In Activity 1, students traced the origins of pizza ingredients back to atoms, the building blocks of matter. But atoms have their own building blocks—protons, neutrons, and electrons. And protons and neutrons have their own “fundamental particles”—quarks.

In Activity 2, students explored the characteristics of quarks. Quarks and electrons may have been among the first stable particles formed in the early universe. Most students know something about the characteristics of electrons, but few of them know about quarks or their characteristics.

If electrons are free, stable particles in today’s universe, why aren’t quarks? This question is the basis for this final activity of the series, “Tracing the Origins of Our Universe.” Students will combine the “tracing process” they used in the first activity to trace quarks and electrons backwards in time to discover what important role these fundamental particles may have played in those early cosmic periods when the universe was in a state of high density and high energy. This activity will engage students in a discussion of the energy (temperature) changes that have occurred from the beginning of the cosmos until now.

• Before class make copies of the following handout in the form most appropriate for each of your students:
  1. Student Texts One through Nine, Tracing the Origins of Quarks”
  2. Glossaries that accompany the Student Texts, “Tracing the Origins of Quarks”
• Preview the text material in Braille and using your audio-amplified computer software. Give your visually-impaired students any instructions they need to take advantage of their appropriate learning aids.
• Prepare (or order) a set of the thermally-enhanced tactile cards for each student.

In the Student Text, “Tracing the Origins of Quarks," we have chosen to trace the origins of quarks by running the movie of the beginning of the universe “in reverse.” During this time the universe is getting smaller and smaller. If you continue this process back in time, you come to a point where the mass of the universe is “crammed” into an infinitely dense point. At this time, matter is thought to have been a mixture of quarks, leptons (particles, including electrons, that are not influenced by the strong nuclear force), and theoretical particles, which may have been the source of quarks (and antiquarks).

Where did the particles in the “primal stew” come from? If we had an answer to this question, we would have insight into the beginning of the universe. They may have been produced from energy during the second, very brief epoch or during the Mysterious Epoch immediately preceding it, when the universe was very compact and temperatures were very high. This is in agreement with a premise of the standard cosmological model that the early universe was in a state of high density and high energy.

If this is the case, then matter is frozen energy. The universe, which began in a high-energy state, has been cooling off ever since and hot energy congealed into cold matter. We continue to study quarks in this activity because they appear to be one the first forms of matter in the universe and they are still present today. Not only are they fundamental particles of matter, but they also played a vital role in the formation of atoms and molecules that form the vast structures of today’s universe.

As your students work with this model, emphasize that it is consistent with observations of chemical constituents in the universe. These observations include studies of young and old stars; planetary nebulae; shells of gas ejected by unstable stars; glowing gas clouds; lunar soil samples that Apollo astronauts brought to Earth; and particles of solar wind gathered by sheets of aluminum foil deployed on the surface of the moon. The observed abundances of hydrogen and helium in space match the abundances of those elements predicted from this model.

This model is also consistent with known physical laws and properties of fundamental forces. Examples include the fact that the temperature of matter decreases as it expands (so the reverse would be true as matter condenses) and that the fundamental attractive forces have different strengths and operate through different distances.

As you guide your students through this activity, continue to use the background material in “The Universe is Expanding” and “Remnants of the Big Bang” sections of Appendix A from the original Cosmic Chemistry: Cosmogony module.

For additional background reading, see Appendix A and Appendix C, Student Texts, “The Invisible Fire” and “ Models in Science” from Cosmic Chemistry: Sun and Solar Wind.

This would be a good opportunity to have students address the density changes that occurred during the epochs. Have students examine a set of “Density Balls” that have the same mass in different volumes.

Have students arrange the balls according their masses. [Students will probably think that the steel ball bearing has the most mass. However, this ball is exerting the most force on the smallest area so it only FEELS like it has the most mass.]

Use double-pan balances to show students that all the balls have the same mass. Then tell them that these balls model the size of Epochs 5, 6, 7, and 8. Emphasize that the mass, the amount of matter in the universe, did not change as it went through the epochs.

Now have students arrange these balls in order of size. Then ask:

• Which of these balls would model Epoch 8? [Beach ball]
• Which of these balls would model Epoch 7? [Plastic ball]
• Which of the balls models Epoch 6? [Clay ball]

That leaves steel ball bearing to model Epoch 5.

Now ask, if the density is the amount of matter in a given volume, in which of the Epochs was matter the least dense? [In Epoch 8, 79 grams are contained in the largest volume.]

In which of these Epochs was matter the most dense? [Matter is the most dense in Epoch 5 because the same amount of matter is compressed into the smallest volume.]

What is trend in density of matter as you go back in time from Epoch 8 to Epoch 5? [The density increases.]

Do you think this trend in density continued through Epochs 4 through 1 when matter was in the physical state of plasma? [Accept student answers without comment.]

Plasma is a gas made of charged particles. Scientists have found that when you compress a gas, the temperature of the gas increases. How does the temperature change as we trace the change in the Universe back through Epochs 4, 3, 2, and to Epoch 1?