Making 20th Century Science: How Theories Became Knowledge

Making 20th Century Science: How Theories Became Knowledge

Making 20th Century Science: How Theories Became Knowledge

Making 20th Century Science: How Theories Became Knowledge


Historically, the scientific method has been said to require proposing a theory, making a prediction of something not already known, testing the prediction, and giving up the theory (or substantially changing it) if it fails the test. A theory that leads to several successful predictions is more likely to be accepted than one that only explains what is already known but not understood. This process is widely treated as the conventional method of achieving scientific progress, and was used throughout the twentieth century as the standard route to discovery and experimentation. But does science really work this way? In Making 20th Century Science, Stephen G. Brush discusses this question, as it relates to the development of science throughout the last century. Answering this question requires both a philosophically and historically scientific approach, and Brush blends the two in order to take a close look at how scientific methodology has developed. Several cases from the history of modern physical and biological science are examined, including Mendeleev's Periodic Law, Kekule's structure for benzene, the light-quantum hypothesis, quantum mechanics, chromosometheory, and natural selection. In general, it is found that theories are accepted for a combination of successful predictions and better explanations of old facts. Making 20th Century Science is a large-scale historical look at the implementation of the scientific method, and how scientific theories come to be accepted.


Historians have chronicled the observations, experiments, and theories of scientists from antiquity to the present. This book could not have been written without surveying their publications. But only a few historians have presented evidence to answer the question: why were these theories accepted, at least for a while, as valid knowledge? Was it because the theories successfully explained the observations and experiments, or because they successfully predicted the results of observations and experiments not yet done?

This question seems to have been left for philosophers to answer. Yet it calls for historical research plus, in some cases, interviews with scientists. Philosophers sometimes seem more interested in discussing whether scientists should accept theories because of predictions or explanations, rather than what they actually do. So I have to persuade philosophers to consider historical evidence, and to convince historians that they should answer—in their reception studies—questions of interest to philosophers.

Of course the first thing I needed for my project was access to a good library. I was able to use the Library of Congress and the Princeton University libraries for short periods of time. the Niels Bohr Library at the American Institute of Physics in College Park, Maryland has a unique collection of textbooks, which happens to be just what I needed to study the reception of physics theories in the early twentieth century; the University of Maryland library, also in College Park, owns Max Born’s personal library. the University of Pennsylvania Library and the Chemical Heritage Foundation, both in Philadelphia, have excellent collections of older chemistry books.

If you already know what book you need to look at, because someone else has cited it, you may have to rely on interlibrary loan. I have to thank the librarians at three institutions for efficiently obtaining books from other libraries for me: McKeldin Library at the University of Maryland, the Institute for Advanced Study at Princeton, and the Brandywine Hundred Library in Wilmington, Delaware.

What about archives of unpublished letters and manuscripts? in general I have not used these sources, for two reasons: First, to search the archives of the hundreds or thousands of scientists who might have recorded their opinions of one of the theories included in my project would be impractical. Therefore, I have included only a few such documents, mainly those of Einstein and his correspondents that have been published in the Collected Papers of Albert Einstein. Second, published comments on a theory are likely to have more influence on the scientific community and (through textbooks) on the next generation.

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