time view and may well frustrate the scien spa,ce and time which well suits both asymmetry is clearly available, and it tific reader who probably regards the scientists and philosophers of science. is unlikely that any future considera whole issue as sterile overemphasis, n is inclined to be a little tedious and tions of detail will introduce anything especially as the author termina'tes the repetitive, but contains plenty of excit qualitatively new". Although the book coniroversy with an admission of in ing and interesting material for students certainly seems to do more than any conclusiveness. of these disciplines. P. C. W. Davies