Inflation Epoch: Creation to 10-35 seconds
We now come to one of the key events in the very early history of the Universe. Remember that this event is supposed to have happened before the Big Bang.
In a short time, perhaps 10-35 of a second after the Universe was created, the Universe expanded from something smaller than a proton, to perhaps 10 centimeters across.
The inflaton field expanded at constant energy density. This is quite different to our experience today, where energy density falls as space expands. The reason was that the energy came from the inflaton field, which was at its lowest possible energy level. Its energy density could not fall, and so non-zero energy continued to fill the newly expanded space.
Since the volume of the Universe was increasing, but the energy density stayed the same, the total energy in the Universe must have increased. Where did this energy come from? Since (as I have mentioned) nothing could come in from the Multiverse, the energy must have come from the pressure of the inflaton field.
Gravitational Repulsion
It can be shown mathematically that this pressure must have been negative. This created a repulsive gravitational field. Note that this had exactly the same effect as Einstein's cosmological constant. It made all parts of space try to move away from each other. This led to a dramatic increase in the size of the Universe.
The very rapid growth of a region due to the gravitational repulsion created by the false vacuum is called inflation. The increase in size was exponential, that is, the more it expanded the faster the expansion happened. In an incredibly short time the Universe increased in size from a tiny speck to a huge space comparable with the space we see today. It is almost impossible to imagine such a change, the greatest revolution in this whole story.
It is because the Universe inflated that it now seems flat. Space in the Multiverse might have been curved, so that, for example, the angles in a triangle did not add up to 180 degrees. But as the tiny region which would eventually become the Universe was expanded, this curvature was almost entirely flattened out, in the same way as the curvature of the surface of a soccer ball would be almost flattened out if you blew it up to the size of the Earth.
Supercooling of Inflaton Field
Once it was created, the Universe expanded and cooled rapidly to below the critical temperature for the inflaton field. That means that the inflaton field became unstable - that is, it wanted to decay, to stop being zero and get some other value, but could not.
It was similar to a ball balanced on the top of a hill. The ball wants to roll down, but cannot decide which way to roll. We also meet the same situation today in pure water, which can be supercooled below its freezing point without being able to turn to ice, because it cannot decide in which direction the ice crystals should line up.
So for a short time the young Universe continued to expand, and the unstable inflaton field had a very important effect.
Spontaneous Symmetry Breaking
After a very short time, perhaps 10-35 of a second after the Universe was created, the inflaton field gradually began to break down into the four fundamental forces which we find in the Universe today. These four fields are of fundamental importance in our story, so I will examine them in turn in the following sections.
Furthermore, as the symmetry of the inflaton field broke down to produce these four forces, its energy was converted into particles. These now make up the world around us, including ourselves.
This process is called spontaneous symmetry breaking of the inflaton field.
Suddenly the Universe became filled with tiny objects hurtling around at high speed and colliding with each other, their energy changing from one form of particle to another.
