In our science for non-science majors course “21st Century Physics,” we investigate modern “Hubble plots” (plots of velocity versus distance for deep space objects) in order to discuss the Big Bang, dark matter, and dark energy. There are two potential challenges that our students face when encountering these topics for the first time. The first challenge is in understanding and interpreting Hubble plots. The second is that some of our students have religious or cultural objections to the concept of a “Big Bang” or a universe that is billions of years old. This paper presents a guided inquiry exercise that was created with the goal of introducing students to Hubble plots and giving them the opportunity to discover for themselves why we believe our universe started with an explosion billions of years ago. The exercise is designed to be completed before the topics are discussed in the classroom. We did the exercise during a one hour and 45 minute “lab” time and it was done in groups of three or four students, but it would also work as an individual take-home assignment.

Explosion graphs and Hubble plots for this exercise were created with a custom script using the R programming language. The script and the full text of the guided inquiry exercise are available at
Image created by Dr.
University of Northern Iowa. Used with permission. Type 1a Supernova data from A. Riess, W. Press and R. Kirshner, “A Precise Distance Indicator: Type IA Supernova Multicolor Light-Curve Shapes,”
Astrophysical Journal
, (
The one group that said “no” complained that the data points were not “exactly” on the line. This shows a weakness in the exercise, which used synthetic “perfect” data with no experimental uncertainty. It would be easy to modify the graphs to include small random errors.
“Dark matter,”
Phys. Teach.
, (March
“The Nobel Prize in Physics 2011,”,
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