The Expansion of the Universe and the Curiosity of Its Observable Radius

Understanding the expansion of the universe and the concept of its observable radius is crucial for grasping the vastness of space and time. If we consider the Big Bang as the moment the universe began some 13.8 billion years ago, why is the observable radius of the universe approximately 93 billion light years today?

The second figure mentioned in your question is indeed wrong; it suggests the universe being much smaller than the actual observable radius. However, this is a common point of confusion. The observable universe is a vast expanse, and it is only a tiny fraction of the entire cosmic expanse created by the Big Bang.

Expansion of Space

The reason the universe is much larger is due to the expansion of space itself. This expansion isn’t a speed in the traditional sense, so it doesn’t suffer from the speed-of-light limit. Space itself is stretching, much like when you blow up a balloon. As the balloon inflates, the surface area and distances between points on the balloon increase, but objects on the surface do not move at high speeds.

Similar to the inflation of a balloon, the universe is constantly expanding. Therefore, when we observe galaxies, they don’t travel at 46 billion light years. Rather, the distance between us and these galaxies has expanded from a much smaller distance in the past to the current distance. From our perspective, it may appear as if the galaxies are moving away very fast, but in reality, they are not actually moving. It is the space in between that is expanding.

The Role of Light

A significant complication is the role of light in our observations. The light from these distant galaxies has been traveling for roughly 13.77 billion years to reach us. When the light first started its journey, the distances between galaxies were much smaller. As the light traveled through space, the expansion of space increased the distance that the light had to travel. This is why we see these galaxies as being 46 billion light years away, even though the light has only taken 13.77 billion years to reach us.

It is important to note that the observable universe is a sphere with a diameter of about 93 billion light years, but this is just a fraction of the total universe. Estimates suggest that the total universe may be at least 250 times larger than the observable universe, with some estimates even suggesting it could be as large as 1000 times. A light year is defined as the distance light travels in one year.

Conclusion

Therefore, if the Big Bang occurred approximately 13.77 billion years ago, how can the universe be 93 billion light years across? The key is the expansion of space itself. The light speed limitation applies to objects within the universe, but the universe itself can expand at a rate faster than the speed of light. This concept is challenging to grasp but is crucial for understanding the vastness and dynamics of our universe.