# Why of probability in QM

• Pjpic
In summary, the "why" of probability in quantum mechanics refers to the underlying reason behind the probabilistic nature of quantum systems. Probability plays a fundamental role in quantum mechanics, as it is used to make predictions about the behavior of particles described by wave functions. It is used instead of determinism due to the uncertainty at the quantum level, and measurement is crucial in observing and confirming this probabilistic nature. While not directly observable, probability in quantum mechanics also plays a significant role in understanding and predicting macroscopic events through statistical methods.

#### Pjpic

Is there an amateur level book that talks about why QM depends on probability (assuming that is the actual teaching)?

Pjpic said:
Is there an amateur level book that talks about why QM depends on probability (assuming that is the actual teaching)?

Jaynes, E. T., 1990, `Probability in Quantum Theory,' in Complexity, Entropy, and the Physics of Information, W. H. Zurek (ed.), Addison-Wesley, Redwood City, CA, p. 381
http://bayes.wustl.edu/etj/articles/prob.in.qm.pdf

Not exactly a book, and not exactly amateur level but a good discussion of the topic I think.

Probability is a fundamental concept in quantum mechanics and plays a crucial role in understanding the behavior of particles at the microscopic level. In classical mechanics, the behavior of particles can be precisely predicted using deterministic equations. However, in the quantum world, the behavior of particles is described by probabilistic equations such as the Schrödinger equation.

The reason for this reliance on probability in quantum mechanics is due to the nature of particles at the subatomic level. In quantum mechanics, particles such as electrons and photons exhibit both wave-like and particle-like behavior. This means that their exact position and momentum cannot be simultaneously known with certainty, as is the case in classical mechanics. Instead, the behavior of these particles is described by a wave function, which represents the probability of finding the particle in a particular state.

The concept of probability in quantum mechanics is not just a theoretical construct, but it has been experimentally verified numerous times. The famous double-slit experiment, for example, demonstrates the probabilistic nature of particles, where a single particle can interfere with itself and produce an interference pattern, similar to waves.

As for an amateur level book that discusses the role of probability in quantum mechanics, one recommendation could be "Quantum Mechanics for Dummies" by Steven Holzner. This book offers a beginner-friendly explanation of quantum mechanics and covers the concept of probability in depth. Other popular books on the subject include "Understanding Quantum Mechanics" by Roland Omnes and "The Elegant Universe" by Brian Greene.

## 1. What is the "why" of probability in quantum mechanics?

The "why" of probability in quantum mechanics refers to the underlying reason behind the probabilistic nature of quantum systems. It is a fundamental question that has puzzled scientists for decades and has led to various interpretations of quantum mechanics.

## 2. How does probability play a role in quantum mechanics?

In quantum mechanics, the behavior of particles is described by a mathematical framework called wave functions. These wave functions contain information about the probability of finding a particle in a certain location or having a certain property. Therefore, probability is a fundamental aspect of quantum mechanics and is used to make predictions about the behavior of particles.

## 3. Why is probability used instead of determinism in quantum mechanics?

In classical mechanics, determinism states that the future behavior of a system can be predicted with complete certainty based on its initial conditions. However, in quantum mechanics, this concept is replaced by probability due to the inherent uncertainty at the quantum level. This is due to the principles of superposition and measurement, which state that a particle can exist in multiple states simultaneously and can only be described probabilistically.

## 4. What is the role of measurement in the probability of quantum systems?

Measurement plays a crucial role in the probability of quantum systems. It is through measurement that the probabilistic nature of quantum systems is observed and confirmed. The act of measurement causes the wave function to collapse into a definite state, and the probability of obtaining a specific outcome is determined by the wave function at the time of measurement.

## 5. How does the concept of probability in quantum mechanics relate to the macroscopic world?

The probabilistic nature of quantum mechanics is typically only observed and relevant at the microscopic level. However, the behavior of individual quantum particles can be used to explain macroscopic phenomena through statistical methods. This means that while the probabilistic nature of quantum mechanics may not be directly observable in the macroscopic world, it still plays a crucial role in understanding and predicting macroscopic events.