This investigation explores the evolution of the large-scale structure of the Universe by viewing the distribution of galaxies at different redshifts.

Vera C. Rubin Observatory will greatly contribute to the refinement of our model of the large-scale structure of the Universe by discovering billions of previously undetected galaxies. These refinements may validate existing theories about the fundamental nature and interactions of matter and energy, or they may uncover new questions to investigate.

Students begin by exploring how cosmological redshift affects galaxy color, and how color can be used to determine distances and lookback time. Students then consider how light is used to define the observable Universe. Finally, they devise an explanation for what forces drive the observed changes in the large-scale structure of the Universe over time.

Prerequisite Concepts

• Students should know the definition of light-year (ly) as a distance unit.
• Students should be able to distinguish between Doppler shift (due to a galaxy’s recessional velocity) and cosmological redshift (due to the expansion of the Universe.
• Students should understand look back time: the image of a galaxy with a look back time of one million years shows what the galaxy looked like one million years ago.
• Students should be familiar with the way mass and distance affect gravitational forces (Newton’s Laws).
• Students should be familiar with the Law of Conservation of Mass.
• Students should be familiar with the Hubble-LeMaitre Law as supporting evidence for the expansion of the Universe.

Learning Outcomes

• Students interpret the redness-distance plots of galaxies to show that the Universe is expanding (cosmological redshift).
• Students make observations of galaxy distributions to determine that the Universe is the same in all directions (the cosmological principle).
• Students calculate a minimum size for the observable Universe using galaxy redshift data.
• Students analyze galaxy concentration maps to determine how the large scale structure of the Universe has become less homogenous (more clumpy) over time due to gravitational interactions.

Essential Questions

• How can observations of light from distant galaxies be used to determine some characteristics of the observable Universe, such as its minimum size, early history, and expansion?
• How has the distribution of galaxies in the Universe (the large-scale structure) changed over time?
• What is the role of gravity in the evolution of the large-scale structure of the Universe?