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

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

Epoch Six was twenty-eight minutes and forty seconds long.

The left section of the card represents the end of the epoch. At this time, the temperature was one hundred million kelvins.

Box A at the left side of Epoch Six Tactile Card shows a hydrogen nucleus above the line and a helium nucleus below the broken line. Can you feel that the quarks

are found in the hydrogen and helium nuclei and that the electrons are free, just as they we left them at the beginning of Epoch Seven?

As you go from left to right, through Boxes A, B, and C of the Epoch Six Tactile card,

you are going backward in time. During that time the temperature increases to nine hundred million kelvins.

As the temperature increases, the strong force of the gluons holding the quarks in the proton together still holds the hydrogen nucleus together. Compare what you find above the line as you go from Box A to Box B to Box C. Can you feel that hydrogen nucleus, with two up quarks and one down quark stays the same as the temperature increases as we go back to the beginning of the epoch?

Now go from left to right below the line in the middle of the card. In Box D you will find one helium nucleus. In Box E you will find that the helium nucleus has separated into two smaller nuclei.

The strong force holding together the two protons and two neutrons in the helium nucleus is partially overcome as the temperature increases and two deuterium nuclei are formed.

Deuterium is another form, or isotope, of hydrogen. All hydrogen atoms have one proton in the nucleus, but in each deuterium nucleus, we also find one neutron. Less than three percent of the hydrogen in our atmosphere is in the form of deuterium.

So midway through the epoch, we have one hydrogen nucleus and two deuterium nuclei and three free electrons to balance the charge.

Deuterium nuclei are not stable, however. As the temperature continues to rise, the protons and neutrons in these nuclei are separated from each other. This is shown in Box F.

The mixture of particles present at the beginning of Epoch Six when the temperature is the hottest is shown in the Boxes C and F. The actual universal “brew” at the end of this epoch contained about six times more protons than neutrons.

Quarks are now found bound tightly together in those free protons and neutrons. Electrons remain as free particles.