In the earliest moments of the Big Bang, the universe was in an extremely hot and dense state. According to current scientific understanding, the fundamental forces of nature were unified into a single force during this period. At such high temperatures and densities, the energy associated with these unified forces was not yet separated into distinct particles as we know them today.
The term "pure energy" is often used to describe this state because it represents the concentrated form of energy that existed prior to the formation of particles. In the context of the early universe, this energy was not associated with any specific particles or matter. Instead, it manifested as intense radiation and fluctuations in the energy fields that pervaded space.
In modern physics, energy is often understood in terms of various fields and particles. During the initial stages of the Big Bang, the energy was in a more fundamental and undifferentiated state. As the universe expanded and cooled down, the energy gradually transformed into different forms, giving rise to particles and the various types of matter we observe today.
It's worth noting that our understanding of the very early universe and the nature of energy during that time is based on theoretical models and the principles of quantum field theory. While these models are supported by a wealth of observational evidence, including the cosmic microwave background radiation, they are still subjects of ongoing research and exploration in the field of cosmology.