What is dark matter and why can't we see it?

The answer

Dark matter is a mysterious substance that makes up about 27% of the universe's total mass-energy content (85% of all matter). It doesn't emit, absorb, or reflect light, making it invisible to all telescopes. We know it exists because its gravitational effects are unmistakable: galaxies rotate too fast, galaxy clusters are too massive, and the cosmic web's structure can only be explained by vast halos of invisible matter. Despite decades of searching, dark matter particles have never been directly detected. Leading candidates include WIMPs and axions, but its true nature remains one of physics' greatest mysteries.