Vacuum

In inflationary theory, the Universe started from almost nothing. What do we mean by nothing? We mean a space which is almost empty: a vacuum. But what is a "vacuum"?

The word is widely mis-used. For example, we talk about a "vacuum cleaner". But such a device works by creating low pressure and depends upon atmospheric pressure to move the air. A vacuum cleaner does not really create a true vacuum.

True Vacuum

A true vacuum is a space which is completely empty. It has the lowest possible energy.

But, according to inflationary theory, the very young Universe was not like that. Yes, it contained a vacuum, but it was not completely empty: it was not a true vacuum.

False Vacuum

The young Universe appeared stable, that is, it seemed to be at the lowest possible energy state, and yet it was not empty. Instead it contained some energy. This state is described as the false vacuum.

Illustration suggesting how a false vacuum may contain some energy

In fact, far from being empty as a true vacuum is, the false vacuum contained a huge amount of energy packed into a very tiny space. The energy density was much higher than anything we see in the Universe today.

Scientists propose that the very young Universe contained something they call "a field", so next we will examine what a field is.