“The nature of time is perhaps the greatest remaining mystery,” according to the author. This book is an attempt to remove some of that mystery. The book is divided into three sections. In the first we learn what modern physics has to teach us about time. In the second, things get a little weird. We see a landscape that is empty, windswept, and almost devoid of all trace of temporality. In the third, we try to figure out how time must emerge around us.
It was interesting to learn that the only basic law that distinguishes the past from the present is the flow of heat. The arrow of time appears only when heat is involved. This irreversible progress in one direction came to be known as entropy. Boltzmann has shown that entropy exists because we view the world in a “blurred” fashion. There is this notion of “particularity,” that is “born only at the moment we begin to see the universe in a blurred and approximate way.” This is an interesting concept, which means that if we could account for all the details of the microscopic characteristics of the world, the appearance of the flow of time would somehow vanish. In fact, the equations of physics do not distinguish between past, present, and future. Even the idea of the present or a well-defined now existing throughout the universe is an illusion. It is “an illegitimate extrapolation of our own experience.” In this first section, we are also introduced to three fundamental discoveries of quantum mechanics that demolish our concept of time further: granularity, indeterminacy, and the relational aspect of physical variables. Time actually has a minimum interval below which the notion of time does not exist – Planck time. And space-time, like an electron, can fluctuate and can be in a superposition of different configurations. The physical substratum –the gravitational field – determines duration and physical interval. It too is a quantum entity that does not have determined values until it interacts with something else. This is indeterminacy.
How about a world without time? This is the title of the second section. Here we see the world as a collection of events or processes, not things. In fact, it seems that “past” and “future” may not have a universal meaning. Instead their meaning changes between here and there. On a quantum level, the fundamental equations of quantum gravity do not even have a time variable. The world is described by indicating the possible relations between variable quantities. We are introduced at this point to a theory called loop quantum gravity.
This is followed in section three by two chapters that are described as brief and technical, in which the author discusses the reconstruction of time. Here we talk of microscopic configurations and a “blurring,” which itself determines a particular variable called time. We have thermal time and we have quantum time – perhaps aspects of the same phenomenon. This is all interesting, and you’ll just have to read it, and see what you make of it. We also learn about different ingredients that combine to produce our identity. So “we human beings are an effect of this great history of the increase of entropy, held together by the memory that is enabled by these traces,” says the author. This is an interesting read, to say the least, and I certainly recommend it to those interested on an understanding of the concept of time. My short review can’t do it justice.
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