Entangled particles stay in immediate and direct contact, by sharing the same system wavefunction, over any-size space or time interval {non-locality}|. Changes in one particle immediately affect the other particle, seemingly sending information faster than light speed. Conservation laws hold, because particle travels as fast as information, and same particle can go to both detectors. Perhaps, non-locality is due to quantum-mechanical space and time being discrete, foam-like, and looping.
Particles, energies, fields, and quanta are always in space-time. Physical objects and events happen only in space-time.
Wavefunctions are abstract non-physical mathematical objects that describe possible particle or system states and their probabilities. Particle and particle-system wavefunctions are not physical forces, are not energy exchanges, and are not objects in space-time. Wavefunctions describe all space-time points simultaneously. Waves have wavelength, and so are not about only one point, but all wave points at once. Wavefunctions account for and connect all space points, and so appear infinitely long.
As particles interact (and so form an interacting-particle system), the particle wavefunctions superpose to make a system wavefunction, in which all particle states depend on each other. Because wavefunctions connect all space, particles separated by arbitrary distances have states that affect each other. If one particle changes state, the other particle instantaneously changes state, no matter how far apart in space the particles are, because the system wavefunction (and all waves) collapse at all points simultaneously. Experiments that measure energy and time differences, or momentum and position differences, show that particles can remain entangled over far distances and long times, and that wavefunction collapse immediately affects all system particles, fields, and points, no matter how distant. (Because later times involve new wavefunctions, wavefunction collapse never changes particles at same place at different times.) State-vector reduction seemingly violates the principle that all physical effects must be local interactions, because coordinated changes happen simultaneously at different places.
Particle and system wavefunctions are about particles in indefinite states. Observation of one particle's definite state instantaneously collapses the system wavefunction and puts all system particles in definite states, no matter how far apart they are. No physical force or energy at the other particle causes the definite state, but the no-definite-state simultaneously changes to definite state {action at a distance}. The cause seemingly travels faster than light speed to make an effect. Therefore, the cause is non-physical.
Physical causes and effects must occur at one event in space-time. All physical communications, forces, and energies require local interactions through field-carrying particle exchanges in space-time. Physical interactions can have no action at a distance.
theories
Perhaps, wavefunctions reflect something physical that can account for action at a distance. Perhaps, particles can travel backward in time, from measured position to previous position, to make cause and effect at same space-time point. Perhaps, wavefunctions have retrograde wave components, so particles are always interacting at same space-time point. For example, in double-slit experiments, backward-flowing waves (from detectors to incoming particles) determine particle paths and explain whether wave or particle phenomena appear. However, general relativity does not allow time to flow backward. Furthermore, space-time points cannot have different times simultaneously.
theories: no-space-time
Perhaps, every space-time point touches an abstract outside-space-time structure. Perhaps, quantum foam has no-space-time in it. Perhaps, just as all sphere points touch sphere interior, all space-time points touch a no-space-time interior. By whatever method, every space-time point communicates with all others through no-space-time. No-space-time has no distances or time intervals, so space and time do not matter, and action at a distance can occur.
No-space-time is an abstract mathematical object, just as are quantum-mechanical waves. Perhaps, no-space-time carries quantum-mechanical waves.
Before measurement, particles can be said to be everywhere {Copenhagen interpretation}|, not necessarily close to the observed position. Because particle is everywhere, measured particle is always adjacent to other system particles, so there is no non-locality.
Spin-zero-particle decay can make two entangled coupled spin-1/2 particles, one +1/2 and one -1/2, which have one coherent system wavefunction {Einstein-Podolsky-Rosen experiment} {EPR experiment}. After particle-pair production, one particle always has spin opposite to the first, by conservation of angular momentum, but observation has not yet determined which particle has which spin. If an instrument detects one particle's spin direction and collapses the system wavefunction, the other particle immediately has the opposite spin, even over long distances. Einstein, Podolsky, and Rosen said instantaneous information transmission was impossible, so particles changed to the measured spins when the particles separated. Experiments showed that both particles have no definite spin until measured, so particles had superposed states until measured. By quantum mechanics, neither particle has definite spin-axis direction, so particles have superposition of +1/2 and -1/2 states until measured.
Experimenters must choose direction around which to measure spin and can measure in any direction. If they measure opposite direction, they can observe opposite spin. Therefore, particle production alone does not determine measured spin, and realism does not happen. Measuring system and particle together, as a new system, determine measured spin.
spin detection
If two spin-1/2 particles are in singlet state, three detectors oriented at -120, 0, and +120 degree angles perpendicular to moving-particle path can measure one particle's spin. Probability that both spins have opposite values is cos^2(A/2), where A is angle.
5-Physics-Quantum Mechanics-Wavefunction-Collapse-Non-Local
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Date Modified: 2022.0225