The nature of dark matter remains an open question in physics. While the prevailing hypothesis suggests that dark matter consists of an, as yet undiscovered, subatomic particle, alternative theories and ideas have been proposed to explain the observed effects attributed to dark matter. Here are a few alternative possibilities:
Modified Gravity: Instead of postulating the existence of new particles, some scientists have proposed modifying the laws of gravity to explain the observed gravitational effects attributed to dark matter. These modifications, such as Modified Newtonian Dynamics (MOND) or Modified Gravity (MOG) theories, suggest that gravity behaves differently on large scales than predicted by general relativity.
Primordial Black Holes: Another possibility is that dark matter is made up of primordial black holes, which are hypothetical black holes that formed in the early universe. These black holes could have relatively low masses and not emit significant amounts of detectable radiation, making them difficult to observe directly.
Axions and Axion-Like Particles: Axions are hypothetical particles proposed to solve certain problems in particle physics. They are very light and interact weakly with ordinary matter. Axion-like particles (ALPs) are similar hypothetical particles that also arise in certain extensions of the Standard Model. Both axions and ALPs have been proposed as candidates for dark matter.
Macroscopic Objects: It is also conceivable that dark matter could consist of macroscopic objects, such as compact astrophysical objects like brown dwarfs, rogue planets, or other massive yet dark astronomical bodies that are difficult to detect.
These alternative explanations for dark matter are actively explored and studied, but it is important to note that the majority of scientific research has focused on the particle-based hypothesis. The search for dark matter particles is ongoing, with experiments such as the Large Hadron Collider (LHC) and dedicated dark matter detectors seeking to directly or indirectly detect dark matter particles and shed light on their nature.