A Kinesthetic Model of the Big Bang

[Level]{.underline}: High School, grades 9-12

[Courses for the Topic]{.underline}: Physical Science, Space Science,
Astronomy, Chemistry, Physics

[Topics Involved]{.underline}: Models, Scales of Time and Temperature,
Kinetic Theory of Heat, Atoms, Elements, Isotopes, Nuclear Fusion

[Introduction]{.underline}:

*The accumulated, interwoven evidence is so strong, precise, varied and
direct that most*

*[cosmologists now regard the]{.underline} [Big Bang not as a theory or
a model, but as a fact]{.underline}.*

Dr. Craig J. Hogan

> \"Observing the Beginning of Time, \"*American Scientist* (90),
>
> September-October, 2002, pp. 420-427):

Different groups of elements in the universe have formed in different
ways. In this activity students will model the time after the Big Bang
when the first nuclei of hydrogen and helium were created. The students
will move and display cards that show the elements that are formed.
Before forming the model, discuss the concept of the Big Bang. Emphasize
the need to be quiet and follow directions for this activity. Depending
on how much study and discussion of the topic has preceded the modeling,
more or less \"cuing\" by the teacher or a student will be needed.
Caution students to move safely and not bump one another hard. A
caller\'s use of a megaphone will help everyone to hear the cues,
especially if the models are performed outdoors. Use a large area\--an
outside location, a large classroom with seats moved back, or a gym.
Before and/or after the models are made, ask students what features of
the models match and which do not match the conclusions now reached by
science. Students should mention that the numbers of protons, neutrons,
and other particles were much greater than the class number and that the
time involved in the nuclear changes was much shorter.

[Elements to be formed (as nuclei)]{.underline}: Deuterium (H2 or D) and
H3, tritium, and Helium (He3 and He4). along with a single
representative nucleus of lithium (Li7). [Time represented]{.underline}:
About 20 minutes in the early universe.

[Materials Needed]{.underline}: Small cards or stiff paper (index cards
or other) with **p** or **PROTON** printed on one end, and **n** or
**NEUTRON** printed on the other end, in large letters, one for each
student. Also give each student cards individually marked **DEUTERIUM**
**(H2)**, **HELIUM 3 (He3**), and **HELIUM 4 (He4**). These can be
color-coded, for easiest identification. Two different, larger signs
with 10 BILLION DEGREES K (or 10,000,000,000 billion kelvins or 10^10^
kelvins) on one and 1 BILLION DEGREES K (or 1 billion kelvins or 10^9^
kelvins) on the other. One ping pong ball, held by the teacher. Make two
cards, held by the teacher for **BERILLIUM 7** **(Be7**) and **LITHIUM7
(Li7)**.

[Concepts to discuss before the activity]{.underline}

-In the very early universe protons and neutrons formed, [1 neutron for
every 7 protons]{.underline}.

In a class of about 24, 3 students will represent neutrons while 21
represent protons.

-In the very early universe (and in this activity) only the
[nuclei]{.underline} of atoms formed.

-A single proton is a normal hydrogen (H1) nucleus.

-An [element changes when its proton number changes]{.underline}. If a
nucleus adds neutrons but keeps the same number of protons, it remains
the same element.

-A nucleus with a neutron and a proton is \"heavy hydrogen\" or
deuterium (D).

-Helium is any nucleus with 2 protons. Helium 3 (He3) is two protons
with 1 neutron. Helium 4 (He4) is two protons with 2 neutrons.

-He3 and He4 join to become Li7 by first being Be7 and then ejecting an
electron. Only a small amount of Li7 was formed in the early universe.

\- Discuss different ways that protons and neutrons can go together to
get the correct nuclear mass. There are many different types of
reactions between nuclei. A few of them can be modeled easily and are in
the activity sequence. One basic idea for a change is that a neutron can
become a positively charged proton by emitting an electron. This is an
important example of the conservation of electric charge. Discuss ways
that protons and neutrons can form H2, H3, He3, and He4. [Always keep in
mind the conservation of charge.]{.underline} The electrons, positrons
(positive particles like electrons) and neutrinos were an important part
of the reactions, but they have been omitted in the description, except
for the token electron thrown out at the end of the activity.

-At about 100 seconds, Deuterium (D or H2) began to form, and at about
1000 seconds, Helium (He3 and He4) began to form. Lithium (Li7) formed
at about this time as well. This is the period which is modeled in this
activity.

The final outcome in the universe is about 90 percent H nuclei and about
10 percent He nuclei, with practically all the free neutrons gone. (They
should be all gone in this activity.)

-At 10^-34^ -10^-10^ second, a great speed-up in expansion took place.
This acceleration is known as *inflation*. Inflation caused variations
in density of the universe that made the universe eventually break up
into stars, quasars, and galaxies.

-It should be noted that neutral atoms, nuclei plus electrons, did not
form until the universe had cooled adequately. The universe was then
about 400,000 years old. And when the electrons joined the nuclei,
electrons were no longer able to scatter radiation from the Big Bang.
Atomic hydrogen absorbs radiation. The universe became dark, a time
called the *dark ages,* until the universe was about 900 million years
old. Then early stars created enough ultraviolet light to again ionize
the hydrogen atoms. The universe was flooded with light (radiation) just
short of one billion years ago. The radiation came from first stars and
quasars and radiation left over from the Big Bang.

-The elements heavier than hydrogen, helium, and lithium were formed
mostly within stars. (This is the second major cause of element
formation, besides the Big Bang.) Early stars and heavier elements
formed during the universe\'s *dark ages,* 400,000 years to 900 million
years. Galaxies formed after the first stars, the first galaxies
appearing about 1 billion years after the Big Bang. These events
occurred after the time modeled in this activity.

[Note]{.underline}: A common misconception is that both matter and
energy existed in some form at the time of the Big Bang. They did not.
Both were created shortly after the Big Bang, as forces separated from
one another. Scientists now conclude that the Big Bang created
*spacetime*, that is, both space and time. It is not possible to learn
what happened before the Big Bang.

Sequence:

1\. To begin, students arrange themselves in a tight central group
representing the matter that emerges in the first second, a soup of
elementary particles. Students in the model represent parts of forces
that will explode apart to become protons (p\'s or normal H nuclei) and
neutrons (n\'s). Give one student the two temperature cards. Students
have sets of cards with names or formulas: p and n, H2, H3, He3 and He4.

Students hide all cards, since there are no elements before the Big
Bang. If indoors, turn out the lights, representing the absence of
electromagnetic energy before the Big Bang

2\. When the lights are turned on, the teacher or a student calls \"Big
Bang.\" With this cue, the student inside the tight group with the
temperature sign (10 BILLION DEGRES K) sticks it up. Most students hold
up **PROTON** card and a few hold up **NEUTRON.** Students should bend
back and forth rapidly, modeling

particle vibration at the high temperature. While bending, students
start moving out from the dense center.

3\. Some students should encounter (that is, safely bump) other
students. For a while, the \"particles\" should not stick together.

4\. Give the cue call of [\"100 seconds.\"]{.underline} The student with
the temperature signs pulls away the 10 BILLION DEGREES K and sticks up
1 BILLION DEGREES K. Students hold the **PROTON** signs and continue to
bend and move outward. When two **PROTONS** meet, the two students
decide if they want to bounce away or stick by holding hands to form a
deuterium nucleus. Then these students hide their PROTON cards and one
displays a **DEUTERIUM (H2**) card. Couples representing deuterium
continue bending and moving outward to encounter other **PROTONS**.
Couples representing deuterium cannot stick to other single or couples
of students until the next time cue is given. The reaction is: p + p -\>
D + positron + neutrino

There are other ways to get D. One is: p + n -\> D

5\. If a **DEUTERIUM** bumps into a neutron and they join, **HYDROGEN
3** is formed. The three students should hold hands and exchange their
cards for a **H3**. The reaction is: D + n -\> H3

6\. Give the cue call of \"[1000 seconds]{.underline}.\" The
**DEUTERIUM** couples do not have to join to other single or couples of
students when they bump. However, now students can join if they wish.
For a **DEUTERIUM** sticking to a free **PROTON**, the three students
should all hold hands, hide the DEUTERIUM and NEUTRON cards, and show a
**HELIUM (He3**) card. The reaction is: D + p -\> He3

7\. Following formation of He3, if an **He3** joins another **He3**,
only four of the six students should hold hands, hide the **DEUTERIUM**
cards, and show a **HELIUM 4 (He4**) card. Two of the students who were
part of the **He3**\'s should leave the HELIUM 4 group and hold up their
original **PROTON** cards. (Note: Students may want to stick more often
that what correctly models the early universe.)

The reaction is He3 + He3 -\> He4 + p + p

Other possible reactions to produce He4 are: He3 + D -\> He4 + p

He3 + D -\> He4 + n + positron

He3 + n -\>He4

8\. Direct a remaining **HELIUM 3 (He3**) to join with an **HELIUM 4
(He4)** and give them the **BERILLIUM 7** **(Be7)** card and a ping-pong
ball representing an electron. First this group should [hold
up]{.underline} the **BERILLIUM 7 (Be7)** card, then throw out the
ping-pong ball. Then they should [hide]{.underline} the **BERILLIUM 7**
card and hold up the **LITHIUM 7** **(Li7)** card.

9\. The cue call of \"End\" is given. Students freeze in position with
signs up so that all can see what has occurred. Ask students if what the
model shows is the correct ratio of nuclei from element formation in the
Big Bang (90 percent total H and 10 percent total He with almost no free
neutrons). Probably the outcome will be wrong. Ask students what can be
done to make the H to He ratio correct. Students probably will need to
split some nuclei. Discuss who should split and then do it. Student with
the temperature card pulls it down, indicating a further cooling of the
universe.

[Follow-up questions]{.underline} (while still in model positions or
later)

1\. What is wrong with \"freezing\" the motion at the end of the
activity? ([Answer:]{.underline} The atoms continue to move, both
outward from the original source and with kinetic motion, modeled by the
bending.)

2\. How are the numbers of particles and atoms we have formed different
from what really occurred? ([Answer:]{.underline} Actually there were
trillions of hydrogen and helium atoms formed right after the Big Bang.
The small number of students in this model would be a tiny part of the
total.) Most electrons, positrons, and neutrinos were not included.

3\. Why can\'t the groups keep combining like they did in this activity
to form all the elements heavier than hydrogen, helium, and lithium?
([Answer:]{.underline} The universe is not hot and dense enough for
further joining of nuclei (fusion) in this way.)

4\. Since the atoms are moving away from the Big Bang, what caused the
atoms to clump together to form stars, quasars, and galaxies
([Answer]{.underline}: Inflation fluctuations were frozen into
spacetime. That means they were converted into slightly denser and
slightly less dense regions. The force of gravity locally collected
large groups of the atoms to clump together.)

[Extensions:]{.underline}

Use two colors of ping pong balls, one to represent electrons and one to
represent positrons. A flash of a small flashlight at the moment a
neutrino is supposed to be produced can represent a neutrino Have
students discuss and list as many possible nuclear reactions as
possible. In this advanced situation, have many electrons and positrons
join and annihilate one another in the earliest moments after the Big
Bang. When a proton hits an electron, a neutron and a neutrino are
created. When a neutron hits a positron, a proton and a neutrino are
created. When a proton hits a proton, a positron and a neutrino are
created along with the deuterium. Describe the neutrinos as very
energetic particles with no mass.

Discuss the law of conservation of mass and (modified to) law of
conservation of mass and energy as demonstrated by the Big Bang nuclear
reactions.

Let students discuss and then model further stages in the universe: 1)
about 400 000 years, when electrons joined nuclei and the darkening of
the universe as radiation could not get past unionized H atoms. 2) The
forming of stars in the darkness. 3) stars producing light that ionized
H atoms and made the universe transparent again about 900 million years
after the Big Bang.

Add more terminology to discussions: *isotopes* are forms of the same
element with different numbers of neutrons in the nuclei. *Atomic
number* is the number of protons and *atomic mass* is the number of
protons plus neutrons. Deuterium nuclei also are known as *deuterons*.
*Nucleosynthesis* is the production of heavier elements, both in the Big
Bang and in aging stars.

Use scientific (powers-of-ten) notation to represent the large
temperatures and they tiny intervals of time in the very early Big Bang.
Convert 100 seconds and 1000 seconds into minutes; into years.