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Before the early s, scientists used Classical Mechanics, or Newtonian Physics to describe the macroscopic world that we see today. The problem was that come the twentieth century, physicists began to notice that when we got down to a smaller scale, the scale dealing with atoms and bonds, classical mechanics no longer applied and particles could no longer be described by the rules and the system that they were familiar with. As a result, there was soon a need for a new system that would be able to accurately predict the outcome of an experiment involving objects on the angstrom scale.

The goal of the development of a new system was not to replace classical mechanics, but rather to complement it. In fact, the new system needed to "become" classical mechanics once expanded to a large enough scale. This new system is known as quantum mechanics and this necessity for quantum mechanics to become classical mechanics and vice versa depending on the scale of the experiment is formally known as the correspondence principle.

## Introduction to Quantum Mechanics Exposed

One of the hard things to accept about quantum mechanics is that when considering a particle such as an electron, you can no longer measure something that seemed trivial before in classical mechanics: position. The position of an electron cannot be known exactly, rather you can only know the probability that an electron might be somewhere. The uncertainty that is associated with quantum mechanical measurement is illustrated in the system used to describe objects. In quantum mechanics, the state of a given system is described mathematically by a wave.

Everything that you would want to extract about the particle can be extracted from the wave function. An important feature of the wave function is the superposition principle, which states that wave functions can be written as a linear combination of multiple wave functions. Conceptually, this means that the state of function is equal to the sum of the probability of all possible states.

## Quantum mechanics: a new introduction - Kenichi Konishi, G. Paffuti - Google книги

For example, in the case of the position of an electron, its position can be described by the sum of the possibility of every place it could be. In physics, an observable is anything that you can explicitly measure in a system, such as energy, position, momentum, velocity, etc.

In classical mechanics these observables can be known simultaneously and the accuracy of the measurement is dependent on the instrument used to take the measurement. Making a measurement on a quantum mechanical system is equivalent to collapsing a superposition wave function system down to a single wave function. In the case of quantum mechanics, only certain observables can be known at a time, and there are some observables that can never be known simultaneously.

For example, the position and momentum of a particle in a quantum mechanical system cannot be known at the same time. This is because if you were to measure position, for example, then measure momentum, and then measure position again, you will not get the value for position that you measured before, this is because measuring momentum perturbed the system and caused the wave function describing position to return to its superposition state.

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Classically, it was observed that energy depends on intensity amplitude. This resulted in the ultraviolet catastrophe, which described a blackbody at low wavelengths, predicting that the emitted radiation would approach infinity. About this product. Stock photo.

### Introduction to Quantum Mechanics – What Is It?

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## Quantum Mechanics Books

About this product Product Information This is a modern, and relatively comprehensive introductory textbook on Quantum Mechanics. It is intended to correct the lack of such a book today, in spite of the ever-increasing importance of the subject in contemporary science, technology, and everyday life. With its clear, pedagogical presentation, and with many examples discussed and problems solved both analytically or with numerical methods, the book is a unique and enjoyable textbook on Quantum Mechanics, useful for physics students, researchers and teachers alike.

Additional Product Features Dewey Edition. Part I: Basic Quantum Mechanics1. Quantum mechanical laws3. The Schroedinger equation4. Angular momentum5. Symmetry and statistics6. Three-dimensional problems7. Finer points of quantum mechanics8. Perturbation Theory Variational Methods Time Evolution Meta-stable states Electromagnetic interactions