Fisica.

P H Y S I C S : T H E

F U N D A M E N T A L

S C I E N C E

What is physics?

Physics deals with the way the universe works at the most funda-

mental level. The same basic laws apply to the motion of a falling

snow¯ake, the eruption of a volcano, the explosion of a distant

star, the ¯ight of a butter¯y or the formation of the early universe.

It is not dif®cult to imagine that, some thirty thousand years

ago, during a cold, dark spring night, a young child, moved per-

haps by the pristine beauty of the starry sky, looked at his mother

and, in a language incomprehensible to any of us today, asked

her: ``Mother, who made the world?''

To wonder how things come about is, of course, a universal

human quality. As nearas we can tell, human beings have been

preoccupied with the origin and nature of the world for as long

as we have been human. Each of us echoes the words of the

great Austrian physicist Erwin SchroÈdinger, ``I know not whence

I came norwhitherI go norwho I am,'' and seeks the answers.

Here lies the excitement that this quest for answers brings to

ourminds. Today, scientists have been able to pierce a few of the

veils that cloud the fundamental questions that whisperin our

minds with a new and wonderful way of thinking which is

®rmly anchored in the works of Galileo, Newton, Einstein,

Bohr, SchroÈdinger, Heisenberg, Dirac and many others whom

we shall meet in our incursion into the world of physics.

Physics, then, attempts to describe the way the universe

works at the most basic level. Although it deals with a great

variety of phenomena of nature, physics strives for explanations

with as few laws as possible. Let us, through a few examples,

taste some of the ¯avorof physics.

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S U P E R S T R I N G S A N D O T H E R T H I N G S

Figure 1.1. The laws of physics apply to a falling snow¯ake (courtesy

W P Wirgin), the explosion of a star or the eruption of a volcano (courtesy

NASA).

We all know that if we drop a sugar cube in water, the sugar

dissolves in the waterand as a result the waterbecomes thicker,

denser; that is, more viscous. We, however, are not likely to pay a

great deal of attention to this well-known phenomenon. One

inquisitive mind did.

One year after graduating from college, the young Albert

Einstein considered the same phenomenon and did, indeed,

pay attention to it. Owing to his rebellious character, Einstein

had been unable to ®nd a university position as he had wanted

and was supporting himself with temporary jobs as tutor or as

a substitute teacher. While substituting for a mathematics teacher

in the Technical School in Winterthur, near Zurich, from May to

July 1901, Einstein started thinking about the sweetened water

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P h y s i c s : T h e F u n d a m e n t a l S c i e n c e

problem. ``The idea . . . may well have come to Einstein as he was

having tea,'' writes a former collaborator of Einstein.

Einstein simpli®ed the problem by considering the sugar

molecules to be small hard bodies swimming in a structureless

¯uid. This simpli®cation allowed him to perform calculations

that had been impossible until then and that explained how the

sugarmolecules would diffuse in the water, making the liquid

more viscous.

This was not suf®cient forthe twenty-two-year-old scientist.

He looked up actual values of viscosities of different solutions of

sugar in water, put these numbers into his theory and obtained

from his equations the size of sugar molecules! He also found

a value forthe numberof molecules in a certain mass of any

substance (Avogadro's number). With this number, he could

calculate the mass of any atom. Einstein wrote a scienti®c paper

with his theory entitled ``A New Determination of the Sizes of

Molecules.''

Figure 1.2. Albert Einstein.

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S U P E R S T R I N G S A N D O T H E R T H I N G S

On the heels of this paper, Einstein submitted for publication

another important paper on molecular motion, where he

explained the erratic, zigzag motion of individual particles of

smoke. Again, always seeking the fundamental, Einstein was

able to show that this chaotic motion gives direct evidence of

the existence of molecules and atoms. ``My main aim,'' he

wrote later, ``was to ®nd facts that would guarantee as far as

possible the existence of atoms of de®nite ®nite size.''

Almost a century earlier, Joseph von FraunhoÈfer, an illustri-

ous German physicist, discovered that the apparent continuity of

the sun's spectrum is actually an illusion. This seemingly unre-

lated discovery was actually the beginning of the long and tortu-

ous road toward the understanding of the atom. The eleventh and

youngest child of a glazier, FraunhoÈferbecame apprenticed to a

glass maker at the age of twelve. Three years later, a freak acci-

dent turned the young lad's life around; the rickety boarding

house he was living in collapsed and he was the only survivor.

Maximilian I, the elector of Bavaria, rushed to the scene and

took pity of the poorboy. He gave the young man eighteen

ducats. With this small capital, FraunhoÈferwas able to buy

books on optics and a few machines with which he started his

own glass-working shop. While testing high-quality prisms

FraunhoÈfer found that the spectrum formed by sunlight after it

passed through one of his prisms was missing some

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