Mermin habitually answers opinions, real and abstract
Rodney Brooks
I am that friend of David Mermin’s “who was enchanted by the revelation that quantum fields were the real stuff that makes up the world.” I plead guilty to reification and offer the following defense.I started out, as I think we all did, with the notion that there is a reality out there and that space and time are part of it—not just “an extremely effective way to represent relations between distinct events.” When I read Arthur Eddington’s The Nature of the Physical World (J. M. Dent & Sons, 1942) in high school, I learned that reality was not what it seemed—that Eddington’s solid writing desk, for example, was mostly empty space. The next step in my understanding of reality came in college when I found that the electromagnetic field offered a more satisfying picture of the world than action at a distance, which even Isaac Newton derided. 1 1. H. Boorse, L. Motz, eds., The World of the Atom, Basic Books, New York (1966), p. 319. When I encountered quantum mechanics, of course, everything became confusion. However, along with David, I was fortunate to attend Julian Schwinger’s courses at Harvard University just after he had perfected his treatment of quantum field theory. 2 2. J. Schwinger, Ann. Phys. 2, 407 (1957). https://doi.org/10.1016/0003-4916(57)90015-5 I sat enthralled throughout the three-year series (1956–59), in which Schwinger developed QFT as a seemingly inevitable consequence of the most basic assumptions.However, I came away with a different understanding of QFT than David’s. I understood that the fields are physical properties of space that are described by field strengths—just as in classical physics, except that in QFT the state of the field at each point is represented by a vector in Hilbert space rather than by a pure number. That use of Hilbert space, which followed naturally from Schwinger’s “measurement algebra,” allows superpositions of values. The operators in Hilbert space, as I understood it, are mathematical tools that describe the evolution of the state vectors, and they are not to be reified.When I saw how QFT resolves the paradoxes of modern physics, it became irresistible. The special relativity paradoxes—for example, Lorentz contraction and time dilation—are a natural result of the way fields behave. 3 3. J. Schwinger wrote a six-part series on the theory of quantized fields: Phys. Rev. 82, 914 (1951); 91, 713 (1953); https://doi.org/10.1103/PhysRev.82.914 91, 728 (1953); 92, 1283 (1953); 93, 615 (1954); 94, 1362 (1954). The spacetime curvature of general relativity, which I could never really visualize, does not exist in QFT; the gravitational field equations are equivalent to spacetime curvature for those who can visualize it, but equivalent is not the same as identical. 4 4. S. Weinberg, Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity, Wiley, New York (1972), pp. vii–147. Finally, the mysterious wave–particle duality of quantum mechanics vanishes; in QFT, reality consists of fields and only fields.Because QFT is so neglected by the public (and by many physicists), I am writing a book that presents it without equations. A draft copy of the work, The Theory That Escaped Einstein, can be found through an internet search. Feedback is appreciated.For those who can’t kick the reification habit, QFT is the way to go. It is the only theory that offers a consistent and visualizable picture of reality. Reifiers of the world, unite! You have nothing to lose but your abstractions.REFERENCESSection:ChooseTop of pageREFERENCES <<1. H. Boorse, L. Motz, eds., The World of the Atom, Basic Books, New York (1966), p. 319. Google Scholar2. J. Schwinger, Ann. Phys. 2, 407 (1957). https://doi.org/10.1016/0003-4916(57)90015-5 , Google ScholarCrossref, ISI3. J. Schwinger wrote a six-part series on the theory of quantized fields: Phys. Rev. 82, 914 (1951); 91, 713 (1953); https://doi.org/10.1103/PhysRev.82.914 , Google ScholarCrossref, ISI 91, 728 (1953); , Google Scholar 92, 1283 (1953); Google Scholar 93, 615 (1954); Google Scholar 94, 1362 (1954). Google Scholar4. S. Weinberg, Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity, Wiley, New York (1972), pp. vii–147. Google Scholar© 2009 American Institute of Physics.
Physics Today•Sep 1, 2009•0 citations