Allan Franklin offers an accurate picture of science to both a general reader and to scholars in the humanities and social sciences who may not have any background in physics. Through the examination of
non-technical case studies, he illustrates the various roles that experiment plays in science.
He uses examples of unquestioned success, such as the discoveries of the electron and of three types of neutrino, as well as studies that were dead ends, wrong turns, or just plain mistakes, such as the �fifth force,� a proposed modification of Newton's law of gravity.
Franklin argues that science is a reasonable enterprise that provides us with knowledge of the natural world based on valid experimental evidence and reasoned and critical discussion, and he makes clear that it behooves all of us to understand how it works.
This book is intended to give an accurate picture of science to both a general reader and my colleagues in the humanities and social sciences, who may not have any background in physics.
I present several case studies from the history of recent physics and one from molecular biology that illustrate the various roles that experiment plays in science.
These cases show that experiment plays legitimate and important roles in science and that it provides the basis of our knowledge of the physical world.
In short, I argue that science is a reasonable enterprise based on valid experimental evidence and on reasoned and critical discussion.
Most of the examples are from physics, because that is the science I know best, but I believe that the episodes presented are typical of all science.
I also show that the strategies that I suggest are used to validate an experimental result are used in both physics and evolutionary biology.
I must make one disclaimer. Presenting an accurate picture of the practice of physics requires the inclusion of some technical content.
This includes both graphs of the experimental results and, very rarely, an equation.
The reader can be assured, however, that there will be no examination.
These studies should be read as stories -- evidential fables, perhaps.
This will allow the reader to understand the important elements of the episodes.
However, the term fables should not imply that these case studies are in any way fanciful or imagined.
They are accurate and somewhat simplified accounts of the actual history, which are intended to illustrate the roles that experiment legitimately plays in science.
Because these are necessarily condensed histories, I include footnotes on the first page of most chapters that refer readers to a more detailed study.
I also provide a glossary of technical terms. The case studies in this book were compiled over a period of
twenty-five years. During that time I have been helped by so many friends and colleagues that merely listing all of them and the assistance they have provided would add another chapter to this book.
I believe that all of them have been acknowledged in my previous work, so I will only say that this work could not have been done without their help and encouragement.
I also thank Valerie Melendez, Jessica Rodriguez, Tom Lyons, and Jeffrey Robinson for helpful comments on parts of the manuscript.
Last, and certainly not least, I thank my wife, Cynthia Betts, without whom none of this would have been possible.
Blas Cabrera and the Search for Magnetic Monopoles
One of the interesting problems concerning experimental results is what happens when an experiment gives a null result, when the phenomenon expected is not observed.
It could happen because the experimental apparatus and the associated analysis procedures cannot detect or measure the phenomenon in question or because the phenomenon is not present.
This is a real problem in physics investigations. In the Michelson-Morley experiment, one of the most famous experiments in modern physics, Albert Michelson and Edward Morley expected to detect a shift in a pattern of light caused by the motion of the earth relative to the ether (the proposed medium though which electromagnetic waves traveled).
They observed no such shift. Possibly it was because the apparatus was faulty or because the earth's velocity relative to the ether was zero.
Other explanations were later offered for this null result. They included the ether-drag hypothesis, that the earth dragged a layer of the ether along with it; the Lorentz-Fitzgerald contraction, that an object shrank in the direction of its motion relative to the ether; and the ballistic theory, that the velocity of light was constant relative to the source of the light.
Eventually, all of these alternatives were rejected on the basis of experimental evidence, and it was accepted that the earth had zero velocity with respect to the ether.
Later, Albert Einstein's special theory of relativity dispensed with the need for the ether and explained the result of the Michelson-Morley experiment.
A related problem occurs when an effect is initially observed but later--and presumably better--experiments do not replicate the observation.
Then experimenters have to argue that these later experiments are indeed better and that their results are more reliable.
The history of Blas Cabrera's searches for magnetic monopoles (single, north or south magnetic poles) is fascinating because in his first experiment, Cabrera observed a signal that not only was consistent with the existence of a magnetic monopole, but was precisely the size that theory predicted.
Despite this observation, Cabrera made no discovery claim. That was because he could not rule out all alternative causes for his observed signal.
Cabrera made several improvements to his experimental apparatus and continued the search.
None of the later searches found evidence for magnetic monopoles. Cabrera and his colleagues used several arguments to demonstrate that these later experiments were in fact better and that they would have observed magnetic monopoles had they been present.
They then concluded, quite reasonably, that magnetic monopoles had not been observed.
Perhaps the most typical strategy used by experimenters to demonstrate that their apparatus would have observed the phenomenon in question is the use of a surrogate signal.
Producing an adequate surrogate can involve considerable ingenuity by physicists.
Some commentators on science have questioned whether the adequacy of such surrogate signals is examined in sufficient detail
(see, for example, Collins 1985, 1994). I have argued elsewhere in detail that scientists do consider the question of the adequacy of a surrogate signal quite carefully and do present arguments for their validity
(Franklin 1997b). In the magnetic monopole investigation, the creation and use of a surrogate signal not only helped to establish the ability of the apparatus to detect the phenomena, but also helped to cast doubt on the initial observation.
Are There Magnetic Monopoles?
One interesting fact about electromagnetism is that single electric charges, positive and negative, exist, whereas single magnetic charges--magnetic monopoles--do not.
All known magnetic fields have two poles, north and south.
In 1931 Paul Dirac, winner of the Nobel Prize for his work on relativistic quantum theory, began a theoretical investigation that led to interesting conclusions about magnetic monopoles, if they existed.
Dirac's original intent was to try to provide a reason for the existence of the smallest unit of electric charge,
e, the charge of the electron. (All known charges are integral multiples of
e.) His paper, he wrote, "will be concerned essentially, not with electrons and protons, but with the reason for the existence of the smallest electric charge.
This smallest charge is known to exist experimentally and to have the value
e given approximately by hc/2πe2 = 137
[h is Planck's constant and c is the speed of light].
The theory of this paper, while it looks at first as though it will give a theoretical value for
e, is found when worked out to give a connection between the smallest electric charge and the smallest magnetic pole.
It shows, in fact, a symmetry between electricity and magnetism quite foreign to current
Dirac had found something surprising in his theory: that the fundamental unit of electric charge was related to the fundamental unit of magnetic pole.
"The theory leads to a connection, namely equation (9), between the quantum of magnetic pole and the electric
charge." Dirac's equation (9) was hc/2πeg =
2, where g was the strength of the magnetic pole. Dirac further noted,
"This means that the attractive force between two one-quantum poles of opposite sign is
(137/2)2 = 4692 1/4 times that between electron and proton.
This very large force may perhaps account for why poles of opposite sign have never yet been
observed." The force was too large to easily separate the poles.
In later work Dirac presented a more general theory of the interaction of charged particles and magnetic poles.
"If one supposes that a particle with a single magnetic pole can exist and that it interacts with charged particles, the laws of quantum mechanics lead to the requirement that the electric charge be quantized--all charges must be integral multiples of a unit charge e connected with the pole strength g by the formula
eg = hc/4π. Since electric charges are known to be quantized and no reason for this has yet been proposed apart from the existence of magnetic poles, we have a reason for taking magnetic poles seriously. The fact that they have not yet been observed may be ascribed to the large value of the quantum of
This theoretical work formed the background to searches for magnetic monopoles and provided an enabling theory for the experiments by giving an estimate of the strength of the magnetic pole and of the size of the effects that might be observed.
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