Three Simple Experiments
In this chapter, we consider a series of simple experiments. By contemplating the meaning of the outcomes of these experiments we are forced to adopt some very counterintuitive conclusions about the behaviour of quantum particles.
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Three Simple Experiments
In this chapter, we consider a series of simple experiments. By contemplating the meaning of the outcomes of these experiments we are forced to adopt some very counterintuitive conclusions about the behaviour of quantum particles.
1.1 The Purpose of Physical Theories Since antiquity, people have tried to understand the world around them in terms of simple principles and mechanisms. The Greek philosopher Aristotle (who lived in the 4th century bce in Athens, Greece) believed that all heavenly bodies moved in perfect circles around the Earth. The discrepancy of this basic principle with the observed movement of the planets led to increasingly complicated models, until Copernicus introduced a great simplification by assuming that the planets orbit the Sun instead. Galileo, Kepler, and Newton refined this theory further in the sixteenth and seventeenth century, with only Mercury’s orbit resisting accurate description. Solving this last puzzle ultimately culminated in Einstein’s theory of general relativity in the early twentieth century. What makes science different from other human endeavours is that our theories about the world we live in must conform to the outcomes of our observations in welldesigned and well-executed experiments. Particularly in physics, our experiments form the ultimate arbiter whether we are on the right track with our theories or not. A theory that can predict the outcomes of our experiments is considered successful. However, it is not enough to just predict the motion of the planets, the behaviour of magnets, or how electrical components should be wired to build a radio. We want to know why planets, magnets, resistors, and capacitors behave the way they do. We Electronic supplementary material The online version of this chapter (https://doi.org/10.1007/978-3-319-92207-2_1) contains supplementary material, which is available to authorized users. © Springer International Publishing AG, part of Springer Nature 2018 P. Kok, A First Introduction to Quantum Physics, Undergraduate Lecture Notes in Physics, https://doi.org/10.1007/978-3-319-92207-2_1
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1 Three Simple Experiments
naturally assume that there is an underlying microscopic world that determines the way resistors and capacitors respond to currents, and how magnets interact. Indeed, this has been an extraordinarily successful programme. Electricity and magnetism are explained by only four basic equations, called Maxwell’s equations, and gravity is understood by a single equation, called Einstein’s equation. These equations tell us not only how to describe the behaviour of planets and magnets, but they give an explanation of that behaviour in terms of underlying physical “stuff”. In the case of electricity and magnetism the underlying stuff is charges, currents, and electric and magnetic fields. In the case of gravity, the underlying stuff is space-time, which has properties like curvature. These fields and curved space are assumed to really exist, independent of whether we look at it or not. Similarly, we al
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