The Big Bang

Introduction

How did the universe begin and when? How has it developed? How will it end and when? These questions have occupied astronomers' minds for centuries. They think they know how the universe has developed from the first millisecond till now. Astronomy doesn’t know for sure how the universe will end.

The expanding universe

About 1915 no one was sure if other galaxies were part of our galaxy. Later Edwin Hubble proved that there were other galaxies besides our galaxy. All the galaxies are moving away from us. This means that the universe is expanding. From this you can conclude that the universe used to be smaller. When you look even further back you will see that all substance was packed up in one spot.

You can picture this as a balloon with little dots. The balloon is the universe and the dots are the galaxies. When the balloon is blown up bit by bit, the universe is growing and the galaxies are moving away from each other.

People think that the universe started as a result of a gigantic explosion, the big bang, which started the current expansion of the universe.

After the Big Bang

The big bang was not a normal explosion, in which matter is hurled into the surrouding space. After all there was nothing before the big bang – no matter, no energy, no space and no time. The universe didn’t exist. Matter, energy, space and time originated in the big bang. Probably the big bang took place about 15 billion years ago.

A millionth second after the big bang there was a temperature higher than 10 billion degrees Celcius (!). The universe was filled with energy in the form of photons (little packages of radiation or radiation parts). Under some circumstances photons can change into matter. This happened at the birth of the universe. After that, most of the photons changed back to radiation, but the remaining part formed the atomic parts that form the universe as it is now. When the universe was 10 seconds old, all the protons, neutrons and electrons had already been formed.

Immediately the universe started to expand and cool down. After 3 minutes the temperature was "only" 1 billion degrees Celsius. There was a chemical reaction between the protons and the neutrons. After the reaction kernels of atoms developed, like helium.

After a couple of thousands of years the temperature had decreased to about 3000 degrees Celsius. The effect was that the protons and the electrons melted into hydrogen atoms and the helium kernels became helium atoms. Furthermore the universe became transparent because it was still expanding.

These days the radiation in the universe is giving a temperature of about –270 degrees Celsius or 3 Kelvin. That is only 3 degrees above the absolute zero.

The future of the universe

Almost all the astronomers think that the universe started with a big bang and has afterwards developed itself. However, they don’t know what the future will bring. The universe will probably keep on expanding for some billions of years, but if it will always go on in this way is still a question.

Most astronomers think that the universe will go on expanding. They speak about an open universe. There are also astronomers that think that there is enough matter to stop the expansion of the universe. They speak about a closed universe. The universe will collapse and will end in a big "shrink". After that there could be a new big bang and the story will start all over again from the beginning.

Big Bang | Stars | Nebulas | Galaxies | TMR-1C