Energy, matter and light: waves and particles at the same time
Reminder: Have you read the previous page: "Quantum mechanics"?
Central to quantum mechanics is the concept that water, light, energy and matter itself are all comprised of tiny quanta or packets, that is, small particles having discrete values, but which have wave like properties at the same time. We can understand this better if we consider water, which from our everyday experience we know to be composed of individual droplets (molecules at their most basic level) and also waves as seen in the ocean. There is a duality between waves and particles in quantum mechanics: for some purposes it is helpful to think of particles as waves and for other purposes to think of waves as particles[1].
It was Planck who originally guessed (an intuition subsequently confirmed by experiment) that the energy carried by an electromagnetic wave in an oven comes in lumps, and that these lumps do not permit of fractions. Further, the energy determination of a wave – the minimal lump of energy it can have – is proportional to its frequency, not its brightness. Larger frequency (shorter wavelength) implies larger minimum energy; smaller frequency (longer wavelength) implies smaller minimum energy, and if the minimum energy a particular wave can carry exceeds the energy it is supposed to contribute, it can’t contribute and instead lies dormant.
Thus, in the oven example, only a finite number of waves can contribute to its total energy. The proportionality factor between the frequency of a wave and the minimal lump of energy it can have (known as Planck’s constant) means that one can predict accurately the measured energy of an oven for any selected temperature, but the units involved are so small (about a billionth of a billionth of a billionth) that you can’t discern the fluctuations between one step and the next as the temperature increases, much the same as you can’t determine the changes in volume along the energy of a wave on a violin string when it is vibrating. In both instances, it appears as a continuous process[2].
The fact that energy comes in lumps (as well as waves) helps explain why electrons are emitted by some substances when light or other radiation is shone on them. This is known as the photoelectric effect and was another of Einstein’s discoveries for which he won the Nobel Prize in 1921. Light also presents in particles (photons) and waves, as also do the particle properties of matter (eg electrons), an insight by the French nobleman Louis de Broglie in 1924, subsequently demonstrated in experimental form by Davison and Germer in their double-slit experiment, which encapsulates the whole of the essence of quantum mechanics in one basic experiment. This built upon Young’s original double slit experiment of the early nineteenth century using light.
For an animated graphic of wave-particle duality using the double-slit technique and dealing with partices, waves, quantum objects and with an observer present, see the link to http://toutestquantique.fr/en/ on the page en.wikipedia.org/wiki/Wave%E2%80%93particle_duality
[1] Hawking 56
[2] Greene (2000), 91 – 93; see also Hawking (1998), 54.
Central to quantum mechanics is the concept that water, light, energy and matter itself are all comprised of tiny quanta or packets, that is, small particles having discrete values, but which have wave like properties at the same time. We can understand this better if we consider water, which from our everyday experience we know to be composed of individual droplets (molecules at their most basic level) and also waves as seen in the ocean. There is a duality between waves and particles in quantum mechanics: for some purposes it is helpful to think of particles as waves and for other purposes to think of waves as particles[1].
It was Planck who originally guessed (an intuition subsequently confirmed by experiment) that the energy carried by an electromagnetic wave in an oven comes in lumps, and that these lumps do not permit of fractions. Further, the energy determination of a wave – the minimal lump of energy it can have – is proportional to its frequency, not its brightness. Larger frequency (shorter wavelength) implies larger minimum energy; smaller frequency (longer wavelength) implies smaller minimum energy, and if the minimum energy a particular wave can carry exceeds the energy it is supposed to contribute, it can’t contribute and instead lies dormant.
Thus, in the oven example, only a finite number of waves can contribute to its total energy. The proportionality factor between the frequency of a wave and the minimal lump of energy it can have (known as Planck’s constant) means that one can predict accurately the measured energy of an oven for any selected temperature, but the units involved are so small (about a billionth of a billionth of a billionth) that you can’t discern the fluctuations between one step and the next as the temperature increases, much the same as you can’t determine the changes in volume along the energy of a wave on a violin string when it is vibrating. In both instances, it appears as a continuous process[2].
The fact that energy comes in lumps (as well as waves) helps explain why electrons are emitted by some substances when light or other radiation is shone on them. This is known as the photoelectric effect and was another of Einstein’s discoveries for which he won the Nobel Prize in 1921. Light also presents in particles (photons) and waves, as also do the particle properties of matter (eg electrons), an insight by the French nobleman Louis de Broglie in 1924, subsequently demonstrated in experimental form by Davison and Germer in their double-slit experiment, which encapsulates the whole of the essence of quantum mechanics in one basic experiment. This built upon Young’s original double slit experiment of the early nineteenth century using light.
For an animated graphic of wave-particle duality using the double-slit technique and dealing with partices, waves, quantum objects and with an observer present, see the link to http://toutestquantique.fr/en/ on the page en.wikipedia.org/wiki/Wave%E2%80%93particle_duality
[1] Hawking 56
[2] Greene (2000), 91 – 93; see also Hawking (1998), 54.