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 areexamples of natural phenomena that have affected livesin important ways. People have sought to control thesephenomena, or at least their impact on human lives.Over the years people have built “models” or “schema”of how natural phenomena worked. In earlier timesthese models often claimed a supernatural relationshipamong humans, gods, and natural phenomena. Ourmodels of the physical world today have evolvedsignificantly from those of our ancestors of just a fewgenerations ago.

Whatever the motivation, we now know moreabout the universe than our ancestors did. Their curios-ity and study helped unveil a structure and order that ismore profound, yet simpler, than they could have ima-gined. We truly do live in the age of science. Our livesare partly controlled and greatly enriched by the fruitsof our knowledge, and science gives us the power tocontinue improving the conditions under which we live.

Those who have little control over their societymight argue that they need not pay attention to theknowledge and ideas of science. However, in a freesociety, citizens are often able to make decisions aboutthe interaction of science and their lives. Wrong choic-es might unleash a destructive mechanism or mightdeny them the use of a technology that could be thebasis of future prosperity and peace. The freedom tochoose implies the responsibility to understand. If weuse our knowledge unwisely, we have the power todestroy our civilization.

Our purposes in this book are to describe the uni-verse and the rules that govern it and to help you gainsome experience with the scientific method of thinking.We will do this without using sophisticated mathemati-cal notation even though the description is more elegantin that form. We cannot describe every detail in a bookof this size, so we have chosen those parts of the uni-verse that seem to us most interesting and important andthose rules or laws that have the broadest range of appli-cation. Further, we will explain some of the evidencethat leads us to believe that what we describe is valid.You will gain the most from your study if you make sureyou understand the relationship between the evidence

and the ideas it supports (or does not support). In doingso, you will gain experience in using the scientificmethod as you learn about our modern understanding ofour surroundings.

The task of physical science is to describe the entireuniverse, 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, wewill sketch a description of the universe and show howthe universe is constructed from a few simple compo-nents. You may think of this description as a kind ofmap of the material we will discuss in this book. Eachstep in the description will be elaborated in subsequentchapters, 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 dazzlingarray 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. Rainfalls, rivers flow, the wind blows, cars and people startand stop, waves move across a lake, objects fall to theground, smoke rises, the sun and stars move through theheavens, and the grass grows. Matter also seems tochange form in arbitrary ways. Wood burns and disap-pears, whereas water does not burn but may disappearall the same.

This variety in motion and matter at first seemsunfathomable. How can mere humans, so limited insenses and mobility, hope to comprehend it all? Canany order exist in such diversity? Are there rules whichgovern change?

The answers have come through the centuries, littleby little. Gifted and persistent people have learned toask the right questions and how to induce nature to yieldthe answers. Each stands upon the shoulders of thosewho went before and thereby gains a more completeview. We together stand at the apex of a great pyramidof 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 ofonly a few kinds of pieces, which can be arranged incountless ways. The motion we see around us dependson just a few simple rules. Changes in form and sub-stance are also easy to understand in terms of a fewcomparatively simple ideas. When these rules and ideasare understood, chaos becomes order. Order and lawreally do govern our world. Even living things seem tooperate on the same principles. The laws of force andmotion and chemical change govern the processes oflife as well as the behavior of nonliving objects.

But the view is not yet complete. As we considerour knowledge and observations, we encounter ques-tions for which the answers are not yet known. Perhapswe have not asked the right questions. Perhaps we arejust not yet wise enough to understand the answers. Atany rate, asking and trying to solve the puzzle is half thefun. We will try to let you share the mysteries as wellas the answers as we proceed.

A distinctive nomenclature is worth noting. Whenwe speak of objects too small to be seen without amicroscope, we refer to them as microscopic objects.Atoms, molecules, and their constituents are micro-scopic, as are most living cells. Objects large enough tobe seen without the aid of a microscope are macro-scopic. Thus, one way to characterize this chapter is tosay that we are describing the macroscopic parts of theuniverse in terms of its microscopic constituents (astrategy called reductionism). This, as you will see, isthe key to understanding the structure and behavior ofthe universe in terms of a few simple ideas.

It is often useful in the study of physical objects tocategorize and compare them on the basis of their sizeand the forces that hold them together. The size of aphysical object may be given in terms of its spatialdimensions. 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 ameter). The extremely small nuclei of atoms typicallyhave dimensions of milli-micro-micrometers (thou-sandth-millionth-millionths of a meter). Buildings havedimensions of a few tens to a few hundreds of meters.The earth is approximately spherical in shape with adiameter of about 13,000 kilometers. The earth movesabout the sun in an approximately circular orbit with adiameter of about 300 million kilometers. The MilkyWay has a diameter of about 100,000 light years. (A lightyear is approximately 10 million million kilometers.)

There are four basic forces in nature: strong force,electromagnetic force, weak force, and gravity. Insome structures these four forces may be at work simul-taneously and may even have opposite effects. Thestrong force is operative only over very short distanceswhile the electromagnetic force and gravity, in contrast,reach much further, although they weaken with distance.

Some objects have a characteristic called electriccharge. Charge may be positive or negative and is acharacteristic associated specifically with the electro-magnetic force. Objects with like charges are repelledby the electromagnetic force while objects with oppo-site charges attract one another. Objects may also havea characteristic called mass. Objects with mass areattracted (never repelled) by the force of gravity.

Nuclear Matter

All matter as we currently understand it is made upof elementary particles, point-like objects without sizeor structure. Among these particles we number quarksand electrons. The electron carries a unit of negativeelectric charge. Quarks are charged particles, each car-rying a positive or negative charge equal to one-third ortwo-thirds the charge of a single electron.

Structures called nucleons consist of three quarksbound together by the strong force. Positively chargednucleons (called protons) are made of two quarks withcharge !2/3 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 toyield zero net charge.

Nucleons are so small that it would take one mil-lion million (or 1012) lined up next to each other to reachacross the head of a pin. (We will use the notation 1012

[spoken “ten to the twelfth”], because it is an easy wayto keep track of the zeros in large or small numbers. By1012 we mean that we start with 1.0 and move the deci-mal 12 spaces to the right, resulting in the number1,000,000,000,000. On the other hand, 10–12 wouldmean that the decimal point is moved 12 spaces to the

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

left, resulting in the number 0.000,000,000,001.)Nucleons are so dense, however, that a pinhead-size ballmade of nucleons packed next to each other wouldweigh 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 areneutrons 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. Nucleonsattract each other (that is, protons attract other protonsas well as neutrons; neutrons do the same) by means ofthe strong force. This means the strong force must over-whelm the electromagnetic repulsion of the positivelycharged protons. (The electromagnetic force holdsatoms, molecules, and people-sized objects togetherwhere the separations exceed the range of the strongforce.) The strong force is responsible for the energyreleased by the sun, nuclear reactors, and nuclear ex-plosives. The weak force is also involved in the nucleusbut does not control any of the common structures.

Some of the nuclei found in nature are unstable.These spontaneously emit high-speed particles. Suchnuclei are called radioactive.

Atoms

Each atomic nucleus carries a positive electric chargeand 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 mayvary for atoms that are otherwise identical.

Compared with its nucleus, an atom is enormous.If you imagine the nucleus to have a diameter the sizeof a ballpoint pen tip, the atom would have a diameterequal to the length of a football field (Fig. 2.2). Anatom is mostly empty space. In some ways the nucleusis like a small gnat in the center of a large building. Thewalls and ceiling of the building and all the space insideare patrolled by the electrons, which move rapidly aboutlike 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 toform a line across the smallest dot. The electrons havelittle mass (about 1/1,836 that of nucleons), so atomshave about the same mass as their nuclei. A pinhead-size ball of atoms has about 1021 atoms and weighsabout as much as a pinhead.

Although individual atoms are much too small to see,you are undoubtedly familiar with objects composed oflarge 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 coppercomposed 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 theunaided eye contains about 1018 atoms. A sample of airthe size of a sugar cube has about the same number.

Certain atoms join together in small groups bysharing electrons in a way that takes advantage of elec-tromagnetic interactions. Such a group of atoms iscalled a molecule. Molecules are the basis of many ofthe common materials you see around you. Sugar iscomposed of molecules, each containing 12 carbonatoms, 22 hydrogen atoms, and 11 oxygen atoms. Manymolecules 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 isshown in Figure 2.3.

Figure 2.3. A butane molecule (carbon atoms are shownin 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.

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 manycommon processes can tear molecules apart andreassemble them in different ways. For instance, sugarcan be burned. It can also be digested to release itsstored energy for use in muscles. This stored chemicalenergy (based on electromagnetic forces) has beenmankind’s most common source of energy.

Atoms attract each other, because the protons ineach 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, becausethe positively charged protons in each atom repel theprotons in the other. The strong force is inoperative atthese distances. Electrons also repel each other. Thenet result of these electrical attractions and repulsions isthe force that holds atoms together. We feel this forcewhen, for example, we tear a piece of paper (separatingsome of its atoms from each other), bend a piece ofmetal, strike our head against a solid object, or walkacross a room. In fact, these interatomic electric forcesare involved in almost everything we do and are respon-sible for almost all the forces we experience directly.

Most common materials contain several kinds ofmolecules. Milk has over a hundred kinds of moleculesand the human body has somewhere near 50,000. Thetask of identifying important molecules and studyingtheir properties has been one of the great challenges ofmodern chemistry and biology.

Some materials are just large numbers of identicalatoms or molecules piled on top of one another. In liq-uids these slide around each other much like small ballbearings or buckshot in an open can. In solids the atomssometimes arrange themselves in an orderly array calleda crystal. For example, common table salt is a collectionof equal numbers of sodium and chlorine atoms in a cubi-cal arrangement. Many solid materials are collections ofsmall crystals held together by the electrical force. Thetype of atomic organization in crystals generally deter-mines the properties of the bulk material. Carbon atoms,for example, can be arranged in two different ways—oneforms diamond; the other, graphite (the “lead” in a pen-cil). Diamond is clear, colorless, and hard; graphite isopaque, black, and soft. Yet both are composed of thesame kind of atoms. Color Plate 1 (located in the colorphoto 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 asimaged with a scanning tunneling microscope.

Complexes of Molecules

Some physical objects that we have firsthandexperience with are composed of one or more complex-

es of molecules. Our bodies are composed of variousbony and tissue structures which are very large integrat-ed collections of complex molecules. The living plantsand 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 composedof molecular complexes.

The Earth

The earth on which we live is a huge ball with aradius of almost 6400 kilometers (4000 miles). It is solarge that we generally perceive it to be flat from ourperch upon its surface. We do not generally notice thatthe surface of a lake curves downward so that it is about30 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 thinskin composed of a variety of rocks and materials. Themountains, which seem so magnificent and overpower-ing to us, are no more than the smallest wrinkles whencompared with the earth as a whole—thinner, by com-parison, than the skin on an apple.

We may think of the whole earth as being the sameas the crust we experience. But the crust is not at allrepresentative of the interior (Fig. 2.4). The core of theearth is thought to be a hot (3500 °C or more) ball ofiron and nickel under tremendous pressure. The coreseems to have two parts: a solid inner core and an outercore. The latter has many properties normally associ-ated with liquids. The core constitutes about 30 percentof the earth’s volume and one-half its mass.

Figure 2.4. The internal structure of the earth.

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Inner Core

Mantle

Outer Core

Surrounding the core is the mantle, a 2900-kilo-meter-thick layer of solid rock that constitutes most ofthe earth. The mantle is composed almost entirely ofrocks 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 intoseveral sections, or plates, upon which the continentsrest. These plates move slowly over the surface of theearth, sometimes colliding with each other with enor-mous force and sometimes separating to leave a riftthrough which molten rock from lower levels mayescape onto the ocean floor. Many of the phenomenawe observe (e.g., earthquakes, volcanic activity, andmountain building) can be understood in terms of themotion of these plates. Their discovery and study, afield of inquiry known as plate tectonics, has been oneof 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, theresult being a net force directed toward the center of theearth. As the atoms that make up the earth are pulledclose together by gravity, their interatomic (electromag-netic) forces begin to resist. Otherwise, the earth wouldcollapse into a much smaller ball. The nuclear forcealso plays an important role in the earth’s dynamics,releasing energy from radioactive nuclei that keeps theinterior 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 ofsmaller objects called asteroids. Together these bodiesform the solar system (Fig. 2.5). The nine planets areMercury, 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 billionkilometers from the sun and sometimes carries the plan-et inside the orbit of Neptune. Again, the scale is hardto comprehend. If we were to start today and travel witha constant speed of 40,000 kilometers/hour, about asfast as the fastest rocket, it would take about 14 years toreach Pluto.

The planets differ in their speeds as they travelaround the sun. Mercury, the fastest at a speed of170,000 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 tocomplete its orbit. The earth’s 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 ofspace to hold the planets in their orbits. The sun itselfis a vast collection of atomic nuclei, mostly hydrogen,and electrons. These charged particles are free to moveabout independently of one another in a kind of gaseousstate called a plasma. (Over 99 percent of all visiblematter in the universe is in the plasma state.) The tem-perature of the sun is quite high, ranging from about 15million degrees Celsius at the center to about 5500 °Cnear its surface. The nuclear furnaces of the sun providethe light that illuminates its satellites. This light is theprincipal source of terrestrial energy, providing theenergy for atmospheric motion, for plant and animalgrowth, and for virtually every process that occurs onthe planetary surface.

The Milky Way Galaxy and Beyond

The sun is just one of the billions of stars, a few ofwhich can be seen on any clear night, particularly ifinterference from artificial lighting is not too great.Those closest to us form the Milky Way galaxy (ColorPlate 3, see color photo section near the end of thebook), an immense collection of 100 billion stars heldtogether by their mutual gravitational attractions. Thestars of the Milky Way are, on the average, about 30 tril-lion miles apart, a distance so great that it takes light sixyears to traverse it. The distance that light can travel ina year is called a light-year. The galaxy itself is600,000 trillion miles across; it requires 100,000 yearsfor 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 thesize of an orange, the stars in the galaxy would be about1,000 miles from their nearest neighbors and the galaxyas 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 galaxiesare grouped together in clusters, with individual clusters

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Figure 2.5. The solar system.

containing as many as 10,000 galaxies. Our Milky Wayis part of a smaller cluster, called the Local Group,which contains one other spiral galaxy and severalfainter objects. The typical distance between galaxiesin a cluster is a million light years.

With all this, keep in mind that the universe ismostly empty space. The stars and galaxies, althoughimmense from our perspective, are mere specks whencompared to the immensity of the universe in whichthey move. The space between them is emptier than themost perfect vacuum attainable on the earth.

Summary

By now you might feel a little unstable. Think ofthe range of things we have described—from nucleonsso tiny that a quadrillion of them could fit in a lineacross a small pinhead, to clusters of galaxies so vastthat even light takes many millions of years to go fromone side to the other. As the structure is built up levelby 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 andnames. The important names will recur in subsequentchapters so that you will become familiar with them aswe 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 anaccurate 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 haveappeared as early as 3000 B.C. in observations of theheavens. The Babylonians developed the “art” of astrol-ogy from their observations and charting of lunar cyclesand the apparent motions of the sun and planets. TheEgyptians had a rather sophisticated understanding of theseasonal cycles, probably motivated by their need to pre-dict the yearly overflow of the Nile. At Stonehenge inEngland stones were arranged so as to predict theeclipses. In these civilizations the apparent motion of thesun 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 thenotion of the atom as the smallest particle into whichmatter 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 andstars. Aristotle taught the young Alexander whobecame Alexander the Great and who established a city

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1026

1024

1022

1020

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1016

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1010

108

106

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100

10-2

10-4

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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

NucleusProtons, Neutrons

Quarks

?

?S

ize

[in m

eter

s]

Gravity

Electrom

agnetic Force

Strong F

orce

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

10n is 10n+1?

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 AlexandrianAcademy.

The Ptolemaic model of the universe had a spheri-cal earth at rest at its center. The planetary motionswere explained in terms of epicycles—one circularmotion about a point which in turn moved in a circularmotion about some other point.

When Islamic forces conquered Alexandria (ca.A.D. 500) there was a flow of scientific information tothe East. Baghdad became a center for the exchange ofknowledge, and many works were translated intoArabic. Much of the body of scientific knowledge waspreserved and enlarged in nations under Islamic influ-ence. Many Greek ideas were preserved during thisperiod at Constantinople, which was not conquered byIslamic forces until the 15th century.

The Dark Ages encompassed Europe until aboutthe 15th century, when the Renaissance developed. Asthe Greeks lost Constantinople they fled into Europeand carried with them their scientific and cultural trea-sures. At this time the Moorish influence in southernSpain 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 ofmany specific cases are generalized as the laws ofnature. In contrast, the deductive method employs gen-eral assumptions (which may or may not be true) fromwhich specific conclusions are logically deduced.

STUDY GUIDEChapter 2: Science and the Universe

A. FUNDAMENTAL PRINCIPLES1. The Strong Interaction: The interaction between

objects that gives rise to one of four fundamentalforces in nature, called the “strong force.” Thestrong force is a short-range, nuclear force which isresponsible for the binding of the nucleus togetheras 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 interactionbetween objects that gives rise to the weakest of thefundamental forces, the gravitational force. Thegravitational force is responsible for binding struc-tures such as the solar system and galaxies.

B. MODELS, IDEAS, QUESTIONS, OR APPLICA-TIONSNone

C. GLOSSARY1. 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 theelectromagnetic force.

2. Core: The spherical center of the earth. The solidinner core consists of iron and nickel while the liq-uid outer core surrounds the inner core and consistsof molten iron and nickel.

3. Crust: The relatively thin outer layer of rock thatforms the surface of the earth.

4. Crystal: A form of solid in which atoms or mole-cules arrange themselves in orderly arrays to createdistinctive geometric shapes. Common table saltexists as crystals.

5. Electric Charge: A characteristic of objects thatdetermines the strength of their electromagneticinteraction (force) with matter, specifically withother charged objects.

6. Electron: A particular kind of elementary particlethat carries a negative charge, has an electromag-netic interaction with matter, and is a constituentpart of atoms. Electrons are best represented as apoint without spatial extent.

7. Element: A substance made up of atoms, all ofwhich contain the same number of protons.Hydrogen, helium, silver and gold are elements.

8. Light-Year: The distance light can travel in oneyear, i.e., about 6 trillion miles.

9. Macroscopic: A descriptive adjective referring tothe sizes of objects large enough to see with theunaided eye. Automobiles and basketballs aremacroscopic 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 determinesthe degree to which they can be accelerated byapplied forces. Mass is also a characteristic ofobjects that determines the strength of their gravita-tional interaction with matter, specifically withother objects with mass.

12. Microscopic: A descriptive adjective referring tothe sizes of objects at the limit of visibility with theunaided eye or smaller. Molecules and atoms aredescribed as microscopic objects.

13. Molecule: A microscopic structure usually made upof more than one atom.

14. Neutrino: A particular kind of elementary particlethat carries no electrical charge, is best representedby a point without spatial extent, and is particularlynotable for having neither a strong nor an electro-magnetic interaction with matter. The neutrinointeracts with matter through the fundamental forcecalled the “weak force.”

15. Neutron: A composite, strongly-interacting parti-cle made up of three quarks, but which carries no

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net electrical charge. Neutrons are a constituentpart of the nucleus of atoms.

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

17. Nucleus: The very small core structure at the cen-ter of an atom. The nucleus is a structure of protonsand 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 andnegative electric charges move independently.

19. Plates: Pieces or sections of the fractured rigidouter layer of the earth on which the continents andocean basins sit.

20. Proton: A composite, strongly interacting particlemade up of three quarks. The proton carries a posi-tive electrical charge and is a constituent part of thenucleus of atoms.

21. Quarks: The elementary particles of which pro-tons and neutrons consist. A proton and a neutroneach consist of three quarks.

22. Reductionism: A strategy of science to understandcomplex structures by reducing them to their small-er and simpler parts.

23. Solar System: A star with its associated revolvingplanets, moons, asteroids, comets, etc.

24. Weak Force: One of four fundamental forces ofnature (strong, electromagnetic, weak and gravity).Unlike the other three, the weak force is not direct-ly associated with binding together the commonstructures of the universe.

D. FOCUS QUESTIONS1. Identify at least five levels of organization observed

in the universe. Describe these levels of organizationin order, beginning with the smallest, and explainhow each structure is held together. Identify the fun-damental force which dominates in each structure.

E. EXERCISES2.1. For each of the following structures, identify

their primary constituent parts and their sizes and thefundamental force(s) which maintain the integrity of thestructure.

cluster of galaxiesgalaxysolar systemstarearthcrystalmoleculeatomnucleusnucleonquarkelectron

2.2. By analogy or number, contrast the size of thenucleus and the size of the atom.

2.3. By analogy or number, contrast the distancesbetween stars, the size of the galaxy, and the distancebetween 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 thereal 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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