The Universe does not arrive at us as facts. It arrives as light in our eyes, pressure on our skin, and motion through space. From these experiences, we begin to build understanding. What’s the first thing you remember about the night sky? For me, it was the brightness of the full Moon.
In this activity, students retrace that journey, as we are switching definitions with perception, to uncover a simple way to organise the cosmos: matter, space, and radiation, three baskets and one Universe.
Big idea
We can understand the Universe by organising it into:
Radiation (what travels and allows us to see)
Matter (what things are)
Space (where things are)
Students begin with their own experiences and build toward a scientific model of the Universe.
Teacher Notes
Students may initially think we “see objects directly.”
Guide them toward the idea that we see light interacting with objects.
This activity builds a conceptual model rather than a complete physical description.
NASA astronaut Christina Koch is illuminated by a screen inside the darkened Orion spacecraft on the third day of the agency’s Artemis II mission. To the right of the image’s center, CSA (Canadian Space Agency) astronaut Jeremy Hansen is seen in profile peering out of one of Orion’s windows. Lights are turned off to avoid glare on the windows. Credit: NASA
The core idea
Instead of starting with physics, we can start with:
“How do we know anything about the world?”
And let the students reverse-engineer reality.
Activity Structure (3 Phases)
Phase 1: “What can we detect?”
Prompt:
“Imagine you are on an alien world.
What are all the different ways you can detect or experience things?”
Students brainstorm:
You’ll get things like:
- touch
- seeing
- hearing
- movement
- temperature
Write everything up.
Group their answers into 3 clusters:
1. Things we can touch
- solid objects
- surfaces
- resistance
2. Things about where things are
- distance
- direction
- movement
3. Things we detect without touching
- light
- heat
- signals
Do NOT name the baskets yet.
Let them sit in that structure.
Phase 2: “What must exist for these to happen?”
So the question is…
“If these are the ways we experience the world… what must exist out there for this to be possible?”
Now they’re doing physics without knowing it.
Guide them toward:
For touch → something must exist
“stuff”
For distance/movement → there must be separation
“space”
For seeing/heat/signals → something must travel
“something moving through space”
Drumroll …
Phase 3: Naming the Universe
The great reveal:
“Physicists organise the Universe in a very similar way.”
Introducing:
Matter
→ the “stuff” we can touch
Space
→ the “between”
Radiation (Light)
→ what travels and lets us see. Radiation (light) is one of the main ways we detect the Universe — it travels through space and allows us to see.
Are we there yet?
(super) Cool fact – Advanced Students
“We don’t actually see objects.
We see light coming from them or bouncing off them. We perceive heat coming from a certain source.”
Then ask:
“So what are we really seeing /feeling?”
Answer:
radiation
How can you tell? If you turn the lights off or at night, it is very hard to distinguish – see, objects.
Next level additions
- add a misconception trap (“Do we see objects directly?”)
- use a dark room + torch demo
- integrate your brain/perception discussion
For older students
You can then drop:
“Sometimes light can turn into matter.” – This is where the good old T-shirt with E=mc^2 makes sense.
Briefly describe:
- gamma ray → electron + positron
No equations needed — just the idea.
Variant: Physical role-play
Assign roles:
- some students = matter (stand still, form objects)
- some = radiation (move across the room carrying “information”)
- the room itself = space
Then:
- radiation “bounces” off matter
- “observer” students only see via radiation
Now they feel the model.
This isn’t the only way to describe the Universe but it’s a powerful way to begin understanding it.
