Science · Year 10 · Earth in the Cosmos · Term 3

The Expanding Universe

Students will examine Hubble's Law and the evidence for an expanding universe, including redshift.

• ACARA Content Descriptions
• AC9S10U05

About This Topic

The Big Bang theory is the leading scientific explanation for the origin and evolution of our universe. In this topic, students evaluate the evidence for this theory, including the redshift of light from distant galaxies and the cosmic microwave background radiation. This aligns with AC9S10U05, focusing on the scale of the universe and its development over billions of years.

Students explore the life cycles of stars and the formation of elements, connecting the 'small' world of atoms to the 'large' world of galaxies. This topic encourages critical thinking about how scientific theories are constructed and revised based on new data. This topic comes alive when students can physically model the expansion of space and use simulations to visualize the vastness of cosmic time.

Key Questions

1. What is redshift, and how does observing it in the light from distant galaxies provide evidence that the universe is expanding?
2. How did Hubble's observations of galaxy velocities and distances lead to the conclusion that the universe had a beginning?
3. What different lines of observational evidence support the idea that the universe is still expanding today?

Learning Objectives

• Explain the concept of redshift and its relationship to the Doppler effect for light waves.
• Calculate the recessional velocity of galaxies using Hubble's Law and provided data.
• Analyze observational data, such as galaxy distances and velocities, to support the conclusion of an expanding universe.
• Evaluate the significance of Hubble's Law in inferring a beginning point for the universe.
• Compare different lines of observational evidence that support the ongoing expansion of the universe.

Before You Start

Light and the Electromagnetic Spectrum

Why: Students need to understand the nature of light and its properties, including wavelength, to grasp the concept of redshift.

Introduction to Astronomy: Our Solar System and Beyond

Why: Familiarity with basic astronomical objects like galaxies and concepts of distance in space is helpful context.

Key Vocabulary

Redshift	The stretching of light waves from objects moving away from an observer, causing their spectral lines to shift towards longer, redder wavelengths.
Hubble's Law	A relationship stating that the recessional velocity of a galaxy is directly proportional to its distance from Earth, indicating an expanding universe.
Cosmological Redshift	Redshift caused by the expansion of space itself, stretching the wavelengths of light as it travels across the universe, distinct from Doppler shift.
Light Year	A unit of astronomical distance representing the distance that light travels in one year, approximately 9.46 trillion kilometers.

Watch Out for These Misconceptions

Common Misconception

The Big Bang was an explosion of matter into empty space.

What to Teach Instead

Explain that it was an expansion of space itself, carrying matter with it. Using the balloon analogy helps students visualize that there is no 'outside' or 'center' to the expansion.

Common Misconception

The universe has always existed in its current state.

What to Teach Instead

Show evidence of redshift and the cosmic microwave background. Discussing how we can 'look back in time' by observing distant light helps students grasp that the universe is dynamic and changing.

Active Learning Ideas

Simulation Game: The Expanding Balloon

Students draw 'galaxies' on a partially inflated balloon. As they blow it up, they measure the distance between galaxies to see how those further apart appear to move away faster, modeling Hubble's Law and the expansion of space.

30 min·Pairs

Gallery Walk: The Cosmic Timeline

Post cards representing major events (Big Bang, first stars, formation of Earth, first life) around the room. Students must work together to place them in the correct chronological order and at the correct relative scale on a long string.

40 min·Small Groups

Formal Debate: The Future of the Universe

Based on their research into dark matter and dark energy, students debate the three potential fates of the universe: the Big Freeze, the Big Crunch, or the Big Rip. They must use evidence from current cosmological models to support their stance.

50 min·Whole Class

Real-World Connections

• Astronomers at observatories like the Keck Observatory in Hawaii use spectrographs to measure the redshift of light from distant galaxies, helping to map the large-scale structure of the universe and search for exoplanets.
• Cosmologists use data from space telescopes such as the Hubble Space Telescope and the James Webb Space Telescope to test and refine models of the universe's expansion and its origins, contributing to our understanding of fundamental physics.

Assessment Ideas

Quick Check

Provide students with a simplified graph showing galaxy distance versus recessional velocity. Ask: 'Based on this graph, what is the relationship between a galaxy's distance and its speed? What does this imply about the universe?'

Discussion Prompt

Pose the question: 'If the universe is expanding, what might it have looked like billions of years ago?' Guide students to connect this to the idea of a denser, hotter state and the concept of a beginning.

Exit Ticket

On an index card, have students write two sentences explaining what redshift is and one piece of evidence, other than redshift, that supports the idea of an expanding universe.

Frequently Asked Questions

How do I explain redshift to Year 10 students?

Use the Doppler effect analogy with sound. Just as a siren's pitch drops as it moves away, light from receding galaxies shifts toward the red (longer wavelength) end of the spectrum. This familiar connection makes the complex concept of light-shift much more accessible.

What are the best hands-on strategies for teaching the Big Bang?

Modeling activities that deal with scale and expansion are vital. Because the concepts are so vast, using physical representations (like the balloon expansion or a 13.8-meter timeline) helps students ground the abstract numbers in a spatial reality they can see and touch.

How do I handle the 'before the Big Bang' question?

Be honest and explain that current physics cannot yet describe the conditions before the expansion began. This is a great opportunity to discuss the limits of scientific knowledge and the role of ongoing research in fields like quantum gravity.

How can I include Indigenous Australian astronomy in this topic?

Incorporate First Nations perspectives on the cosmos, such as the 'Emu in the Sky.' Discuss how Indigenous astronomers used the dark spaces in the Milky Way, rather than just the stars, to navigate and track seasons, showing a sophisticated, long-term observation of the night sky.