This student text describes Epoch Five in our Evolving Universe. It is the fifth student text of the Tracing the Origins of Our Universe activity.

The time frame for the Fifth Epoch is about one and a half minutes—from ten to the negative third second to 100 seconds.

Things really begin to heat up, light up and become compressed as we go backwards during this short time.

They heat up because during this Fifth Epoch, the temperature is about one billion kelvins.

They light up because there is high-energy radiation being given off during nuclear changes.

It is compressed because the universe continues to shrink in size as we get closer to the Epoch One.

The Epoch Five Tactile Card illustrates what happened to quarks as we go back through this epoch. Feel the number Five in the upper left corner of the card. Place your Epoch Five Tactile Card to the right of the Epoch Six Tactile card on the table.

Quarks play a major role in the changes taking place during this epoch. In the upper right section of the Epoch Five Tactile card, there is one proton and one neutron with an equal sign between them.

This shows us that at the beginning of the epoch, at ten to the negative third second, there were equal numbers of protons and neutrons.

This means that there were also equal numbers of “up” and “down” quarks present at the beginning of the epoch.

By the end of the epoch, there were about six times as many protons as neutrons. In the Box A of Epoch Five Tactile there are six protons and one neutron. The number of “up” quarks is greater than the number of “down” quarks.

What happened to change the numbers of different varieties of quarks during this short epoch? The simple answer is that the neutrons underwent a process called nuclear decay.

Neutrons are slightly greater in mass than protons and they are not stable at the high temperatures present in Epoch Five. The average life of a “free” neutron—one that is not in a nucleus—is ten minutes at the temperatures of today’s universe. At the very high temperatures in the Fifth Epoch, many of them decayed in the one hundred seconds that made up this epoch.

Protons are more stable than neutrons. Their average life is more than ten to the thirtieth power years even at high temperatures. So none of them decayed during this epoch.

Box C of Epoch Five Tactile Card shows the important changes that happened during nuclear decay.

The one “up” quark and two “down” quarks at the right side of Box C is the symbol for a neutron.

Immediately to the left of the neutron, the arrow indicates that a nuclear decay is taking place.

To the left of the arrow, you will find four symbols that represent the result of the decay.

When a neutron decays, the stable particles that result are a proton and an electron. In addition, a positron and a neutrino are formed.

Immediately to the left of the arrow, the two “up” quarks and one “down” quark symbolize the stable proton that results from a neutron decay.

The dash represents a negatively-charged electron.

Moving to the left, the cross represents a positively-charged electron, called a positron.

And farther to the left, an open circle represents a neutrino, which is an electrically neutral, almost massless particle.

Note what happens to the number of “up” and “down” quarks as a neutron decays. A neutron contains two “down” and one “up” quark. The proton consists of two “up” quarks and one “down” quark.

For every neutron that decays, there is a gain of one “up” quark and a loss of one “down” quark.

What happens to the other products of neutron decay? Neutrinos isolate themselves and lead rather independent lives. Because all of this is taking place in rather limited space, they occasionally collide with electrons and other particles.

Electrons and positrons immediately collide with each other because they have opposite charges. They then undergo matter-antimatter annihilation that results in the formation of high-energy electromagnetic photons.

Comparatively few of the newly-formed electrons survive this mass extinction. The ones that do are those that we found in the plasma brew of the Sixth Epoch.