Physics Matters

The following sections are included:

• Dedication
• Contents
• Abbreviations
• Preface
• About the Author

Almost all undergraduate textbooks on physics treat the simple harmonic oscillator in detail because it is the key to understanding much of physics. Apart from direct applications such as in a pendulum clock, it can be used to understand collective excitations like phonons in a solid. But perhaps the most important reason to study them is that it is first step in understanding light. A light wave is like a harmonic oscillator, except that instead of position and velocity oscillating as in a mechanical oscillator, it is the electric and magnetic fields that oscillate in a light wave. In addition, as we will see in this chapter, it can be used to understand many phenomena that are normally associated with quantum mechanics. The reason for this is that the main equation governing quantum mechanics is the Schrödinger equation, which is just a modified wave/oscillator equation.

This chapter is devoted to an analysis of the radiation that emanates from cell phones, and how they cannot cause cancer. Understanding this is important because the number of cell-phone users worldwide has increased exponentially in the past few years. Students have a moral obligation to understand these ideas, and explain it to other users.

EINSTEIN's famous statement that “God does not play dice with the universe” has two misconceptions in the popular interpretation—his use of the words God and dice—which are corrected in this chapter. After reading this chapter, the reader should hopefully come away with a deeper understanding of Einstein's mind.

This chapter is devoted to the modus operandi of the genius Einstein. We look at his 1917 paper in which he predicted the existence of stimulated emission in radiative processes, well before the formalism of quantum mechanics was developed. In that sense, the paper belongs to the “old” quantum theory—but its prediction of stimulated emission is the key to understanding the operation of the laser, which finds myriad applications today.

Community living of humans has necessitated the adoption of a common set of measures for quantities such as mass, length, and time. While settlements with little or no trade with others could afford to have their own set of measures, inter-community trade and commerce has made it necessary for people to adopt common ones. This requirement is all the more important in modern science, because the results of experiments in different labs can be compared only if all scientists agree on a common set of measures. The scientific study of such measures is called metrology. In most countries, standards for units are maintained by national institutions, in coordination with similar bodies in other countries. In this chapter, we will see the evolution of standards for commonly used units from early times to their modern “democratic” definitions.

The twin or clock paradox is an important result of relativity which requires careful deliberation by students. In the standard resolution, the traveling twin ages less than the stay-at-home twin. In this chapter, we show that this resolution is incorrect because it rests on untenable assumptions. The new resolution also avoids logical conclusions necessitated by the kind of time travel allowed by the standard resolution.

Robert Dicke, the person featured in this chapter, was a pivotal figure in 20^th century physics. Apart from his contributions to atomic physics discussed here, he made fundamental contributions to several other areas of physics. In particular, he made a calculation of the temperature of the afterglow left over from the big bang signaling the birth of our universe—called the cosmic background radiation—made an estimate that the temperature was in the microwave regime, and hence amenable to experimental technology. As luck would have it, the same was accidentally discovered by Penzias and Wilson working at Bell Labs (just a few miles away from Princeton, where Dicke was a professor of physics), for which Penzias and Wilson got the Nobel Prize. Dicke was also instrumental in developing the Brans-Dicke theory of gravity, which provided an alternative to the general theory of relativity and hence made it testable. This is because a scientific theory becomes testable only if there are alternatives which predict different results, so that experiments can decide in favor of one or the other. Needless to say, general relativity has come out with flying colors after every test.

The 1997 Nobel Prize in Physics was awarded to Steven Chu of Stanford University (USA); Claude Cohen-Tannoudji of College de France (France); and William Phillips of National Institute of Standards and Technology, Gaithersburg (USA). They have been cited for their seminal work in the use of laser light to cool and trap atoms. This award represents the recognition of more than two decades of work by many leading atomic physicists around the world. Indeed, several of the key ideas in this field have not originated in the laboratories of the above scientists. However, they have been chosen for the award because, in a remarkably productive period in the late 1980's, these three researchers, working independently, discovered new experimental results that surpassed the predictions of existing theories of laser cooling. Soon after, they also developed new theories that explained the strange results and helped zero in on the best conditions for laser cooling. It is one of those rare instances in physics where experiments have worked better than anticipated, and is a tribute to careful experimentation.

The 2001 Nobel Prize in Physics was awarded to Eric Cornell of the National Institute of Standards and Technology, Boulder (USA); Wolfgang Ketterle of the Massachusetts Institute of Technology, Cambridge (USA); and Carl Wieman of the University of Colorado, Boulder (USA). They have been cited for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates. The scientists have been recognized for their pioneering work in a field that has grown explosively around the world in the past few years. Though the phenomenon of Bose-Einstein condensation (BEC) was predicted by Einstein in 1925 (based on the new statistics of Bose), it was observed only in 1995. In this chapter, we review the basic physics behind the phenomenon, the experimental techniques involved in achieving it, and highlight some of the potential applications of condensates.

The 2005 Nobel Prize in Physics was awarded in the area of laser physics. One half of the prize (theory part) has been given to Roy Glauber of Harvard University, Cambridge (USA) “for his contribution to the quantum theory of optical coherence”, which became important soon after the invention of the laser. The second half of the prize (experimental part) was jointly awarded to two physicists, John Hall of the National Institute of Standards and Technology in Boulder (USA); and Theodor Hänsch of the Max Planck Institute for Quantum Optics, Garching (Germany). They have been cited “for their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique”. In this chapter, we will discuss the contributions of Hall and Hänsch, which led to their being awarded the experimental part of the Prize.

The winners of the 2009 Nobel prize in physics have been recognized for two achievements in optics that have revolutionized modern life in the past few decades. The first is the invention of the optical fiber, which makes long-distance communication literally lightning fast. Our modern life is fundamentally dependent on optical communication, from the Internet to the ubiquitous mobile phone. The second invention is the CCD (short form of charge-coupled device) camera, the electronic eye that has changed optical imaging and put the traditional photographic film out of use. Today, even the cheapest cell phone has a high-resolution (mega-pixel) CCD camera that allows you to take a picture and email it to a friend halfway across the world. A child growing up in this interconnected world would find it hard to believe that these things were in the realm of science fiction just a short generation ago.

Quantum mechanics describes the weird world of microscopic particles, which is completely different from the macro world that we are used to in our daily lives. Perhaps the most defining characteristic of that world is that it is discrete—hence the name quantum—as opposed to the continuous nature of physics at the macrolevel. The discreteness of the microscopic world was first explained by Planck in 1900 with his derivation of the blackbody spectrum. Since then, we have understood that discreteness is an inherent feature of both matter (atoms, or a collection of them) and its interactions (light in the form of photons, for example).

The following sections is included:

• Index