eng Science and Education Publishing International Journal of Physics 2333-4576 2021-04-23 9 3 139 150 10.12691/ijp-9-3-1 IJP2021931 article Hui Peng davidpeng1749@yahoo.com Young¡¯s double slit experiments, which represent the mystery of quantum mechanics, have been interpreted by quantum probability waves and by de Broglie-Bohm trajectories/pilot waves. Computer simulations of Bohm¡¯s theory predict that (1) trajectories cannot cross, and (2) there is a triangle-shape area behind the double slit, in which there is no trajectory, i.e., no photons. In this article, we report the observations of novel comprehensive double slit experiments, which show that trajectories exist and cross in the triangular area. We show new phenomena that, in 2D cross double slit experiments and which way 2D cross double slit experiments, photons propagate along trajectories in the far field, and behave as particle and distribute as wave. http://pubs.sciepub.com/ijp/9/3/1/ijp-9-3-1.pdf double slit experiments comprehensive double slit experiment cross double slit experiments which way double slit experiments which way cross double slit experiments de Broglie-Bohm theory trajectory theory