• Share
Send to a Friend via Email

### Your suggestion is on its way!

An email with a link to:

was emailed to:

Thanks for sharing About.com with others!

Discuss in my forum

# Paradox: The Nine Greatest Enigmas in Physics by Jim Al-Khalili

## Explaining science by tackling its toughest questions

User Rating 5 Star Rating (1 Review)

Cover of Paradox: The Nine Greatest Enigmas in Physics by Jim Al-Khalili

This is a great book for anyone who likes science and logical conundrums (and interest in one often leads to interest in the other, I've found).

In this engaging book, physicist Jim Al-Khalili tackles the concepts of paradoxes, those contradictory results where our logical analysis of a situation seems to lead us to two conclusions that are fundamentally at odds with each other, such as cats being both alive and dead at the same time, objects being both long and short, and the universe being both full of stars and dark at night. It turns out that this result is often a case of mistaken thinking, as Al-Khalili shows through careful explanation of the scientific evidence and thinking behind each paradox, providing something of a backdoor way to teach the reader about fundamental scientific concepts from physics.

### The Book's Science

The goal of the book is to present the reader with engaging scientific contradictions, known as paradoxes, and then using that as the motivation for delving into the deeper science. Toward that end, Khalili begins his book with a variety of logical paradoxes to set the stage for the concept before moving into the scientific paradoxes that represent the core of the book. Once he sets the stage with this introductory chapter on the logical paradoxes, some of which (like the classic Monty Hall problem) require some basic mathematics to follow, he moves on into the physical paradoxes:

• Zeno's Paradox - This is a classic paradox typically attributed to the ancient thinker Zeno of Elea, which demonstrates a problem in our understanding of motion. The basic formulation of the paradox is that in order to cross a given distance, you must first cover half the distance. But to get there, you must cover half of that distance, but first half of that, and so on. As such, there are infinite halves that require traversing, therefore you can never reach your destination. As I said, there are some other formulations as well, but they all circle around this same basic idea. It's pretty clear that we can traverse these distances, though, so obviously something in this argument is off kilter. Al-Khalili explains the way out of the paradox, then proceeds to touch on a related concept known as the quantum Zeno effect.
• Olbers' Paradox - We take for granted that the night sky is dark, but some astronomers over the ages have questioned why this is so. If there are an infinite number of stars in all directions, no matter how far out they are, shouldn't the sky at night be as bright as during the day?
• Maxwell's Demon - In this paradox, physicist James Clerk Maxwell proposed a situation where a consciousness (a little "demon" in the traditional formulation) could make a decision that resulted in cumulative effects that violated the Second Law of Thermodynamics, but could do so without exerting any additional physical effort.
• The Pole in the Barn Paradox - This is a fairly involved problem related to Einstein's theory of special relativity, which focuses on the idea that two observers moving at different speeds will observe the lengths of objects to be different. This is, in my opinion, one of the more mind-bending paradoxes discussed in the book and its resolution, even though I fully understand the science behind it, for some reason strikes me as more counter-intuitive than the next two paradoxes, both of which involve time travel of various sorts.
• The Twin Paradox - This is a classic demonstration of the unusual behavior of time under Einstein's theory of relativity, where fast-moving objects are affected by time dilation.
• The Grandfather Paradox - As Al-Khalili points out, this is the only true paradox in the book. A classic trope in science fiction, this paradox only applies when you have a time machine. In the most common formulation, the time traveler goes back to kill their grandfather before he had children and thus is never born ... so isn't able to go back and kill the grandfather. (Al-Khalili wonders why it's the grandfather who does instead of the parents. My theory is that it's because you're less likely to recognize your grandfather as a young man than your father. That is presuming, of course, that you stumble into a situation where you accidentally kill your grandfather, rather than it being a bizarre targeted assassination ... or perhaps an elaborate suicide.) In order to "resolve" this paradox, Al-Khalili delves into what science can tell us about time travel. I won't give away the conclusion of this chapter other than to say that Al-Khalili seems to be a fan of the multiverse, at least when it comes to time travel.
• Laplace's Demon - One way of exploring the concept of determinism is to ask yourself whether a being that knew the position and motion of every particle in the universe would be able to predict everything about the universe, a notion often attributed to the French scientist Laplace. It turns out, however, that such an all-knowing being allows for some paradoxical situations just by virtue of existing.
• Schroedinger's Cat - This classic demonstration of the absurdity of scaling the standard interpretation of quantum physics up to the macroscopic level results in a boxed cat who is both alive and dead at the same time. Don't worry, though. It's only a thought experiment. No real cats have ever been harmed in the making of this paradox.
• Fermi's Paradox - The pioneering particle physicist Enrico Fermi once proposed a very simple question: if aliens exist, then why haven't any of them visited us? Resolving this paradox involves a discussion of how probable it is that aliens may exist, which touches on concepts like the Drake equation, the search for exoplanets, and the anthropic principle.

Al-Khalili does an excellent job of presenting the various paradoxes in a way that's accessible to any reader that has an interest in science, even without a strong background in the discipline. Though some of the resolutions to these paradoxes are pretty involved, requiring a fairly sophisticated application of complex scientific principles such as relativity and quantum physics, you most definitely need to be a scientific expert to get through the material as presented.

### The Book's Author

Jim Al-Khalili, OBE, is an Iraqi-born British quantum physicists from the University of Surrey, where he is a professor of theoretical physics and chair in the Public Engagement in Science program. (OBE means Officer of the Order of the British Empire, but apparently this designation doesn't earn the honorific "Sir.") In his capacity in the Public Engagement of Science, he has become a regular radio and television broadcaster for the BBC. He has an impressive array of credentials including, at the time of this writing (Oct. 2012), Vice President of the British Science Society. This is his fifth book, having previously authored:

### The Book's Specs

Publishing Date: October 23, 2012
Pages: 256 pages
Structure: Preface, 11 Chapters, Acknowledgements, & Index
Disclosure: A review copy was provided by the publisher. For more information, please see our Ethics Policy.
User Reviews

Reviews for this section have been closed.

5 out of 5
Certainty vs. Uncertainty, Member ehcnald

0 out of 0 people found this helpful.

Andrew Zimmerman Jones