Friday March 21, 2008 6:30 am Edmonton, Alberta

How should one tackle a book like this?

A glance at the table of contents shows a list of 10 chapters with no obvious structure to them. Each chapter ends with a two page essay by a famous scientist or science writer. The book is full of superb diagrams in full color.

I will make notes of important points and insert a tan box when I want to make a personal comment.

Introduction

Let's begin with the Introduction, a short 4-page section.

Here are a few quotes that I have noted:

• "... it is not the theory of quantum mechanics thai is weird or illogical. On the contrary, it is a beautifully accurate and logical mathematical construction that describes Nature superbly well." [p. 7]
  
  
• "Quantum mechanics accurately predicts and explains the behavior of the very building blocks of matter - not just the atoms, but the particles that make up the atoms - with incredible accuracy." [p. 8]
  
  
• "... what right do we have to expect nature at the unimaginably tiny scale of atoms to behave in a way familiar to us from our everyday experiences on the scale of humans, cars, trees, and buildings?" [p. 8]

Al-Khalili then goes on to say that many physicists ignore the debate about how to interpret or make meaningful the results of various experiments. He calls this the "shut up and simply use the quantum tools to make predictions" group and notes that this is itself an unscientific position.

I agree - the whole point of science is to create a description that is understandable and meaningful.

He then says that he supports a position called the "shut up while you calculate" interpretation. I had to read this twice to appreciate the difference.

Chapter 1 Nature's Conjuring Trick

This chapter describes the famous "2 slit" experiment with light. Basically it consists of a series of experiments involving passing a beam of light through either one slit or two slits and then noticing the pattern of light on a screen behind the barrier. Under some conditions the pattern is consistent with an interpretation that light is composed of waves, under other conditions the only possible interpretation in that it is composed of particles.

• "In fact, quantum mechanics does provide us with a perfectly logical explanation of the two-slit trick. But it is an explanation only of what we observe and not of what is going on when we are not looking. But since all we have to go on is what we can see and measure, maybe it makes no sense to ask for more." [p. 20]

Al-Khalili then notes that in everyday life ... "we should in principle be able to analyse the behavior based on the notion of cause and effect ... There may be new processes at work, new forces or properties of nature that have not yet been understood or even discovered. All that matters is that we can use logic, however convoluted, to explain what might possibly be going on.

He then writes the following paragraph:

• "Physicists have been forced to admit that, in the case of the double-slit trick, there is no rational way out. We can explain what we see but not why. However strange you may find the predictions of quantum mechanics, it must be emphasized that it is not the theory - mankind's invention - that is strange, but rather Nature herself that insists on such a strange kind of reality on the microscopic scale." [p. 21]

I am not sure that I agree with this statement. The theory may indeed be strange, it is strange when compared with other situations that we are familiar with.

Al-Khalili says that the two-slit experiment is "just one example of the way in which the quantum phenomenon known as 'superposition' manifests itself". [p. 22]

Okay, but ... he fails to mention what this "superposition" phenomenon is about. I am sure he will elaborate on this in the following pages, but I am impatient. Let's see if a quick look in wikipedia will help. http://en.wikipedia.org/wiki/Quantum_superposition Here is the first sentence of this entry: The principle of superposition states that if the world can be in any configuration, any possible arrangement of particles or fields, and if the world could also be in another configuration, then the world can also be in a state which is a mixture of the two, where the amount of each configuration that is in the mixture is specified by a complex number. That makes some sense to me, but it is clearly more complicated (i.e. see the reference to complex numbers) than it might appear. It seems to me that this is also a statement that physical reality is continuous since a mixture can be described by a complex number. I will want to revisit this later! Now back to the book.

The chapter ends with a description of the two-slit experiment using a large carbon molecule (C60 or C70) called a buckeyball instead of a light beam, and the results are the same. The pattern on a screen behind the slits exhibits a pattern consistent with a wave-interpretation of the molecule.

I am pleased with my notes so far. Now to have a quick skim of chapter 2 Origins before making a few more notes.

Tags: physics, science, quantum