What's in the universe?
The universe has big things like Galaxies and small things like cosmic rays. The universe has crazy things like black holes. The universe has our Solar System and other Planets orbiting other suns or Stars. There are gas clouds that will later condense to form new stars and planetary systems in the future. And there may be other intelligent life in the universe. Scientists don’t know yet.
Astronomers and applied physicists have one main theory as to how the universe was formed: one "Big Bang," where everything existed as one "superdense" speck which then exploded, creating first gravity, then electromagnetism, the strong force, and the weak force. The universe has been expanding ever since. We know the universe is expanding because astronomers can tell that other galaxies are moving away from our galaxy. Galaxies that are further away recede faster. Why there is more matter in the universe than antimatter (1,000,000,001:1,000,000,000, to be exact) is still a mystery.
Possible grand finales
Our universe might end in a variety of ways:
- A "Big Rip," when all atoms are torn apart by the expiration of the strong force
- A "Big Crunch," when the Universe falls back upon itself into another superdense speck. This is very unlikely because a repulsive force is making the universe expand at ever-increasing rate.  
- A "Big Freeze," when all energy is expended. You see, the gammar and X-rays were the only waves around at one point, but eventually they expanded into visible light (light... duh) and infrared (heat). One day, they may expand into very long wavelengths that cannot be used for energy.
- A "Big Expand," when the Universe keeps expanding as it is today until all atoms are extremely far apart
- A "Big Flood," when neocons destroy everything. They may yet. See Flat earth society and/or Young Earth Creationism
The last item is a real scientific theory?