Local realism

Definition

Local realism is a philosophical concept asserting that physical processes occurring at one location do not instantaneously affect outcomes at distant locations, and that physical properties exist before they are measured. This idea underlies classical physics and suggests that the world is deterministic, where objects have definite properties that can be measured without influencing other distant objects. In the context of quantum mechanics, local realism is challenged by phenomena such as quantum entanglement and the implications drawn from Bell's theorem.

5 Must Know Facts For Your Next Test

1. Local realism relies on the belief that information cannot travel faster than light, maintaining a causal structure in physical processes.
2. Bell's theorem shows that certain experimental results, particularly involving entangled particles, cannot be explained by any local hidden variable theories that adhere to local realism.
3. Many experiments, including those testing Bell's inequalities, have shown results consistent with quantum mechanics while contradicting local realism.
4. The implications of rejecting local realism lead to interpretations of quantum mechanics, such as non-locality, which suggests instant correlations between distant particles.
5. Local realism challenges traditional intuitions about separability and independence of distant events in a way that has profound philosophical implications for our understanding of reality.

Review Questions

• How does local realism conflict with the phenomenon of quantum entanglement?
  • Local realism posits that physical processes at one location cannot influence those at another distant location instantly. However, quantum entanglement demonstrates that when two particles are entangled, measuring the state of one particle affects the state of the other immediately, regardless of the distance separating them. This instantaneous influence contradicts the principles of local realism, leading to significant debates about the nature of reality in quantum mechanics.
• Discuss how Bell's theorem provides evidence against local realism and its implications for our understanding of quantum mechanics.
  • Bell's theorem presents a mathematical framework showing that no local hidden variable theory can reproduce all predictions made by quantum mechanics. Experiments testing Bell's inequalities have consistently shown violations of these inequalities, supporting the predictions of quantum mechanics while undermining local realism. This implies that either locality or realism must be abandoned, leading to interpretations like non-locality or an alternative understanding of reality where measurements play a crucial role.
• Evaluate the philosophical implications of rejecting local realism in light of experimental findings related to Bell's theorem and quantum mechanics.
  • Rejecting local realism due to experimental findings related to Bell's theorem opens up profound philosophical questions about the nature of reality and our understanding of causality. It suggests that events may not be independent and separable as classical physics assumes, introducing concepts like non-locality where distant objects can instantaneously affect each other. This challenges our intuitive grasp of space and time and compels a reevaluation of determinism and how we interpret measurements in quantum mechanics. As such, it leads to various interpretations like many-worlds or relational quantum mechanics, each with their own implications for reality.

Related terms

Quantum entanglement: A quantum phenomenon where two or more particles become correlated in such a way that the state of one particle instantaneously influences the state of another, regardless of the distance between them.

Bell's theorem:

A fundamental result in quantum mechanics that demonstrates that no local hidden variable theories can reproduce all the predictions of quantum mechanics, effectively challenging local realism.

Hidden variables: Theoretical constructs that attempt to account for the unpredictability of quantum mechanics by suggesting that underlying parameters determine outcomes, aiming to restore determinism and local realism.