Quantum reality in physics
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Quantum Reality in Physics: Objective Reality vs. Observation
The question of what is "real" in quantum physics has been debated for decades. Unlike classical physics, where objects are assumed to exist independently of observation, quantum mechanics challenges this view and introduces a complex relationship between measurement, observation, and reality D'espagnat2011Rohrlich1986.
The EPR Paradox and Elements of Reality
The famous Einstein-Podolsky-Rosen (EPR) paper argued that if a physical property can be predicted with certainty without disturbing a system, then that property must correspond to an element of reality Einstein1935Bohr1935. However, quantum mechanics shows that for certain pairs of properties (like position and momentum), knowing one with certainty means the other cannot be known—these are called non-commuting observables Einstein1935Caetano2024. Recent work further demonstrates that quantum mechanics generally prevents non-commuting observables from having joint elements of reality, challenging the classical notion of joint reality .
Measurement, Observation, and the Role of the Observer
Standard quantum mechanics suggests that measurement outcomes are not simply revealing pre-existing properties, but are instead created in the act of measurement Woodward2021D'espagnat2011Rohrlich1986. The results of measurements are considered "phenomenal reality"—they emerge from the interaction between the system and the measuring device, rather than reflecting an underlying, observer-independent "noumenal" reality Woodward2021D'espagnat2011. This view is supported by the Heisenberg Uncertainty Principle, which states that certain properties do not have definite values until they are measured .
Quantum States: Reality or Knowledge?
There is ongoing debate about whether the quantum state (the wavefunction) represents something real or merely our knowledge about a system. Some argue that the quantum state is a direct reflection of reality, while others see it as a tool for predicting measurement outcomes . However, recent theoretical results show that if the quantum state is just information about an underlying reality, then quantum theory's predictions would be violated. This suggests that the quantum state has a more direct connection to reality than previously thought .
Realism, Locality, and Quantum Correlations
Quantum mechanics also challenges the principle of locality—the idea that objects are only directly influenced by their immediate surroundings. Experiments inspired by the EPR paradox and Bell's theorem show that quantum systems can exhibit correlations that cannot be explained by any local, classical theory Woodward2021Rohrlich1986Drummond2020. Some models propose that reality consists of random fields in space-time, with well-defined probabilities for different configurations, and that measurement outcomes can be explained without invoking wavefunction collapse or the need for an observer .
Open Realism and the Limits of Classical Objectivity
While standard quantum mechanics undermines the classical, strongly objective view of reality, some physicists propose "open realism," which allows for a broader, mind-independent reality that is not fully captured by quantum predictions but is not entirely denied either . This approach tries to reconcile the predictive power of quantum mechanics with the intuition that there is a real world independent of observation.
Conclusion
Quantum reality in physics is fundamentally different from classical reality. Measurement and observation play a central role in defining what is real at the quantum level, and many classical assumptions about independent, objective reality do not hold. The quantum state appears to have a direct connection to reality, and quantum correlations defy classical explanations. While the debate continues, it is clear that quantum mechanics forces us to rethink the nature of reality itself Woodward2021D'espagnat2011Rohrlich1986+4 MORE.
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