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Simple Nature - Light and Matter

Simple Nature - Light and Matter

Simple Nature - Light and Matter

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k / In recent decades, a huge hole in the ozone layer has spreadout from Antarctica. Left: November 1978. Right: November 199213.2 <strong>Light</strong> As a ParticleThe only thing that interferes with my learning is my education.Albert EinsteinRadioactivity is r<strong>and</strong>om, but do the laws of physics exhibit r<strong>and</strong>omnessin other contexts besides radioactivity? Yes. Radioactivedecay was just a good playpen to get us started with concepts ofr<strong>and</strong>omness, because all atoms of a given isotope are identical. Bystocking the playpen with an unlimited supply of identical atomtoys,nature helped us to realize that their future behavior could bedifferent regardless of their original identicality. We are now readyto leave the playpen, <strong>and</strong> see how r<strong>and</strong>omness fits into the structureof physics at the most fundamental level.The laws of physics describe light <strong>and</strong> matter, <strong>and</strong> the quantumrevolution rewrote both descriptions. Radioactivity was a good exampleof matter’s behaving in a way that was inconsistent withclassical physics, but if we want to get under the hood <strong>and</strong> underst<strong>and</strong>how nonclassical things happen, it will be easier to focus onlight rather than matter. A radioactive atom such as uranium-235is after all an extremely complex system, consisting of 92 protons,143 neutrons, <strong>and</strong> 92 electrons. <strong>Light</strong>, however, can be a simple sinewave.However successful the classical wave theory of light had been— allowing the creation of radio <strong>and</strong> radar, for example — it stillfailed to describe many important phenomena. An example thatis currently of great interest is the way the ozone layer protects usfrom the dangerous short-wavelength ultraviolet part of the sun’sspectrum. In the classical description, light is a wave. When a wave836 Chapter 13 Quantum Physics

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