Science and Universe

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2. Science and the Universe

Humans have always been curious about their envi-

ronment and how they relate to and control it.

Earthquakes, volcanoes, hurricanes, and drought are

examples of natural phenomena that have affected lives

in important ways. People have sought to control these

phenomena, or at least their impact on human lives.

Over the years people have built models or schema

of how natural phenomena worked. In earlier times

these models often claimed a supernatural relationship

among humans, gods, and natural phenomena. Ourmodels of the physical world today have evolved

significantly from those of our ancestors of just a few

generations ago.

Whatever the motivation, we now know more

about the universe than our ancestors did. Their curios-

ity and study helped unveil a structure and order that is

more profound, yet simpler, than they could have ima-

gined. We truly do live in the age of science. Our lives

are partly controlled and greatly enriched by the fruits

of our knowledge, and science gives us the power to

continue improving the conditions under which we live.

Those who have little control over their society

might argue that they need not pay attention to theknowledge and ideas of science. However, in a free

society, citizens are often able to make decisions about

the interaction of science and their lives. Wrong choic-

es might unleash a destructive mechanism or might

deny them the use of a technology that could be the

basis of future prosperity and peace. The freedom to

choose implies the responsibility to understand. If we

use our knowledge unwisely, we have the power to

destroy our civilization.

Our purposes in this book are to describe the uni-

verse and the rules that govern it and to help you gain

some experience with the scientific method of thinking.

We will do this without using sophisticated mathemati-

cal notation even though the description is more elegant

in that form. We cannot describe every detail in a book

of this size, so we have chosen those parts of the uni-

verse that seem to us most interesting and important and

those rules or laws that have the broadest range of appli-

cation. Further, we will explain some of the evidence

that leads us to believe that what we describe is valid.

You will gain the most from your study if you make sure

you understand the relationship between the evidence

and the ideas it supports (or does not support). In doing

so, you will gain experience in using the scientific

method as you learn about our modern understanding of

our surroundings.

The task of physical science is to describe the entire

universe, from its tiniest components to its largest col-

lections of matter, living and nonliving, and to under-

stand the rules governing its behavior. To begin, we

will sketch a description of the universe and show how

the universe is constructed from a few simple compo-nents. You may think of this description as a kind of

map of the material we will discuss in this book. Each

step in the description will be elaborated in subsequent

chapters, where we will elaborate each level of descrip-

tion, explain the rules governing the changes that occur,

and present some of the relevant evidence.

The World Around Us

As we go through life we encounter a dazzling

array of objects and materials. Bricks, rocks, sand,

glass, soil, air, cans, footballs, rain, mountains, trees,

dogs, and many other things are forms of matter thatenrich our lives. And there is motion all around. Rain

falls, rivers flow, the wind blows, cars and people start

and stop, waves move across a lake, objects fall to the

ground, smoke rises, the sun and stars move through the

heavens, and the grass grows. Matter also seems to

change form in arbitrary ways. Wood burns and disap-

pears, whereas water does not burn but may disappear

all the same.

This variety in motion and matter at first seems

unfathomable. How can mere humans, so limited in

senses and mobility, hope to comprehend it all? Can

any order exist in such diversity? Are there rules which

govern change?The answers have come through the centuries, little

by little. Gifted and persistent people have learned to

ask the right questions and how to induce nature to yield

the answers. Each stands upon the shoulders of those

who went before and thereby gains a more complete

view. We together stand at the apex of a great pyramid

of giants from which we view the truth more complete-

ly than people in any other age.

What we see is astounding. Much of the physical

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world can be understood simply. Matter is made up of

only a few kinds of pieces, which can be arranged in

countless ways. The motion we see around us depends

on just a few simple rules. Changes in form and sub-

stance are also easy to understand in terms of a few

comparatively simple ideas. When these rules and ideas

are understood, chaos becomes order. Order and law

really do govern our world. Even living things seem to

operate on the same principles. The laws of force andmotion and chemical change govern the processes of

life as well as the behavior of nonliving objects.

But the view is not yet complete. As we consider

our knowledge and observations, we encounter ques-

tions for which the answers are not yet known. Perhaps

we have not asked the right questions. Perhaps we are

just not yet wise enough to understand the answers. At

any rate, asking and trying to solve the puzzle is half the

fun. We will try to let you share the mysteries as well

as the answers as we proceed.

A distinctive nomenclature is worth noting. When

we speak of objects too small to be seen without a

microscope, we refer to them as microscopic objects.

Atoms, molecules, and their constituents are micro-

scopic, as are most living cells. Objects large enough to

be seen without the aid of a microscope are macro-

scopic. Thus, one way to characterize this chapter is to

say that we are describing the macroscopic parts of the

universe in terms of its microscopic constituents (a

strategy called reductionism). This, as you will see, is

the key to understanding the structure and behavior of

the universe in terms of a few simple ideas.

It is often useful in the study of physical objects to

categorize and compare them on the basis of their size

and the forces that hold them together. The size of aphysical object may be given in terms of its spatial

dimensions. People-sized objects have typical dimen-

sions of a meter or a few meters or a fraction of a meter.

Much smaller objects, such as cells in the human body,

have typical dimensions of micrometers (millionths of a

meter). The extremely small nuclei of atoms typically

have dimensions of milli-micro-micrometers (thou-

sandth-millionth-millionths of a meter). Buildings have

dimensions of a few tens to a few hundreds of meters.

The earth is approximately spherical in shape with a

diameter of about 13,000 kilometers. The earth moves

about the sun in an approximately circular orbit with a

diameter of about 300 million kilometers. The MilkyWay has a diameter of about 100,000 light years. (A light

year is approximately 10 million million kilometers.)

There are four basic forces in nature: strong force,

electromagnetic force, weak force, and gravity. In

some structures these four forces may be at work simul-

taneously and may even have opposite effects. The

strong force is operative only over very short distances

while the electromagnetic force and gravity, in contrast,

reach much further, although they weaken with distance.

Some objects have a characteristic called electric

charge. Charge may be positive or negative and is a

characteristic associated specifically with the electro-

magnetic force. Objects with like charges are repelled

by the electromagnetic force while objects with oppo-

site charges attract one another. Objects may also have

a characteristic called mass. Objects with mass are

attracted (never repelled) by the force of gravity.

Nuclear Matter

All matter as we currently understand it is made up

ofelementary particles, point-like objects without size

or structure. Among these particles we number quarks

and electrons. The electron carries a unit of negative

electric charge. Quarks are charged particles, each car-

rying a positive or negative charge equal to one-third or

two-thirds the charge of a single electron.

Structures called nucleons consist of three quarks

bound together by the strong force. Positively charged

nucleons (called protons) are made of two quarks with

charge2/3 and one with charge 1/3. Neutral nucle-

ons (called neutrons) have one quark with charge

2/3 and two with charge 1/3, adding together to

yield zero net charge.

Nucleons are so small that it would take one mil-

lion million (or 1012) lined up next to each other to reach

across the head of a pin. (We will use the notation 1012

[spoken ten to the twelfth], because it is an easy way

to keep track of the zeros in large or small numbers. By

1012 we mean that we start with 1.0 and move the deci-

mal 12 spaces to the right, resulting in the number

1,000,000,000,000. On the other hand, 1012 would

mean that the decimal point is moved 12 spaces to the

12

Figure 2.1. Models of atomic nuclei: (a) helium, (b)

oxygen, (c) uranium.


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left, resulting in the number 0.000,000,000,001.)

Nucleons are so dense, however, that a pinhead-size ball

made of nucleons packed next to each other would

weigh about a million tons. No crane could lift it.

Nucleons coalesce into incredibly small lumps con-

taining from 1 to 238 nucleons, half or more of which are

neutrons and the rest protons. Each of these tiny aggre-

gates is the nucleus of an atom (Fig. 2.1). Larger col-

lections of nucleons have been formed in laboratories,

but these always break up quickly into smaller groups.

The strong force also holds the protons and neu-

trons in the nucleus of an atom together. Nucleons

attract each other (that is, protons attract other protons

as well as neutrons; neutrons do the same) by means of

the strong force. This means the strong force must over-

whelm the electromagnetic repulsion of the positively

charged protons. (The electromagnetic force holds

atoms, molecules, and people-sized objects together

where the separations exceed the range of the strong

force.) The strong force is responsible for the energy

released by the sun, nuclear reactors, and nuclear ex-plosives. The weak force is also involved in the nucleus

but does not control any of the common structures.

Some of the nuclei found in nature are unstable.

These spontaneously emit high-speed particles. Such

nuclei are called radioactive.

Atoms

Each atomic nucleus carries a positive electric charge

and attracts a certain number of negatively charged elec-

trons. The nucleus and electrons together form an atom.

There is normally one electron in the atom for each pro-

ton in a nucleus, so that the atom is electrically neutral.

Neutrons are in atomic nuclei as well, but the number may

vary for atoms that are otherwise identical.

Compared with its nucleus, an atom is enormous.

If you imagine the nucleus to have a diameter the size

of a ballpoint pen tip, the atom would have a diameter

equal to the length of a football field (Fig. 2.2). An

atom is mostly empty space. In some ways the nucleusis like a small gnat in the center of a large building. The

walls and ceiling of the building and all the space inside

are patrolled by the electrons, which move rapidly about

like a swarm of bees protecting the atom from intruders.

Atoms are 100,000 times as large as their nuclei,

but they are still so small that 5 million are needed to

form a line across the smallest dot. The electrons have

little mass (about 1/1,836 that of nucleons), so atoms

have about the same mass as their nuclei. A pinhead-

size ball of atoms has about 1021 atoms and weighs

about as much as a pinhead.

Although individual atoms are much too small to see,

you are undoubtedly familiar with objects composed of

large groups of essentially identical atoms. For instance,

a copper penny is made of approximately 30 billion tril-

lion (3 1022) copper atoms. A material like copper

composed of only one type of atom is called an element.

Additional examples are iron, helium, and uranium.

Molecules and Crystals

Atoms, in a variety of combinations, make up mat-

ter as we know it. The tiniest speck of dust visible to the

unaided eye contains about 1018 atoms. A sample of air

the size of a sugar cube has about the same number.

Certain atoms join together in small groups by

sharing electrons in a way that takes advantage of elec-

tromagnetic interactions. Such a group of atoms is

called a molecule. Molecules are the basis of many of

the common materials you see around you. Sugar is

composed of molecules, each containing 12 carbon

atoms, 22 hydrogen atoms, and 11 oxygen atoms. Many

molecules contain fewer than 50 atoms, although poly-

mers like nylon are long chains that may contain a mil-

lion or more. A molecule of the common fuel butane is

shown in Figure 2.3.

Figure 2.3. A butane molecule (carbon atoms are shown

in black, hydrogen in white).

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Figure 2.2. An atom is mostly empty space. On this scale,

the nucleus is still only the size of a ballpoint pen tip.


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Molecules do not deteriorate easily, as your experi-

ence with sugar will tell you. Sugar does not sponta-

neously change into some other material. Yet many

common processes can tear molecules apart and

reassemble them in different ways. For instance, sugar

can be burned. It can also be digested to release its

stored energy for use in muscles. This stored chemical

energy (based on electromagnetic forces) has been

mankinds most common source of energy.Atoms attract each other, because the protons in

each atom and the electrons in its neighbors are attract-

ed to each other by the electromagnetic interaction.

Adjacent atoms do not get too close, however, because

the positively charged protons in each atom repel the

protons in the other. The strong force is inoperative at

these distances. Electrons also repel each other. The

net result of these electrical attractions and repulsions is

the force that holds atoms together. We feel this force

when, for example, we tear a piece of paper (separating

some of its atoms from each other), bend a piece of

metal, strike our head against a solid object, or walk

across a room. In fact, these interatomic electric forces

are involved in almost everything we do and are respon-

sible for almost all the forces we experience directly.

Most common materials contain several kinds of

molecules. Milk has over a hundred kinds of molecules

and the human body has somewhere near 50,000. The

task of identifying important molecules and studying

their properties has been one of the great challenges of

modern chemistry and biology.

Some materials are just large numbers of identical

atoms or molecules piled on top of one another. In liq-

uids these slide around each other much like small ball

bearings or buckshot in an open can. In solids the atomssometimes arrange themselves in an orderly array called

a crystal. For example, common table salt is a collection

of equal numbers of sodium and chlorine atoms in a cubi-

cal arrangement. Many solid materials are collections of

small crystals held together by the electrical force. The

type of atomic organization in crystals generally deter-

mines the properties of the bulk material. Carbon atoms,

for example, can be arranged in two different waysone

forms diamond; the other, graphite (the lead in a pen-

cil). Diamond is clear, colorless, and hard; graphite is

opaque, black, and soft. Yet both are composed of the

same kind of atoms. Color Plate 1 (located in the color

photo section near the end of the book) shows regularlyordered carbon atoms in graphite as imaged with a scan-

ning tunneling microscope. Color Plate 2 shows regular-

ly spaced sulfur atoms in molybdenum disulfide as

imaged with a scanning tunneling microscope.

Complexes of Molecules

Some physical objects that we have firsthand

experience with are composed of one or more complex-

es of molecules. Our bodies are composed of various

bony and tissue structures which are very large integrat-

ed collections of complex molecules. The living plants

and animals around us share similar molecular com-

plexes in their structure.

The fuel we burn may be composed of homoge-

neous collections of molecules, as in natural gas, or het-

erogeneous collections of molecules, as in wood.

Buildings are made of steel and concrete and glass;vehicles of metal and plastic. Each in turn is composed

of molecular complexes.

The Earth

The earth on which we live is a huge ball with a

radius of almost 6400 kilometers (4000 miles). It is so

large that we generally perceive it to be flat from our

perch upon its surface. We do not generally notice that

the surface of a lake curves downward so that it is about

30 feet higher at our feet than it is 5 miles away.

Nevertheless, pictures taken from space reveal the over-

all spherical shape, a shape which has been known indi-

rectly for centuries.

The outer layer, or crust, is a comparatively thin

skin composed of a variety of rocks and materials. The

mountains, which seem so magnificent and overpower-

ing to us, are no more than the smallest wrinkles when

compared with the earth as a wholethinner, by com-

parison, than the skin on an apple.

We may think of the whole earth as being the same

as the crust we experience. But the crust is not at all

representative of the interior (Fig. 2.4). The core of the

earth is thought to be a hot (3500 C or more) ball of

iron and nickel under tremendous pressure. The coreseems to have two parts: a solid inner core and an outer

core. The latter has many properties normally associ-

ated with liquids. The core constitutes about 30 percent

of the earths volume and one-half its mass.

Figure 2.4. The internal structure of the earth.

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Inner Core

Mantle

Outer Core


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Surrounding the core is the mantle, a 2900-kilo-

meter-thick layer of solid rock that constitutes most of

the earth. The mantle is composed almost entirely of

rocks made of the elements silicon, oxygen, mag-

nesium, and iron. Evidence indicates that its tempera-

ture ranges from 2700 C just outside the core to 1000

C just inside the crust.

The rigid outer layer of the earth is divided into

several sections, or plates, upon which the continentsrest. These plates move slowly over the surface of the

earth, sometimes colliding with each other with enor-

mous force and sometimes separating to leave a rift

through which molten rock from lower levels may

escape onto the ocean floor. Many of the phenomena

we observe (e.g., earthquakes, volcanic activity, and

mountain building) can be understood in terms of the

motion of these plates. Their discovery and study, a

field of inquiry known as plate tectonics, has been one

of the major triumphs of modern geology.

The gravitational and electromagnetic forces com-

bine to govern the size of the earth. Each piece of theearth is attracted to every other piece by gravity, the

result being a net force directed toward the center of the

earth. As the atoms that make up the earth are pulled

close together by gravity, their interatomic (electromag-

netic) forces begin to resist. Otherwise, the earth would

collapse into a much smaller ball. The nuclear force

also plays an important role in the earths dynamics,

releasing energy from radioactive nuclei that keeps the

interior of the earth hot.

The Solar System

Circling the sun with the earth are eight other plan-

ets (with their moons), several comets, and a variety of

smaller objects called asteroids. Together these bodies

form the solar system (Fig. 2.5). The nine planets are

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,

Neptune, and Pluto. Pluto, usually the outermost, trav-

els in an elliptical orbit that varies from 4 to 5.5 billion

kilometers from the sun and sometimes carries the plan-

et inside the orbit of Neptune. Again, the scale is hard

to comprehend. If we were to start today and travel with

a constant speed of 40,000 kilometers/hour, about as

fast as the fastest rocket, it would take about 14 years to

reach Pluto.

The planets differ in their speeds as they travelaround the sun. Mercury, the fastest at a speed of

170,000 kilometers/hour (110,000 miles/hour), com-

pletes its orbit in just 88 days. Pluto, the slowest, trav-

els only one-tenth as fast and takes almost 250 years to

complete its orbit. The earths orbital speed is a moder-

ate 107,000 kilometers/hour (67,000 miles/hour).

The sun governs these motions through the gravita-

tional force that reaches out through the immensity of

space to hold the planets in their orbits. The sun itself

is a vast collection of atomic nuclei, mostly hydrogen,

and electrons. These charged particles are free to move

about independently of one another in a kind of gaseous

state called a plasma. (Over 99 percent of all visible

matter in the universe is in the plasma state.) The tem-

perature of the sun is quite high, ranging from about 15

million degrees Celsius at the center to about 5500 C

near its surface. The nuclear furnaces of the sun provide

the light that illuminates its satellites. This light is the

principal source of terrestrial energy, providing the

energy for atmospheric motion, for plant and animal

growth, and for virtually every process that occurs on

the planetary surface.

The Milky Way Galaxy and Beyond

The sun is just one of the billions of stars, a few of

which can be seen on any clear night, particularly if

interference from artificial lighting is not too great.

Those closest to us form the Milky Way galaxy (Color

Plate 3, see color photo section near the end of the

book), an immense collection of 100 billion stars held

together by their mutual gravitational attractions. The

stars of the Milky Way are, on the average, about 30 tril-

lion miles apart, a distance so great that it takes light six

years to traverse it. The distance that light can travel in

a year is called a light-year. The galaxy itself is

600,000 trillion miles across; it requires 100,000 years

for light to go from one side to the other, so the diame-ter of the galaxy is about 100,000 light-years. If the uni-

verse were to shrink so that the sun was reduced to the

size of an orange, the stars in the galaxy would be about

1,000 miles from their nearest neighbors and the galaxy

as a whole would be 20 million miles across.

The picture is still not complete. Millions of galax-

ies have been seen through our most powerful tele-

scopes. Each contains billions of stars. Some galaxies

are grouped together in clusters, with individual clusters

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Figure 2.5. The solar system.


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containing as many as 10,000 galaxies. Our Milky Way

is part of a smaller cluster, called the Local Group,

which contains one other spiral galaxy and several

fainter objects. The typical distance between galaxies

in a cluster is a million light years.

With all this, keep in mind that the universe is

mostly empty space. The stars and galaxies, although

immense from our perspective, are mere specks when

compared to the immensity of the universe in whichthey move. The space between them is emptier than the

most perfect vacuum attainable on the earth.

Summary

By now you might feel a little unstable. Think of

the range of things we have describedfrom nucleons

so tiny that a quadrillion of them could fit in a line

across a small pinhead, to clusters of galaxies so vast

that even light takes many millions of years to go from

one side to the other. As the structure is built up level

by level, perhaps you can see that each level of organ-

ization is a logical combination of simpler ones.

Try not to be overwhelmed by all the numbers and

names. The important names will recur in subsequent

chapters so that you will become familiar with them as

we proceed. The short exercises at the end of this chap-

ter will help you to put things into proper perspective.

The purpose of this chapter is to help you develop an

accurate framework into which you can fit the more com-

plete and precise information that follows (Fig. 2.6).

Historical Perspectives

Science as practiced today has evolved over five orso millennia. Some early roots of science may have

appeared as early as 3000 B.C. in observations of the

heavens. The Babylonians developed the art of astrol-

ogy from their observations and charting of lunar cycles

and the apparent motions of the sun and planets. The

Egyptians had a rather sophisticated understanding of the

seasonal cycles, probably motivated by their need to pre-

dict the yearly overflow of the Nile. At Stonehenge in

England stones were arranged so as to predict the

eclipses. In these civilizations the apparent motion of the

sun and the planets played an important role.

The Greek civilization produced many philoso-

phers who pondered nature and described its workings.As we have already noted, Pythagoras (ca. 550 B.C.)

introduced the notion of a spherical earth and a spheri-

cal universe. Democritus (ca. 450 B.C.) introduced the

notion of the atom as the smallest particle into which

matter could be divided. Aristotle (ca. 350 B.C.) envi-

sioned a universe consisting of a spherical earth sur-

rounded by spherical shells containing the planets and

stars. Aristotle taught the young Alexander who

became Alexander the Great and who established a city

16

1026

1024

1022

1020

1018

1016

1014

1012

1010

108

106

104

102

100

10-2

10-4

10-6

10-8

10-10

10-12

10-14

10-16

Universe

Clusters of Galaxies

Galaxies

Distance to nearest stars

Solar System

Stars

Planets

Continents

Mountains

Plants, Animals, People

One-celled organisms, bacteria

Viruses

Molecules

Atoms

Nucleus

Protons, Neutrons

Quarks

?

?

Size[inmeters]

Gravity

ElectromagneticForce

StrongForce

Figure 2.6. The sizes of things. How much larger than

10n is 10n+1?


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and center of learning at Alexandria, Egypt.

Archimedes (ca. 250 B.C.) and Ptolemy (ca. A.D. 150)

were two of many important pupils of the Alexandrian

Academy.

The Ptolemaic model of the universe had a spheri-

cal earth at rest at its center. The planetary motions

were explained in terms of epicyclesone circular

motion about a point which in turn moved in a circular

motion about some other point.When Islamic forces conquered Alexandria (ca.

A.D. 500) there was a flow of scientific information to

the East. Baghdad became a center for the exchange of

knowledge, and many works were translated into

Arabic. Much of the body of scientific knowledge was

preserved and enlarged in nations under Islamic influ-

ence. Many Greek ideas were preserved during this

period at Constantinople, which was not conquered by

Islamic forces until the 15th century.

The Dark Ages encompassed Europe until about

the 15th century, when the Renaissance developed. As

the Greeks lost Constantinople they fled into Europe

and carried with them their scientific and cultural trea-

sures. At this time the Moorish influence in southern

Spain also provided an infusion into Europe of the sci-

ence preserved by the Islamic culture.

In England, Francis Bacon (1561-1626) intro-

duced the inductive method, in which observations of

many specific cases are generalized as the laws of

nature. In contrast, the deductive method employs gen-

eral assumptions (which may or may not be true) from

which specific conclusions are logically deduced.

STUDY GUIDE

Chapter 2: Science and the Universe

A. FUNDAMENTAL PRINCIPLES

1. The Strong Interaction: The interaction between

objects that gives rise to one of four fundamental

forces in nature, called the strong force. The

strong force is a short-range, nuclear force which is

responsible for the binding of the nucleus together

as a structure.

2. The Electromagnetic Interaction: The interac-

tion between objects that gives rise to the electrical

(or, better, the electromagnetic) force. The electro-

magnetic force is also fundamental and is responsi-

ble for binding atoms and molecules as structures.3. The Gravitational Interaction: The interaction

between objects that gives rise to the weakest of the

fundamental forces, the gravitational force. The

gravitational force is responsible for binding struc-

tures such as the solar system and galaxies.

B. MODELS, IDEAS, QUESTIONS, OR APPLICA-

TIONS

None

C. GLOSSARY

1. Atom: A structure made up of a nucleus (contain-

ing protons and neutrons) and surrounding elec-

trons. The electrons are bound to the nucleus by the

electromagnetic force.

2. Core: The spherical center of the earth. The solid

inner core consists of iron and nickel while the liq-

uid outer core surrounds the inner core and consists

of molten iron and nickel.3. Crust: The relatively thin outer layer of rock that

forms the surface of the earth.

4. Crystal: A form of solid in which atoms or mole-

cules arrange themselves in orderly arrays to create

distinctive geometric shapes. Common table salt

exists as crystals.

5. Electric Charge: A characteristic of objects that

determines the strength of their electromagnetic

interaction (force) with matter, specifically with

other charged objects.

6. Electron: A particular kind of elementary particle

that carries a negative charge, has an electromag-

netic interaction with matter, and is a constituent

part of atoms. Electrons are best represented as a

point without spatial extent.

7. Element: A substance made up of atoms, all of

which contain the same number of protons.

Hydrogen, helium, silver and gold are elements.

8. Light-Year: The distance light can travel in one

year, i.e., about 6 trillion miles.

9. Macroscopic: A descriptive adjective referring to

the sizes of objects large enough to see with the

unaided eye. Automobiles and basketballs are

macroscopic objects.

10. Mantle: The spherical shell of rock that lies underthe crust of the earth but overlies its core.

11. Mass: A characteristic of objects that determines

the degree to which they can be accelerated by

applied forces. Mass is also a characteristic of

objects that determines the strength of their gravita-

tional interaction with matter, specifically with

other objects with mass.

12. Microscopic: A descriptive adjective referring to

the sizes of objects at the limit of visibility with the

unaided eye or smaller. Molecules and atoms are

described as microscopic objects.

13. Molecule:A microscopic structure usually made up

of more than one atom.14. Neutrino: A particular kind of elementary particle

that carries no electrical charge, is best represented

by a point without spatial extent, and is particularly

notable for having neither a strong nor an electro-

magnetic interaction with matter. The neutrino

interacts with matter through the fundamental force

called the weak force.

15. Neutron: A composite, strongly-interacting parti-

cle made up of three quarks, but which carries no

17


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net electrical charge. Neutrons are a constituent

part of the nucleus of atoms.

16. Nucleon: A generic name for either a proton or a

neutron.

17. Nucleus: The very small core structure at the cen-

ter of an atom. The nucleus is a structure of protons

and neutrons held together by the strong force.

18. Plasma: A physical state of matter (such as solids,

liquids, and gases) that is characterized by fluidproperties, but in which particles with positive and

negative electric charges move independently.

19. Plates: Pieces or sections of the fractured rigid

outer layer of the earth on which the continents and

ocean basins sit.

20. Proton: A composite, strongly interacting particle

made up of three quarks. The proton carries a posi-

tive electrical charge and is a constituent part of the

nucleus of atoms.

21. Quarks: The elementary particles of which pro-

tons and neutrons consist. A proton and a neutron

each consist of three quarks.

22. Reductionism: A strategy of science to understand

complex structures by reducing them to their small-

er and simpler parts.

23. Solar System: A star with its associated revolving

planets, moons, asteroids, comets, etc.

24. Weak Force: One of four fundamental forces of

nature (strong, electromagnetic, weak and gravity).

Unlike the other three, the weak force is not direct-

ly associated with binding together the common

structures of the universe.

D. FOCUS QUESTIONS

1. Identify at least five levels of organization observedin the universe. Describe these levels of organization

in order, beginning with the smallest, and explain

how each structure is held together. Identify the fun-

damental force which dominates in each structure.

E. EXERCISES

2.1. For each of the following structures, identify

their primary constituent parts and their sizes and the

fundamental force(s) which maintain the integrity of the

structure.

cluster of galaxies

galaxy

solar systemstar

earth

crystal

molecule

atom

nucleus

nucleon

quark

electron

2.2. By analogy or number, contrast the size of the

nucleus and the size of the atom.

2.3. By analogy or number, contrast the distances

between stars, the size of the galaxy, and the distance

between galaxies.

2.4. Describe the organization of the universe.

Show how clusters of galaxies are ultimately composedof the simplest entities we know about.

2.5. Is it true that matter is mostly empty space?

Explain what this statement means by describing the

real structure of

(a) an atom

(b) a steel ball bearing

(c) a galaxy

2.6. Of the five levels of organization listed here,

which is second in order of increasing size and com-

plexity?

(a) quark

(b) apple

(c) moon

(d) gold nucleus

(e) protein molecule

2.7. Which of the following forces is electrical?

(a) weight of a book

(b) force exerted by book on table

(c) gravitational force of earth

(d) force keeping the moon in orbit

(e) force keeping the solar system together

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Science and Universe

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