By: Alfredo Lopez-Salas
When you look up at the night sky, you see stars, galaxies, and planets—everything that makes up the universe as we know it. But what if I told you that everything we can see, from the smallest atom to the largest galaxy, only makes up about 5% of the universe? The rest is composed of dark matter and dark energy, mysterious substances that we cannot see, touch, or directly detect—yet they shape the very fabric of our cosmos.
Dark matter is a form of unseen mass that exerts gravitational forces but does not emit, absorb, or reflect light. Scientists first hypothesized its existence in the 1930s when astronomer Fritz Zwicky noticed that galaxies in distant clusters were moving much faster than expected. According to Newtonian physics, they should have flown apart, but some unseen force was holding them together—this force was later attributed to dark matter.
Today, we estimate that 27% of the universe is made up of dark matter. But if we can’t see it, how do we know it’s there? One of the biggest clues comes from gravitational lensing, a phenomenon where massive objects (like galaxy clusters) bend the light from objects behind them, similar to how a magnifying glass bends light. The amount of bending suggests the presence of extra mass—dark matter—that we cannot see.
So, what is dark matter made of? While its exact composition remains unknown, scientists believe it could be WIMPs (Weakly Interacting Massive Particles) or axions, both hypothetical particles that interact only through gravity and possibly the weak nuclear force. Physicists around the world, including those at CERN and underground labs like XENON1T, are conducting experiments to detect these particles, but so far, dark matter remains elusive.
Understanding dark matter is crucial because it shapes galaxies and the universe’s large-scale structure. Without it, galaxies would not have enough gravity to hold their stars together. While dark matter remains one of the greatest mysteries in modern physics, its discovery could revolutionize our understanding of the universe, potentially leading to new physics beyond the Standard Model.
As we continue our cosmic quest, one thing is clear—dark matter is out there, waiting to be understood. The universe holds secrets far beyond what we can see, and solving them could change everything we know about reality.
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