History of the Universe

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Big Bang 10-36 seconds


As the inflaton field decayed, so its energy was transformed into not just the energy of the four fundamental fields but also into tiny little bundles of energy called particles. Very rapidly the young Universe became full of these objects.

Everything around us, including ourselves, is made of particles. Therefore it is both important and interesting to understand what particles are and what they are made of. In the following sections I will examine the most important ones.

The first thing to note is that particles are extremely small. Even on Soccearth, particles would be far too small to see. Particles have properties such as mass and electric charge. They are subject to the four fundamental forces we have just seen.


In the young Universe, the particles moved about very quickly and collided with other particles very often. This movement energy is what we normally call heat. The young Universe was very hot. This state of hot particles filling the Universe is called the Big Bang.

So far, our account of the creation of the Universe has been theoretical, based on incomplete theories and a lot of speculation. But now we leave the realm of speculation and enter the realm of scientific observation. The Big Bang is not just predicted by theory but is supported by evidence.

So what is the evidence that the Big Bang actually happened?

Evidence for Big Bang

There are four main pieces of evidence.

1.  As we saw earlier, there is strong astronomical evidence to believe that the Universe is expanding. The most likely way for this to have started is with an explosion.

2.  The Universe is bathed in very weak radiation which is almost uniform in all directions (the Cosmic Microwave Background Radiation). This is exactly what we would expect if the Universe was much smaller and hotter in the past. It's the echo of a very bright flash of X-rays, now stretched out and weakened but still visible as interference on a TV when it is not tuned to any station!

3.  The ratio of hydrogen to helium we now see in the Universe is exactly what we would expect if the Big Bang theory was correct.

4.  Ignoring "small details" such as planets and galaxies, the Universe is more or less the same everywhere, exactly as science would predict if it had started from a tiny point.

It was Russian-American George Gamow who (working with others) realized points 2 and 3, and he is widely credited with establishing the Big Bang theory in the popular imagination, although not the name. The name was coined by British astronomer Fred Hoyle, although he personally did not believe the theory and used these words with a derogatory tone of voice.

So the Big Bang was filled with hot particles. Now the time has come to examine them in more detail.

Standard Model

Our current understanding of the nature of particles is called the Standard Model. This tells us that particles occur in two basic types called quarks and leptons.

Quarks dominated the Universe during the Quark Epoch, and leptons were more abundant in the Lepton Epoch.

We give a little more detail about the Standard Model in the Reference Section. However we know that it is incomplete. For example it does not explain what Dark Energy is.

Dark Energy

The date is 1999. Members of the Supernova Cosmology Project are using the light from distant supernovae to measure the history of the expansion of the Universe. To their astonishment, contrary to all expectations, they find that the rate of expansion is increasing. The Universe is getting bigger at a faster and faster speed.

Up until that date, cosmologists had assumed that the rate of expansion would be slowing down due to the force of gravity tending to shrink the Universe. So what can account for this apparently increasing rate of expansion?

The cause is disputed but the most widely accepted explanation is that the Universe is filled with some unknown form of energy that fills all space and causes a repulsive force which makes the Universe expand faster and faster. Because we cannot detect this energy directly it is called Dark Energy.

Dark Energy must be enormous. It seems to be responsible for about 75% of the total energy in the universe.

Notice that Dark Energy seems to be a scalar field, very similar to the inflaton field which filled the young Universe and caused inflation.

In addition to dark energy, there is another mysterious source of mass-energy called Dark Matter.

Until we solve the mysteries of Dark Matter and Dark Energy, our understanding of the earliest moments of the Universe must remain incomplete and provisional.

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History of the Universe eBook
History of the Universe eBook
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Written by Wyken Seagrave
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