A history of the universe in one screen image.
(Ignorance expands to fill the available space.)
There is no commonly agreed upon description for the beginning of the universe. There is not even a consensus that such a phrase makes sense.
However, as I understand it, cosmologists appear to prefer a description that goes a bit like this.
Ignoring questions involving the very beginning, after a very short period of time there were a large number of subatomic particles flying around and occasionally bumping into one another. The temperature of this primordial soup is in the billions of degrees. Such collisions resulted in a number of subatomic reactions, creating among other things, quarks.
As the universe expands the temperature cools to just a few billion degrees. The quarks combine to form new particles such as protons and neutrons. Further expansion and cooling permits collisions between neutrons and protons that result in the formation of a new combination - a helium nucleus. After a third of a billion years the temperature has cooled to only 3000 degrees. Now electrons are capable of attaching to the nuclei, and we have the first atoms, of hydrogen and helium. Still later collections of particles mass together to form stars and the creation of still more atoms. When these stars then explode (supernova) the force of the explosion creates more atoms (the heavier elements). We now have the building blocks of our present universe. It has taken about 4 or 5 billion years for this sequence to have unfolded.
This may also be written as 4.5x109. But this can be a bit tricky. The word billion means 109 in the United States and 1012 in much of the rest of the world. I am not always sure where Canada is.
There is no ambiguity in the expression 109 (or 1012) but there is ambiguity in the word "billion". Mathematics and language may coexist, but not always happily. Is it no wonder that young children sometimes have difficulty? Be consistent, we say one moment. Be flexible, we say the next. Make up your mind, they say. We can't, we reply.
