A Field Guide to the Invisible Universe

It's out there. You can go ahead and look—but you won't find it. Although astronomers can't observe it, most believe the universe is composed of ""dark forms"" of everyday earthly energy and matter. They've come to this conclusion by studying the behavior of light, stars and galaxies. The often warped path or unpredicted change in appearance of these stellar objects suggests the presence of unseen gravitational forces generated by huge amounts of matter. Yet, no matter can be seen!

By Michael DiSpezio|Thursday, December 04, 2003

Making Inferences

Astronomers, like other scientists, often use inference to help explain observations. If the path of a moving object changes, it can be inferred that a force has acted upon the object. In terms of stars and galaxies, that force is gravity. In this activity, you'll make inferences concerning hidden magnets based upon the way their magnetic force field influences a moving steel bearing.

Shoebox lid


Several small magnets

Steel ball-bearing

Graph paper



1. Work in teams of two. Use scissors to cut a rectangle of graph paper that fits within the inner lid of a shoebox.

2. Press out the paper, making sure that it is smooth. Secure it in place with tape.

3. One team member then places magnets on the upper surface of the shoebox lid. Position the magnets randomly and secure with tape. Don’t let the other team member see where you place these "unseen forces."

4.  Next, turn the lid over so the positions of the magnets cannot be seen. Prop the lid against a thick textbook, producing a gentle slope.

5. The team member who didn't place the magnets is challenged to uncover their positions. The strategy involves letting a steel ball-bearing roll down the slope of the lid. Any changes in the path of the bearing are used to make inferences about the location of the magnets.

6. As evidence is collected, the team member marks their assumed positions on the graph paper. When the activity is finished, turn the lid over and verify the positions.

7. Once completed, team members exchange roles and repeat the activity.

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1. What force initially accelerated the ball-bearing? (Gravity.)

2. What force affected the gravity-defined path? (Magnetic force exerted on the steel ball-bearing.)

3. How could the path of the ball-bearing be used to infer the position of the unseen magnet? (The ball's downward path veered toward the magnets. By comparing a series of paths, the bending could be used to infer the location of the magnets.)

4. How can this classroom activity be applied to our understanding of dark matter? (Inferences were made about the location of a force-generating magnet without seeing the actual magnet. That models astronomers assumptions about the presence of dark matter.)

Animated Consumption

Examine the series of nine frames on pages 44 and 45. They are taken from a computer simulation that illustrates the dismantling of a small galaxy by dark matter. That's what a computer can do. Now, it's your turn. Use what you've learned about our unseen universe to create a flipbook animation that illustrates the effect of large mass of dark matter on a spiral galaxy such as our Milky Way.

A Math Connection

According to the pie graph on page 45, what is the most prevalent “component” of the universe? (Dark energy.) How many times more prevalent is dark energy than the luminous matter that makes up the stars, nebulas and galaxies we can see? (Exactly 182.5 times.)

The Evening News


Suppose you were a newscaster reporting the birth and expansion of the universe. Compose a humorous radio script that describes these events. Make sure it is based upon scientific theory and takes into account all forms of matter and energy.

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