Why is the Universe accelerating? Nobel Laureate Brian Schmidt explains

Brian Schmidt introduces the concept of the accelerating universe, setting the stage for a discussion on cosmology and its developments over the past century. He emphasizes the vastness of the universe, using the speed of light as a measure to illustrate distances and scales, such as the size of the sun and the distance to nearby stars like Alpha Centauri. He also touches on the concept of light years and the number of stars in our galaxy and beyond, leading into the discussion of the universe's expansion and its implications.

Schmidt delves into the observations made by Vesto Melvin Slipher in 1916, who noticed that the light from galaxies was red-shifted, indicating that they were moving away from us. This phenomenon is explained through the Doppler shift, similar to how sound waves change pitch based on the motion of the source. The implications of these observations are discussed, leading to the understanding that the universe is expanding, with galaxies moving away from each other.

Edwin Hubble's work is highlighted, showing how he used the brightness of stars in galaxies to measure distances, leading to the discovery that the further away a galaxy is, the faster it is moving away. This relationship, now known as Hubble's Law, suggests an expanding universe. Hubble's data from 1929 is presented, illustrating the correlation between distance and velocity, and the concept of the universe not being static but in motion.

Albert Einstein's theory of general relativity and its implications for cosmology are discussed. Einstein's realization that acceleration due to motion and gravity are indistinguishable led to his field equations, predicting a dynamic universe that must be expanding or contracting. The introduction of the cosmological constant as a 'fudge factor' to counteract gravity is explained, showing how it was initially used to allow for a static universe model.

Schmidt shares his own work on measuring the expansion rate of the universe, leading to the conclusion that the universe is about 14 billion years old. The discussion includes the impact of gravity on the universe's expansion and how it affects the age and ultimate fate of the universe. The concept of a universe that could be finite or infinite based on its density and the role of dark matter and dark energy are introduced.

The use of Type Ia supernovae as 'standard candles' for measuring cosmic distances is explained. Fritz Zwicky's initial discovery of supernovae and the subsequent work by the Calan-Tololo Supernova Search are discussed. The importance of these supernovae in understanding the expansion of the universe and their role in providing precise measurements of distances across the universe is highlighted.

The importance of technological advancements in astronomy, particularly in the 1990s, is discussed. The advent of large-format CCD cameras and the Keck telescopes enabled the collection of more detailed data, crucial for studying supernovae and the universe's expansion. The challenges of processing large amounts of data and the competition between different research teams are also touched upon.

The groundbreaking discovery that the universe's expansion is accelerating, rather than slowing down due to gravity, is detailed. The use of distant Type Ia supernovae to observe this acceleration is explained, leading to the realization that an unknown force, later termed dark energy, is driving this acceleration. The implications of this discovery for our understanding of the universe's ultimate fate are discussed.

The current understanding of the universe's composition, including the proportions of normal matter, dark matter, and dark energy, is outlined. The role of dark energy in the accelerating expansion of the universe and its potential future effects are explored. The possibility of a 'Big Rip' scenario, where dark energy becomes dominant enough to tear apart the universe, is introduced as a speculative but intriguing outcome.

Schmidt concludes by discussing the long-term future of the universe, focusing on the dominance of dark energy and its potential to cause a runaway expansion. The implications for galaxies, stars, and even atoms are considered, leading to a vision of a universe that eventually fades away as it expands. The scientific community's ongoing efforts to understand the nature of dark energy and its role in the cosmos are emphasized.