Space refers to the region where something that makes up this world can exist existentially, and the size of this region is called volume. Then, what exists in space? Our world, the universe, consists of matter and energy, so we can be confident that what exists in space is ultimately composed of matter and energy. Without space, these cannot exist, and space without existence is meaningless.

According to scientific achievements to date, matter has mass, and the interaction between masses (including charged bodies, magnetic bodies, protons, and neutrons) causes a distribution of potential energy in the region, and its spatial gradient appears as a force. This results in the four fundamental forces in nature: gravity, electromagnetic force, strong force, and weak force. In this process, the mass moves to a lower energy level, and the accompanying energy reduction is emitted in the form of motion or waves. (For example, the potential energy of a mass in a gravitational field turns into kinetic energy, and when an electron at a high energy level transitions to a lower one, it emits electromagnetic waves.)

Furthermore, according to quantum mechanics, these (motion and waves) have both particle and wave properties simultaneously. The masses that make up matter have not only particle properties but also wave properties like matter waves, and non-mass bodies such as electromagnetic waves and vibration waves are known to have particle properties (photons, phonons) as well as wave properties. Thus, particles and waves are one entity appearing in two forms. By the same logic, matter and energy are not different things, but rather one entity appearing in different forms. In fact, antimatter exists in the world, and when matter and antimatter meet, they disappear, and the energy corresponding to E=mc² is released. That is, matter has a duality, a symmetry of matter-energy-antimatter mediated by energy.

Then, might there exist antimass bodies that cause phenomena, like the formation of black holes, where masses attract each other and gather in one place due to gravity (universal gravitation), reducing the distance (space) between them, and conversely, create new spaces causing the masses to move further apart (such as the expansion of the universe)? Indeed, the astronomical (physical) efforts to find dark matter to explain the expansion of the universe continue today. Could it be that while masses generate more gravity as they gather, antimasses create more space as they gather?