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The Direction of Time

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Ever a source of philosophical conjecture and debate, the concept of time represents the beating heart of physics. This final work by the distinguished physicist Hans Reichenbach represents the culmination and integration of a lifetime's philosophical contributions and inquiries into the analysis of time. The result is an outstanding overview of such qualitative, or topological, attributes of time as order and direction.
Beginning with a discussion of the emotive significance of time, Reichenbach turns to an examination of the time order of mechanics, the time direction of thermodynamics and microstatistics, the time direction of macrostatistics, and the time of quantum physics. He offers coherent explanations of the analytic methods of scientific philosophy in the investigation of probability, quantum mechanics, the theory of relativity, and causality — methods that he not only applies here but also helped to develop and refine.
Physics Today observed that "For a generation Professor Reichenbach has worked as almost no other man to bring to the interpretation of modern physics the critical and reflective thinking of a trained philosopher. Most physicists who retain an interest in philosophy, and many who wanted simply to understand physics, have read some of the earlier books of Reichenbach. This one is . . . the best by a good deal." Introduction. Appendix. Index.

304 pages, Paperback

First published July 17, 1991

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Hans Reichenbach

70 books25 followers

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Displaying 1 - 10 of 10 reviews
Profile Image for Nick Black.
Author 1 book712 followers
March 23, 2008
Requires a serious effort, but well worth it. Deep, deep, deep, throw-me-into-shallow-water-before-I-get-too-deep-style deep.
Profile Image for Xander.
420 reviews141 followers
May 9, 2018
I will not write a review about this book, since I tried to complete it but simply couldn't follow Reichenbach's analysis of thermodynamical concepts of time. I'm vaguely familiar with the main concepts but he uses theories and equations that are way above my head (as with the latter parts of the book focused on quantum mechanics).

And sadly, Reichenbach died of a heart attack while writing this book (1953), so the final chapter is missing. In this chapter he wanted to connect the physical concept of time with our psychological concept of time. Instead, this chapter is substituted by some earlier material.

As I understand it: since we are products of nature (i.e. determined by physical laws), we experience the exact same order and direction of time that we observe in physical processes (i.e. from a determined past to an undetermined future). Our 'now' seems to be a unique viewpoint, but it is nothing but the determination of past processes; when envisioning the future, this is viewed from the viewpoint of 'now'. So, ultimately, we are simply instruments registering events in memory and hence, determining the past (the same way a thermometer or computer determine the past yet leave open the future).

What we should think about this theory I honestly don't know. What I should think about the whole book I honestly don't know either. Maybe in the future I will try to re-read it - see if it 'clicks' into place.

Profile Image for Edward Champion.
686 reviews25 followers
February 21, 2023
Folks, quantum physics ain't exactly my strong suit. But since I am now writing the third season of my audio drama and it involves time travel, I figured that giving Reichenbach a spin was in order. Well, this "small" book took me forever to read. To comprehend all the entropic calculations, I was forced to summon dormant brain cells that had been devoted to calculus more than two decades ago. And while this was tough sledding for me at times, I am grateful to Reichenbach for outlining the advances from classical physics to quantum physics in the way that he did. For now I see time from numerous angles, particularly reference time. It seems we are hopelessly riddled with our foolish human perspective rather than the great cosmic whole.
Profile Image for LS.
63 reviews
December 8, 2014
Meh. After being initially very excited about this book, I dragged the reading of it out for about four years until I could hardly stand it anymore. Granted the scope that the author sets for the book is very wide and it is admirable that he meets his objective within such a small volume. Reichenbach follows the trajectory of time from classical to atomic, from statistical to quantum statistical and finally to quantum physics, each time asking,"Gee, can we just think of time the way we did before?" Why we would ever want to do that is beyond me, yet he and a lot of other authors of his ilk seem to find comfort in the issue. By the way, the answer is no. Although his thoroughness in covering the topic and its ramifications was exemplary, I found his attempts at math and proofs rather disturbing--which is the typical reaction from mathematicians and physicists to philosopher style math. I think I even exclaimed "OMG" after reading a footnote to one of his "mathematical derivations" which informed the reader that a similar derivation in another one of his writings was eventually found to be incorrect. Since his math is not rigorous who knows if the present work is "correct".

However, from a broad philosophical perspective he and his pet theories do pose some interesting questions and come to some thought provoking conclusions which can be appreciated by both the casual reader and professionals.
Profile Image for Quiver.
961 reviews1,331 followers
April 24, 2019
No light reading from Reichenbach, though anyone with a university degree in one of the hard sciences should have a decent shot at understanding the gist of the technical bits, if not every detail.

Parts I and II are the introduction (on the emotive significance of time) and on the time ordering in mechanics. Parts III and IV are where things go haywire with thermodynamics, micro and macrostatistics; if you're looking for a review of Boltzmann's work, this is the material to read. Part IV is time in quantum physics—you're on your own! (I was intrigued by the concept of genidentity).
July 11, 2020
Amazing book: very clear explanation of some very complex concepts. Surprisingly readable for one not initiated in the jargon of physics. What's most refreshing though is that the author refrains from using vaguely defined or unclear language, which is very uncommon when treating a fringe subject like this.
In short, a masterpiece!
Profile Image for Maurya.
713 reviews14 followers
December 6, 2022
I can't rate this book - cause really I can't read it... over my head. I gave it the old college try and am deciding this is not adding to my life.

I tried this book because it was referenced in another book on time I was reading - which I enjoyed more than this. Think I get the gist...
29 reviews
August 31, 2020
It is interesting how much this book seems like an antecedent (parent) to Judea Pearl's causal inference and Bayesian network work! I loved the concepts of entropy and the direction of time, which this book definitely delves into with Boltzman's contributions to the field. Of note to potential readers, most of the content in the book seems to hold up against the passing of time - given it was written ~70 years ago.

P.S., the book does contain many formulas and physics concepts.
2 reviews
October 22, 2020
Estremamente preciso e interessante. Forse un po' troppo per gli addetti ai lavori. Consiglio libri più divulgativi sul tema prima di leggere questo. Uno su tutti quello di Carlo Rovelli, l'Ordine del Tempo.
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