The Limits of Our Understanding: Why We Can't Know the Exact Size of the Unobservable Universe

The exact size of the unobservable universe remains a mystery despite our understanding of its age and expansion rate. Several factors complicate our ability to determine its size accurately.

Finite Speed of Light

The most straightforward reason for our inability to estimate the size of the unobservable universe is the finite speed of light. Our observable universe is limited by the speed at which light travels. We can only observe events that occurred long enough ago for their light to reach us since the Big Bang, which took place around 13.8 billion years ago. However, due to the expansion of the universe, the actual distance to the farthest observable objects is significantly greater than 13.8 billion light-years.

Expansion of Space

Since the Big Bang, the universe has been expanding, and as space itself expands, distances between objects that were once close have grown. This means that the distances we calculate based on the age of the universe do not directly translate to the size of the universe. Our current estimate of the observable universe is about 93 billion light-years in diameter, which is a result of this expansion.

Cosmic Horizon

The unobservable universe extends beyond what we call the cosmic horizon, which is the limit of what we can see. Light from regions beyond this horizon has not had enough time to travel to us, so we cannot observe those areas. Therefore, while the actual size of the universe could be much larger than the observable part, we cannot measure it directly.

Cosmological Models

Different cosmological models suggest various possibilities for the overall shape and extent of the universe. Some models propose that the universe is infinite, while others suggest it is finite but unbounded. Determining the size of the unobservable universe depends on the underlying geometry and topology of the universe, which remain theoretical at this point.

Unknown Physics

There are still many aspects of cosmology and physics that are not fully understood, in particular, concerning dark energy and its role in the expansion of the universe. These unknowns significantly impact our understanding of the universe's size and structure.

In summary, while we have good estimates for the age and expansion rate of the universe, the combination of the finite speed of light, the expansion of space, the limitations of our observational capabilities, and uncertainties in cosmological models complicate our ability to determine the size of the unobservable universe. Understanding and overcoming these challenges is crucial for furthering our knowledge of the cosmos.