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

Solution:-

(a)  The cosmic epoch of inflation in the early universe are following-

Radiation Era
(The radiation era lasted for about 50,000 years)

• Planck Epoch
  • First 10^-43 seconds after the Big Bang
  • No current theory of physics (quantum gravity) exists
• GUT (Grand Unified Theory) Epoch
  • After 10^-43 seconds, temperature fell to 10³² K
• Quark Epoch
  • Creation of protons and neutrons continued for about 10^-4 seconds
  • Temperature drops below 10¹³ K, and protons and neutrons are no longer produced in pairs
• Lepton Epoch
  • Ends when the universe is about 100 seconds old
  • During this epoch, the leptons (electrons, neutrinos, and other light particles) are still produced in pairs, because they are light
  • Ends when temperature drops below 1 billion K
• Nuclear Epoch (first few minutes)
  • Protons and neutrons fuse into nuclei
  • By the time the universe is about 15 minutes old, much of the helium had been formed

Difference from the usual expansion of the universe:

Matter Era (Crossover from radiation to matter dominance begins at 50,000 years at a temperature of 16,000 K)

• Atomic Epoch
  • Begins about 50,000 years after the Big Bang
  • Atoms form and remain intact (electrons attached to nuclei)
    • Electromagnetic radiation decouples
    • Cosmic Microwave Background appears
  • Ends 200,000,000 years after Big Bang
• Galactic Epoch
  • Large scale structure and bulk of most galaxies form
  • Lasts from 200,000,000 years to 3,000,000,000 after Big Bang
• Stellar Epoch
  • Stars continue to form up to today
  • Extends into the Dark Energy Era
• Dark Energy Era
  • Today
  • Expansion of the universe is accelerating

(b) Similarities and differences between inflation and dark energy:

Both the inflation field and dark energy are scalar energy fields. One possibility is that the inflation field decayed away to a small residual value that is the current field of dark energy.

Both have negative pressure and drive exponential expansion. The timescales are very different, being around 10−3510−35seconds in the case of the inflation field and around 12 billion years in the case of dark energy.

It is generally supposed that dark energy is at a minimal value since its value is so very small, but it could conceivably decay to an even lower energy state .

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 space-time 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.