a physicist's guide to skepticisim - milton a. rothman

8/22/2019 A Physicist's Guide to Skepticisim - Milton a. Rothman

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GUIDE TO SKEPTICISM

Applying laws of physics to faster-than-

ight travel, psychic phenomena, telepathytime travel, UFO's, and other

pseudoscientific claims

MILTON A. ROTHMAN

PROMETHEUS BOOKS

Buffalo, New York

A PHYSICIST'S GUIDE TOSKEPTICISM. Copyright 1988 by Milton

A. Rothman. Printed in the United Statesof America. No part of this book may beused or reproduced in any manner whatsoever without written permission,

except in the case of brief quotations


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embodied in critical articles and reviewsnquiries should be addressed to

Prometheus Books, 700 East Amherst

Street, Buffalo, New York 14215.

91 90 89 88 4321

Library of Congress Cataloging-in-Publication Data

Rothman, Milton A.

A physicist's guide to skepticism

1. Science—Philosophy. 2. Physics. 3.

Reality. 4. Skepticism. I. Title.

Q175.R5648 1988 501 88-4077

ISBN 0-87975-440-0


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To Miriam


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NTRODUCTION

This book is philosophy of science as

understood by an experimental physicist,written for the nonspecialist. It contains aminuscule amount of mathematics and nosymbolic logic. Thus, it follows in the

radition of Percy Bridgman and Peter Medawar.1,2

The underlying theme of this book is: How

do we trace the boundary between fantasyand reality? This question is not merelyhypothetical; successful existence in thereal world requires a good ability to

define this boundary with some accuracy.Because illusions and hallucinationsabound, rational man has been forced tocreate a system of elaborate mechanisms


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and methods which aid in recognizingreality and separating it from the world offantasy. These methods make up the

system of knowledge called science.Thinking outside of science's domainnvariably involves a large measure of

fantasy. Disciplines that do not

ncorporate reality-testing into their methods are non-sciences.

The philosopher Mario Bunge has defined

a number of criteria that must be met by ascience to distinguish it from non-science.3,4 I will paraphrase some of hese criteria:

1. A science deals with real entities inspace and time.


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2. A science has a philosophic outlook according to which the real world consistof lawfully changing concrete things (as

opposed to unchanging, lawless, ghostlyhings) described by a realistic theory of

knowledge rather than an idealistic theoryBy an idealistic theory we mean a theory

n which ultimate reality consists of themmediate perceptions of our minds andhe world outside the mind is nothing butnference. A realistic theory reverses this

position, holding that real things are outhere in the world and that we infer their

nature on the basis of signals collected by

our brains.)

3. The contents of a science change over ime as a result of the accretion of new

knowledge. This knowledge (as opposed


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o eternal verities handed down by higherauthority) is acquired through research.The regular increase in validated

knowledge is one of the most reliablemeasures of a science.

4. The members of the scientific

community are specially trained,communicate information amonghemselves, and carry on a tradition of

free inquiry.

5. Theories in science are logical or mathematical (as opposed to theories thatare empty or formal).

6. A science has a fund of knowledgeconsisting of up-to-date and testableheories (which may or may not be final),


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hypotheses, and experimental data.

7.The aims of a science include the

systematizing of data and hypotheses intoheories and laws, followed by the use of hese laws to make specific predictions

about the workings of natural systems and

man-made devices.

The ability of a science to make specificpredictions is central to our confidence in

ts validity. If a system of theories cannotmake predictions about observable eventshen there is no reason to believe in it andt is not a science.

The first two criteria for a science givenabove explicitly imply the principle of reductionism. Reductionism is the


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philosophical position that the structureand behavior of all objects (includingiving things) can be reduced to the laws

governing the behavior of the fundamentalparticles out of which everything is built.However, we are far from being able tomake specific predictions about the

behavior of living things starting with theknown laws governing the motion of electrons and protons, because structuresnvolved are simply too complicated.

Reductionism, when applied to thebiological sciences, raises so manydifficulties that a number of scientists

doubt its validity. But either the laws of physics apply to living things or there arespecial laws, forces, or forms of energyhat act only within living beings. Those

who assert the existence of special forces


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attempt thereby to introduce vitalism andother religious concepts into scientificphilosophy; those who deny them maintain

science on a strictly materialistic level, inaccordance with the criteria above.

The opponents of reductionism base their

arguments upon the fact that we are unableo show how the laws of physics explainhe assemblage of fundamental particlesnto living organisms. Therefore, they

argue, other laws that apply specifically those living systems must be used.

n this book I will show that our thinking

about the laws of nature can be simplifiedby dividing these laws into two major classes— laws of permission and laws ofdenial:


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1. Laws of permission are those thatenable us to predict what things are likelyo happen to a system under a given set of

circumstances. In classical mechanics,ewton's second law of motion and

Hamilton's equations are representative osuch laws. In quantum mechanics, the

Schroedinger and Dirac equations areamong the many recipes for predicting thefate of a system.

2. Laws of denial are rules that tell uswhat cannot happen to a system of objectsSuch laws are known to physicists as"symmetry principles": space symmetry,ime symmetry, and Lorentz symmetry arehe most prominent among them. They are

alternative, abstract ways of stating the

classic laws more familiarly known as


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conservation of momentum, conservationof energy, and the principle of relativity.All events that take place in the universe

must obey these laws; that is, they mustfollow these symmetries, which veryprecisely separate the class of events thatmay happen from that that is forbidden.

Hence the appellation "laws of denial."

As we will see in Chapter 5, predictionsmade from the laws of permission may

often be quite imprecise. Some systems—even very simple ones—may be sochaotic that predictions of their motion arcompletely impossible. On the other handpredictions made with the laws of denialare always exceedingly precise andunequivocal. They put strict limits on wha

s allowed to happen. They permit us to


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use the word impossible with greatconfidence, in spite of protests from thosewho would like to believe that "anything

s possible."

n this book I survey the reasons for believing that the laws of denial describe

nature to a very high degree of precisionand explore the manner in which theseaws define the boundary between the

possible and the impossible, between

fantasy and reality. It will becomeapparent that even science requires the usof some fantasy, so that even under thebest of circumstances there is someuncertainty as to what is fantasy and whats reality. But we will also see that the

aim of science is to reduce this uncertaint

o a minimum.


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Understanding the laws of denial gives aogical basis for skepticism.

Pseudosciences make claims of

extrasensory perception, psychic energy,poltergeists, unidentified flying objects,and other exotic phenomena. It requireshe knowledge of only one basic principle

of science, namely, the law of conservation of energy, to justify aposition of extreme skepticism towardhese claims. Conservation of energy, as

we shall see in Chapter 4, isexperimentally verified to a degree of precision that makes it one of the most

firmly grounded and solid pieces of knowledge in history. With such apermanent bit of knowledge in hand, wecan justify our skepticism toward claims

for phenomena that purport to do what in


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reality cannot be done.

One word of caution for the reader with

ittle background in physics: Chapters 2,3, and 4 are a quick summary of essentialphysical fundamentals. Those who havenot read much in the way of modern

physics may find it heavy going. Iencourage you to persevere. Chapter 5 ishe heart of the book, and the chapters

after that deal with matters more

philosophical and less technical.

otes

1. P. W. Bridgman, The Nature of Physical Theory (Princeton, N.J.:Princeton University Press, 1936).


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2. P. B. Medawar, The Limits of ScienceNew York: Harper & Row, 1984).

3. M. Bunge, Understanding the WorldDordrecht: D. Reidel, 1983).

4. M. Bunge, Skeptical Inquirer, 9 (Fall

1984): 36.


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BELIEFS AND DISPUTATIONS

1. Everybody's a philosopher

Everyday anarchy romps through thecurrent intellectual scene: an engineer writes books on evolution, a science

fiction writer becomes a psychotherapyguru and founds a new religion, apsychoanalyst rewrites the laws of celestial mechanics, theologians give

pronouncements on physics, physicistswrite books on theology, and legislatorswrite laws defining life.

Within this confusion a few fundamentalsremain constant:

a. A strong belief is more important than a


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few facts.

b. The stronger the belief, the fewer the

facts.

c. The fewer the facts, the more peoplekilled.

Recall the image of Jacob Bronowski inhis historic television show, The Ascentof Man, standing in a pool at Auschwitz,

dredging up a handful of mud possiblycontaining the ashes of his parents,describing how factless theories believedwith total certainty by the Nazis resulted

n the death of 50 million humanshroughout the world during the period

from 1939 to 1945.1


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f disputes between facts and beliefs wereeasy to decide, Galileo would not havebeen threatened for claiming that the earth

moved. He had the correct fact in hand,but was powerless to change the beliefs oothers with that fact. His adversaries, onhe other hand, had only beliefs and

powers.

Have matters improved since 1600? Tohe extent that our lives no longer literally

depend on our cosmological theories, weare better off. Nobody is in fear of tortureand execution for advocating evolution orhe big-bang theory (at least in countries

of the West). However, the fortunes of extbook writers still depend to some

extent on the way they treat evolution in

heir writings. In addition, the livelihoods


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of all of us depend on economic theoriesheld by elected officials, theories whichoften assume the character of theological

passions. In the years following 1980, theAmerican public was subjected to aneconomic experiment intended to test theheory that lowering the tax rate would

ncrease the government's income. Therony of this is that while medical

experimentation on humans is forbiddenexcept under strict controls, there are nosuch safeguards governing economicexperimentation. Implementing the Laffer economic theory resulted in an immediate

decrease of government income, with aconsequent record leap in budget deficits.Here is an example of a governmentbasing its actions on a theory unsupported

by material facts or serious mathematical


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analysis. In cases of this nature, faith in aneconomic theory cannot be distinguishedfrom religious faith.

While killing for the sake of beliefs isofficially frowned upon in the UnitedStates, there are plenty of people willing

o jail anybody who acts on the belief thata one-month-old fetus is not a humanperson. A physician who believes that theife of a severely deformed infant should

not be indefinitely and artificiallyprolonged can end up in serious trouble ifhe or she acts accordingly.

Wars of philosophical belief are wageddaily in the media and on picket lines.Unfettered by standards of scholarship,undaunted by peer review, every citizen


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feels entitled to express his or her view ohe most profound subject. Advocacy

groups pressure legislators to dictate wha

brand of science should be taught inpublic schools, what form of prayer should be encouraged, and how life maybe legally terminated. We have become a

democracy of philosophers.

These disputes of pop philosophy arecarried out with a freeform logic whose

favorite rhetorical weapons are a series oquestions beginning with the lethal prefix,"How do you know . . . ?"

n abortion debates the refrain is:

How do you know a fetus is not a humanbeing?


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How do you know a fetus doesn't feelanything?

How do you know when life begins?

n environmental conflicts:

How do you know smoking causescancer?

How do you know radiation from a

microwave oven or a computer terminalor a digital watch) will not harm the

user?

How do you know that radioactivewastes can be stored safely for a thousandyears?

How do you know TMI won't blow up


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as soon as it's rebuilt? In arguments over evolution and creationism:

How do you know the earth was createdor not created) 10,000 years ago?

How do you know that the laws of natur

which existed thousands of years ago arehe same as the laws that hold today?

How do you know that a creature as

marvelously complex as a human beingcould have been created without a guidingplan from a higher power?

n discussions of science fiction, UFOs,parapsychology, and the like:

How do you know we can't find a way to

ravel faster than light?


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How do you know antigravity ismpossible?

How do you know that the laws of naturwe believe true today won't be found falsn the future?

How do you know there is no life after death?

How do you know ESP (telepathy, etc.)

s impossible?

How do you know that paranormalphenomena, such as teleportation,

elekinesis, and poltergeists, arempossible?

How do you know parapsychology is a

pseudoscience?


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Each question is hurled as a challenge,with the implication that there is no wayof knowing the answer. It follows, then,

hat the theory backed by the questioner isat least as good as his opponent's.

n fact, the insinuation behind the question

s that if the opponent cannot answer thequestion with perfect certainty, then theheory he supports must be all wrong.

The ultimate weapon in this form of logics the claim that all theories are equal— he final democratization of philosophy. Ifheory A cannot be proved with complete

certainty, then it is no better than theory Bever mind that theory B cannot be

proved at all. This is the philosophybehind the legal claims of the creationists


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since the proof of evolution is notcompletely without holes and loose ends,hen the competing theory of creationism

must be just as good and therefore must beaught on an equal footing in the schoolseven though there is no validation at all

for creationism).

n the face of such logic we might wonderwhether we can know anything for sure.

There is nothing new about this problem.The Greeks also wrestled with it, givingus the word epistemology—the study of how we know what we know. Assuming,

of course, that we know something.Otherwise, none of this makes sense andwe may as well give up thinkingaltogether.


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A better way to formulate the question is:How much of what we think we knowrepresents something real in nature, and

how much is fantasy, opinion, hypothesis,or sheer delusion? And finally we ask:How does knowledge get into our heads?Does it enter only through our senses, or

are there other, more direct ways of knowing? These are serious questions.

A good part of epistemology has been

aken over by modern science— particularly physics, psychology, andneurophysiology. Through physics weearn the nature of the world around us.

Psychology gives us insight into the waywe put elementary observations together o make complex thoughts. It is the study

of the world within the mind. A cautionar


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science, it warns us that not every sensoryperception is valid. The psyche is proneo accidents ranging from misperceptions,

fantasies, illusions, delusions, all the wayo hallucinations. The link between

psychology and physics isneurophysiology, which, through detailed

study of the nervous system, attempts toshow how thoughts are related to specificactivities going on in the brain.

n spite of the inroads being made by thenatural sciences, epistemology is stillalive and well, most commonly under theheading of philosophy of science.Whenever scientists try to go fromobservations to theories, they becomephilosophers. The interpretation of

observations is as important in science as


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performing the observations. Getting in thway of interpretations are the knottyquestions:

What are the assumptions built into ascience?

What is the relationship between theoryand observation?

Is it possible to make an observation

without using some theory hidden withinhe observation itself?

How do we make general laws that

apply to the whole universe

when we can observe only a very limitedsample of that universe?


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When even our best scientists disagree onanswers to these questions, it is notsurprising that the public remains

confused and that anyone can withcheerful abandon parade his beliefs asfacts.

Yet, in spite of disagreements, somedegree of certainty can be assigned toscientific knowledge. Scientists haveearned some things during the past few

centuries; science does accumulate. Theaccumulation of knowledge is, in fact, oneof the criteria for distinguishing a sciencefrom a non-science. While we read fromime to time that "establishment"

knowledge is unsure and subject toconstant change, the fact is that at least

some of the things we now know are


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known "for sure" and are not going tochange. After all, planes do fly, computercompute, and a man-made space vehicle

can travel for many years past Jupiter,Saturn, and Uranus, following a calculatedpath with exquisite precision. When youpush the appropriate switch, the electric

ight always goes on (barring malfunctionof the system, of course). The existence ofour technological civilization depends onhe certain knowledge of discrete facts

and general principles. Without suchknowledge you are never sure that theelectric light will go on every time you

flip the switch.

t's fashionable to raise the cry: "How doyou know the laws we believe now won't

be overturned in the future?" (This plaint


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s commonly raised in science-fictioncircles whenever a scientist disputes thepossibility of cherished fantasies such as

faster-than-light travel or ESP.) To provehat one has read a book on philosophy of

science, one makes obeisance to ThomasKuhn's concept of paradigm change. To

prove open-mindedness, one implies thatall paradigms are subject to change,sooner or later.2

But, in fact, nowhere does Kuhn imply thaall theories are subject to change. The fachat a theory went through one revolutionn the past doesn't mean that it is

automatically subject to further revolutionn the future. The first revolution may hav

established the theory with sufficiently

strong evidence to make it a permanently


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grounded theory. It required a violentrevolution to establish the idea that theplanets go around the sun. Does anybody

outside of a tiny band of extremists)believe that this theory is subject to furthechange? We can go to the planets becausewe know their precise orbits. Reaching

he planets verifies the theory. That's asdirect a proof as you can get.

Quite simply, one of the jobs of scientists

s to search through mankind's collectivenformation bank and to decide which of he bits of information stored there are

facts known with a high degree of certainty and which others are in actualityopinions, theories, or conjecturesmasquerading as "facts" and subject to

change in the future. This is not an easy


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ob. To decide between fact andconjecture requires an enormous fund of detailed knowledge, together with a talent

for discerning how knowledge fits itself nto patterns.

Facts by themselves mean nothing. What

separates a fine scientist from a simpledata collector is a highly developed skilln pattern recognition. In physics, patterns

of knowledge are called laws of nature.

More precisely, they are laws written byhumans to describe what exists in nature.An understanding of these laws allows uso answer at least some of the questionshat begin, "How do you know. . . ."

These philosophical problems belong tous all, not just to academics and dwellers


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n ivory towers. Attacks on the teaching oevolution in schools have a chilling effecton school boards and textbook publishers

have felt the weight of criticism for merely using the word "evolution" in achemistry textbook. If the teaching of science is to be dictated by those who

understand neither science nor the logic oscientific discovery, then our entirecountry will suffer from the ignorance of he next generation.

2. How do you know perpetual motion ismpossible?

To some people the word "impossible" isoffensive. "Anything is possible if youonly try hard enough," is their battle cry.The obvious absurdity of this statement


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seems to escape a large number of peoplefor it is uttered often enough to create afog of optimism permeating the national

psyche. Yet I know I will never play thepiano like Vladimir Horowitz, no matter how hard I try. The proof is that thousandof piano students try exceedingly hard;

none of them play like Horowitz, and mosof them are better than me. There areimitations to my nervous system, as well

as limitations to the human nervous systemn general.

There are also limitations to whatmachines can do. For hundreds of yearshere have been attempts to build a

perpetual motion machine: a machine thatwould operate indefinitely, doing useful

work without burning fuel. The quest for


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he perpetual motion machine has rivaledhe search for the holy grail, everlastingife, and the transmutation of lead into

gold.3 Some perpetual motion seekers of he past spent lives pathetically obsessed

with their compulsion to turn fantasy intoreality. Others were simply con men,

preying on the credulity of their fellowcitizens to make a fast buck.

A typical example of perpetual motion as

a con game was the device created by oneJ. M. Aldrich late in the 19th century. Thehistory and operation of this device washoroughly exposed in the Scientific

American of July 1, 1899. The deviceconsisted of a wheel with a number of weights attached by levers to its

periphery. It was designed so that the


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weights on one side of the wheel layfurther from the center than the weights onhe other side. The imbalance thereby

created was supposed to keep the wheelrotating forever, since gravity presumablypulled more strongly on one side of thewheel than the other.

Unfortunately—for the investors whohought they were going to get rich by

harnessing this machine to an electrical

power generator— what really kept themachine going was a secret spring hiddenn the mechanism's wooden base. With the

spring unwound, the wheel stubbornlyrefused to remain in motion for very long.t was very much a non-perpetual motion

machine. As a result, Mr. Aldrich spent

some time in jail, and those who had


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bankrolled him bid adieu to their money.

The tragedy of this story is that any good

physicist of the time could have told thesebenighted folk that the machine could notpossibly work, and that if they hadperformed some elementary engineering

analysis they might have seen that theapparently unbalanced wheel was inactuality perfectly balanced. Their reasonfor not asking advice could have been any

one of the following:

It did not occur to them that scientistsmight have a set of rules that allowed the

o predict how the machine might or mighnot work.

Or, they thought: What do scientists


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know? They've been proved wrongbefore, so they are probably wrong now.

Or, they thought: Anything is possible if you try hard enough.

Scientists are no strangers to these

problems. Attempts to create perpetualmotion machines have been made sincehe era of Plato and Archimedes. Detailed

records of these attempts started

appearing in the 15th century. During thefollowing three centuries, the generalnability of inventors to build a working

perpetual motion machine began to alert

he scientific community to the fact that anmportant folly was being perpetrated. As

a result, perpetual motion's perpetualfailure became a significant contributor to


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he budding science of mechanics duringhe 16th, 17th, and 18th centuries.

Pragmatic scientists such as SimonStevinus, Galileo Galilei, and ChristianHuygens, observing the fact that perpetualmotion machines have never been seen to

work, jumped to the conclusion thatperpetual motion machines cannotpossibly work. However, they did nothave a fundamental reason for coming to

his conclusion. It was an induction from anumber of known facts, not a deductionfrom a more general and more powerfulheory. Therefore it suffered from the

universal flaw of induction, namely, howcan one generalize from a small number oobservations to a rule that is true for ever

possible situation? If you observe, say, 24


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perpetual motion attempts that end infailure, how can you be sure that all futureattempts will also end in failure? To be

sure of this, you must find a general lawhat is known to be true in all situations.

A general law covering the perpetual

motion situation began to emerge duringhe 18th century, when the concept of

mechanical energy (kinetic plus potentialenergy) was created. Theoreticians such

as Joseph Louis Lagrange were able toshow that under very general conditionse.g., in the absence of friction),

mechanical energy was something whosequantity never increased or decreasedwithin any closed system). Starting withhat observation, scientists could, with

some degree of confidence, advance the


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principle that no mechanical device canbe built that creates energy out of nothing,or that puts out more energy than is put

nto it. Accordingly, the French Academyof Science decided, in 1775, to cease thedrain of resources occasioned bynterminable reviews of the many

proposals received for perpetual motionmachines. The reason was not simply thatnone of these machines had worked in thepast, but that there was now a well-established law of nature from which itcould be predicted that none would work n the future.

Of course that didn't stop the inventorswho took up the cry, "How do you knowyour theory applies to all kinds of

energy?"


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For energy turned out to be a most plasticand changeable idea, as demonstrated byhe rise in the 18th century of an entirely

new technology, that of engines creatingmotion from the marvelous properties of expanding steam. Some thought that thesenewfangled heat engines could somehow

get around the restrictions of a theory thatapplied only to mechanical systems. Andater on came the science of electricity.

Who knew what wonders might arise fromhese developments? And so the inventors

persisted.

But the physicists also persisted. As weshall see in the next section, one major scientific trend of the 19th century was thegrowing recognition that each new form o

energy discovered was convertible


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without loss or gain into all the formsalready known. In this way, energyevolved into a powerful general concept,

and the principle of conservation of energy became one of the most powerfuland fundamental laws of nature, assuringus that in any closed system energy cannot

be created or destroyed, regardness of how it may change from one form toanother.

Even though our belief that energy cannotbe created from nothing presently rests onan extraordinarily firm basis, attempts tobuild machines that put out more energyhan is put in are still taking place. Annventor named Joseph Newman is

currently besieging the U.S. Patent Office

n the courts because it turned down his


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application for a patent on an "EnergyGeneration System having Higher EnergyOutput than Input."4 Interestingly enough,

ewman does make obeisance to theprinciple of conservation of energy,nsisting that his device does not create

energy from nothing, but rather only make

available energy that was always storedwithin it, so that it will eventually rundown. Nevertheless, tests performed byhe National Bureau of Standards indicatehat the Newman machine does not in

actuality put out more energy than is putn.

Significantly, the Patent Office has never made workability a prerequisite for patentability in general. I have seen many

patents for processes which have clearly


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never been tried experimentally, andwhich probably would not have worked iried. These ideas simply represent the

overheated imagination of the inventor ashe attempts to cover all bases and layclaim to every variation of the inventionhat enters his mind.

However, in the case of perpetual motionhe Patent Office plays a harder game.

Right at the outset it lays down the rule:

Perpetual motion is impossible, so wewill waste no time looking at anyapplications on the subject. This is mereself-defense; it is the same rule the FrenchAcademy of Science adopted in 1775.

Fortunately for us all, attempts at aclassical perpetual motion device have


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become a rarity. Few professionalphysicists will concern themselves for amoment over any machine claiming to

create energy from nothing. The laws of physics appear to have won the battle.However, severing one head of the dragononly brings forth newer and more

enacious heads. As we will see later inhis book, there are new obsessions

abroad—even within academia—that tripheadlong over the same fallacy as didperpetual motion, but in ways more subtleso that the fallacy goes unnoticed. Thesenew variations of perpetual motion sprout

undaunted, their flaws obscured, their abuse of the energy concept hidden byntellectual sleight-of-hand.

How can we be so sure that perpetual


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motion in all its variations andramifications may be dismissed asmpossible? Haven't philosophers warned

us that no knowledge is completelycertain?

The answer lies within the discoveries of

modern physics. While a proper agnosticattitude requires us to admit that nothing isknown with absolute certainty, modernmethods allow us to compute the

probability that a given piece of knowledge is true. One of the aims of thisbook is to demonstrate that the correctnesof certain physical principles has such anoverwelmingly high degree of probabilityhat for all practical purposes we mayhink of this knowledge as certain and

rue. In making this demonstration, we are


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forced to burrow deep into the foundationof physics. As we do so, we discover thatwithin the ebb and flow of intellectual

fashion and changing theories, some partsof our increasing store of knowledgeresist change and remain steadfast. Theseare areas of knowledge where the

evidence is so precise, compelling, andnvariant, that we are forced to the

stubborn conclusion that at least someknowledge is both definite and permanent

The law of conservation of energy isknowledge of this kind. It is one of thefoundation stones of physics, embedded inour understanding of fundamentalparticles, elementary interactions, andsymmetry principles—abstract concepts

hat not only define physics, but which


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define how we think about all of nature.

n order to understand any kind of science

t is essential to know what is meant byenergy, to understand its role in physicalprocesses, and to have a feeling for thencredible precision with which changes

of energy can be detected in physicalreactions. Only then can we understandwhy scientists believe that the amount of energy in a closed system cannot change.

We will also see how an understanding ofconservation of energy enables us todispose of many delusions prevalent evenoday—among laymen and scientists alike

3. How do you know you can't makeenergy out of nothing?


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The history of the energy conceptdemonstrates how hypothesis, theory, andexperimentation interact to create new

knowledge. Prior to the invention of thisconcept, fantasies of creating motion bypure mechanism, without the motivepower of either sun, wind, or fire,

possessed a certain reasonableness basedon ignorance of fundamental principles.Early perpetual motion seekers had noreason to know that what they were tryingo do was forbidden by nature.

speak purposely of the invention of theenergy concept. Energy, as an abstractconcept, is truly a human invention, asopposed to the things that really exist innature—which, from the point of view of

he scientist, are the fundamental particles


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quarks, electrons, photons, gluons, andother miniature entities. All of thesenteract and combine to form objects that

we observe either through our senses or by means of instruments. Without livingcreatures to observe them, they wouldsimply exist, going through their motions

and interacting with each other. Theywould get along perfectly well without usAfter all, the stars in a distant galaxy don'care if we are looking at them. They dowhat they have to do.

By contrast, abstract qualities such asbeauty, goodness, momentum, and energyare concepts invented by humans to helpmake sense out of the behavior of observed things. Once invented and

defined, these concepts are treated as


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observable properties, as aids to patternrecognition and to the solution of problems. But they have no existence

ndependent of the fundamental particlesand of our interpretations of their activities. Energy, for example, is never measured directly. What we actually

observe is the curvature in the path of acharged particle in a magnetic field, or theamplitude of an electrical pulse in a wireEnergy, as a physical quantity, is inferredfrom these observations; it is, in other words, a high-level abstraction.

Why, for example, did the Germanphilosopher Gottfried Leibniz (1646-1716) find it necessary to invent the termvis viva—the mass of a moving object

multiplied by the square of its velocity—


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n order to describe the object's quantityof motion? After all, he already had theconcept of velocity to describe how fast

he object was moving. Why create yetanother abstract concept?

Leibniz needed (or wanted) this concept

because he had noticed that when twobilliard balls (or other elastic objects)collide, the total vis viva of the system isunchanged. Such a "constant of the

motion" seemed to be a useful property todescribe the state of the system. Ingeneral, whenever you have somethinghat remains constant while everything

around it moves and changes, it wouldappear to be a useful and important thing.t certainly aids in the solution of

problems in mechanics. Leibniz therefore


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chose vis viva to be the quantity thatdescribes the amount of motion in asystem, and defined it in such a way that i

was just twice the quantity we now callkinetic energy. (We might picture 17th-century scientists standing around thebilliard table .arguing about the puzzling

behavior displayed by little ivory ballscareening about on the green cloth. Thestudy of billiard-ball collisions was anactive topic of 17th century physics, andstill finds applications in many areas of atomic and nuclear physics.)

Complicating the matter, however, washe prior observation by Rene Descartes1596-1650) that in a billiard-ball

collision it is the momentum of the system

hat remains unchanged. (The momentum


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of an object was defined as the massmultiplied by the velocity, with thevelocity in one direction being positive

and in the opposite direction negative.)There followed a long dispute betweenhe Cartesians and the Leibnizians, the

former claiming that conservation of

momentum was fundamental, the latter nsisting that conservation of vis viva washe rule.

Gradually the confusion was cleared upby Christian Huygens (1629-1695), Jeand'Alembert (1717-1783), JohannBernoulli (16671748), and DanielBernoulli (1700-1782), who showed thatwhen elastic objects bounce against eachother, both the total momentum and the

otal vis viva remain unchanged.5 Both


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Leibniz and Descartes were correct, but aot of blood was spilled proving it. New

knowledge, after all, is not easy to come

by.

t was not until the 19th century that thefactor of 1/ 2 was put in front of the

formula for vis viva to give the quantitywe now know as kinetic energy (1/2mv2)One of the first to recognize the need for hat factor was Gaspard de Coriolis

1792-1843), better known for theCoriolis force felt by inhabitants of spinning bodies.6 The reason for makingkinetic energy of a moving object half theclassical vis viva is so that the kineticenergy will equal the mechanical work done by the force that set the object into

motion in the first place. The work, in


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urn, is defined as the magnitude of theforce multiplied by the distance throughwhich the object moves while the force is

applied (in the simple case where theforce is in the same direction as themotion). But when we calculate thevelocity attained by the object as the force

s applied to it over a given distance, wefind that the amount of work needed to sethe object in motion can be stated entirelyn terms of the object's mass (m) and final

velocity (v). The calculation shows thatforce times distance equals 1/ 2 mv2,which is then, by definition, the value of

he object's kinetic energy.

Let us try to imagine the logical processesgoing on in physicists' minds as the energy

concept gradually emerged:


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Observation of moving objects suggestshat certain simple regularities exist

within complicated systems.

After considerable fumbling, certainabstract quantities are defined—mass,force, momentum, vis viva; and the like.

With the use of these definitions, it isfound that equations can be writtendescribing the motion of particles in

specific situations: under the influence of known forces, or during collisions witheach other. These equations representgeneral laws of nature. One kind of law,

exemplified by Newton's second law of motion, describes how to compute themotion of a system of objects given their nitial positions and velocities and given


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he magnitude and direction of the forcesacting on the objects.

Another kind of law is represented byequations that are particularly simple: theaffirm that if a system is isolated, then nomatter how complex the motions of the

objects within the system, certainproperties of the system (momentum,energy) remain unchanged. This secondclass of laws is made up of the

conservation laws, laws dealing withconserved quantities: properties of asystem which—under certain specifiedconditions—stay constant, regardless of he detailed behavior of the system as a

whole. The laws of conservation of energy and conservation of momentum

hus become part of the foundations of


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mechanics, the branch of physics dealingwith the motion of objects.

Clearly the process was not a simple one;ts consummation required the effort of the

greatest intellects in civilization for aperiod of three centuries. The key was the

formulation of suitable definitions for fundamental physical properties such asmass, momentum, and energy.

The criteria for the usefulness of adefinition are hard to state. We can, if wewant to, wave our arms and argue that agood definition helps us "understand" how

nature works. This is true to some extent,and indeed is the reason for the inventionof all abstractions. However, in dealingwith the fundamentals of physics, more


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precise motivations are needed, for thenature of "understanding" is not wellunderstood. In the case of momentum and

energy, two considerations were of majormportance:

First, momentum and kinetic energy are

quantitative concepts— they representquantities that can be measured (at leastndirectly) with appropriate instruments

and procedures. Accordingly, the core of

hese definitions consists of descriptionsof the appropriate measurementprocedures. Definitions of this nature arecalled operational definitions.

Operational definitions are a necessarypart of any scientific theory, as theyprovide the only basis for agreement on


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what is being discussed.

Second, the definitions of energy and

momentum deal with quantities that areconserved during interactions betweenobjects. They are quantities that remainconstant while all else is changing. That i

why they were perceived to be important.This property of invariance provides anmportant motivation for defining a

number of important concepts in modern

physics.

Throughout the development of physics,he most fundamental work has been done

—and is still being done—by those whosearch among all the variables of naturefor things that are absolutely constant.Among such fundamental constants are the


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speed of light and the rest-masses andelectric charges of the fundamentalparticles. (Electric charge is another

quantity that obeys a conservation law: inany closed system the total electric chargecannot change. This rule puts restrictionson the types of reactions that may take

place when particles interact.)

While the conservation laws made greatsimplifications possible in the solution of

specific physical problems, in the 18thand 19th centuries some alert workersbegan to see that the law of conservationof energy appeared to have someoopholes. How, for example, could one

account for the fact that no real machinecontinues to move indefinitely all by

tself? The best wheel with the most


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precise and well-lubricated bearingsnsists on slowing down and stopping

unless propelled by an engine of some

sort. Where does its energy go? The lawof conservation of energy seemed to bedeeply flawed. While energy was never created spontaneously, it seemed to

disappear like water from a leaky barrel.

The solution to this problem began toappear late in the 18th century, in the

midst of a philosophical movement knownas Natur philosophie, which had becomenfluential in Germany under theeadership of Friedrich Wilhelm Joseph

von Schelling. Schelling wrote that all theforces of nature arose from the samecause: "magnetic, electrical, chemical,

and finally even organic phenomena


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would be interwoven into one greatassociation . . . [that] extends over thewhole of nature."7 Starting with this

belief, it was logical to suspect that theenergy concept could be extended beyondhe domain of mechanical motion tonclude electricity, heat, and even the life

sciences. Significantly, among Schelling'sstudents were a number of scientistswhose later work culminated in such anexpanded concept of energy. Thesescientists began their conceptualrevolution with the conmon observationhat heat is generally evolved when two

objects are rubbed against each other. Forsome time heat had been visualized as akind of fluid, called caloric. The rubbing,according to theory, was supposed to

release the caloric from the objects being


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rubbed together, thus warming them. Thechief flaw in the caloric theory was thathere appeared to be an inexhaustible

amount of caloric fluid available for release as long as the rubbing went on.Where did it all come from? Could annfinite amount of caloric be contained

within a finite object?

An alternative explanation was offered byCount Rumford (Benjamin Thompson,

1753-1814), an American adventurer exiled as a result of his support of theKing of England during the revolution of 1776. In 1798, while engaged in themanufacture of munitions for King Ludwigof Bavaria, Rumford observed that cannonbarrels became intensely hot while they

were being bored, and made a suggestion


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hat changed the focus of thinking aboutheat. Summarily dispensing with thecaloric fluid as an unnecessary concept,

Rumford proposed that the heat caused bydrilling was nothing more than another form of energy: thermal energy, into whiche drill's mechanical energy was

converted by friction. A triumph of American pragmatism.

Experiments performed during the 1840s

by James Prescott Joule (1818-1889)verified that whenever mechancial work was done by a drill, or by a paddle wheelspinning in a bucket of water, or by apiston compressing a cylinder of gas, theamount of mechanical energy that"disappeared" during this process

equalled the amount of heat created. Thus


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simply by recognizing that heat was a for of energy (thermal energy), physicistswere able to save the law of conservation

of energy. They could show that the totalamount of energy in the system— mechanical plus thermal—remainedunchanged while work was being done.

The secret to saving conservation of energy lay in the definition of thermalenergy. First of all, the quantity of thermal

energy had to be defined by prescribinghow to measure it. The difference betweeemperature and quantity of heat had been

recognized by Joseph Black as far back a1760.8 Temperature was something youmeasured by the increase in length of amercury column in a glass tube. Quantity

of heat, on the other hand, was measured


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by the increase in temperature of a knownmass of water. From this definition camehe British Thermal Unit (the Btu)—the

amount of heat needed to raise theemperature of a pound of water by one

degree Fahrenheit.

Mechanical energy, on the other hand, wameasured by an entirely different processA foot-pound of energy was defined as thework done by a force of one pound

pushing something through a distance of one foot. What Joule showed by hisexperiments was that whenever mechanical energy was converted intoheat, it always took about 772 foot-poundof energy to warm one pound of water byone degree (say from 55 to 56 degrees F)


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The essential feature of Joule's discoverywas this: One Btu of thermal energy wasalways created from the same amount of

mechanical energy, no matter what thesource of mechanical energy— whether itcame from friction or from thecompression of a gas. This constancy

meant that the mechanical equivalent of heat (772 foot-pounds per Btu) was not anaccidental feature of the particular way ofmeasuring heat or mechanical energy.Even more striking was the fact that thesame conversion factor emerged when theheat was generated by passing electric

current through a wire.

Here was something new: theransformation of electrical energy into

hermal energy. How could one measure


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he quantity of energy delivered by anelectric current? It was very simple. Joulenoticed that when a current-carrying wire

was immersed in water, the water becamewarmer. The amount of thermal energygained by the water was measured in theusual way: by weighing the water and

using a thermometer to find the change inemperature of the water. Joule found, in

addition, that the thermal energy deliveredby the wire to the water in a given amountof time depended on only two factors: theelectrical resistance of the wire and thesquare of the amount of current passing

hrough the wire. But detailed analysis of he electrical circuit showed that thisquantity of energy was the same as theamount of mechanical work done by the

source of electric current to force the


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electric charges through the resistance.

n this way the relationship between

electrical energy, thermal energy, andmechanical energy was established.Heating by electric current passinghrough a resistance is still called Joule

heating.

The essential point of our story is this:When it was found that thermal energy

was generated by an electric currentpassing through a wire, it was notassumed that this energy was created fromnothing. Rather, in order to preserve

conservation of energy, a new form of energy was defined: electrical energy.Furthermore, the definition of electricalenergy was based on its equivalence to th


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mechanical work done in forcing theelectric current through the circuit. Thusdefined, a given amount of electrical

energy was always found (experimentallyo convert to the same amount of thermal

energy.

This intellectual process was repeatedmany times during the following century.Every time a known form of energy wasseen to mysteriously appear or disappear,

definition of a new kind of energy would,at the last minute, uphold the inviolabilityof the law of conservation of energy.

For example, during the second half of the19th century, it became necessary toexplain how a hot object could cool downlose thermal energy) even though it was


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completely isolated, so that there could beno conduction or convection by materialmedia. Or—the other side of the coin—

how could bright sunlight transmit radiantheat through a vacuum 93,000,000 milesacross so that bare skin was warmed onEarth?

Here again a new concept was invented:hat of electromagnetic radiation. Throughhe theoretical work of James Clerk

Maxwell (18311879), physicists wereable to understand that visible light andradiant thermal energy (infrared light) arenothing more than oscillations propagatinghrough the electromagnetic fields that

occupy empty space. Such waves have theability to convey energy with the speed of

ight from the most distant stars through a


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space almost completely devoid of matter

Once more conservation of energy was

saved. Given a suitable definition of radiant energy (in terms of electromagnetic field strength), we canmake precise measurements which show

hat the thermal energy lost by the hot bodexactly equals the energy carried off byhe radiation.

Like the heroine of a cinematic adventure-melodrama, conservation of energy hasbeen saved repeatedly from destruction byast- minute rescues. Every time the law

appears to be violated, we simply define new form of energy that brings nature bacnto conformity with the law. Indeed, it

would almost appear as if conservation o


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energy had been defined into existence.How then can we claim that it is anexperimentally proved law?

The experimental part of the law is basedon these facts:

First of all, every time we find a systemn nature where energy appears to

disappear (or to appear from nowhere),we are able to identify the existence of a

new natural phenomenon quantitativelyequivalent to a known form of energy.

We have seen, for example, that

mechanical energy lost through frictionalways reappears in the form of heat.nvestigation of that loss showed that a

quantity of heat (the Btu) could be defined


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n such a way that it was equivalent to aspecific number of mechanical energyunits (foot-pounds). The convertibility of

a unit of thermal energy into a knownnumber of units of mechanical work waspossible only if units of heat had the samedimensionality as units of work. Similarly

he unit of electromagnetic energy, definedn terms of electric and magnetic field

strength, was shown to be equivalent tohe unit of mechanical work. In general,

all energy units, regardless of type, aredimensionally equivalent to units of mechanical work.

Second, the macroscopic phenomenonbeing studied is found to be reducible tohe actions of entities at a lower

microscopic) level.


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n the case of heat, it was found (late inhe 19th century) that what had been

defined as thermal energy was actually a

high-level abstraction for a more basicreality. The reality was that atoms andmolecules moved about on a microscopicevel within macroscopic objects, and tha

he thermal energy of these objects wasnothing more than the total kinetic energyof their atoms and molecules. Once thiswas realized, it was clear that thermalenergy was not really fundamentallydifferent from classical mechanicalenergy. Thermal energy only appeared to

be a different kind of energy because themotion of individual atomic particlescould not be observed; however, it wasnevitable that thermal energy could be

measured with the same units as those


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used for mechanical energy.

Similarly, electromagnetic energy could

be explained in terms of a fundamentalparticle called the photon, not discovereduntil early in the 20th century. However,since the photon is an entity basically

different from an atom, electromagneticenergy is not the same as mechanicalenergy. Nevertheless, it can beransformed into mechanical energy

because matter contains charged particleshat interact with the photon according to

specific rules which have the property of conserving energy.

Once measurement procedures for mechanical energy, thermal energy, andelectromagnetic energy are described,


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when we observe the ways in which theseforms of energy are transformed into eachother we find that a given quantity of

mechanical energy always transforms intohe same amount of thermal or

electromagnetic energy. Theransformation of one form of energy into

another does not depend on the methodused, and—most importantly—it takesplace the same way every time. Thisconsistency or invariance of energyransformations is the fundamental

experimental content of the conservationaw. Once a joule of mechanical energy

and a joule of electromagnetic energy areoperationally defined, every time wemeasure them in the future we will findhat they are still equal.


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The proliferation of forms of energy leadso a new and serious question: How do

we know that some new kind of reaction

will not be found in the future—a reactionhat allows energy to be created or

destroyed, and for which no other newform of energy can be found to save the

conservation law? After all, we have notexperimented on all possible reactions orsystems, and it would be physicallympossible to do so. How do we knowhat in some strange part of the universein a black hole, in the center of a galaxy,

or even within our own minds) there are

not natural laws which have not yet beendiscovered, and which allow violation ofconservation of energy?

Such doubts have threatened conservation


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of energy on at least three occasionsduring this century. One occasion was thediscovery of radioactivity, which

demonstrated that energy could be emittedfrom apparently inert matter. Was theenergy being created upon emission of theradiation? Soon it was realized that the

radiating matter was not quite as inert ashad been imagined, and was simplyemitting energy that had been stored in itong ago.

t did not take long for another mystery toarise in connection with the emission of one particular kind of radiation (betaparticles) from certain radioactivesubstances. Measurements of the energycarried away by beta particles showed

hat a finite amount of energy was being


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ost. Where did it go? It required manyyears to demonstrate that the apparentlyost energy was being carried off by an

nvisible and elusive particle: theneutrino. The lost energy had been found.

The third doubt involved the steady-state

heory of the expanding universe proposedby Thomas Gold and Fred Hoyle in 1948,according to which the universe, insteadof being created in one big bang billions

of years ago, was being createdcontinuously and so had no beginning or end. This theory required the formation ofmatter and energy in small quantitieshroughout all of space in order that the

density of matter be kept constant as theuniverse expands. However, there has

been no verification of this theory, and no


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observation of the creation of matter inspace. On the contrary, all the evidencesupports the big bang theory. Therefore, in

spite of all threats, conservation of energyhas remained inviolate.

Furthermore, and most significant, while

he first half of this century found thenumber of manifestations of energyncreasing apparently without end, as a

new century approaches the tendency is to

reduce the energy concept into a singleglobal phenomenon. Rather than aproliferation of numerous "forms of energy," all forms are now merging intoone. Physics, while becomingmathematically more complex, becomesconceptually simpler, in that it requires

fewer elementary ideas to explain the


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universe. In the following chapters weshall look at some of the consequences ofhis new trend. In particular, it will

become apparent that the new model of matter greatly strengthens the universalnature of the law of conservation of energy.

otes

1. J. Bronowski, The Ascent of Man

Boston: Little Brown, 1973), p. 375.

2. T. S. Kuhn, The Structure of ScientificRevolution (Chicago: University of

Chicago Press, 1962).

3. For a complete history of the perpetualmotion idea, see A. W. J. G. Ord- Hume,


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Perpetual Motion (New York: St. Martin'Press, 1977).

4. R. J. Smith, "An Endless Siege of mplausible Inventions," Science, 226Nov. 16, 1984), p. 817.

5. A. Wolf, A History of Science,Technology, and Philosophy in the 18thCentury, vol. 1 (New York: Harper,1961), p. 62.

6. G. G. de Coriolis, Cakul de l'effet demachines, ou considerations sur l'emploides moteurs et sur leur evaluation (Paris:

1892).

7. F. W. von Schelling, Von der WeltseeleHamburg: 1798). Also, P. Edwards, ed.,


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The Encyclopedia of Philosophy (NewYork: Macmillan and Free Press, 1967).

8. R. Taton, The Beginnings of ModernScience (New York: Basic Books, 1964)


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2. MODELS OF REALITY: PARTICLES

1. The Atomic Model

The repeated resurrection of conservationof energy through the discovery of newkinds of energy leads to a new source of

worry: What if there is no end to thedifferent kinds of energy that might exist?Physics would then be intolerablycomplicated. Every new perpetual motion

machine would have to be investigated indetail to rule out the possibility of somehitherto unknown force creating energybehind our backs or sneaking it in through

nvisible interstices in space. Under suchconditions there could be no appeal to asimple and universal law to deny thepossibility of a machine's creating energy


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out of nothing.

Fortunately, however, we may breathe a

sigh of relief, for recent work suggests thaa simple structure hides beneath thecomplex surface of natural phenomena,which would mean that there are very few

fundamentally different kinds of energy inhe universe. Some physicists would evenike to believe that all the different forms

of energy are just various aspects of one

basic energy. Proof of that conjecture liesnot too far in the future.

n the meantime, we have good reason to

believe that all forms of energy can beclassified into the following categories:

Rest-mass energy—an intrinsic energy


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proportional to the mass of an object atrest.

Kinetic energy—energy associated withhe motion of an object.

n relativistic mechanics, both re t-mass

and kinetic energy are combined in theobject's total mass; the energy associatedwith this total mass is given by the

familiar formula E = mc2, where m is the

mass and c is the speed of light.

Potential energy—energy associatedwith the four fundamental forces or

nteractions:

1. gravitation


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2. electromagnetism

3. strong nuclear force

4. weak nuclear force

The relationships between the concepts

of energy, force, and interaction will bedetailed in Section 3.1)

All the miscellaneous varieties of energy

named in classical physics books— mechanical energy, acoustic energy,hermal energy, radiant energy, chemical

energy, electrical energy, Gibbs free

energy, and so on, as well as numeroussubsidiary forces, such as the van der Waals force, Bernoulli force, Coriolisforce, adhesion, cohesion, and surface


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ension—can be reduced to manifestationsof the four fundamental interactions.

t is for this reason that it does not take annfinite number of experiments to verifyhe law of conservation of energy in all

conceivable aspects. As a result it is not

necessary to look in detail at every newperpetual motion proposal.

The possibility of describing the working

of the entire universe in terms of just afew kinds of energy is an intrinsic part of he world view that underlies all of

modern physics: the atomic model. This

model describes all matter as composedof a few thousand kinds of atomsincluding isotopes), comprising roughly

100 elements. Each of these atoms is mad


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up of a smaller number of elementaryparticles. All the possible ways in whichhese particles may interact to form

compounds, crystals, and galaxies, togenerate chemical reactions as well as themultifarious activities of living matter— all these complex goings-on result from

he operation of the four fundamentalforces listed above. This atomic (or particle) model of nature represents a wayof thinking that did not exist prior to the19th century except in the isolatedspeculations of Democritus, Newton, anda few others.

The atomic model did not begin toapproach its present form until the firsthalf of the 20th century, after a century of

difficult gestation. The model is still


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undergoing development and has not yetreached its final form. However, enoughs known to answer many fundamental

questions. I do not intend to make thischapter a textbook on particle physics, bu

would like to describe how the conceptof "particle" evolved and how the concep

of "fundamental interaction" permitsanswers to the questions with which thisbook is concerned.

The struggle for a true understanding of matter began in 1803. In that year, thechemist John Dalton (1766-1844)proposed that all matter is composed of atoms and molecules, basing his proposalon measurements of the volumes andmasses of various compounds taking part

n chemical reactions. After a lengthy


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period of infighting over the clarificationof some technical details (most notably thfact that a molecule of hydrogen contains

wo atoms instead of the one claimed byDalton), chemical theory emerged fromgreat confusion into a more rational era.The acceptance of the atomic hypothesis

by chemists was a difficult processrequiring over half a century—from 1803o 1860—to accomplish. (1860 was the

year of the First International ChemicalCongress in Karlsruhe, Germany, at whichStanislao Cannizzaro presented a lectureshowing how Avogadro's hypothesis of

1811 could create order out of chaos byallowing chemists to make sense out of formulas and equations. In particular, theproblem of the number of atoms in a

hydrogen molecule was solved.)


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Some physicists, more stubborn thanchemists, did not fully accept the atomichypothesis until the very end of the 19th

century. Their reluctance was partly areaction to the excesses of physicalheories of the 18th and early 19th

centuries, which typically appealed to

nvisible and essentially mystical entitieso explain observed phenomena.

Phlogiston, for example, had been used toexplain combustion, while caloricpurportedly explained heat. Similarly, theether had provided a universalexplanation for everything not understood

about light and other forms of radiation. Ina pendulum swing away from such easyand unprovable explanations, manyphysicists adopted an extremely

hardheaded and skeptical point of view.


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Scientists such as Ernst Mach (1838-1916) and Friedrich Ostwald (1853-1932) contended that science should

concern itself only with objects and eventhat are directly observable, and should

eliminate from its domain theories aboutnvisible and undetectable objects. This

was the early positivist position.

Even though the kinetic theory of gasesthe idea that gases consist of small

molecules in rapid motion) provided aneat way of explaining their Behavior— namely, the variation in volume under different temperatures and pressures— here was great resistance to treating the

concept of invisible, minute particles asmore than a "convenient hypothesis." Eve

hough gases behaved as though they


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consisted of molecules, the earlypositivists denied that the molecular hypothesis was anything more than a

creation of the mind. (The notion thatscience does nothing more than construct hypothetical model of what is out there innature, based on the evidences of our

senses, was advanced both by thephysicist Ernst Mach and the statisticianand philosopher Karl Pearson, under thename of "sensationalism."9

However, as though on signal, physicsexploded at the advent of the 20th centurywith a horde of technological advanceshat brought microscopic reality close to

human perception. Influential in theconversion of molecules from a

convenient hypothesis to a reality as solid


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as the chair you sit on was the obscure anmysterious phenomenon first noticed byRobert Brown (1773-1858) as far back as

1827, and explained by no one until 1905The phenomenon was the jittery motion—called Brownian motion—of small dust opollen particles suspended in water,

which anyone with a good microscope caobserve.

The year 1905 was the miraculous year in

which Albert Einstein (1879-1955)published four revolutionary papers, eachof Nobel Prize stature. In one of thesepapers Einstein described a mathematicalheory explaining Brownian motion on the

basis of a model according to which theittering of suspended particles was

caused by the pushing and shoving of tiny,


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nvisible molecules, like a giant oceaniner moved by many small tugboats. One

result of Einstein's work was an equation

hat described the manner in which thenumber of particles in a given volumevaries with their vertical position in thewater (in the same way that the density of

he atmosphere varies with altitude).

Shortly thereafter, in 1908, Jean Perrin1870-1942) began experiments to study

he behavior of microscopic particlessuspended in fluids. Patiently countinghrough a microscope tiny particles of gu

resin suspended in water, Perrin not onlyverified Einstein's predictions, but usedhis observations to calculate thedimensions of the molecules responsible

for the buoyancy of the resin globules.


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After Perrin completed his measurementst became difficult to be skeptical abouthe physical existence of molecules. After

all, when the size of an object has beenmeasured, then the inadequacy of calling isimply a "convenient hypothesis" becomeapparent. With Einstein's theory and

Perrin's experiments the fantasy of molecules had been realized—turned intoreality. Though each individual moleculewas invisible to the naked eye, themolecules en masse interacted with largerobjects to produce visible effects. Theability of microscopic, invisible things to

produce effects visible on a macroscopichuman level has become the paradigm forall our particle-detection procedures.

Even before Einstein's Brownian motion


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paper, physicists had begun to realize thatnature was much more complicated thanhey had previously suspected. The last

decade of the 19th century saw thediscovery of many new types of radiationcathode rays, X-rays, and, most baffling oall, the invisible radiation emitted by

uranium through a mysterious processcalled radioactivity.

n order to explain these newly-found

rays, scientists were forced to visualize aevel of existence beneath that of the atom

and thereby opened up most of the major fields of 20th-century physics. In 1897,so-called cathode rays were shown by J.J. Thomson (1856-1940) to be streams ofelectrically charged "corpuscles," each

with the same mass and quantity of charge


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n the years that followed, H. A. Lorentz1853-1928) and others began to callhese objects electrons. With this

development, the science of fundamentalparticles was begun.

X-rays remained an enigma until 1912,

when Max von Laue (1879-1960)demonstrated that they were simplyransverse electromagnetic waves,

differing from waves of visible light only

n their shorter wavelength. The clincher was von Laue's direct measurement of theX-ray wavelength, using diffraction by acrystal of zinc sulfide. If you can measurea wavelength, there must be a wave (or ateast something that behaves like a wave)

The fact that X-rays simultaneously

exhibited properties reserved for particle


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was an embarrassment that eventuallynecessitated the development of quantumheory, which will be discussed in Sectio

2.3.

As for the radiation issuing from theuranium atom, arduous work during the

first decades of the 20th century by ErnestRutherford (1871-1937), Marie Curie1867-1934), and others showed this

emission to consist of a threefold mixture

1) a stream of helium nuclei (alphaparticles), (2) a stream of fast-movingelectrons identical to the cathode raysbeta particles), and (3) gamma rays,

which were identical to X-rays, excepthat they issued from within uranium atom

rather than from man-made machines.


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Over a period of two decades, a shortime in the history of science, the

physicists' concept of matter took on great

depth and detail. Not only were moleculecomposed of atoms, but atoms themselveswere complex structures of smaller particles, with electrons of airy lightness

whirling about massive nuclei. Far frombeing inert, the nucleus was a dynamicfurnace of seething energy, periodicallyexploding with emissions of radiation.Both nucleus and orbital electrons wereso tiny that there was no hope of ever observing them visually, for they were far

smaller than the wavelengths of visibleight, and to image such an object withvisible light would be like trying to snarea flea with a fish net; the mesh would be

oo big.


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What were scientists to think of thoseelectrons found in cathode rays? Howshould they fancy those alpha, beta, and

gamma rays emitted from the cores of radioactive atoms? Were they to beconsidered convenient but ultimatelyfictitious ways of describing invisible

forms of energy, just as the caloric fluidhad provided a handy but deceptive wayof visualizing heat?

ot at all. Improvements innstrumentation at the turn of the century

had made it possible to measure preciselyhe masses and electric charges of cathode

ray electrons and of beta particles, whichn turn made it possible to demonstratehat electrons and beta particles were one

and the same. If you can measure an


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object's mass and electric charge, then bydefinition it has real existence, evenhough it may not be visible (either to the

naked or to the aided eye).

n other words, an electron is anything

whose mass is found to be 9.109534 x 10

1 kilograms and whose electric charge isnegative in sign, with a magnitude of

1.6021892 x 10-19 coulombs. The particle

s defined in terms of the totality of itsmeasurable properties. Visualappearance, such properties as shape,color, odor, hardness, etc., are not only

rrelevant, but meaningless. Even "size" ia property of ambiguous meaning.

The development of instrumentation

especially radiation and particle


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detectors) displaced the human eye as thearbiter of reality. Instrumentation extendedhe limits bounding the kinds of objects

permitted into the realm of scientificdiscussion. Although the early positivisticphilosophers continued to caution, "Don'talk about anything you can't see," the

physicists went blithely ahead with their experiments, discovering hordes of nvisible particles. The philosophers' tunehen changed to: "Don't talk about anything

you can't measure by means of a specificset of operations"—a principle calledoperationalism.2

To a large extent this is still good advice—particularly in the physical sciences.

The wonderful cloud chamber (invented i


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1911 by C. T. R. Wilson), as well as itsvarious offspring, such as the bubblechamber and the spark chamber, added

another dimension of reality to scientists'hinking. Anyone who has ever seen

fragile trails of white vapor spurt throughhe inner space of a cloud chamber cannot

doubt that the particles causing those trailare real objects—be they electrons,protons, or alpha particles. Even thoughhe particles themselves are invisible tohe naked eye, their effect on the

environment is so dramatic and immediatehat their reality forcibly impresses itself

on any observer's consciousness.nstrumentation transforms fundamentalparticles from abstract concepts into realhings. We need no longer depend on the

deceptive naked eye.


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The particle model, which was madepossible by instrumentation, ushered in aparadigm change equal in importance to

he Galilean revolution a total change inscientists' ways of thinking. For with thismodel the meaning of the word"explanation" underwent a change. In the

past, scientific explanations had sufferedfrom an excess of vague argumentationand appeals to imaginary entities such asphlogiston, ether, and caloric. By contrasthe particle model encouraged

explanations in terms of measurableentities interacting according to known

rules.

t is also instructive to note that the atomicmodel originated as a fantasy, an

maginative thought in the mind of John


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Dalton, a genuine visionary. Many of Dalton's notions concerning atomicstructure were the purest fantasy, but the

difference between his fantasies and thoseof a simple crank was that many of Dalton's enabled one to make specificpredictions about the behavior of matter,

predictions which could then beexperimentally verified.

Fantasy, measurement, prediction,

verification, and falsification are thecentral weapons in the scientist'smethodical arsenal. The merits of eachwill become clear as we proceed.

2. The Particle Model

A particle is a thing that can be detected a


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a particular point in space, and that hascertain measurable properties such asmass, electric charge, and angular

momentum (or spin).

What do we mean by detecting a particle?Consider a simple example: A stream of

alpha particles is directed at aphotographic film. One of the alphaparticles encounters a silver iodidecrystal in the emulsion and displaces som

of the crystal's electrons from their normastates. When the film is later developed,silver atoms separate from the iodineatoms in that crystal, forming a black spotThis black spot is evidence that the alphaparticle has been detected. The location ohe spot indicates where the particle came

o rest. It is not necessary that a human


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being see that spot. The permanent changen the state of the photographic emulsion i

a sufficient condition for the detection of

he alpha particle, in the technical sense ohe word.

Since there are those who say (or at least

mply) that human observation isnecessary for the detection of a particle,3et us clarify this point with another

example. This time, let us imagine a fast-

moving electron entering a geiger counterThis energetic particle knocks orbitalelectrons out of some of the atoms in thegas within the counter. The releasedelectrons initiate an electrical discharge—a

a physicist's guide to skepticisim - milton a. rothman

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