======Balloon Expanding Universe======


<WRAP right box>
**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
\\
**Categories:** {{$demo.categories}}
\\


**Alternative titles:** Expanding Balloon Model
</WRAP>

====Summary====                   
{{$demo.summary}}



====Procedure====  
  - Provide each group of students with a balloon, small stickers, and a marker.  
  - Inflate the balloon slightly so that it just takes shape, and hold it closed without tying.  
  - Place 5–10 stickers (or draw dots) on the surface to represent galaxies. Mark them so they can be replaced if they fall off.  
  - Draw a wavy line between two stickers to represent a lightwave traveling across space.  
  - Measure and record the distance between two galaxies and the wavelength of the drawn wave.  
  - Inflate the balloon a little more, hold it closed, and repeat the measurements.  
  - Continue inflating in steps until the balloon is nearly full, recording how distances and wave lengths change.  
  - Compare observations to animations or diagrams showing constant versus accelerating expansion.



====Links==== 
Modeling the expanding universe with a balloon and pen - Simon Lloyd: 
{{youtube>5hYGdHW5qVw?}}\\

Expanding Universe Balloons - Science Never Stops - U.S. Space & Rocket Center: 
{{youtube>hWefRsdIhJM?}}\\

📄 Model the Expanding Universe - NASA Jet Propulsion Laboratory: [[https://www.jpl.nasa.gov/edu/resources/lesson-plan/model-the-expanding-universe/]]\\

====Variations====
  * Use a balloon pump for steadier inflation.  
  * Try placing galaxies close together and far apart, and compare how the spacing changes.  
  * Color-code galaxies or draw different types of waves to track changes.  
  * Connect this demo to a math activity by graphing galaxy separation versus balloon size.



====Safety Precautions====
  * Balloons can pop unexpectedly; have extras available.  
  * Keep balloons away from faces while inflating.  
  * Use a balloon pump if students are sensitive to latex or blowing balloons.




====Questions to Consider====
  * What does each sticker represent? (Galaxies.)  
  * Why do all galaxies move farther apart as the balloon inflates? (The balloon’s surface expands everywhere, modeling universal expansion.)  
  * What happens to the drawn wave as the balloon stretches? (Its wavelength increases, showing redshift of light in an expanding universe.)  
  * Do the galaxies themselves expand? (No, only the space between them expands.)  
  * What are limitations of this model? (It represents only the balloon’s surface, not three dimensions, and expansion only occurs when inflated rather than continuously.)