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By Laurie M. Brown

Richard Feynman’s by no means formerly released doctoral thesis shaped the center of a lot of his great and profound paintings in theoretical physics. Entitled “The precept of Least motion in Quantum Mechanics,” its unique intent used to be to quantize the classical action-at-a-distance electrodynamics. simply because that thought followed an total space–time perspective, the classical Hamiltonian strategy utilized in the traditional formulations of quantum idea couldn't be used, so Feynman became to the Lagrangian functionality and the main of least motion as his issues of departure. the end result used to be the trail indispensable technique, which chuffed — and transcended — its unique motivation, and has loved nice luck in renormalized quantum box idea, together with the derivation of the ever present Feynman diagrams for effortless debris. direction integrals have many different purposes, together with atomic, molecular, and nuclear scattering, statistical mechanics, quantum beverages and solids, Brownian movement, and noise idea. It additionally sheds new gentle on primary matters just like the interpretation of quantum thought due to its new total space–time standpoint. the current quantity contains Feynman’s Princeton thesis, the comparable evaluation article “Space–Time method of Non-Relativistic Quantum Mechanics” [Reviews of contemporary Physics 20 (1948), 367– 387], Paul Dirac’s seminal paper “The Lagrangian in Quantum Mechanics’’ [Physikalische Zeitschrift der Sowjetunion, Band three, Heft 1 (1933)], and an advent via Laurie M Brown.

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Example text

A(T − tm ) where in the sum we shall write Q for q m+1 , and T for tm+1 . In the limit as we take finer and finer subdivisions of the interval t 0 to T and thus make an ever increasing number of successive integrations, the expression on the right side of (47) becomes equal to ψ(Q, T ). T ˙ q)dt with the integral The sum in the exponential resembles t0 L(q, written as a Riemann sum. 32 Feynman’s Thesis — A New Approach to Quantum Theory In a similar manner we can compute ψ(q 0 , t0 ) in terms of the wave function at the later time T = tm+1 , by the equation; ψ ∗ (q0 , t0 ) = ψ ∗ (qm+1 , tm+1 ) ··· × exp i m L i=0 qi+1 − qi , qi+1 · (ti+1 − ti ) ti+1 − ti √ √ gm+1 dqm+1 · · · g1 dq1 .

12 Feynman’s Thesis — A New Approach to Quantum Theory The conservation of a physical quantity is of considerable interest because in solving problems it permits us to forget a great number of details. The conservation of energy can be derived from the laws of motion, but its value lies in the fact that by the use of it certain broad aspects of a problem may be discussed, without going into the great detail that is often required by a direct use of the laws of motion. To compute the quantity I(t), of equation (11), for two different times, t1 and t2 that are far apart, in order to compare I(t 1 ) with I(t2 ), it is necessary to have detailed information of the path during the entire interval t1 to t2 .

F = −V (x)), then the integrand is a perfect differential, and may be integrated to become 1 2 + V (x(t)). A comparison of I for two times, t and t , ˙ 1 2 2 m(x(t)) now depends only on the motion in the neighborhood of these times, all of the intermediate details being, so to speak, integrated out. We therefore require two things if a quantity I(t) is to attract our attention as being dynamically important. The first is that it be conserved, I(t1 ) = I(t2 ). The second is that I(t) should depend only locally on the path.

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