Local realism

Definition

Local realism is a philosophical viewpoint that combines two main ideas: locality, which states that an object is directly influenced only by its immediate surroundings, and realism, which asserts that physical properties exist independently of measurement. This concept plays a crucial role in the discussion of quantum mechanics, challenging our understanding of reality, especially when considering phenomena like entanglement and the implications revealed in experiments.

5 Must Know Facts For Your Next Test

1. Local realism was a significant point of contention for Albert Einstein, who believed that quantum mechanics should adhere to classical notions of causality and reality.
2. The Einstein-Podolsky-Rosen (EPR) thought experiment was designed to demonstrate that if local realism holds true, then quantum mechanics must be incomplete.
3. Bell's theorem provides a way to test the predictions of local realism against those of quantum mechanics through experiments involving Bell's inequalities.
4. Many experiments have been conducted to test Bell's inequalities, and the results generally favor quantum mechanics over local realism, suggesting that local hidden variable theories cannot fully explain quantum phenomena.
5. The measurement problem in quantum mechanics raises questions about how and when quantum systems transition from multiple potential states to a single observed outcome, further challenging the validity of local realism.

Review Questions

• How does local realism challenge our understanding of quantum entanglement as demonstrated in the EPR thought experiment?
  • Local realism posits that information cannot travel faster than the speed of light and that objects are only influenced by their immediate surroundings. The EPR thought experiment showed that if local realism were true, then entangled particles should have definite properties before measurement. However, quantum mechanics suggests that entangled particles do not have predetermined states until observed, contradicting the core principles of local realism and raising questions about the nature of reality itself.
• What implications does Bell's theorem have on local realism and how has it been experimentally tested?
  • Bell's theorem suggests that no local hidden variable theory can reproduce all the predictions of quantum mechanics. By formulating Bell's inequalities, researchers have conducted various experiments to test these inequalities against the predictions made by quantum mechanics. Results from these experiments typically violate Bell's inequalities, providing strong evidence against local realism and supporting the idea that entangled particles can exhibit correlations that cannot be explained by classical notions of locality.
• Evaluate how the measurement problem in quantum mechanics challenges both local realism and traditional understandings of reality.
  • The measurement problem highlights a fundamental issue in quantum mechanics regarding how and when a quantum system transitions from a superposition of states to a single outcome upon observation. This problem poses significant challenges to local realism because it questions whether physical properties exist prior to measurement. If local realism were true, one would expect definitive states before observation, but the behavior of quantum systems suggests otherwise. This disconnect forces us to reconsider our understanding of reality itself, as it implies that observation plays a critical role in shaping physical existence.

Related terms

Quantum Entanglement: A phenomenon where two or more particles become interconnected such that the state of one particle instantly influences the state of another, regardless of the distance between them.

Hidden Variables: Theoretical constructs that suggest that outcomes in quantum mechanics may be determined by underlying factors not accounted for in standard quantum theory.

Nonlocality: A principle in quantum mechanics where objects can instantaneously affect each other’s states regardless of distance, contradicting the idea of locality inherent in local realism.