The Impossible Observed



In 1979 in Heidelberg, Germany, Dr. Werner Neuhauser looked up from the eyepiece of a low-power microscope and fancied he heard the ghost of Mach whispering: “Now I believe in atoms.” Neuhauser had just glimpsed what appeared to be a bright blue star floating in the void; it was a single barium ion, caught in an electromagnetic trap and fluorescing in a laser’s beam. Thus transpired the first observation of an isolated atom using a lens; soon one would be glimpsed with the naked eye as well. (When I was a child, elementary science textbooks claimed that no one would ever see an atom with the naked eye. The authors had erred by assuming that smallness was the important issue; actually, brightness and isolation from other atoms are what matters. The laser-stimulated barium atom produces 108 photons per second; your eyes can collect several thousand. The normal retina is sensitive to even a few photons, so you can see the atom, just as you would a distant star or any other bright, isolated object.)


Barium Atom Nickel Wire Electromagnetic Trap EPRB Experiment Nonzero Radius 
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  1. [p. 137]
    For the visible barium ion, see Phys. Rev. A, 22, no. 3 (1980), pp. 1137 – 1140, and the color snapshot from Dehmelt’s lab reproduced in the Phys. Scripta article. (Unfortunately, “Astrid,” Dehmelt’s pet barium ion, was not available for viewing the day I visited his lab, but I accept that others have seen it. I haven’t seen Antarctica either.)Google Scholar
  2. [p. 137]
    Schrödinger quote: Brit. J. Philos. Sci. III, no. 11 (Nov. 1952).Google Scholar
  3. [p. 138]
    R. H. Dicke and H. A. Tolhoek earlier (in 1956) attempted to measure the electron’s magnetic moment, and W. H. Louisell, R. W. Pidd, and H. R. Crane first succeeded (accuracy 3 percent); see Van Dyck et al., op cit. (1986).Google Scholar
  4. [p. 138a]
    For a report on the 1989 Nobel Prize in Physics, see Science. 20, (Oct. 1989), p. 327. Dehmelt’s Nobel lecture was published in Rev. Mod. Phys. 62, no. 3 (1990), pp. 525–530. (The values for the electron’s g-factor, which may change over the years with refinements in experimental and numerical technique, are taken from that lecture.) Other interesting articles include Van Dyck et al., Phys. Rev. D 34, no. 3, (1986), pp. 722–734;ADSCrossRefGoogle Scholar
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    H. Dehmelt, Phys. Scripta T22 (1988), pp. 102–110,ADSCrossRefGoogle Scholar
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    H. Dehmelt Z. Phys. D. 10 (1988), pp. 127–134.ADSCrossRefGoogle Scholar
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    For quantum jumps observed, see W. Neuhauser and Th. Sauter, Comments At. Mol. Phys 21, no. 2 (1988), pp. 83–95, and Dehmelt’s papers above.Google Scholar
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    For Kinoshita’s heroic calculations, see Proc. of the Conference on Precision Electromagnetic Measurements, Gaitherburg, 1986. The error is less than the experimental uncertainty in the fine structure constant since the latter enters into the calculations raised to a power of four or higher. Numeric evaluation of integrals accounts for the remaining error.Google Scholar
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    Kerson Huang’s paper on electron spin is in Am. J. Phys. 20 (1952), p. 479. On the history of spin, see Jammer (1966), pp. 147–53.Google Scholar
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    Bohr on spin is from an unpublished English-language manuscript dated 1929 entitled “The Magnetic Electron,” in the Niels Bohr Archives, microfilm MSS, no. 12. Pauli’s article from the Sixth Solvay Conference can be found in Le Magnetism. Rapports et Discussions de Sixieme Conseil de Physique…, Gauthiers, Paris (1932), in French, or in the Bohr Archives in English. Mott’s article was in Proc. Roy. Soc. A 124 (1929), p. 440; see also pp. 214–219 of Mott and Massey (1965), reprinted on pp. 701–706 of Wheeler and Zurek. Rosenfeld’s recollection is quoted in Wheeler and Zurek, p. 699.Google Scholar

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