Dark Energy In the Accelerating Universe

Professor Tapei Cheng
University of Missouri, Saint Louis

About a decade ago, astronomical observations indicated that the expansion rate of the universe, rather than slowing down as the standard Big Bang theory predicted, was actually increasing over time. In the original Big Bang theory, matter and energy explode from a tiny super-hot, super-dense state, then continue to expand outwards, coasting on the momentum injected by the initial explosion. As billions of years passed, the rate of expansion gradually slowed due to the pull of gravity. But the new observations showed that, beginning a few billion years ago, the outward acceleration began increasing. The best guess for the reversal is that an unknown repulsive force has overcome the force of gravity. Since the force is not directly visible, it has been attributed to “dark energy”- but the nature of this dark energy is still to be discovered. Professor Cheng will discuss how scientists determined that the expansion of the universe is accelerating and examine some of the possibilities for the dark energy.

At UM-St. Louis, Dr. Cheng is a professor in the Department of Physics and Astronomy. His primary research interests involve particle physics, particularly in the nature of quarks, the particles thought to make up the structure of nuclear particles such as the proton and the neutron. This year the Oxford University Press has published “Relativity, Gravitation, and Cosmology”, the latest of several books Dr. Cheng has authored.