Science often starts with the investigation of what Jim Al-Khalili describes as “perceived paradoxes”. These are strange results or observations that defy explanation, or run contrary to accepted theory. When an explanation is puzzled out, it may frequently have larger implications.
This book focuses on nine such, which the author discusses in simple, non-mathematical terms. Mr Al-Khalili, a well-known TV personality and professor of theoretical physics at Surrey, is an easy communicator with a wry sense of humour. He once offered to eat his boxer shorts live on TV if neutrinos turned out to be faster than photons as appeared to be the case in a recent experiment where the data were skewed by faulty equipment.
He says he had great fun writing this book. The enjoyment is obvious and infectious. He’s stayed away, by and large, from genuinely unsolved problems. He has, however, dealt with some areas where physicists differ on the possible explanations.
A logical paradox is something like the following paired statements. A) The statement “B” is false. B) The statement “A” is true. This sort of thing gave Russell and Whitehead nightmares, and eventually prompted Russell to quit maths for philosophy.
Mr Al-Khalili mentions logical paradoxes only in passing in his preface. He does, however, warm up by dealing with a problem of “restricted choice” that has stumped many smart people, including maths genius, Paul Erdos. On a game-show, a player is shown three closed boxes. One contains a prize, the other two, nothing. He picks one, which is set aside unopened. The show host then opens another box, which is empty, and offers the player an option to switch. Should he switch? The answer is yes, assuming the host knows which box contains the prize. Work it out for yourself.
Chapter Two introduces Zeno’s paradoxes of motion and builds from there to what is known, 2,500 years after Zeno’s death, as the “Quantum Zeno Effect”. Zeno “proved” motion was impossible, citing the example of an arrow in flight being motionless at every given instant of time.
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Mr Al-Khalili points out the fallacy (if successive slices of time are taken, the arrow moves slightly in every instant) and then goes on to discuss an interesting experiment. In 1977, Misra & Sudarshan published a paper called “Zeno’s paradox in Quantum Theory” in which they described how radioactive atoms never decay while continuously observed.
Next up is Olber’s Paradox: why does the sky get dark at night, given light is available from many stars? The answer involves an understanding that the universe has an origin (the Big Bang) and also provides evidence for its expansion. Oddly enough, as the author points out, the first correct explanation to Olber’s Paradox came from Edgar Allen Poe, who intuited that the vastness of the universe meant that light from more distant stars couldn’t reach us. It was only about 50 years later that Lord Kelvin did the calculations that proved the poet was correct.
The next chapter is about thermodynamics, entropy and energy conservation. It embarks on an analysis of Maxwell’s Demon, which conceptualised a perpetual-motion machine. This has been picked to death, but Mr Al-Khalili’s description of the issues involved is both succinct and entertaining.
After this, the next three chapters look at different consequences of relativity. First, there is the famous thought experiment of the the pole pushed through a barn door. The pole lengthens or shortens, depending on the speed at which it’s travelling with respect to the observers’ frame of reference. Then, there are the time-dilation effects caused by high-speed travel. The third chapter deals with time travel, as encapsulated in the grandfather paradox: if a man travels back in time and kills his own grandfather before he is born, what happens?
The final sections deal with philosophical questions that have been resurrected by modern science. Laplace’s Paradox is about free will versus determinism: could a super-intellect calculate everything that has happened, and will ever happen, in the universe, given perfect knowledge and the laws of science? The short answer is “no”. Then there’s Schroidinger’s Cat, of course. The celebrated feline takes centre stage in the most famous of scientific paradoxes. Discussions can lead into strange theories of multiverses.
The book moves on to a discussion of aliens, the anthropic principle and possible answers to Fermi’s Paradox: given a multitude of stars with habitable planets, there must be many extra-terrestrial civilisations. Why haven’t they got in touch? This is a highly speculative area and the author describes serious attempts to find habitable planets and to contact aliens. Finally, Mr Al-Khalili does state 10 unanswered questions that continue to intrigue physical scientists. He winds up with a short note on the flawed Opera neutrino result referred to above.
The book is written for a general audience. It avoids mathematical complexity in dealing with a set of staple enigmas. Speaking personally, I found the chapters on Olber’s Paradox and Laplace’s Paradox exceptionally good. But every concept is presented elegantly and in thought-provoking style, and that makes it a great introductory work for the layperson.
PARADOX
The Nine Greatest Enigmas in Science
Jim Al-Khalili
Bantam Press; 234 pages; £13.99