the universe is expanding every second...
Radiation started with the initial moment of the Big Bang, continues ever since, and will continue as long as there is a universe.
the big bang theory
Still now the most acceptable theory on the origin of universe has been the big bang theory. you can get more info on big bang theory from wikipedia.
Basically, all energy that currently exists in the Universe was there from the start - i.e., from the moment of the Big Bang. It is not currently known what caused the Big Bang, or where the energy came from.
Since the Big Bang
In the current model of the universe the big bang was the 1st thing to happen in the universe since time itself was created in the big bang.
The universe began rapidly expanding and cooling. This expansion was NOT an explosion because there is nothing around the universe for it to explode into.For what it is worth the Big Bang never ended, it is still happening.
The distance is getting larger as the universe expands.
All the energy that is now in the Universe was there since the time the Universe started - that is, since the Big Bang.
Right after the big bang happened, the universe was expanding at a speed of light. While it was expanding, it started to cool itself down since the big bang caused the universe to heat up to ridiculous temperature.
The big bang began the expansion of spacetime with great rapidity. The Universe began with the Big Bang. In other words both space and time began at the big bang. The big bang started the Universe from the point t=0.
Our concept of the "big bang" has no explanation about how or why, but our hypothesis is that there was NOTHING before the Big Bang created the universe.
The big bang was the BEGINNING of the universe so there was no temperature before it :P
The Universe! Initially everything was crammed into an infinitesimally small point but since the Big Bang all the matter and energy that make up our Universe has been expanding outwards.
The Big Bang Theory tells what happen at the begning of the universe. How the Earth comes into the universe
Current theory is the Big Bang
Everything. Although technically, the Big Bang is still happening.