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Original Title:	Time's Arrows: Scientific Attitudes Toward Time
ISBN:	0671617664 (ISBN13: 9780671617660)
Edition Language:	English

Time's Arrows: Scientific Attitudes Toward Time

Richard Morris

Paperback | Pages: 244 pages

Rating: 3.61 | 38 Users | 6 Reviews

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The question “What is time?” might sound silly to many. A simplistic answer describes time as the thing that goes in one direction, marking events and separating the past from the future by a point called “present.” Yet, the question is one of the deepest ones in science/philosophy today, creating disagreements and paradoxes, instead of answers. This book tries to explain the roots of the difficulty, in a way that is understandable to a literate person with minimal background in science.

Besides the main question addressed, the book contains a great deal of useful material on physics and philosophy. For example, I learned that the universe is made up of two elements for the most part: hydrogen (H) 75% and helium (He) 25%; all other elements appear in negligible quantities. As another example, we get clear explanations of special and general relativity. Special relativity describes situations where observers move relative to each other at constant velocities. General relativity explains what happens when observers accelerate with respect to one another. To an observer, the effects of acceleration in space are indistinguishable from those of gravity. So general relativity can be viewed as a theory of gravity as well. Both special and general relativity predict changes in times and lengths, but changes resulting from general relativity are more far-reaching.

Discussion of time-keeping devices and attempts at establishing the age of the universe are also quite interesting. Mechanical clocks were invented in the 1200s; they were accurate to within 15-30 minutes per day. In 1345, the hour was divided into minutes and seconds. Early clocks did not have hands; they would strike a bell periodically. Minute hands did not appear until the 16th century. With the ability to measure time, came the notions of saving and squandering of time. Estimates for the age of our universe began with numbers that were way off the mark (less than 1M years). It wasn’t until the late 19th century that Lord Kelvin (William Thomson) derived his “upper bound” of 500M years based on laws of thermodynamics.

Now, going back to the book’s main focus, one can divide the question “What is time?” into four fundamental questions, discussed in the rest of this review.

(a) Does time have a direction? The word “Arrows” in the book’s title refers to various directional explanations of time. In addition to “the subjective arrow” that we all use without thinking, there are “the thermodynamics arrow” based on natural increases in entropy or disorder, “the expansion of the universe arrow” which reflects the fact that the universe is expanding and is unlikely to go back, “the beta-decay arrow” based on the extreme difficulty of reversing particle decay, and “the electromagnetic radiation arrow” reflecting the general agreement that radiation is not emitted into the past. There are, of course, theories contesting each of the time arrows just named. A “yes” answer to our question about time having a direction isn’t as easy to justify as one might think; most natural phenomena can go in either direction. For example, if a glass is dropped and shatters into tiny little pieces, it is conceivable, though very unlikely, that the pieces might then come together under suitably applied forces, to form the intact glass, in essence making time go “backward.”

(b) Does time flow uniformly? Clearly, saying that time flows at a rate of one hour per hour is unsatisfactory, because the statement is circular. What does the flow of time really mean? It turns out that time, like space, is relative and it passes at different rates depending on the observer’s speed and acceleration. In fact, the view of time with a “now” point that moves along at a constant rate and always separates the past from the future, as natural as it may seem, isn’t uncontested. An alternative is to view time as a dimension like other dimensions. There is no “now”; just earlier and later. The time at which distant events take place can be ambiguous, since each observer will “see” a different time. In fact, there is really no such thing as absolute simultaneity of events. If two events are so close in time or so far apart in space that light cannot reach from one to the other before the latter takes place, the order of the two events is ambiguous. However, causality is not violated. No observer will see a basketball fall through a hoop before it is released by the player who shot it. So the statement “Time is relative” is a tad too strong. To make things worse, it is possible for an event to occur in the past of one observer and in the future of a second observer.

(c) Does time have a beginning? Did time begin at the Big Bang, or was the Big Bang simply a point on the infinite arrow of time? One of the grand pursuits of physics is to unify the notions of gravity, electromagnetism, strong nuclear force, and weak nuclear force. The latter three have been unified (by Steven Weinberg and Abdus Salam), but gravity has defied unification. At Planck distance (~10^–33 cm) and Planck time (~10^–43 sec), all known physical laws break down. So, we have no idea what went on in the initial Planck time after the beginning. At that time, the universe was unimaginably hot (10^32 C) and dense (10^18 tons per cubic cm). We don’t even have the tools to discuss time and space right after the Big Bang.

(d) Does time have an end? Whether time will end depends on the ultimate fate of the universe. It will not end if the Universe continues to expand forever or comes to a halt. However, if there is a Big Crunch, causing the universe to collapse back in on itself, spacetime as we know it would be destroyed and time could be considered to have ended.

The latter two questions about the beginning and end of time do not arise if time is viewed as circular. The circular time view was held by many ancient civilizations, including the Chinese, the Aztecs, and the Mayas. Plato and others believed in the notion of “Great Year,” a time after which things begin to repeat; for example, the planets return to their original starting positions and things start over. The notion of circular time almost goes hand in hand with fate and destiny: humans have free will only to become virtuous, not to change their fates. The church repudiated theories of circular time (as well as astrology), promoting instead the notion of linear time, with a clear beginning at creation and an equally clear end. Nietzsche believed in infinite time and finite universe, which led him to the conclusion that events must recur.

To recap, we do not yet have an answer to the question “What is time?” However, readers of this book will develop an appreciation of the question’s inherent difficulty and will learn a great deal about steps that have been taken in the direction of finding a satisfactory, noncircular answer.

Specify About Books Time's Arrows: Scientific Attitudes Toward Time

Title	:	Time's Arrows: Scientific Attitudes Toward Time
Author	:	Richard Morris
Book Format	:	Paperback
Book Edition	:	Deluxe Edition
Pages	:	Pages: 244 pages
Published	:	January 7th 1986 by Touchstone (first published January 1st 1984)
Categories	:	Science. Psychology. History. Nonfiction

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Ratings: 3.61 From 38 Users | 6 Reviews

Article About Books Time's Arrows: Scientific Attitudes Toward Time

Librarian Note:There is more than one author in the Goodreads database with this name.This profile may contain books from multiple authors of this name.The question What is time? might sound silly to many. A simplistic answer describes time as the thing that goes in one direction, marking events and separating the past from the future by a point called present. Yet, the question is one of the deepest ones in science/philosophy today, creating disagreements and paradoxes, instead of answers. This book tries to explain the roots of the difficulty, in a way that is understandable to a literate person with minimal background in science. Besides the

This may not be the best book of all time, but it does provide some interesting insights into how time can be viewed. It was worth my time.

This is a great read for science fiction lovers.

Even though the 80s cover design drew a few comments, the book really helped bring me a little further into the present. I bought after flipping it open and encountering a brief mention of the psychological arrow. A science book that can give a nod to experience intrigues me. I am still walking around, contemplating with awe the fact that the heavier something is, the more it slows time. What an incredible universe we live in.

A very interesting lay person's overview of the physicists' understanding of time

The question What is time? might sound silly to many. A simplistic answer describes time as the thing that goes in one direction, marking events and separating the past from the future by a point called present. Yet, the question is one of the deepest ones in science/philosophy today, creating disagreements and paradoxes, instead of answers. This book tries to explain the roots of the difficulty, in a way that is understandable to a literate person with minimal background in science. Besides the