01 January 1970 19 2K Report

Mach said [1], the principle of minimum xxxx, are they the natural purpose?

Born said in his "Physics in My Generation"[2], that while it is understandable that a particle chooses the straightest path to travel at a given moment, we cannot understand how it can quickly compare all possible motions to reach a point and pick the shortest path —— a question that makes one feels too metaphysical.

Speaking of the Hamiltonian principle and the minimum light path, Schrödinger recognizes the wonder of this problem [3]: Admittedly, the Hamilton principle does not say exactly that the mass point chooses the quickest way, but it does say something so similar - the analogy with the principle of the shortest travelling time of light is so close, that one was faced with a puzzle. It seemed as if Nature had realized one and the same law twice by entirely different means: first in the case of light, by means of a fairly obvious play of rays; and again in the case of the mass points, which was anything but obvious, unless somehow wave nature were to be attributed to them also. And this, it seemed impossible to do. Because the "mass points" on which the laws of mechanics had really been confirmed experimentally at that time were only the large, visible, sometimes very large bodies, the planets, for which a thing like "wave nature" appeared to be out of the question.

Feynman had a topic of minimum action in his "Lecture of Physics" [4]. It discusses how particle motion in optics, classical mechanics, and quantum mechanics can follow the shortest path. He argues that light "detects" the shortest path by phase superposition, but when a baffle with a slit is placed on the path, the light cannot check all the paths and therefore cannot calculate which path to take, and the phenomenon of diffraction of light occurs. Here, Feynman defined the path of light in two parts, before and after the diffraction occurs. If we take a single photon as an example, then before diffraction he considered that the photon travels along the normal geometric optical path, choosing the shortest path. After diffraction occurs, the photon loses its ability to "find" the shortest path and takes a different path to the diffraction screen, with different possibilities. This leads to the concept of probability amplitude in quantum mechanics.

To explain why light and particles can choose the "shortest path", the only logical point of view should be that light and particles do not look for the shortest path, but create it and define it, whether in flat or curved spacetime. Therefore, we should think about what light and particles must be based on, or what they must be, in order to be able to define the shortest paths directly through themselves in accordance with physics.

[1] Ernst Mach, Popular Scientific Lectures.

[2] Born, M. (1968). Physics in My Generation, Springer.

[3] Schrödinger, E. (1933). "The fundamental idea of wave mechanics. Nobel lecture " 12 (1933).

[4] Feynman, R. P. (2005). The Feynman Lectures on Physics(II), Chinese ed.

Keywords: light, Fermat principle of the shortest light time, Hamilton principle, Feynman path integral, Axiomatic

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