Relativity, Universe Expansion, and Wave-Particle Duality

The Theory of Relativity: Revolution in the Macrocosm

Einstein published the theory of special relativity in 1905. Space and time are, therefore, a four-dimensional continuum. Einstein generalized this theory with the theory of general relativity. One of the underlying principles of relativity is that nothing can go faster than light, even gravitational interaction. It was, therefore, necessary to develop the theory of gravitation, taking this limit into account. To achieve this, Einstein introduced the idea of a gravitational field. In the proximity of a large body, space is curved, and time passes more slowly. If space is curved, the planets draw an orbit around it. Thus, the theory of relativity explains the orbital motions of the planets.

The Expansion of the Universe

From ancient times, the prevailing idea was that the universe is static; namely, that the planets move. It was Edmund Hubble, not Einstein, who showed that there was no error: indeed, the universe is expanding. This discovery showed that the Milky Way is not the only galaxy in the universe, but one among myriad galaxies scattered like islands through space. These findings obliged scientists to rethink issues such as the dimensions of the universe and its static character. The confirmation of the expansion of the universe generated, in turn, new questions: if the cosmos is not static, but dynamic, it is, therefore, affected by change.

The Wave-Particle Duality

From the research of Einstein and Max Planck, the traditional opposition between matter and energy was destroyed since both can be interpreted and studied by attributing wave and particle nature to them. Traditionally, it was considered that matter is discontinuous and of particle nature. In contrast, according to quantum physics, both matter and energy behave as particles and waves, a deeply paradoxical fact, as wave and particle properties are incompatible. Max Planck discovered that energy is not emitted continuously but in 'packets' or quanta of discontinuous nature. Shortly after, Einstein identified the quanta of light, called photons. Moreover, Louis de Broglie proposed that not only photons but also electrons behave as particles and waves. In this sense, science faced an unexpected problem, which has yet to be solved. In line with this duality of reality, within quantum physics, two alternative but equivalent theories were drawn:

• Werner Heisenberg's Matrix Mechanics: This formulation prefers the interpretation of physical processes as discontinuous processes of particle nature, since such are our observations and the knowledge we can have of them.
• Erwin Schrödinger's Wave Mechanics: This formulation prefers the interpretation of physical processes as continuous processes and, therefore, stresses the wavelike behavior of matter.