Can CMB show that the universe was accelerating at the time the CMB formed thus measuring dark energy early in the universe?
The cosmic microwave background (CMB) radiation is the relic radiation from the Big Bang. It provides us with valuable information about the early universe and its evolution. While the CMB itself does not directly measure dark energy, it allows us to indirectly study the expansion rate of the universe, which is influenced by dark energy.
The key quantity related to the expansion rate of the universe is the Hubble parameter (H), which describes how fast the universe is expanding. In the early universe, the expansion was primarily driven by matter and radiation. However, as the universe aged, the influence of dark energy became significant, causing the expansion to accelerate.
To study the expansion rate at different times, scientists use techniques such as measuring the temperature anisotropies in the CMB. These temperature fluctuations provide information about the state of the universe when the CMB was emitted.
By analyzing the pattern of these temperature fluctuations, scientists can extract a quantity known as the angular power spectrum. This spectrum represents the distribution of temperature fluctuations at different angular scales on the sky.
The angular power spectrum reveals the fluctuations created by various physical processes in the early universe. It can be used to constrain cosmological parameters, including the expansion rate of the universe. By comparing the observed angular power spectrum to theoretical predictions, scientists can estimate the matter and energy content of the universe, including the influence of dark energy.
While the CMB alone cannot directly measure dark energy, it plays a crucial role in constraining cosmological models and confirming the existence of dark energy. Further observations and experiments, such as those carried out by satellite missions like Planck and ground-based telescopes like the Sloan Digital Sky Survey, have helped refine our understanding of the influence of dark energy on the early universe expansion.