Periodic Universal Gravitation Resulting in the Phenomenon of Dark Matter and Dark Energy(Recently)

The research on the periodic universal gravitation aims to explain the phenomenon of dark matter and dark energy through periodic universal gravitation. Periodic gravitation is different from Newton’s universal gravitation, since the coefficient of periodic gravitation is the difference of a constant and a cosine function of cosmic age, while the coefficient of Newton’s universal gravitation is a constant. Periodic gravitation and Newton’s universal gravitation are not contradictory, and the latter is approximately correct for a period of time which is decided by acceptance of errors. In the first half of period of cosmic life, the universe expands from the big bang to the maximum. In the later half of cosmic life, cosmic contraction occurs. Energy provided by periodic gravitation is the energy behind cosmic expansion or contraction. Such energy is not an unknown dark energy once it is identified. The space expansion acceleration between the star and the galaxy center is always negative, and then at any time, between the star and the galaxy center exists a mutually-approaching vaccum energy, which is equivalent to dark matter in the center of galaxy. Because expanding acceleration is negative, the expanding speed of space between two stars is always decreasing, so the star under observation is always pulling away from the view direction. Periodic universal gravitation results in periodic cosmic evolution, therefore the end of a period of universe is the beginning of a new one.