Big Bang Evidence Explorer Task

Standards Alignment:

• Performance Expectation: HS-ESS1-2
• Evidence Statements: Students identify and describe the evidence to construct the explanation, including the composition of stars, the hydrogen-helium ratio of stars and interstellar gases, the redshift of the majority of galaxies and the redshift vs. distance relationship, and the existence of cosmic background radiation.
• Science and Engineering Practice: Constructing Explanations and Designing Solutions
• Disciplinary Core Ideas: ESS1.A: The Universe and Its Stars; PS4.B: Electromagnetic Radiation
• Crosscutting Concept: Energy and Matter

Simulation Link: Big Bang Evidence Explorer

Introduction

In 1929, Edwin Hubble published a paper demonstrating that the universe is expanding. Decades later, scientists discovered the Cosmic Microwave Background radiation, and carefully measured the abundance of elements in the universe. These three pillars of evidence—redshift, the cosmic microwave background, and the composition of matter—form the foundation of the Big Bang Theory.

In this task, you will use the Big Bang Evidence Explorer simulation to collect data and construct an explanation for the origin and expansion of the universe.

Part 1: Redshift and the Expanding Universe

Navigate to the Expanding Universe (Redshift) tab in the simulation. This section models the observation of distant galaxies.

1. Observe and Collect Data:
   • Set the “Time (Expansion)” slider to its minimum value (1). Click on a galaxy in the visual model to observe its light spectrum.
   • Slowly move the slider to the right to simulate the expansion of the universe over time. Notice what happens to the vertical lines (the spectrum) in the “Galaxy Light Spectrum” box.
   • Record data for at least five different galaxies across various distances by clicking the “Record Data” button.
2. Analyze the Data:
   • Look at the “Hubble’s Law Data” graph. Describe the relationship between a galaxy’s distance from the observer and its velocity.
   • What does the shift of the spectral lines towards the red end of the spectrum indicate about the motion of the galaxies relative to Earth?
3. Synthesize: How does the relationship you described in question 2 provide evidence that the universe is expanding from a smaller, denser state in the past?

Part 2: Composition of Matter

Navigate to the Composition of Matter tab. The Big Bang Theory predicts that the early universe was incredibly hot and dense, allowing for a brief period of nuclear fusion before stars even existed.

1. Analyze Samples:
   • Select the “Primordial Gas Cloud” from the dropdown menu and click the sample to analyze it. Record the mass percentage of Hydrogen and Helium.
   • Repeat this process for the “Old Star (Pop II)” and “Young Star (Pop I)”.
2. Compare and Contrast:
   • How does the composition of the Primordial Gas Cloud differ from the composition of the stars?
   • The Big Bang Theory predicts that the initial matter in the universe should be approximately 75% Hydrogen and 25% Helium by mass. Do the simulation’s results for the primordial cloud align with this prediction?
3. Synthesize: Explain how the observed ratio of hydrogen to helium in the oldest, least disturbed regions of the universe (like primordial gas clouds) supports the idea of an early, incredibly hot and dense universe.

Part 3: Cosmic Microwave Background (CMB)

Navigate to the Cosmic Microwave Background tab. The CMB is often described as the “afterglow” of the Big Bang.

1. Observe the Shift:
   • Start with the “Time since Big Bang” slider at the far left (~380,000 Years). Record the approximate temperature and the peak wavelength of the radiation.
   • Slowly move the slider to the right, advancing time towards the present day (13.8 Billion Years). Describe what happens to both the temperature of the universe and the peak wavelength of the background radiation.

2. Connect Expansion and Temperature: As the universe expands (represented by the growing box and stretching waves), why does the temperature drop? Use the crosscutting concept of Energy and Matter in your explanation.

3. Synthesize: According to the Big Bang Theory, the universe was once filled with a uniform, incredibly hot plasma that emitted intense, high-energy radiation. How does the discovery of the Cosmic Microwave Background—a faint, incredibly cold (2.7 Kelvin) microwave radiation filling all of space—serve as a “relic” or “fossil” supporting this theory?

Part 4: Constructing the Final Explanation

Using the evidence you gathered from all three tabs (Redshift, Composition of Matter, and CMB), construct a comprehensive scientific explanation of the Big Bang Theory.

Your explanation must:

• State the core premise of the Big Bang Theory (that the universe is expanding and was once much hotter and denser).
• Explicitly describe how the redshift of galaxies provides evidence for an expanding universe.
• Explain how the measured composition of early matter (hydrogen and helium) supports the theory of a hot, dense early state.
• Describe how the cosmic microwave background acts as remnant radiation from the early universe.
• Demonstrate reasoning by connecting these three independent pieces of astronomical evidence to support the single, unifying Big Bang Theory.