Over the years, scientists have attempted to describe the formation and evolution of the universe. Their conjectures have successfully explained some of the many phenomena in the cosmos. This has led to a modified version of a theory explaining the evolution of the universe.

The well-known Big Bang model has faced two major obstacles: the flatness and the horizon problem. Firstly, it fails to explain the observed flatness of the universe. Using basic geometry, if we take two bright points from the Cosmic Microwave Background (CMB) and the third point being Earth to construct a triangle, we can measure the angle. If the sum of angles is 180 degrees, then the surface should be flat. This is how we deduce the apparent flatness of the universe.

Secondly, we know from the CMB that the temperature is uniform across the known universe. However, there was no explanation of how two particles located outside the horizons of each other were able to reach such equilibrium. This is called the Horizon problem.

In 1980, Alan Guth proposed the inflation model of the universe to modify the Big Bang theory. The inflation model suggests that the universe underwent an immensely rapid expansion by a factor of 10^26 in just a fraction of a second prior to the Big Bang. Inflation successfully clarifies the flatness and horizon problems.

The flatness problem is solved when the universe is exponentially inflated to an enormous scale, flattening out the curved geometry. The space gets flattened in a similar way to the surface of a balloon, which gets flattened when it gets bigger. The huge expansion smooths out the curvature and drives critical density close to 1 which gives flat geometry.

The inflationary model assumes that the particles were initially compact and in causal contact with each other in a region smaller than the horizon, allowing them to reach thermal equilibrium and achieve uniformity. Then that region expanded so rapidly that the particles were scattered in the distant parts of the universe observed today. The premise that the far-off homogeneous particles in the CMB radiation map were initially in close contact with each other explains the common temperature across the universe.

The inflation model is based on initial conditions that lead to results consistent with CMB radiation data and redshifts; hence, it has become a rather concrete foundation for cosmological predictions.

References:

1. Guth, A. H. (2007). Eternal inflation and its implications. Journal of Physics A: Mathematical and Theoretical, 40(25), 6811-6826.
2. Schutz, B. F. (1985). A first course in general relativity (Vol. 2). Cambridge university press.