Quantum physics, one of the main branches of modern physics, is the basis for our understanding of all fundamental particles and forces except gravity. Despite continuing controversy over its interpretation, quantum physics has been consistently confirmed by experiments and continues to provide the foundation for many modern technologies, such as atomic energy, lasers, and integrated circuits.
Quantum physics originated during the early twentieth century in response to emerging experimental evidence contradicting the classical laws of physics. According to classical physics, light consists of continuous waves of energy permeating space, while matter consists of particles localized in space. However, experiments showed light sometimes behaving as particles and matter sometimes behaving as waves. These violations of classical concepts forced physicists to search for new fundamental laws of physics. Quantum mechanics, the most elementary form of quantum physics, was discovered independently in 1925 by Werner Heisenberg and in 1926 by Erwin Schrödinger. Now, quantum physics also includes the more comprehensive theories of quantum electrodynamics and quantum field theory.
Although quantum physics is a widely accepted scientific theory, it is difficult to interpret in terms of commonsense notions of reality. The fundamental law of quantum mechanics, Schrödinger's wave equation, describes the state of a single particle by a single quantum wave. The intensity of this wave at any position represents the probability of observing the particle at that position. This quantum wave representing the particle's probable position can be mathematically transformed into a complementary wave representing the particle's probable momentum. Position and momentum are thus examples of complementary observable properties. Heisenberg's uncertainty principle states that a small uncertainty in one property necessarily results in a larger uncertainty in the complementary property. According to the standard Copenhagen interpretation of quantum mechanics developed by the Danish physicist Niels Bohr, this uncertainty represents not a mere lack of knowledge but rather a fundamental lack of definiteness in nature. Thus, to accurately describe quantum phenomena, we must use complementary descriptions. A particle, for example, can only be described as having an objectively existing position or an objectively existing momentum, not both.
In a famous paper published in 1935, Albert Einstein objected to the Copenhagen interpretation of quantum theory because of its inconsistency with certain natural assumptions about the nature of physical reality, namely that the properties of separated objects exist independently of each other (locality) and that objects have real properties independent of observation (realism). Einstein's argument was formalized in 1964 by John Bell, who proved that Einstein's assumptions do, indeed, contradict the predictions of quantum physics. Subsequent experiments have confirmed the validity of quantum mechanics and thus proved that realism and locality cannot both be true of our world. The implication is that one or both of the following is true: (1) Certain properties of physical objects do not exist independent of each other, or (2) certain properties of physical objects do not exist independent of observation.
Although observation appears to play an essential role in quantum theory, the fundamental nature of observation and measurement remains controversial. The problem of measurement derives from the fact that we observe only one of the possible values described by the quantum wave. Thus measurement is represented as a discontinuous "collapse" of the quantum wave of probability into a single actualized value. This sudden and spontaneous collapse, however, is not allowed by the laws of quantum physics. There is no explanation for how, when, or where measurement happens. Moreover, the laws of quantum physics do not predict which of the possible values will be selected in any single measurement.
This apparent break with classical determinism has been viewed by some as an opening within physical laws for the exercise of free will. Some researchers, for example, have speculated that consciousness can freely choose which possibility becomes actualized during a quantum measurement. It has also been suggested that certain parapsychological phenomena might be explained by this mechanism. To be compatible with physical laws, however, any such choices must conform to the probability distribution of the quantum wave. Therefore, if consciousness can exercise choice in selecting the result of particular quantum measurements, the result either violates the laws of quantum physics or has no observable effect.
In a fundamental analysis of the quantum measurement process, John von Neumann argued persuasively that consciousness is necessary for a measurement to occur. Because any physical system is described by a quantum wave of probability, the interaction of two physical objects will simply combine their two probability waves to produce yet another wave of probability. Thus the interaction of a physical system with a measurement apparatus will not result in an actual measured value. The observation of any physical system by any other physical system, therefore, will never result in a "collapse" of the probability wave into one actual value. For observation to occur at all, von Neumann concluded, a nonphysical consciousness is required. This activity of consciousness does not violate the laws of quantum physics, since it only serves to cause the collapse, and not to select or influence the value actualized. Because of this apparent role of consciousness in quantum mechanics, some physicists have suggested that the mind-body relationship can be explained using quantum theory. The codependence of observer and observed in quantum theory has also been compared with similar ideas in Buddhist philosophy.
The radical philosophical implications of quantum physics, although they are still controversial, suggest that (1) objects are intimately interconnected, (2) the observer and the observed are interdependent, and (3) consciousness plays an active role in observation. These new implications of quantum physics have prompted some physicists to interpret modern physics from the perspective of mystical worldviews. From such a perspective, some conceptual problems and paradoxes of quantum physics can be resolved. However, while these interpretations may be compatible with the evidence of quantum physics, they have not been established by scientific evidence and remain controversial.
See alsoBuddhism; Free Will; Paranormal; Psychologyof Religion; Quantumm Healing.
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Thomas J. McFarlane