The Hubble scale during inflation refers to the size of the observable universe during the period of rapid expansion known as inflation. It is significant because it determines the size and structure of the universe that we observe today.
The Hubble scale during inflation increases exponentially, which means that the universe expands at an accelerated rate. This rapid expansion is what leads to the large-scale homogeneity and isotropy of the universe that we observe today.
The energy density during inflation refers to the amount of energy per unit of volume in the universe during the inflationary period. It is believed to be extremely high, much higher than the energy density of the universe today.
The high energy density during inflation is what drives the rapid expansion of the universe. As the universe expands, the energy density decreases, leading to a slowing down of the expansion rate.
Scientists have used observations of the cosmic microwave background radiation and the large-scale structure of the universe to study the Hubble scale and energy density during inflation. These observations support the theory of inflation and provide evidence for its role in shaping the universe we see today.