Cosmologists believe that the universe started much smaller than it is now — a nearly infinitesimal point. The unfathomably rapid expansion during the first moments of our universe’s existence is called the Big Bang.
According to the Big Crunch theory for the ultimate end of the universe, the expansion of the universe will reverse, leading to a massive collapse. This would effectively be like an inverted Big Bang.
A likely outcome for our universe is that as stars continue to die, the universe will slowly cool down, eventually decaying into a cloud of particles. This cosmological outcome is called the Big Freeze.
A dramatic theory for the end of the universe, called the Big Rip, predicts that the universe will expand at an ever increasing rate. This would cause every atom in the universe to be violently torn apart.
Telescopes that are sensitive to electromagnetic radiation in the microwave range can detect a faint signal from all directions in outer space. This signal, called the Cosmic Microwave Background Radiation (or CMBR for short), is a faint remnant from the early history of the universe. It is significant evidence for the Big Bang.
Cosmology is a field of physics devoted to understanding questions about the large-scale structure and evolution of the universe. The generally accepted theory for the origin of the universe is the Big Bang. Three possible outcomes for the future of the universe are the Big Crunch, the Big Rip, and the Big Freeze. Cosmology also encompasses the study of dark matter and dark energy.
For some reason, despite the predictions of our current theories, the universe is expanding faster and faster in all directions. This strange fact has been attributed to dark energy, an elusive substance currently at the cutting edge of physics research.
Physicists have measured unmistakable gravitational effects in the universe where there isn’t any matter to cause it. This invisible substance, called dark matter, can be found in galaxies in large quantities, and has an unknown constitution. One theory proposes that dark matter is composed of weakly interacting massive particles (WIMPs).