The concept of the "Big Bang" refers to the event that marks the beginning of our universe, approximately 13.8 billion years ago. It is important to clarify that the term "Big Bang" does not refer to an explosion that occurred at a specific location in space, but rather it describes the expansion of the universe as a whole.
At the time of the Big Bang, the universe was extremely hot and dense. However, it was not immediately transparent to light. The early universe was filled with a hot, dense plasma of particles and radiation, which effectively scattered and absorbed light. This period is known as the "era of recombination" or the "photon epoch."
About 380,000 years after the Big Bang, the universe expanded and cooled sufficiently for protons and electrons to combine and form neutral hydrogen atoms. This process, called recombination, led to the decoupling of photons from matter. Photons were able to travel more freely through space without being continuously scattered or absorbed.
The photons that were released during this period of recombination have been traveling through the expanding universe ever since. However, due to the vast distances involved, the expansion of space has caused the wavelength of this ancient light to stretch, resulting in a shift towards longer wavelengths. Today, this light is observed as the cosmic microwave background radiation (CMB), which has a characteristic temperature of about 2.7 Kelvin.
So, the reason we haven't observed the light from the exact moment of the Big Bang at Earth's position is that the early universe was not transparent to light during that time. The cosmic microwave background radiation we detect today provides valuable information about the conditions of the universe shortly after the Big Bang, but it does not directly represent the initial moment of the Big Bang itself.