How does the universe work?

Big Bang theory holds that our universe began 13.7 billion years ago, in a massive expansion that blew space up like a balloon.
Just what is the Universe? It is everything that exists. However, from Earth we cannot observe everything in the Universe. Some things are dark (brown dwarf stars, planets, and Dark Matter) and we cannot see them. Additionally, there are parts of the universe whose light has not yet reached us in this part of the Universe. And because light travels at a set speed we actually look back in time when we look into the cosmos.

There are many questions associated with the creation and evolution of the major constituents of the universe. A basic question astronomers must address is, how did the universe create its first stars and galaxies? Once these entities were created, how did they influence subsequent galaxy, star and planet formation? This is an important question, because these later objects are made of elements that can only have been created by the first generation of stars.
It is still unknown whether the universe created black holes with the first generation of stars or whether these exotic objects were created by the first generation of stars. Because black holes represent the most extreme physical conditions of spacetime and generate some of the most energetic phenomena following the Big Bang, they are the ultimate physical laboratories for testing theories of the universe.
Our universe is both ancient and vast, and expanding out farther and faster every day. This accelerating universe, the dark energy that seems to be behind it, and other puzzles like the exact nature of the Big Bang and the early evolution of the universe are among the great puzzles of cosmology.

There was a time when scientists thought Earth was at the center of the universe. As late as the 1920s, we did not realize that our galaxy was just one of many in a vast universe. Only later did we recognize that the other galaxies were running away from us — in every direction — at ever greater speeds. Likewise in recent decades, our understanding of the universe has accelerated.
The universe is filled with stars, galaxies, planets and more, plus a veritable buffet of invisible stuff like dark matter astronomers have yet to see. But scientists have pinned down some of the major ingredients of our universe.
In 1929, the American astronomer Edwin Hubble found hard evidence that the universe was expanding.If the universe is expanding, it must once have been much smaller than it is now. This realization led to the Big Bang theory: the idea that the universe began as something incredibly small, and then expanded incredibly quickly. We can see the "afterglow" of the Big Bang even today, in the cosmic microwave background radiation – a constant stream of radio waves, coming from all directions in the sky.