The Ancient Revelation: When Did Light First Appear After the Big Bang?

The question of when did light first appear after the Big Bang? has puzzled scientists and thinkers for decades. To understand this conundrum, it's important to delve into the nature of light, the state of the early universe, and the fascinating Cosmic Microwave Background (CMB), also known as the photon decoupling event.

Plasma and Light

Initially, after the Big Bang, the universe was a seething plasma. Atoms did not exist, and the fundamental particles were in a chaotic, dense state. In such a plasma, light was not visible as we perceive it today. Individual photons were instantly absorbed and re-emitted by electrons, making the universe opaque. This is similar to the way we cannot see through the sun's core today. The outer portion of the sun's atmosphere is where we see the light due to the rarefied plasma conditions there.

The Cosmic Microwave Background (CMB)

After the universe inflated significantly, it became less dense and cooler. Around 380,000 years post-Big Bang, the universe became transparent to light. This marked a critical moment known as photon decoupling. At this point, photons were no longer interacting with matter, and they could travel freely through the universe. This event is also referred to as the Cosmic Microwave Background (CMB). The CMB is essentially the light that was released from this moment and it has been traveling through our universe ever since, providing a snapshot of the early universe. It is a fundamental piece of evidence for the Big Bang theory, offering a clear picture of the universe at that critical age.

Understanding Relativity and Dimensions

When contemplating the universe, it's essential to consider relativity and the scale at which it operates. At the scale of our visible universe, absolute time might seem to exist. However, at a scale of a Planck length, absolute time does not exist. This raises intriguing questions about the nature of space and time in the early universe and beyond. For instance, is the universe as we perceive it part of our observable universe, or is it a different dimension or era? These concepts are mind-boggling and suggest that the Big Bang might not be as causative and definitive as some theories propose.

The Eternal Universe

Some scientists propose that light-free photons have always existed, and thus the existence of photons does not have a 'first cause.' This intertwines with the notion that the universe could be infinite, both in time and size, with no definitive beginning or end. The Big Bang, therefore, does not necessarily stand as the origin of light or all cosmic phenomena. Instead, it represents a moment of significant transformation in the state of matter and radiation.

Further Reading

David Weintraub's book, How Old Is the Universe, provides a comprehensive and accessible exploration of the history and methods of astrophysics. It is essential reading for anyone seeking a deeper understanding of the cosmic timeline and our place in the universe.