## The Quantum Theory

#### The Development of Quantum Theory

January 15, 2016

Schrödinger and Heisenberg develop to the full the quantum theory begun by Albert Einstein’s idea about electromagnetism in 1904. In 1927, Heisenberg introduces what he calls the uncertainty principle when he observes that it is impossible, even in principle, to measure with great accuracy the exact position and momentum of a particle since the observer and the instrument used immediately changes the particle’s velocity and momentum (Isaac Asimov, p. 120). Why is this so? Let me go back in history a bit farther. The idea of electromagnetic waves is introduced by Michael Faraday (1791-1867), as a result of his experiments in chemistry and his work in electricity and magnetism that resulted to the discovery of electromagnetic induction.

Then, British physicist James Clerk Maxwell (1831-1879), who became professor of physics and astronomy at Cambridge University at the age of 25, pursues Maxwell’s works that results in the merger of electricity and magnetism and, in the process, discovers the nature of light as well (Konrad B. Krauskopf and Arthur Beiser, 1991:200-201). In 1864, Maxwell introduces the concept of electromagnetic waves, which are viewed as disturbances generated by an accelerated electric charge. Their existence is finally discovered in 1887 by German physicist Heinrich Hertz (1857-1894) exhibiting a behavior exactly described by Maxwell.

Already in 1924, Louis de Broglie maintains that the waves associated with moving particles travels with great velocity in a group or packet of waves. In a wave, then, it is difficult to know exactly where a particle is at a given time, much less where it will be a few seconds from now, and how fast it will be moving. The future cannot be known for certain because we cannot even exactly know the present or the “now.” Heisenberg’s idea is even applied to the large-scale Cosmos in the sense that, regardless, of the size, all objects are also believed to be governed by this principle, now known as the uncertainty principle. This uncertainty multiplies since, according to Heisenberg, any device one might use to determine the position of a particle would have an effect of changing the particle’s velocity and also momentum. According to this principle, the position and motion of particles can only be expressed in terms of probabilities. How? According to Heisenberg, the height of the wave would tell us of the probability that the electron would be there at a particular location at any given moment, but that the electron doesn’t have to be there also.

German scientist Erwin Schrödinger presents his analogy of a cat to bring home the uncertainty occurring in the quantum world. He invites us to imagine a sealed box containing a live cat and a canister of poison. The box is arranged in such a manner that if a radioactive decay occurs, the vial containing the poison would be broken and the cat dies. Then, the possibility is such that after some time the cat inside the box would only be either alive or dead. The atomic decay either happened or not. But there is no way of knowing since the box is closed. Quantum mechanics theorists argue that under this condition the cat exists in some indeterminate state, neither dead nor alive, unless an observer opens the box to know whether the cat is alive or dead. In the meantime, nothing is real unless it is observed. Thus, in quantum theory, one only predicts “the probabilities of alternative outcomes” (Alan Guth, 1997:117).