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> Thirty Years that Shoot Physics Issue: 2008-3 Section: Science


Physics has just discovered everything; we only have to clarify some details. After a century these words by Philip von Jolly to Max Plank make us understand that human imagination is limited compared to the infinite expressions of nature. Classic mechanics has dominated the common scenery and the ideas of the world, based on determinism: all that happened had a specific reason and specific effects took place, until in ‘1900 Max Planck changed it radically with a new concept, outside the classic physics. In fact Max Planck formulated in 1900, the concept of the quantum leap of energy to explain the spectrum of emission of a black body. That is an ideal body capable of absorbing the entire radiation incident on its surface and in which a balance between the emitted and the absorbed radiation takes place. So that all the power of the light does not depend from the chemical composition of a body, but only from its temperature. In fact, the latter depends on the relation between emitted and absorbed radiation, which is the same in a specific temperature. Classic physics could not explain the behavior of the light power and for this reason Planck’s constant was employed: the new physics, trained to the classic one, was called quantum mechanics, based on the non-linear conception of energy.

This idea was not accepted by the physicists of the time, since in 1905, Albert Einstein solved the photoelectric effect paradox by describing light as composed of discrete quanta, rather than continuous waves. The photoelectric effect is a phenomenon in which electrons are emitted from matter after the absorption of energy from electromagnetic radiation. According to the energy conservation law, the energy radiated from radiation, moves partly to the kinetic energy of the electrons. Classic mechanics predicted theoretically that each increase of the power of light radiation coincided with the increase of the electron kinetic energy.

The experimental evidence did not confirm this theory, but rather it observed an increase in the number of electrons with the same kinetic energy that was equal to the initial one, according to the energy conservation law. It was understood that energy could be stored only in moderate quantity, called quanta.

In 1913, Niels Bohr used the quantum theory to explain the intermittent spectrum of emission of an atom. He hypothesized that the electrons that were arranged in circular orbits have specific energy value; when an electron absorbs a quantum of energy gains energy and, consequently, travels in a higher level energy orbit. Thus, a condition of instability, for which the electron returns to the initial condition emitting the quantum of energy earlier absorbed in form of electromagnetic radiation. The spectrum of emission resulted non-linear because an atom could absorb and emit only a definite quantum of energy and no intermediate value, according to which a continuous spectrum of emission could be obtained. Experimental evidence, testified that a moderate energy value existed also for electromagnetic radiation, defined as quanta of light or photons. With these discoveries physicists temporally abandoned the wave theory in favour of a revaluation of the particles theory, envisaged for the first time by Isaac Newton in the XVII century.

Yet, Newton’s particle interpretation was challenged by experiments which emphasized phenomena of diffraction and interference of the light, characteristic of wave movements. The first of these experiments was performed by Thomas Young in 1801. A light source that lights up two small cracks made in an opaque screen, and the images of the cracks are projected on a photographic plate. At the end of the experiment he observed an alternation of light and dark lines; this was a consequence of the interference among the waves. It can only take place between two or more waves and, in this case, they are obtained from the diffraction that takes place on the passage of initial light beam between the two cracks. These effects of diffraction and interference are typical of wave-like motions and they are not included in the corpuscular theory.

This theory too, was questioned by the experiment of the photoelectric effect, which envisaged a non-linear energetic behavior of the light and not reckoned for by wave theory. The quantum theory was formulated according to which light is made of quanta of energy. The relativistic theory proposed by Albert Einstein, at the beginning of the XX century, ‘explains that they should be equivalent to small mass concentrations, referring to Newton’s particle theory. Physicist inferred that the two theories, examined separately, could not describe all light phenomena. The wave mechanics in fact, did not provide photons, while quantum theory did not include the phenomena of diffraction and interference.

The only solution was to conciliate both theories: that is the light dual wave- particle theory. In 1925 Louis De Broglie, on experimental evidence, generalized this theory for every body. In the experiments of the two cracks, in fact, substituting the light beam with an electron one, the phenomenon of diffraction and interference was clearly observed. The mathematic relation obtained by De Broglie, as compared to a determinate body, allows to state its wave-length, which is inversely proportional to the quantity of the body motion.

The duality wave-particle is based on the fact that sometimes the electromagnetic waves can behave as particles and vice versa. Particles such as electrons can behave indeterminately because they diffuse in the space.

De Broglie’s theory has been applied to the study of the atom structure; the development of the atomic model is connected to the quantum theory. From Bohr’s atomic model we know that the electrons cannot occupy any orbit, but rather definite orbits with determined energy level.

De Broglie made the understanding of this restriction easier, since every electron describes a stationary wave around the nucleus which, not to cancel itself, can only be a whole multiple of the wave-length.

The electron, therefore, cannot occupy any orbit, because, if so, the delineated wave would cause a destructive overlap. The energetic levels and the relative wave functions that the electron can occupy, are, on the contrary, obtained from the solutions of the equation formulated by the Austrian physicist Erwin Schrodinger, in 1926.

This equation, which considers all the energy contributions of the system, results in discreet values of the possible wave functions and the corresponding energy values; and we are able to calculate the energy leap of an electron from a level to another one, so called quantum jump, already introduced by Bohr.

Later the British physicist Max Born gave further contribution to the quantum mechanics development, interpreting Schrodinger’s equation in a probabilistic way.

Such interpretation, applied to the description of the atomic structure, implied the partial neglect of Bohr’s atomic model. The circular orbits proposed by the latter, in fact, are in contrast with the probabilistic character that the interpretation of Schrodinger’s equation gives to the determination of the electron position in an atom. We have then, the new concept of orbital defined as a region of space in which an electron with a determined energy value is most likely to be found. A further research in the field of the microcosm was made possible, immediately after Schrodinger’s works, by Werner Heisenberg with his principle of indetermination. Such principle was inferred by an ideal experiment, which consist in determining the particle position and speed, and, therefore, in determining its present and future position. These quantities are measured with the emission of electromagnetic waves on the particles, in order to perform these measures their motions have to be disturbed.

The more we want to be accurate in the position, the more the radiation wave-length has to be reduced; in doing so the frequency increases and consequently the energy, too. The particle will be more disturbed, therefore compromising the precise measure of its motion quantity. This indetermination is a limit which derives from the nature of the matter and it does not depend on the precision of our instruments. The mathematic formula, at the basis of indetermination was formulated in 1927 by Heisenberg and it focuses an inversely proportional relation between indetermination on the position and that on the motion quantity. The macroscopic behaviour of the matter is different from the microscopic one. In fact in classic physics the knowledge of the position and speed of a material point in a specific moment is sufficient to predict its future route. Instead the quantum mechanics proposes a model in which the phenomena taking place on atomic level are described on a probabilistic basis.

All that we observe in this field is beyond our imagination, because humans are accustomed to interpreting macroscopic reality with deterministic laws, which cannot be applied to microscopic phenomena and so they appear inexplicable, clashing with our common sense: nature appears unnatural. Albert Einstein, in The Evolution of Physics co-authored by Leopold Infeld, affirms that that science is a book in which the word <end> has not and will never be written. Each important progress sets new questions in motion in time, each development will lead to new and deeper difficulties.

With this consideration it is evident that also the quantum theory, similarly to classic physics, in the future could be substituted by a new theory that, exposing as false the quantum theory principles, will propose a new, innovative and revolutionary vision of the world.

Each theory, in fact, is temporary and its value does not depend on its persistence in an immutable form, but it depends on the fact that new knowledge can lead to a new theory. We are waiting, therefore, for a new Planck who will propose a more complete theory.



  • Davies Paul, Le forze della natura, 1990, Bollati Boringhieri, Torino
  • Einstein Albert e Infeld Leopold, L’Evoluzione Della Fisica, 1938, Universale Bollati Boringhieri, Torino
  • Feynman Richard, Sei pezzi facili, 1963, Adelphi, Milano
  • Gamow Gorge, Trent’anni che sconvolsero la fisica, 1966, Zanichelli, Bologna
  • Gamow Gorge, Biografia della fisica, 1961, Oscar Mondatori, Milano
  • Penrose Roger, La mente nuova dell’imperatore, 2000, Biblioteca Universale Rizzoli, Milano
  • Zeilinger Anton, Il velo di Einstein. Il nuovo mondo della fisica quantistica, 2003, Einaudi, Torino



  • Max Planck,, University of Glasgow – Department of Physics and Astronomy
  • Effetto fotoelettrico, – Wikimedia Commons
  • Modello atomico di Bohr,, ANISN Associazione Nazionale Degli Insegnanti di Scienze Naturali
  • Schrodinger’s Results,, Reasonable Deviations, Image courtesy of N. Harding
  • Wave-Particle Duality,
  •, Quantiki portal

  • The two logical possibilities, Young’s experiment,, people behind informatics – universitat klagenfurt
  • Thomas Young, – Van Renesse Consulting
  • De Broglie’s atomic model,, University of Birmingham – Astrophysics & Space Research Group