This image shows how one artist has drawn the Big Bang. The Big Bang is a theory that explains the origins of the Universe through a massive explosion.
Click on image for full size
Windows original.

The History of the Universe

The theory that best explains the current universe is the Big Bang theory. This theory states that, in the beginning, the universe was all in one place. All of its matter and energy were squished into an infinitely small point, a singularity. The laws of physics which applied at that instant are not understood at all. Something unknown caused the universe to explode, and thus began the expansion that we see today.

The early universe was small, so everything happened very quickly compared to the timescales on which events happen for the present universe. At the start, the universe was very small and dense. This stage was called the primordial fireball. For the first second, only elementary particles, such as protons, neutrons, and electrons, could exist. But the universe quickly cooled and expanded. For about the next 500,000 years, electromagnetic radiation (light) was the most important thing in the universe and hence this time was known as the radiation era. When the universe had cooled to the point where the simplest atoms (hydrogen) could form, radiation no longer dominated and matter took over. The cosmic microwave background radiation was produced at this time. So began the matter era in which the universe exists now.

So how old is the universe? There is much debate over the current age of the universe among astrophysicists. But everyone agrees that it is somewhere between 10 and 20 billion years old.

Last modified May 6, 2008 by Randy Russell.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

NASA Launches Satellite to Study Big Bang

NASA launched its newest satellite on June 24, 1999 from Cape Canaveral.The Far Ultraviolet Spectroscopic Explorer (FUSE) began its mission aboard the new Delta II rocket, which helped get the satellite...more

Pretty Lenses are Caught by Hubble

The NASA Hubble Space Telescope has recently found some awesome mirages produced by lenses in space. These lenses act as giant magnifying glasses for the Universe. A lens is produced when a large object...more

Capturing the Afterglow of the Big Bang

There is a radiation that fills the universe, called Cosmic Microwave Background Radiation (CMB). CMB radiation is the heat left over from the time after the Big Bang, when the universe was really hot!...more

Capturing the Afterglow of the Big Bang (Updated!)

Some of the best news of the week is that the Microwave Anisotropy Probe (MAP) was launched successfully last Saturday! Liftoff on its Delta II rocket occurred on time on June 30, 2001. The MAP teams says...more

The Oldest Light in the Universe

NASA scientists have taken a "snapshot" picture of the oldest light in the universe. The picture shows what is left of light given off during the big bang. The light is over 13 billion years...more

Element (Chemical Element)

An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more


Isotopes are different "versions" of an element. All atoms of an element have the same number of protons. For example, all hydrogen atoms have one proton, all carbon atoms have 6 protons, and all uranium...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA