After the development of quantum mechanical wave Schrödinger and the matrix Heisenber , Paul Dirac made a step further by explaining how the two theories were the same, with a different description. Moreover, Dirac deepened development including electromagnetic radiation and relativistic effects in quantum electrodynamics where it came from, and the prediction of the existence of particles exactly equal to those already known, except that its charge was reversed: Dirac discovered and antiparticles.
Parallel to the development, work is also in the interpretation of quantum theory. If classical mechanics is everyday situations and systems, which are translated into equations, quantum physics, although the first discoveries (black body radiation, photoelectric effect, etc ...) respond to this scheme, to further develop the mechanical presents the opposite case, in which mathematics to develop solutions that must find a physical interpretation. (The antiparticles are a case, for example)
was not until the Solvay conference 1927 in Brussels that the interpretation was finally established, due mainly to Niels Bohr. An interpretation is not free from debate, and scientists of the stature of Einstein shared it, and tried again and again to test it with experiments, trying to prove some kind of contradiction.
Parallel to the development, work is also in the interpretation of quantum theory. If classical mechanics is everyday situations and systems, which are translated into equations, quantum physics, although the first discoveries (black body radiation, photoelectric effect, etc ...) respond to this scheme, to further develop the mechanical presents the opposite case, in which mathematics to develop solutions that must find a physical interpretation. (The antiparticles are a case, for example)
was not until the Solvay conference 1927 in Brussels that the interpretation was finally established, due mainly to Niels Bohr. An interpretation is not free from debate, and scientists of the stature of Einstein shared it, and tried again and again to test it with experiments, trying to prove some kind of contradiction.
Probability and wave function
The interpretation of the wave function is not trivial to do. Depending on the problem, the system can be in different states represented by their position, angular momentum angular momentum, or any other observable quantity; states described by its energy.
But the Heisenberg uncertainty principle shows that it is impossible to determine with precision the same values. Max Born (1882-1970) concluded that the wave function is then the probability of finding a system in a given state. For an atom, representing the probability of finding an electron at a given position, but will not describe how it orbits around the nucleus, just as classical physics describes the trajectory of a planet around the sun and loses sense
the concept of orbit which had been handled, and there is the concept of orbital, which is the region of space which is likely to find the electron. Instead of a circular orbit where a planet occupies a certain position, there are regions of space, more likely than others to find the electron there.
Complementarity: particle duality - Wave
Almost from the beginning of the development of quantum mechanics, it became clear that waves and particles appear to be two properties that can have a single system. For a classical physicist, these two properties are mutually exclusive, and therefore one of the two must be wrong.
However, a quantum physicist wave and particle properties are not exclusive but complementary. Which of the two properties are revealed in an experiment depends on the experiment in question. The same experiment will never show both properties, so that you can not discriminate whether one is more correct than the other.
The wave function can represent this complementarity. A wave function that covers a vast region of space is incompatible with the idea of \u200b\u200ba particle occupying a position. One speaks of a delocalized wave function, and the system will behave more like a wave and a particle. And it can happen otherwise, that the wave function is found highly concentrated in a small region of space, then the system will behave like a particle, and there is talk of a localized wave function.
Collapse of the wave function and Schrödinger's cat
We saw the wave function, mathematically, is the sum (or superposition) of a series of eigenfunctions for which could solve the Schrödinger equation. These eigenfunctions also represent each of the possible states of a system, but when he makes an observation (Or experimental measurement), one and only one of these states is revealed in the experiment, with a certain probability.
This means that before making a measurement, the system is undefined: the state is a mixture of all possible states. But nevertheless, to observe and interact with the system as the system of study, the interaction makes the system opts for a particular state, a collapse of the wave function of a particular state, which will maintain to which is referred to another type of interaction differently.
The best known example is employed to illustrate this collapse is the thought experiment known as Schrödinger's cat. However, Schrödinger did not support precisely this interpretation, and was trying to illustrate how absurd it was:
In one case, a cat locked together with a radioactive source, a Geiger counter, a hammer and a gas container poisonous. The disintegration of the source is a quantum process, which has a 50% probability of occurring. If it happens, the Geiger counter triggers a device by which the hammer broke the bottle of gas, and the cat dies. If not, the cat remains alive. Everything is put in a box, and the only way to know if the cat is alive or dead is opening it. Therefore, the cat has a 50% chance of being alive or dead. According to the interpretation quantum, while not open the box, the cat is both alive and in a dead state, which seems ridiculous.
is however more useful to understand the collapse, talk of Stern and Gerlach experiment . Remember: an electron has a spin that can have two states: up (s = 1 / 2) and down (s =- 1 / 2). Is made through an area with a nonuniform magnetic field. Before crossing, it is unclear whether the state of the electron spin, has a 50% chance of being in one or another. But through it, the spin is oriented (in fact, the superposition of states collapses up and down one of them) so that the electron is deflected of his career in one way or another.
If now the electron, with a particular spin, we will go through another device Stern - Gerlach, with the magnetic field at the same address as above, the collapse will not happen, because the state had already been determined, and therefore, has a 100% chance of passing through the magnetic field, the final state is the same as the original. Under no circumstances may change to the opposite state.
Suppose instead that an electron moving in axis with a spin up after passing through a magnetic field uniform in the z axis , passes through another device Stern - Gerlach, but with the magnetic field in the x-axis . In this case, the spin was determined with respect to the z axis , but it was not on the x axis , and therefore returns to the initial situation: have a 50% probability that the spin is oriented towards way or another in the x-axis .
"God does not play dice"
(Albert Einstein to Niels Bohr on quantum mechanics)
This interpretation of quantum mechanics was primarily exposed by the Danish Niels Bohr, thus bearing the name of the Copenhagen interpretation. Its main feature is that it is based on probabilities, but are inherent in nature.
gas description, or systems with many particles, is based on statistics, probability and chance. But they are likely based on ignorance, and practically impossible to handle a large number of equations, which are used to find average values \u200b\u200bthat determine the properties of the system.
instead Quantum mechanics is probabilistic in nature. There are no unknowns that prevent us from determining their properties, but those odds are the only properties we can know. This view of the nature of the Copenhagen interpretation did not like, among others, Einstein, who over time had tried to prove that hidden variables exist that prevented hear and determine properties beyond their probabilities. Which today has not been possible to demonstrate.
"Stop telling God what to do"
(Niels Bohr responding to Albert Einstein)
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