Activity 12
Universal Expansion
Discussion. From observations made by him and others, Hubble concluded that the
universe was expanding. The galaxies seem to be rushing away from one another. As
seen from Earth, the farther away a galaxy is, the faster is its rate of recession. In this
activity, you will get a "feel" for what is meant by universal expansion. You will do this
with a large rubber band and a meterstick (or a yardstick).
Procedure. Cut a large rubber band so that you have a single length of band at least 20
centimeters (almost 8 inches) long.
If you use a meterstick, follow the directions in this paragraph. Lay the rubber strip
next to the meterstick so that the rubber strip lies flat. Do NOT stretch the strip. Use a
marking pen to make a mark on the strip every 1 centimeter.
If you use a yardstick, follow the directions in this paragraph. Lay the rubber strip next
to the yardstick, so that the rubber strip lies flat. Do NOT stretch the strip. Use a
marking pen to make a mark on the strip every ½ inch.
Each mark on the rubber strip represents a galaxy.
Select a mark to represent the Milky Way Galaxy (our galaxy). Grasp both ends of the
rubber strip and hold it next to the meterstick/yardstick so that the mark representing the
Milky Way is next to the 1-cm/½-inch line of the ruler. See the drawing below.
Rubber band with marks
PULL PULL
Meterstick or yardstick Stretch the strip until the mark that was at the 2-cm/1-inch line is at the 3-cm/1½-inch
line (be sure to keep the Milky Way mark next to the 1-cm/½-inch line). The mark that
moved from the 2-cm/1-inch line to the 3-cm/1½-inch line doubled its distance from the
Milky Way mark.
Answer the following questions on the report sheet.
Question 1. How did the positions of the marks at the 3-, 4-, and 5-cm lines (1½-, 2-,
2½-inch lines) change in relation to the Milky Way mark? Did these marks move 1 cm 65 (½ inch) farther away from the Milky Way mark, double their distances from the Milky
Way, or move some other distance?
Select some other mark on the rubber strip to represent the Milky Way and repeat the
procedure.
Question 2. How did the positions of the marks at the 3-, 4-, and 5-cm (1½-, 2-, 2½-inch
lines) change in relation to the Milky Way mark?
Question 3. How do the results described in your answers to questions 1 and 2 compare
with each other? Were the distances moved the same or different? If different, by what
percents did they differ?
Question 4. Does it take the same time or different times for the marks at the 2-, 3-, 4-,
and 5-cm lines (1, 1½-, 2-, 2½-inch lines) to move to their final positions? If different,
by what percent do the times differ? In general, how are the speeds of the marks related
to the changes in the positions of the marks?
Question 5. Based on your answers to the preceding questions, do you think it is
necessary for our galaxy to be located in a "special" position (such as the center) in the
universe for us to observe the motions of the other galaxies as modeled in the activity? Activity 12 Report Sheet
Universal Expansion
Questions
1. How did the positions of the marks at the 3-, 4-, and 5-cm lines (1½-, 2-,
2½-inch lines) change in relation to the Milky Way mark? Did these marks
move 1 cm (½ inch) farther away from the Milky Way mark, double their
distances from the Milky Way, or move some other distance? 2. How did the positions of the marks at the 3-, 4-, and 5-cm (1½-, 2-, 2½inch lines) change in relation to the Milky Way mark? 66 3. How do the results described in your answers to questions 1 and 2
compare with each other? Were the distances moved the same or different?
If different, by what percents did they differ? 4. Does it take the same time or different times for the marks at the 2-, 3-,
4-, and 5-cm lines (1, 1½-, 2-, 2½-inch lines) to move to their final
positions? If different, by what percent do the times differ? In general, how
are the speeds of the marks related to the changes in the positions of the
marks? 5. Based on your answers to the preceding questions, do you think it is
necessary for our galaxy to be located in a "special" position (such as the
center) in the universe for us to observe the motions of the other galaxies as
modeled in the activity? 67 68

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