Question

Inflation

(a) What is the cosmic epoch of inflation in the early universe? How is this different from the usual expansion of the universe?

(b) What similarities and differences are there between inflation and dark energy?

Answer 1

a)Inflation is a period of supercooled expansion, when the temperature drops by a factor of 100,000 or so. (The exact drop is model-dependent, but in the first models it was typically from 10²⁷ K down to 10²² K. This relatively low temperature is maintained during the inflationary phase.This process is so much fast that all such thing happen from 10⁻³⁶ seconds after the conjectured Big Bang singularity to some time between 10⁻³³ and 10⁻³² seconds after the singularity.(exponential expansion)

But the usual expansion is slow and follows the Hubble law.

b)Dark energy is believed to be a property of space-time itself, a sort of inherent "pressure of the vacuum". It appears directly in the equations of General Relativity which have nothing to say about fields or particles, just about the properties of spacetime and it's relation to the presence of mass in it.
So it is believed to be constant in time and space, everywhere and at all times.

Inflation on the other hand is postulated to have been caused by a field (the inflation) which underwent a phase transition generating a lot of energy in the form of inflation particles which created an enormous repulsive force during very short time, then decayed into the normal particles of the standard model we find around us. So it's nothing constant, it happened just once.

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