PBS Space Time Season 2016 Episode 17 What Does Dark Energy Really Do?

PBS Space Time season 2016 episode 17, titled "What Does Dark Energy Really Do?", explores the mysteries surrounding dark energy and its role in the expansion of the universe. The episode delves into the history of dark energy's discovery and the various theories that attempt to explain its presence.

The show starts by highlighting the key observations that led to the discovery of dark energy including observations made with the Hubble Space Telescope, the Cosmic Microwave Background Radiation, and Type 1a supernovae. The observations were puzzling as they provided evidence that the universe is expanding at an accelerating rate, which shouldn't be possible based on the laws of physics this far outward in the universe.

The show then discusses various theories attempting to explain this phenomenon. The first theory discussed proposes that dark energy is simply the energy associated with the vacuum of space itself, which has a negative pressure that drives the expansion of the universe. The episode shows how the amount of energy that could be associated with the vacuum of space is enough to explain the observed acceleration of the universe’s expansion, but also highlights some of the issues with this theory.

Another theory discussed explains that dark energy may be a new type of field that pervades the universe, much like how the Higgs field is thought to give mass to particles. The field is believed to interact with matter and cause a push that accelerates the rate of expansion. The episode points out that this theory still lacks significant supporting evidence to add credibility to the theory.

Next, the show discusses how dark energy impacts the structure of the universe including the formation of galaxy clusters and the large-scale structure of the universe. Through simulations, the episode shows that dark energy actually leads to less structure formation in the universe, slowing down the growth of galaxies and galaxy clusters. This is counterintuitive as one might expect an accelerating universe to cause more structure formation, but the presence of the negative pressure caused by dark energy seems to counteract gravity, which causes the reduction in structure formation.

Towards the end of the episode, the show explores the implications of dark energy for the future of the universe. The universe is expected to continue expanding at an accelerating rate, but the ultimate fate of the universe will depend on the properties of dark energy. Some theories suggest that the rate of acceleration may increase, causing the "Big Rip" scenario where the universe is torn apart. Other theories predict that the rate of acceleration may decrease to zero, and the universe would eventually come to a stop and contract, resulting in a new Big Bang event.

Overall, the show provides a detailed look at the mysteries surrounding dark energy and how it impacts the universe at the largest scales. It explores the various theories surrounding this phenomena while highlighting the lack of answers that scientists currently have. The viewer is left with the feeling that this topic is still up for debate and the only fact is that we don't know quite yet what exactly is causing the expansion of the universe to accelerate and that is a mystery well worth continuing to explore.