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Volume 27 Issue 12 Dec , pp. It is more precisely called counterfactual definiteness ; it means that we may think of outcomes of measurements that were not actually performed as being just as much part of reality as those that were made.
Locality is short for local relativistic causality. Currently accepted quantum field theories are local in the terminology of the Lagrangian formalism and axiomatic approach. Freedom refers to the physical possibility of determining settings on measurement devices independently of the internal state of the physical system being measured.
In current theory, post, various interpretations i. But some interpretations only violate aspects of a related principle, known as counterfactual definiteness.
Realism in the sense used in physics  is the idea that nature exists independently of the human mind: that even if the result of a possible measurement does not exist before the act of measuring it, that does not mean it is a creation of the mind of the observer contrary to the " consciousness causes collapse " theory in quantum mechanics. A mind-independent property does not have to be a value of a physical variable, such as position or momentum. A property can be potential i. Even though the result of striking a glass object with a hammer does not exist before the act of striking it, that does not mean the broken glass is a creation of the observer.
Ordinary quantum mechanical calculations, if one excludes from consideration proposals such as that of Walker 12 that contain special ad hoc modifications to the conventional theory, do not seem to provide any clear mechanism leading to the occurrence of phenomena where the effects of non-local connections are manifested directly. We do not guarantee individual replies due to extremely high volume of correspondence. But at the same time there are arguments that appear to show that no real physical manifestations of these interconnections actually exist. More options …. Volume 62 Issue 12 Dec , pp. I will also exemplify what relative locality is into specific examples.
A particle accelerator is a sophisticated type of hammer, and the target particles are liable to end up as a heap of broken shards. Such a response, i. Such an outcome would be realistic in a metaphysical sense, without being realistic in the physicist's sense of local realism which requires that a single value be produced with certainty. A related concept is " counterfactual definiteness ", the idea that it is possible to meaningfully describe as definite the result of a measurement which, in fact, has not been performed i.
In most of the conventional interpretations, such as the Copenhagen interpretation and the interpretation based on consistent histories , where the wavefunction is not assumed to physically exist in real spacetime , it is local realism that is rejected. These interpretations propose that actual definite properties of a physical system "do not exist" prior to the measurement; and the wavefunction is nothing more than a mathematical tool used to calculate the probabilities of experimental outcomes.
However, a different challenge to the principle of locality subsequently emerged from the theory of Quantum Mechanics. In theoretical physics, quantum nonlocality is a characteristic of some measurements made at a . However, under the assumption of locality, actions on Alice's system do not affect the "true", or "ontic" state of Bob's system. We see that the ontic.
If the wavefunction is assumed to physically exist in real spacetime, the principle of locality is violated during the measurement process by the occurrence of wavefunction collapse. This is a non-local process because Born's Rule , when applied to the system's wavefunction, yields a probability density for all regions of space and time. Upon actual measurement of the physical system, the probability density vanishes everywhere instantaneously, except where and when the measured entity is found to exist.
This "vanishing" is theorised to be a real physical process, and clearly non-local i. The Bohm interpretation preserves realism, hence it needs to violate the principle of locality in order to achieve the required correlations. It does so by maintaining that both the position and momentum of a particle are determinate, in that they correspond to the definite trajectory of the particle, but that trajectory cannot be known without knowing the physical state of the entire universe.
In the many-worlds interpretation , both realism and locality of action are retained, but the interpretation posits the existence of a universal, nonlocal wavefunction which mediates nonlocal correlations.
Because the differences between the different interpretations are mostly philosophical ones except for the Bohm and many-worlds interpretations , physicists usually employ language in which the important statements are neutral with regard to all of the interpretations. In this framework, only the measurable action at a distance — a superluminal propagation of real, physical information — would usually be considered in violation of the principle of locality by physicists. Such phenomena have never been seen, and are not predicted by the current theories. In , Ronald Hanson reported observing a loophole-free violation in an experimental test of Bell's theorem : in other words, a result which — for the first time — is free of any additional assumptions previous experiments, going all the way back to , had required that various assumptions be made in order to obtain an unambiguous contradiction of local realism.
This result rules out large classes of local realism theories. A experiment demonstrated a single photon, in certain conditions, can have non-local observable physical effects in two places at once. From Wikipedia, the free encyclopedia. Physical principle that only immediate surroundings can influence an object.
This article is about the principle of locality in physics. Permanent link for public information only:. Permanent link for all public and protected information:. SFB Colloquium. Description In this talk I will describe the fundamental tension that forbids us in my view to reconcile gravity with the quantum. I will explain how this tension forces us to profoundly revise the concept of locality and that this can be done by letting go of the hypothesis of Absolute locality. I will formulate what relaxing this hypothesis means and will describe our attempts to flesh out the concept of relative locality.
I will also exemplify what relative locality is into specific examples.