Everyday experiences lead us to believe that time flows in one direction--always forward. And, the Second Law of Thermodynamics tells us that the tendency of the universe is toward greater entropy or disorder. This is why we never see a broken cup spontaneously reassemble into its original, unbroken form. Time reversal is the stuff of science fiction. But, as the saying goes, the truth maybe stranger than fiction.
In Timeless Reality, Victor J. Stenger, retired professor of physics and astronomy at the University of Hawaii, argues that time is, in fact, reversible. The idea of absolute time and an absolute now is strictly a classical physics notion, courtesy of Sir Isaac Newton. At the turn of the 20th century, however, physicists like Einstein, Dirac, and Schrödinger showed that the universe we live in is dramatically different from our everyday experiences. Stenger expertly leads us through the development of this brave new universe and the surprising implications.
He begins with a historical overview of humanity's ideas and perceptions of reality, follows that with a discussion of paradigm shifts in scientific thought, and throws in an obligatory discussion of relativistic physics to emphasize the death of Newton's notions of absolute time and absolute simultaneity. Stenger identifies three arrows of time--the thermodynamic arrow, the cosmological arrow, and the radiation arrow--and argues that all three are indistinguishable. Ultimately he concludes that these arrows of time do not reveal a deterministic law demanding that time immutable flows from past to present; rather, these so-called arrows of time are statistical statements of what is most likely to occur. Thus is may be extremely improbably that our coffee cup magically reassembles into its former self after falling off the table, but it is not impossible.
Having laid the foundation for this idea of time reversibility being possible--albeit highly improbable in our classical world--Stenger takes us into the quantum world. Here he breaks new ground, explaining the evolution of quantum physics and various interpretations, including the Copenhagen interpretation and Schrödinger's cat. We also learn why Einstein had such a great distaste for quantum physics: Quantum physics as it is stated is either incomplete or it is superluminal, requiring signalling faster than the speed of light. In the chapters that follow, however, Stenger shows that this difficulty of faster-than-light signals is easily avoided if time is reversible. Within this timeless reality, it is possible there exists a multitude of universes--each with their own unique structures and laws.
Overall, Timeless Reality is well written and quite fun. Stenger's tone is generally conversational, although a bit didactic at some points. If you've read other books on this subject lately you could skip the first three chapters. A few of the discussions get heavy-handed and those who are faint of (physics) heart can skim the discussion of quantum mechanical state vectors, Hilbert spaces, and the like without too much loss. The book features some good illustrations and a handy glossary of physics, astronomy, and cosmology terms.
In Timeless Reality you'll also find some genuinely unique physics that you haven't read in any other popular astronomy book. This is a particularly nice feature, and--as Stenger mentions several times--I, too, found myself thinking, "Gee, they never talked about that when I was in grad school."
Timeless Reality is at heart a book about astrophysics. Stenger will open your eyes to some fascinating ideas about space, time, and reality.
By Jennifer Birriel, Morehead State University