Is Light Particle or Wave?
Bohr considered electrons as particles and light as a wave in his development, Einstein’s concept of the existence of two theories of light (waves and particles) which had not been connected in a logical way had already been accepted. Then another renowned scientist appears Louis de Broglie, who suggested a similar treatment for electrons, that is, these are not only particles but also waves and that in fact what travels is in orbit around the nucleus of an atom is not a particle but a standing wave, like that of a violin string that is fixed at both ends.
This idea, although rare, allowed to better explain the so-called quantum jump of the electrons when they passed from one energy level to another. Now it could be explained in terms of wave vibration when changing from one harmonica to another. Later another renowned scientist, Erwin Schrödinger, developed a complete mathematical description of the behaviour of electrons in atoms, based on the idea of a wave.
Other mathematical descriptions explaining the behaviours of the electrons appeared from the hand of Heisenberg, Paul Dirac, all of them equivalent but with different visions about the meaning of the same quantum world, thus the different quantum realities emerged. No matter which equations were used, they all described the same phenomena giving the same results. However, since scientists were more familiar with working with wave equations (wave mechanics), they were developed by Schrödinger based on the wave function of the electron, those that became conventional to develop calculations in what was called quantum mechanics.
Already in the late 1920s physicists had different mathematical menus to describe the microworld, all of which worked perfectly well with a high degree of precision in all predictions about actual experiments being carried out; the bad thing was that they all included some of the concepts that were strange to common sense, such as the quantum jump, the wave-particle duality, or the uncertainty principle.
Bohr was the first to develop an idea about the reality of the quantum world, called the Copenhagen interpretation. It says that electrons or any quantum entity do not exist as long as they are not observed, but that what exists is a probability cloud that measures the probability that the entity is in a certain place at a certain time. When we decide to observe said quantum entity (the electron for example), what is called a “collapse” of the wave function occurs, in which the entity randomly chooses a position to locate, that is the position that the observer will detect.
Once observation ceases, here it is necessary to return to the chapter on waves. Max Born another of the physicists of the time connected quantum waves with real events in an innovative way.
Quantum waves, that is, those that describe quantum entities like electrons, follow the same rules as any of the physical waves mentioned, water in the pool, sound, electromagnetic waves. In other words, they can be added, superimposed, interfered with. We have said that waves are characterized by the medium that vibrates to produce the waves that transmit energy; thus water in the case of water waves, air for sound waves, electric and magnetic fields for electromagnetic waves.
In the case of quantum waves that are a special type of wave, they are probability oscillations. Quantum waves, unlike ordinary waves, do not transfer energy, which is why they are called empty waves. The amplitude of the squared quantum wave, known as the intensity of the wave motion, is a measure of probability.
Nearing the end of this story, it is important to mention that two science monsters, Einstein and Bohr, held opposite positions; Bohr defending the fundamentals of quantum by means of explanations that did not fit with common sense.
Einstein on the contrary saying that he could not accept the break implicit in all the explanations of quantum physics. For all the phenomena of nature, they had to be based on what was called “local reality”. What is the meaning of this expression?
reality means that all quantum entities are real even when not observed, and not as it was argued that these quantum entities (the electron) only existed as clouds of probabilities as long as they are not observed, to become a concrete particle by observing them.
Local means that nothing can be transmitted at a higher speed than light, not even information since it will travel in electromagnetic waves at that speed.
These concepts that had the approval of the scientists defending common sense, were not accepted by the quantum (Bohr), who maintained that in the quantum world both cannot occur, or the entities are real and then there is a transmission of information to a speed higher than the speed of light, or if this is not possible, then the quantum entities are not real and only exist at the moment they are observed.
Despite the strangeness of these ideas, in an experiment carried out in Paris in 1982 by the scientist Alain Aspect, using photons as quantum entities, it was shown that the predictions of quantum physics were correct: the quantum world cannot be composed both real entities and being local (light as maximum transmission speed). This means that the microworld does not work according to the rules of common sense determined by our daily experiences.
But as Feynman said more than thirty years ago: “nobody understands quantum mechanics, but let us not worry about wondering why nature behaves like this, but let us marvel admiring ourselves when knowing how nature behaves”.
‘Particle Physics Brick by Brick: Atomic and Subatomic Physics Explained’
by Dr. Ben Still PhD
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