1Everything we can see in the universe, from the smallest asteroid to the brightest galaxy, makes up only a small fraction of what actually exists.
2The rest appears to consist of mysterious substances that neither emit nor reflect any light, and therefore remain completely invisible to our telescopes.
3Astronomers call the dominant component dark matter, and they infer its presence solely through the gravitational influence it exerts on visible objects.
4Galaxies rotate so rapidly that, without enormous quantities of unseen mass, their stars would fly apart into the emptiness of intergalactic space.
5Something invisible must be holding them together, providing far more gravitational pull than all their shining stars and clouds of gas combined.
6Dark matter also bends passing light from distant galaxies, creating distorted images that reveal where the hidden material must be concentrated.
7Physicists have built detectors deep underground, shielded from cosmic rays, hoping to catch a single dark matter particle colliding with ordinary atoms.
8So far, every experiment has returned empty-handed, deepening one of the most perplexing puzzles in the whole of modern science.
9Some researchers suspect the missing matter consists of exotic particles produced in the first moments after the birth of the universe.
10Others argue that our theory of gravity itself may be incomplete and requires revision on the grandest cosmic scales.
11Whatever the answer turns out to be, solving this mystery will fundamentally reshape our understanding of matter, energy and cosmic evolution.