Dark matter is a hypothetical form of matter that cannot be seen directly, but whose presence is inferred from its gravitational effects on visible matter. Dark matter makes up about 85% of the matter in the universe, but we don’t know what it is made of.

There are two main theories about what dark matter is. One theory is that it is a new type of matter that does not interact with light or other forms of electromagnetic radiation. This type of matter would be invisible, but its presence would be inferred from its gravitational effects on visible matter.

The other theory is that dark matter is made up of weakly interacting massive particles (WIMPs). WIMPs are hypothetical particles that interact with gravity and the weak nuclear force, but not with the electromagnetic force. WIMPs would be very difficult to detect, but they would produce a characteristic signal in experiments that search for dark matter.

It is also possible that dark matter is a mathematical correction for our lack of understanding gravity. This theory is called modified gravity, and it suggests that gravity is not as we understand it. Modified gravity theories have been proposed, but they have not yet been able to explain all of the observations that are attributed to dark matter.

The main evidence for dark matter comes from observations of galaxies and galaxy clusters. Galaxies and galaxy clusters rotate much faster than they should if they were made up of only visible matter. This suggests that there is a lot of invisible matter that is providing the extra gravity needed to keep the galaxies and galaxy clusters rotating.

Another piece of evidence for dark matter comes from the cosmic microwave background (CMB). The CMB is a faint afterglow of the Big Bang, and it is a powerful tool for studying the early universe. The CMB data shows that there is more matter in the universe than we can see, and this extra matter is likely to be dark matter.

The nature of dark matter is one of the biggest mysteries in physics. We don’t know what it is made of, but we know that it is there and that it plays a major role in the formation and evolution of the universe.