BIG BANG theory


The universe began with an unimaginably enormous density and temperature – a singularity, which then started inflating over the next 13.8 billion years to what we now know to be the cosmos.

When the universe was 10-34 of a second old, space itself expanded faster than the speed of light. As space expanded, the universe cooled and matter formed. In the first second after the universe began, the surrounding temperature was about 5.5 billion degrees Celsius (10 billion Fahrenheit). During the first three minutes of the universe, the light elements were born during a process known as Big Bang nucleosynthesis. Because of the high temeprature light could not carry inside this early soup – it was too hot for it to shine. Over time the free electrons met up with nuclei and created neutral atoms. About 380,000 years after the Big Bang, was the initial flash of light, the ‘afterglow’.

That, so called, ‘afterglow’ is more widely known as CMB (cosmic microwave background). In other words, this is the heat from that first flash that we can now detect. Astronomers see this glow everywhere in the sky. However, from this point on, the universe was plundged into darkness – otherwise known as the cosmic dark ages.

About 400 million years after the Big Bang, the universe began to emerge from the darkness during the epoch of reionization, during which clumps of gas collapsed enough to form the first stars and galaxies, whose energetic ultraviolet light ionized and destroyed most of the neutral hydrogen.

As the universe was gradually slowing down, about 5 or 6 billion years after the Big Bang a mysterious force began speeding up the expansion of the universe, a phenomenon that continues to this very day. This mysterious force is now know as dark energy – one of the biggest mysteries in science.



Big Bang theory says that at first everything in the universe was in a sinlge point of infinite density. This point is called a singularity. Then that singularity expanded into what we now know as the universe.

The Big Bang certainly wasn’t an explosion, as one would imagine. It was an enormous expansion known as inflation. The analogy of the surface of a balloon is often proposed as an explanation to what the stretching of the universe ‘looks like’. Imagine that you put spots on the surface of the balloon. As the balloon stretches, while being blown up, the spots grow apart. From this many people derive the idea that the universe is spherical in shape. However, the interior of the balloon has no meaning in this analogy and, therefore, the surface shape (spherical in this case) is only one possibility.

This is the only theory that successfully explains the observations made by astronomers. All conclusions are based on those observations.

  • Astronomers see galaxies moving apart from one another – space in the universe is stretching. Which means that at some point in the past galaxies were closer together.
  • Astronomers see a remarkably uniform microwave glow everywhere in the sky; this is the heat left over from an earlier time, when the universe was very hot. This was predicted by the Big Bang theory BEFORE it was discovered!
  • Astronomers measure how much of each of the lightest chemical elements (like hydrogen, deuterium, and lithium) are in space; their abundances agree with what was calculated to have been in an earlier time when the universe was so hot that it was like a nuclear fusion reactor, building up the lightest elements. The heaviest elements (like carbon and nitrogen) were made later in stars. Stars are mostly made of hydrogen.

The Big Bang theory explains the most basic observed properties of our universe. It is one of the most strongly supported theories in all of science. It explains the observed facts; it has made successful predictions; it has stood the test of time; and there is no alternate theory that the professional scientific community deems valid.


SPACE.COM – What is the Big Bang theory?
SPACE.COM – Our expanding universe: age, history & other facts
NASA – Universe 101

This entry was posted in Science & Astronomy and tagged , , , , , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s