The big bang theory: space, time, matter and energy began about 13.8 billion years ago in an extremely hot, dense state, and the universe has expanded and cooled ever since: from particles to atoms, stars, galaxies and planets.
The hydrogen nuclei in the water you drink were made in the first minutes of the universe. The carbon in you was made inside stars.
Before weighing the evidence for the big bang, you need a clear picture of what the theory says.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: an explosion?
ExploreTry it on the board and compare what happens with your prediction.
Explore: 13.8 billion years
Press Later → to move through time. Watch the temperature and what has formed at each stage.
Try it yourselfYour edits are saved in this browser.
Step through all ten stages from the big bang to today.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: the model
In your book: draw a timeline with at least five stages, the times and one thing that formed at each.
Put the stages of the universe in order.
Pieces (click to add)
Your program
Elaborate TypicalUse the same idea in a new context.
Elaborate: stars as element factories
Elaborate WiderUse the same idea in a new context.
Elaborate: open questions
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
The big bang theory: space, time, matter and energy began about 13.8 billion years ago, extremely hot and dense; the universe has been expanding and cooling ever since.
Stages: inflation → protons and neutrons → hydrogen and helium nuclei (3 min) → atoms and free light (380 000 years) → first stars (about 200 million years) → galaxies → the sun and Earth (9.2 billion years).
Heavier elements were made in stars.
For teachers
Students describe the big bang as the origin of space, time and matter about 13.8 billion years ago and outline the main stages as the universe expanded and cooled (AC9S10U03, node 2, a hinge node). About 22 minutes.
I can outline at least three stages from the big bang to galaxies.
I can explain that the universe has been expanding and cooling.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider.
The hinge is a clear model to test evidence against (nodes 3 to 5). The common misconception is an explosion at a point in empty space.
Board notes: ten stages, evenly spaced on the timeline (the real times run from about 10⁻⁴³ s to 13.8 billion years). The patch of universe is a picture, not a simulation: its grid widens to show expansion, and its colour follows the temperature. Times and temperatures are rounded textbook values.
Running the lesson
Engage: count how many chose the explosion.
Explore: ask what happened to the temperature at every step.
Explain: the atoms question is the checkpoint (cooling is the cause).
The hard part (on purpose)
Picturing space itself expanding, not an explosion into empty space. When a student asks what it expanded into, ask whether the model has an 'outside' if space itself began then.
When students get stuck
A student asks what was before the big bang, or what it expanded into. Ask: If space itself began then, is there an 'outside' or a 'before' in the model? Fix: Not in the model: it describes the universe from the first instant. Those are open questions.
Stretch and support
Stretch: Why does looking at very distant galaxies mean looking back in time?
Support: Give a timeline strip with the stage names to place.
Where it leads
Next: redshift and the expanding universe (node 3). Later: the cosmic microwave background and the proportions of hydrogen and helium as evidence (nodes 4 and 5).
What each step is for
Engage: an explosion?: Students who picture an explosion at a point in empty space expect a centre; the board describes space itself expanding everywhere.
Explore: 13.8 billion years: Stepping through the stages with the temperature falling makes 'expanding and cooling' the thread that links them.
Explain: the model: Ordering the stages and linking each to cooling is the model all the evidence lessons test.
Elaborate: stars as element factories: Connecting the first stars to heavier elements explains why later stars and planets differ from the first ones.
Elaborate: open questions: Recognising what the model doesn't yet explain shows how scientific theories grow.
Now you can
Describe what the big bang theory says.
Outline at least three stages from the big bang to galaxies.
Explain that the universe has been expanding and cooling.