This article was automatically translated from the original Turkish version.
When we look at the universe, the stars, galaxies, planets, and gas clouds we observe constitute only a very small fraction of the cosmic whole. Despite all our telescope data, spectroscopic measurements, and electromagnetic wave analyses of observable matter, we know that the majority of the universe remains invisible. This unseen structure is called “dark matter” and “dark energy.” The former is associated with phenomena such as galaxy rotation speeds and clustering patterns, while the latter is defined as a mysterious repulsive force responsible for the accelerating expansion of the universe.
The existence of dark matter was first proposed in the 1930s by Swiss astrophysicist Fritz Zwicky through his studies of galaxy clusters. When Zwicky analyzed the motions of galaxies within the Coma Galaxy Cluster, he noticed that their velocities were too fast to be explained by the visible matter alone. He hypothesized that an unseen mass was gravitationally influencing these galaxies. It became clear that this invisible substance did not interact with light—that is, it neither absorbed nor emitted electromagnetic radiation. Only its gravitational effects could be observed.
Later, Vera Rubin’s work in the 1970s on galaxy rotation curves provided much stronger and more direct evidence for the existence of dark matter. Rubin’s studies showed that stars’ orbital speeds should decrease with distance from the galactic center, yet in reality these speeds remained constant. This implied that stars were surrounded by an invisible but gravitationally detectable form of matter. This discovery laid the foundation for the modern understanding of how dark matter forms a structural skeleton at the galactic level.
However, another equally compelling and mysterious component is dark energy. In 1998, two independent research teams—the Supernova Cosmology Project and the High-Z Supernova Search Team—discovered by studying distant supernovae that the expansion rate of the universe was not slowing down over time, as expected, but accelerating. This surprising observation indicated the presence of an unknown energy in the universe that, despite the presence of matter and gravity, was driving expansion faster. This repulsive force was named “dark energy.”
When dark energy and dark matter are considered together, it becomes clear that only about 5 percent of the universe consists of ordinary matter. The remaining 27 percent is dark matter and 68 percent is dark energy. In other words, everything we consider “normal” in a cosmic sense represents only a small fraction of the universe.
This quest to solve these cosmic mysteries has become one of the foremost goals of modern physics. Yet, the nature of dark matter remains unknown. Some theories propose that dark matter consists of weakly interacting massive particles (WIMPs), while others suggest that lightweight, non-interacting particles called axions fulfill this role.
Alternative approaches even challenge gravitational theory itself, suggesting that “dark matter does not exist; Newton and Einstein may be wrong.”
Similarly, the physical nature of dark energy remains a complete enigma. Although it might be explained by the cosmological constant (Λ), the theoretical value derived from calculations differs from observational values by an astonishing margin—on the order of 10⁶⁰. This inconsistency raises serious questions about how dark energy can be reconciled within classical cosmology.
Modern observational instruments have begun to provide more clues about the nature of these two dark components. For example, the European Space Agency’s Planck satellite measured the cosmic microwave background radiation with high precision, delivering highly accurate data on the universe’s composition. The James Webb Space Telescope may offer indirect insights into the structure of dark matter by enabling a clearer understanding of galaxy formation processes.
All this information brings us face to face with the same fundamental reality: The majority of the universe is invisible. Humanity can understand only a small fraction of the physical universe and still lacks a clear answer to what these vast “dark” components are. But one thing is clear: Without understanding this unseen universe, we cannot truly comprehend how the universe functions.
Today, we conduct experiments in underground laboratories using dark matter detectors and study gravitational lensing of galaxies to understand the effects of dark energy. The visible face of the universe is no longer sufficient. Pursuing the remaining 95 percent has become the greatest scientific challenge of our time.