Niels Bohr |

Quantum Mechanics took
shape about ninety years ago. During the twenties, Niels Bohr and Werner
Heisenberg formulated the

**, which added to the mathematical formulation some additional considerations such as the following:***Copenhagen interpretation*- Physical
systems with properties that can take concrete and opposing values (such
as
or*direction of polarization*) in certain circumstances can be in a state where those properties do not take a defined value, but keep all the possibilities simultaneously open. For example, the direction of polarization of a photon can be simultaneously*spin*and*north-south*. The spin of a particle can be both*east-west*and*up*.*down* - The
one of these properties causes the*act of measuring*, which means that the result of the measurement can only be one of the possible values. The wave function gives us the probability of obtaining each value.*collapse of the wave function* - It is
possible to build a physical system formed by two or more
*interlaced*with respect to some property, which means that if one of the particles collapses with a certain value, the other particle has no choice but to collapse with the other.*particles*

During the 1930s,
Einstein, Podolsky, and Rosen formulated the

**, a mental experiment that indicated that the Copenhagen interpretation of quantum mechanics implies that causality may not be local. In simpler words: there could be causes that would cause instantaneous effects at a great distance. Let’s look at a simplified version of the experiment:***EPR paradox*

*According to the Copenhagen interpretation of quantum mechanics, you can build a physical system made up by two photons, one with north-south polarization and the other east-west. One of these photons stays in our lab, while the other is sent a light-year away. Then we measure the polarization of the first photon and find that it is north-south. We will automatically know that the other has collapsed with the east-west polarization, at the very moment when we measured the first. For that to happen, an instantaneous effect would have to take place at a distance of one light-year. Thus causality would not be local.*John Stewart Bell |

For thirty years, the
EPR experiment remained mental. But in 1964 John Stewart Bell formulated a
mathematical expression (

**) whose result would be different starting from Einstein’s local causality, or from the Copenhagen interpretation. This made it possible to perform experiments that measure the value of that expression, thus automatically transforming the EPR mental experiment into a physical experiment.***Bell’s inequality*
Bell’s inequality has
been measured in numerous experiments carried out from 1972 to the present. In
all cases the prediction of the Copenhagen interpretation has been confirmed,
as against Einstein’s.

Let’s look at some

**regarding Bell's inequality:***typical errors*. This is false. What it proves is*Bell’s inequality shows that there are causeless effects*. Consequently, if this interpretation is true, instantaneous effects may occur at a distance (that is,*a successful prediction of the Copenhagen interpretation of quantum mechanics*). In these experiments there is always a cause: the measurement of the property in question.*causality would not be local*. This is also false. It proves that*Bell’s inequality shows that the Copenhagen interpretation is true*, therefore throws down an attempt to prove it false. But, like any physical theory, it could be overthrown by another experiment.*this interpretation has made a correct prediction*

What would happen if
the Copenhagen interpretation turned out to be wrong? In fact, other
interpretations have been formulated, although at the moment they are followed
by a minority. In such a case,

**, and the conclusion may not follow that causality may not be local.***Bell’s inequality would have to be reinterpreted*
That is, there are
many questions to be solved, as usually happens in science. What can be said is
that the conclusions some attempt to draw from this inequality to favor their
materialist ideology have no basis.

**Manuel Alfonseca**

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