What is the term for the electromagnetic radiation left over from the big bang?

The term for the electromagnetic radiation that remains from the Big Bang is known as cosmic background radiation. This radiation is a remnant from the early universe, specifically from the time when the universe became cool enough for electrons and protons to combine and form hydrogen atoms, allowing photons to travel freely through space. This event occurred approximately 380,000 years after the Big Bang.

Cosmic background radiation is significant because it provides critical evidence for the Big Bang theory, confirming predictions about the conditions of the early universe. It is uniformly distributed across the sky and has a thermal spectrum corresponding to a temperature of about 2.7 Kelvin. This faint glow is detectable in all directions, which offers insight into the overall structure and evolution of the universe.

In contrast, the other terms do not relate to the residual radiation from the Big Bang. The solar nebula refers to the cloud of gas and dust that formed our solar system, dark energy is a mysterious form of energy thought to be responsible for the acceleration of the universe's expansion, and Hubble's law describes the relationship between the distance of galaxies and their recessional velocity, demonstrating the expansion of the universe but not relating to the cosmic background radiation itself.