Accelerating Expansion

Recently, scientists have been amazed by supernova data that indicates that the expansion rate of the universe is not decreasing, but increasing. To fully understand the significance of this type of expansion, let’s look at something we all have seen: a balloon expanding 

Procedure:  Part A
1.	Get a balloon and practice inflating it with: 
a.	constant expansion 
b.	accelerating expansion
c.	decelerating expansion.  
For each type of expansion, explain what is happening to the balloon.
2.	Use the given data below to construct a graph of a balloon’s expansion placing time on the x-axis and the diameter of the balloon on the y-axis.
3.	Connect the points dot to dot on the graph (do not do a best fit line).
4.	Use the graph to determine:
a.	The expansion is speeding up from ___ seconds to ___ seconds.
b.	The expansion is slowing down from ____ seconds to ____ seconds.
c.	The expansion is constant from ___ seconds to ___ seconds.
5.	Calculate the change in time between each time interval (t2-t1) and fill that in the column on the data table.  Then calculate the change in diameter the same way and fill those values into the data table.
6.	Calculate the expansion rate for each time period using this formula: change in diameter / change in time  = expansion rate (Note: time 0 has no expansion rate)

Data Table
Time
 (sec)	Change in
Time (sec)	Diameter
(cm)	Change in
Diameter (cm)	Expansion 
Rate (cm/sec)	
0	  ---------	7	  -----------	  -------------------	
0.1		8			
0.2		10			
0.3		14			
0.4		18			
0.5		22			
0.6		26			
0.7		30			
0.8		33			
0.9		35			
1.0		36			
Part B
Using a motion detector produce four graphs.  Each graph should have the same shape as one of the Four Eras’ graphs showing the Size of the Universe vs. Time. Underneath each graph: 
1.	Label the Era the graph’s shape represents
2.	Explain how you got the graph to have that shape
3.	Explain what happened to the size of the Universe during that Era to produce that shape. 

Discussion
1.	Do your calculated expansion rates agree with your answer form #4 in the procedure?

2.	Considering balloons, why did the expansion rate decrease towards the end ?

3.	Why did scientists think the expansion rate of the Universe should decrease?

4.	In fact some scientists thought the Universe would eventually contract, terming it “the Big Crunch.”  In blue, sketch this shape on your graph and label it “Big Crunch.”

5.	In reality, the Universe’s expansion rate is increasing. Sketch in red on your graph what this shape should look like.  Label it “Accelerating Expansion, Era 4.”