Academic journal article The Science Teacher

Our Place in the Spongy Universe

Academic journal article The Science Teacher

Our Place in the Spongy Universe

Article excerpt

Byline: Donna Bogner, John Ristvey, Benning L. Wentworth, Gil Yanow, and Roger Wiens

Physicist James Trefil once described our universe as "The Spongy Universe," comparing large-scale cosmic structures to the structure of a sponge. The NASA Genesis education module Cosmic Chemistry: Cosmogony features the "Spongy Universe" activity in which pairs of students observe a household sponge, making inferences about how the structures and holes in the sponge were made and, by extension, how the structures and voids in the universe may have formed (Bogner and McCormick 2000). Each student pair explores how distance affects our perspective of the universe by measuring the distance at which the observing partner can no longer see the holes in the sponge. Teachers who want to reference this original activity can visit the Cosmic Chemistry website at www.genesismission.org/educate/ scimodule/cosmogony.html.

Because the sponge is such a good model for the universe (see sidebar "A good model," below), the authors modified this "Spongy Universe" activity for use with visually impaired students and pilot tested it at the Colorado School for the Deaf and the Blind. The modified activity and related free online materials-such as teacher guides, activities, tactile card templates, and student texts-are available on the McREL Adapted Curriculum Enhancement (ACE) website at www.ace-education.org/tg_spongy_universe.asp.

A Good Model

Why is a sponge a good model for the universe? In 1981, astronomers from the University of Michigan discovered a hole, or void, in the Bootes constellation. In 1985, another group of astronomers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, found that the universe was full of large bubbles. Cosmologists now refer to these voids as "Hubble bubbles," in honor of Edwin Hubble, an early pioneer in the exploration of the universe. One of the Cambridge astronomers described the solid matter in the universe as looking like what you would get if you sliced through a sponge. He said that it looked like the solid matter was arranged in an interconnected, stringy network with large bubbles in which little, if any, matter can be seen.

Is there anything in the voids? Are they empty of all matter, or might they contain matter that cannot be seen? We know that although sponges have holes, those holes are filled with the invisible gases in air. How and when did the "Spongy Universe" form?

Most scientists have agreed that explanations fall into two categories that are based on when the bubbles were formed in the universe's history. One group of explanations is based on the theory that the bubbles were formed late in the history of the universe by something digging holes in uniformly distributed matter in space. After all, if you have clumps of structures, whether those structures are found in a sponge or in cosmic structures, you will probably also have holes from which the matter in these structures were dug. But what dug those holes? Could an explosion in space have caused the voids? Or could the bubbles have been formed when several smaller bubbles came together?

The other explanation says that the structures survived from the early times of the universe. This explanation infers that cosmic mass was not uniformly distributed in space at the beginning of the universe and that galaxies were long, very dense cosmic strings that formed around the edges of the bubbles.

A household sponge can be a good model for cosmic structures in two ways. The first is the similarity of the structure of the sponge with stringy solids surrounding voids to cosmic structures. Second, as shown in the pilot test student responses, inferences about how the sponge was formed can be analogous to the explanations for how the Spongy Universe was formed.

Reasons for modification

Observing physical properties of natural objects and phenomena is critical to scientific inquiry. …

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