Appearance and Reality: An Introduction to the Philosophy of Physics

Appearance and Reality: An Introduction to the Philosophy of Physics

Appearance and Reality: An Introduction to the Philosophy of Physics

Appearance and Reality: An Introduction to the Philosophy of Physics


This is a book about quantum mechanics and relativity and their philosophical implications. The central question is whether these theories of modern physics indicate that we can know nature as it really is, or only as it appears to us. The foundational concepts and principles of quantum mechanics and relativity are clearly explained and then used to argue that we can know more than mere appearances of the natural world; we can know the way things really are.


It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.

Niels Bohr

Bohr's assessment of the task and the abilities of physics can be put bluntly in terms of appearance and reality. It is wrong, he claims, to think that physics allows us to know the reality of nature. Physics can tell us only how nature appears.

The distinction is important, since appearance, the human account of things, is unavoidably influenced by our own perspective and preconceptions. The sun and moon, for example, appear to be roughly the same size, but in reality the sun is much bigger. This much at least, we know. In general, the way nature appears may be somewhat altered from the way it in fact is. Appearance is affected both physically and conceptually by the way we interact with things. The appearance of nature is therefore incorrigibly subjective, but at the fundamental level of physics it is, according to Bohr, all we can really know.

It is not Bohr's opinion for its own sake that is of interest here. We want to know the truth of the matter. What is it about physics that motivates such cynicism, and, more importantly, is it warranted? Bohr was indisputably a giant in early twentieth century physics, but we should not believe his conclusion simply on the basis of authority when we can figure it out for ourselves. That is what we are up to in this book, figuring out whether physics can deliver knowledge of reality or only appearance. The question is not of the proper task of physics in the sense of the most desirable goals or the most aesthetic or useful results. It is not about what anyone thinks physics should do. It is about what physics in fact can do. What are the limits of knowledge in physics, constrained as it is to giving responsible proof for the claims it makes? How far can we responsibly go before we have lapsed into mysticism and the occult? If all of the evidence of nature is essentially influenced by those who gather and apply it to knowledge, then all we can know seems bound to reflect this influence. We can speculate about the uninfluenced, independent reality, but speculation without proof is not knowledge, and it is not physics.

This is the sort of reasoning that seems to leave reality, the way nature is, beyond the limits of knowledge and outside the domain of physics. If the argument is right, then as a matter of principle, the best that physics can know is how nature appears to us. Bohr's case for this is based on details of physics, both its scientific results and its methods. It is exactly those details that we must look to in order to understand the distinction . . .

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