Unveiling the Unveilable: Measuring the Observable Universe

One of the most profound questions in cosmology is: how can we measure the size of the universe if there is no edge to it?

That is correct: we cannot see the end of the universe; hence, it is often considered to be infinite in size. However, our current understanding of the universe is limited to what we can observe. This observable universe has tangible limits, even if the entire universe itself might be infinite.

Two Interpretations of the Universe

The term "universe" can refer to two distinct concepts:

Universal Space: This is the vast expanse beyond our local observable universe, which continues indefinitely without an identifiable end. Observable Universe: This is the portion of the universe that we can actually observe, limited by the speed of light and the age of the universe.

For this discussion, we focus on the observable universe, a concept fundamental to modern cosmology.

Understanding the Observable Universe

Universe

The Cosmic Microwave Background Radiation (CMB)

To measure the size of the observable universe, we start by looking back to the cosmic microwave background radiation (CMB). This radiation is a remnant of the Big Bang and provides crucial information about the early universe. The CMB was emitted approximately 380,000 years after the universe's inception, which is a mere 300,000 years after the Big Bang.

Distance and Redshift

The CMB is observed from a distance of about 13.8 billion light-years from our vantage point. However, the universe has been expanding since then, and this expansion is a significant factor in determining the actual size of the observable universe.

The light from the CMB takes 13.8 billion years to reach us, but the universe has been expanding during that time. Therefore, the point where those photons started their journey is now even further away than 13.8 billion light-years due to cosmic expansion. The rate of expansion is influenced by the density of the universe, and with ongoing observations, we have developed a fairly accurate understanding of this density.

Calculating the Observable Universe

Using current scientific models and observations, it is calculated that the size of the observable universe is approximately 94 billion light-years in diameter. This is based on the idea that light travels in a spherical pattern from the initial point of emission, which has been expanding over time.

The actual distance from us to the CMB is around 47 billion light-years, again considering all directions. This measurement reflects the direct travel of light and the expansion of the universe since the CMB was emitted.

Conclusion

While we can never truly measure the entire universe, we can determine the size of the observable universe. This observable universe is finite but vast, expanding with the ongoing expansion of the universe itself. As new observations and technological advancements are made, our understanding and measurements of this observable universe will continue to evolve.

Note: The universe may be infinite, but our ability to measure it is constrained by our current scientific capabilities and the speed of light.