The Understanding and Calculation of ‘Dark Energy and Dark Matter’
Modern cosmology is interested in finding out what matter ingredients and how much of each ingredient are in the universe. According to observational data, the percentages of dark energy, dark matter and the baryonic matter are 72.8%, 22.7% and 4.53% respectively.
Fritz Zwicky (1936) measured velocity dispersion of eight galaxies through Doppler redshift in Coma Cluster. He found that the velocities of the galaxies making up the cluster were about ten times larger than he expected. The observable matter alone could not accelerate the galaxies to higher velocities; in fact, the observable matter provided roughly 0.5% of the required mass. In the 1970s, Rubin, Freeman and Peebles gathered more reliable data by observation of a larger number of clusters that confirmed that luminous matter alone could not account for the high velocities of the galaxies. The amount of the light stars emits as you near the edge of a spiral galaxy decreases and assuming all matter was luminous, the rotational speed would decrease too. This, however, is not the case. Galactic rotation curves are known to be flat. These galactic dynamics, the dynamics of galaxy clusters and Cosmic Microwave Background (CMB) measurements provide a compelling evidence of some sort of invisible matter, called dark matter, which does not interact electromagnetically but participates in the gravitational dynamics.