Era 1: Inflation
Isotropy of the CMB
Inflation was not originally part of the Big Bang Model, but was proposed as an addition to the theory in the early 1980's as a way to solve several problems with earlier versions of the model. One problem inflation successfully explains is the almost perfect isotropy of the CMB. Inflation specifies that a very small region of space could rapidly expand to be very large without changing the scale factor. This would have allowed thermal equilibrium to be established on a scale as large as the surface of last scattering.
Flatness of the Universe
The Universe appears flat as a result of inflation.
Another problem that inflation accounts for is the observed flatness of the Universe. To better understand what this means, imagine the Universe is the surface of a ball. As inflation causes the ball to expand, the curvature of the ball lessens as well. Thus, as the Universe expands, it starts to appear flatter.
Due to inflation, space was almost perfectly homogeneous. However, quantum mechanics predicts that on small scales there must be fluctuations in the energy density of space. These fluctuations were on the order of 1 part in 100,000. As they occurred, the rapid expansion of inflation stretched the fluctuations to astronomical scales.
These fluctuations are the seeds that later formed stars, galaxies, and clusters. Our own galaxy is the result of one such quantum fluctuation.
What Happened Before 10-44 Seconds After the Big Bang?
We have no idea. Era 1 has provided cosmologists with several as-of-yet unanswered questions:
- What were the initial conditions for the Big Bang?
- How did the Big Bang start?
- What physical laws applied before the Big Bang?
- What is time?
Unfortunately, inflation appears to wipe out the clues that might help answer these questions. Inflation spreads out any initial conditions so that they are so diluted that the chance of finding anything from before inflation would be like finding a needle in a hay stack.