Based on Einstein's equivalence principle (EEP), a method of describing the gravitational field by the special relativity formula is proposed. The equation for the transformation of the coordinates between the spacetime point of the gravitational field and the inertial reference system is derived. The conclusion that the mass of an object in a gravitational field follows the strength of the gravitational force is obtained. The gravitational drive (curvature drive) effect is briefly described, and it is pointed out that the gravitational drive effect is the source of the dark energy of the Universe. The gravitational drive effect is calculated to produce a negative pressure of matter on the cosmic scale, with a ratio of pressure to energy density of -2/3. It is also calculated that the rotation of the Earth is faster at aphelion than at perihelion under the gravitational drive effect, and that the length-of-the-day (LOD) is reduced by 0.02851 milliseconds. It is analysed that as the solar system orbits the Milky Way, the Galactic plane, the Galactic centre and the Great Attractor all have an effect on the Earth's mass variation, causing a periodic change in the Earth's mass, which we call a tidal wave of mass. Thus, a galactic year can be divided into four seasons, spring, summer, autumn and winter, according to the influence of the galactic gravitational field environment on the Earth. The Earth is currently in the autumn of the galactic year and is losing mass under the influence of tidal waves of mass caused by gravitational changes in the galactic plane and the galactic centre, which is making the Earth's climate hot and arid. In the future, when the Earth's mass stops decreasing, it will rapidly increase under the influence of tidal waves of mass caused by Great Attractor, and the survival of humanity will be severely tested. We therefore need to establish a broad international cooperation to unite humanity to face the challenges posed by the coming universe.