Physics Final Project- The Universe

The Universe. Defined as everything that exists. 

First, some history. The earliest quantitative models of the universe were developed by the ancient Greeks who thought that the universe had infinite space and had existed eternally, and rotates around the earth. The next models included Copernicus's heliocentric model and the Newtonian model of the Solar System. More and more improvements in astronomy led to the realization that the Solar System is within in a galaxy composed of billions of stars, the Milky Way, and that other galaxies exist outside of it.

Next is the Big Bang theory, which says that the universe expanded from an extremely hot, dense phase called the Planck epoch. Since then, the universe has been expanding to its present form. Recent observations show that this expansion is accelerating because of dark energy, and that most of the matter in the universe may be in a form which cannot be detected by present instruments. This is called dark matter.

Recent observations show that the age of the universe is 13.75 billion years, and that the diameter of the observable universe is at least 93 billion light years. It is unclear whether the size of the universe is finite or infinite.

Some theories have proposed that this universe is only one in a set of disconnected universes,  known as the multiverse. There is no possible way for anything in one universe to affect another universe. The disconnected universes are physical, in the sense that each has its own space and time, its own matter and energy, and its own physical laws. The concept of a multiverse of disconnected universes is very old. 

There are two scientific theories in which multiple universes are discussed. First, disconnected spacetime continuum may exist. Second, there are many parallel universes that exist. The universe "forks" into parallel copies, each one corresponding to a different outcome of something that happened. 

And now for some facts about the universe. The Universe could possibly be flat. Based on Einsteins Theory of General Relativity there are three possible shapes of the universe; open, closed, and flat. There isn't a center of the universe. The universe is always expanding in every direction, so there can't be a center. Lastly, the universe was very hot when it was young, and there is a theory that the universe will be very cold as it grows older.