The 1-d Expanding Universe!

Procedure

• Stretch the spring a small distance. Consider these locations as the Initial Distances. Measure the distances to each galaxy from the zero mark. Record the data in the table.
• Now slowly pull the spring while counting approximate one-second intervals. You can count out the time or use a stopwatch or second hand on the room clock. Stretch for three seconds then stop. Now measure the distances to each mark from the zero mark and record them in the data table as the Final Distances. Caution: do not pull the spring so much that you reach the elastic limit before the 3 seconds are up. You may wish to do this in the hall as it stretches quite a bit.

Galaxy #	Initial Distance (cm)	Final Distance (cm)	Change in Distance (cm)	Velocity (cm/s)
1
2
3
4
5

• Calculate the distance moved by each galaxy in one second by dividing the total distance moved by 3. This is the velocity (remember velocity is equal to distance divided by time). Enter this result in the final column of the data table.
• Plot the data points for each galaxy on the graph below. These would be column 3 (distance) along the X-axis and column 5 (velocity of recession) along the Y-axis. Connect the points for each galaxy with a straight line.

• Calculate the slope for each galaxy. Compare these results to the values you calculated for velocity in the data table. What do you notice?
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• Now do as American astronomer Edwin Hubble did: plot the velocity as the dependent (Y) variable and the Distance as the independent (X) variable.

• What relationship do you see? Discuss.
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This is exactly what Edwin Hubble saw. He realized that the data he obtained by observing the apparent movement of galaxies were explained by the expansion of our Universe!