Simple Nature - Light and Matter

and according to classical physics, any accelerating charged particleemits electromagnetic waves. According to classical physics,atoms should collapse!The solution lies in the observation that a bound state has a minimumenergy. An electron in one of the higher-energy atomicstates can and does emit photons and hop down step by step inenergy. But once it is in the ground state, it cannot emit a photonbecause there is no lower-energy state for it to go to.Chemical bonds example 16I began this section with a classical argument that chemicalbonds, as in an H 2 molecule, should not exist. Quantum physicsexplains why this type of bonding does in fact occur. When theatoms are next to each other, the electrons are shared betweenthem. The “box” is about twice as wide, and a larger box allowsa smaller energy. Energy is required in order to separate theatoms. (A qualitatively different type of bonding is discussed onpage 891. Example 23 on page 887 revisits the H 2 bond in moredetail.)Discussion QuestionsA Neutrons attract each other via the strong nuclear force, so accordingto classical physics it should be possible to form nuclei out of clusters oftwo or more neutrons, with no protons at all. Experimental searches,however, have failed to turn up evidence of a stable two-neutron system(dineutron) or larger stable clusters. These systems are apparently notjust unstable in the sense of being able to beta decay but unstable inthe sense that they don’t hold together at all. Explain based on quantumphysics why a dineutron might spontaneously fly apart.B The following table shows the energy gap between the ground stateand the first excited state for four nuclei, in units of picojoules. (The nucleiwere chosen to be ones that have similar structures, e.g., they are allspherical in shape.)nucleus energy gap (picojoules)4 He 3.23416 O 0.96840 Ca 0.536208 Pb 0.418h / Two hydrogen atoms bondto form an H 2 molecule. In themolecule, the two electrons’ wavepatterns overlap , and are abouttwice as wide.Explain the trend in the data.13.3.4 The uncertainty principle and measurementEliminating randomness through measurement?A common reaction to quantum physics, among both earlytwentieth-centuryphysicists and modern students, is that we shouldbe able to get rid of randomness through accurate measurement. IfI say, for example, that it is meaningless to discuss the path of aphoton or an electron, one might suggest that we simply measurethe particle’s position and velocity many times in a row. This seriesSection 13.3 Matter As a Wave 861