An entity is something that has a distinct, separate existence, a basic matter part. So if we understand the entities of the universe as the basic and indivisible pieces that the Universe is made of, we have to be careful, since our knowledge has changed in the history of science a few times.

Scientists have believed they had reached the smallest parts that the Universe is made of in several occasions. That’s the origin of the word “atom”, which means indivisible. We thought we had reached the basic entity at least, but not for very long. Soon we realized that atoms were made of even smaller entities themselves. We discovered the elementary particles which atoms are made of. Once more we thought we had reached the bottom. And once more we were wrong. We discovered that some elementary particles were made of even smaller entities called quarks. There are some theories today that say that we are not even close to the final answer. The famous String theory is one of theses. We’re working on it.