Part Two: It Depends Upon Your Perspective

Step One: You have felt the holes in the sponge. Now feel the structure on Tactile Card Number One. The raised parts on the card correspond to the solid parts of the sponge, but they may not be exactly the shapes as those that you felt on the sponge. Can you feel that the structures are clearly defined?

Step Two: Your partner will stay in the same location and hold the Tactile Card Number Two. You turn around and take five steps away from your partner. Now face your partner.

Now feel the structure on Tactile Card Number Three. Compare what you feel on this card with the sponge representation you feel on Tactile Card Number Two. Can you feel that this is the same structure as that on Tactile Card Number Two, only smaller in size?

Tell you partner what you feel on Tactile Card Number Three.

Ask your partner if the figure on Tactile Card Number Two has changed size.

What is the only thing that changed?

As you walk away from an object, it appears to be smaller in size. That is what artists call perspective. Things that are close appear to be larger than those same things when they are farther away. The holes and the solid parts in the card would also appear to be smaller in size.

Step Three: Turn around and take another five steps away from your partner. The farther your partner and Tactile Card Number Two are from you, the smaller the card and the sponge representation appears to be. Now it would appear to look something like the structure on Tactile Card Number Four. Feel it and compare it with Tactile Card Number Two and Tactile Card Number Three. Can you still feel all the holes in Tactile Card Number Four?

Step Four: You and your partner change places and repeat Steps Two and Three.

Step Five: You and your partner think about the following questions.

What do you think would happen if you moved another five steps away? Do you think that you could still feel the holes in the sponge representation on a tactile card?

Do you think that if you kept moving away from your partner there would be a distance at which the card would be so small that you couldn’t feel the holes in the sponge representation?

If you couldn’t feel the holes, would that make it appear that the sponge was the same all over?

Homogeneous means that matter is evenly distributed in all parts of the sample. If there are parts of the sample that have distinctly different characteristics, the sample is heterogeneous. If the sponge you observed in Part One of the activity is the sample, would you describe it as being homogeneous or heterogeneous? Explain your answer.

What effect did distance have on your observation of the sponge sample tactile card representation? Could the distance at which astronomers observe the structures of the universe make the same kind of difference in how the universe appears to them?

Do you think that observing a larger sponge would have made a difference in your observations? If so, what differences do you think it would have made?

Step Six: Read Part Two of “The Spongy Universe” student text and answer the following questions.

Is a sponge a good model of a homogeneous and isotropic universe? Why or why not?

Do you think that the universe is isotropic and homogeneous? Why or why not?

What further information or observations would you need to make before you could form a better answer to this question?