The Enormous Expansion of the Universe: Insights from the First Second of the Big Bang

Since the Big Bang, which occurred approximately 13.8 billion years ago, the universe has undergone significant expansion. To better understand the scale of this expansion, especially in the first second after the Big Bang, cosmologists rely on the concept of the scale factor.

Scale Factor in Cosmology

The scale factor in cosmology describes how distances in the universe expand over time. At the time of the Big Bang, the scale factor was defined as 0, and it increases as the universe expands. Today, the scale factor is normalized to 1.

Expansion Rate and Early Universe

By only 1 second after the Big Bang, the universe had already expanded tremendously, despite the universe being in a hot, dense state at that time. Estimates suggest that the universe's scale factor at that point was around (10^{-6}) to (10^{-5}) of its current size. The exact scale factor is difficult to quantify precisely due to the dynamic nature of cosmic expansion.

Overall Expansion and Current Size

Since the first second after the Big Bang, the universe has expanded to a point where it is roughly 100 billion times larger than it was back then. This means that if we consider the universe's size at 1 second after the Big Bang to be a tiny fraction of its current size, the difference is substantial — by many orders of magnitude.

Unprecedented Expansion in Microscopic Time

On an almost microscopic time interval, the size of the cosmos expanded dramatically. In just a fraction of a second, going from a diameter of (10^{33}) centimeters (the Planck length) to one of orders of magnitude greater than the diameter of the observable universe, the universe grew immeasurably. This expansion is a fundamental aspect of the early universe's dynamics.

Unknowns in Universe Expansion

The answer to the question of how much has the universe expanded remains uncertain to some extent due to several factors:

The actual size of the universe is unknown beyond the observable universe, which is tens of billions of light-years across. It is widely believed that the universe may be infinite, although the extremes are impossible to measure. Expansion can be considered in terms of ratios. The scale factor is the ratio between distances on a large scale at some point in time and the distances today. It is observable and defined even if the universe is infinite. General relativity, based on Einstein's theory of gravity, provides the standard cosmological model with a scale factor, but this model has limitations in how it handles singularities.

Dark Energy and the Future of the Universe

The acceleration of the universe's expansion, discovered in the 1990s, is one of the most surprising findings in modern cosmology. General relativity suggests that space is under a slight tension called 'dark energy,' which is responsible for the acceleration. Although the matter in the universe initially slowed down the expansion, dark energy has now become the dominant force, preventing the expansion from decelerating.

As the universe continues to expand, it appears that the rate of expansion will not slow down. This indicates that the universe will continue to grow at an increasing rate, shaped by the ongoing influence of dark energy.

Understanding the universe's expansion helps us glimpse the vastness and complexity of our cosmic home. While precise measurements and full comprehension are challenging, the ongoing exploration of these mysteries is key to advancing our knowledge of the universe.