Knocking on Heaven's Door - Lisa Randall [18]
Newton’s corpuscular theory reproduces results from optics. Nonetheless, Newton’s corpuscles, which don’t have any wavelike nature, are not the same as photons. So far as we now know, the theory of photons is the most basic and correct description of light, which consists of particles that can also accommodate a wave description. Quantum mechanics gives our currently most fundamental description of what light is and how it behaves. It is fundamentally correct and survives.
Quantum mechanics is now much more of a frontier research area than optics. If people continue to think about new science with optics, they are primarily thinking about new effects possible only with quantum mechanics. Modern science, though no longer advancing the science of classical optics, does therefore include a field of quantum optics, which studies the quantum mechanical properties of light. Lasers rely on quantum mechanics, as do light detectors such as photomultipliers, and photovoltaic cells that convert sunlight into electricity.
Modern particle physics also encompasses the theory of quantum electrodynamics (QED), which Richard Feynman and others developed and which includes not only quantum mechanics but also special relativity. With QED, we study individual particles including photons—particles of light—as well as electrons and other particles that carry electric charge. We can understand the rates at which such particles interact and at which they can be created and destroyed. QED is one of the theories that is heavily used in particle physics. It also has made the most accurately verified predictions in all of science. QED is a far cry from geometrical optics, yet both are true in their appropriate domain of validity.
Every area of physics reveals this effective theory idea at work. Science evolves as old ideas get incorporated into more fundamental theories. The old ideas still apply and can have practical applications. But they aren’t the domain of frontier research. Though the end of this chapter has focused on the particular example of the physical interpretation of light through the ages, all of physics has developed in this manner. Science proceeds with uncertainty at the edges, but it is advancing methodically overall. Effective theories at a given scale legitimately ignore effects that we can prove won’t make a difference for any particular measurement. The wisdom and methods we acquired in the past survive. But theories evolve as we better understand a larger range of distances and energies. Advances give us new insights into what fundamentally accounts for the phenomena we see.
Understanding this progression helps us better interpret the nature of science and appreciate some of the major questions that physicists (and others) are asking today. In the following chapter, we’ll see that in many respects, today’s methodology began in the seventeenth century.
CHAPTER TWO
UNLOCKING SECRETS
The methods scientists use today are the latest incarnation of a long history of measurements and observations that have been developed over time to verify and—as importantly—rule out scientific ideas. This need to go beyond our intuitive apprehension of the world to advance our understanding is reflected in our very language. The root used in Romance languages for the verb “to think”—pensum—comes from the Latin verb “to weigh.” English speakers, too, “weigh” ideas.
Many of the formative insights that ushered science into its modern expression were developed in Italy in the seventeenth century, and Galileo was a key player. He was among the first to fully appreciate and advance indirect measurements—measurements made with an intermediate device—as well as to design and use experiments as a means of establishing scientific truth. Moreover, he conceived abstract thought experiments that helped him create and consistently formulate his ideas.
I learned about Galileo’s many insights that fundamentally changed science when I visited Padua in the spring of 2009. One impetus for my visit was a physics conference