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interference of light coming from two in-phase point sources

Interference of light waves coming from two in-phase point sources. Crests blue, troughs red/yellow. via Wikipedia

In the supposedly hard science of physics, interference can be observed when two or more waves of energy interact to create a disturbance in the same medium (e.g. electromagnetic, light, sound, water).

Constructive interference can be observed when two or more wave ‘crests’ meet, the sum being a positive amplitude.

Destructive interference can be observed when two or more ‘troughs’ meet, resulting in a negative amplitude.

In the practical sense, interference patterns can be seen by anyone throwing two or more stones into a lake and observing the interacting ripples.

Thomas Young (1773 – 1829) demonstrated with the double slit experiment that light exhibits interference patterns, which lead to his wave theory of light. However, under different experimental conditions, light can also behave as a particle (i.e. a small unit of matter). This conundrum lead to the idea of particle-wave duality that pertains not just to light but, as it was later theorized, to all objects.

The idea of duality originated in a debate over the nature of light and matter that dates back to the 17th century, when competing theories of light were proposed by Christiaan Huygens and Isaac Newton: light was thought either to consist of waves (Huygens) or of particles (Newton). Through the work of Max Planck, Albert Einstein, Louis de Broglie, Arthur Compton, Niels Bohr, and many others, current scientific theory holds that all particles also have a wave nature (and vice versa).[1] This phenomenon has been verified not only for elementary particles, but also for compound particles like atoms and even molecules. In fact, according to traditional formulations of non-relativistic quantum mechanics, wave–particle duality applies to all objects, even macroscopic ones; but because of their small wavelengths, the wave properties of macroscopic objects cannot be detected.¹

It should be noted that physics, for all its practical success in helping to create technological marvels like the microprocessor or the LED monitor, is still just a set of theories about our world. As Jacob Bronowski puts it in BBC video series, The Ascent of Man, science depends on and, in turn, recreates a human representation of reality, not unlike a work of art.² We can never know the actual thing studied. We can only know how it appears to us (or how it leaves hints or traces of its appearance) as we observe through some apparatus—be it the naked eye, the Hubble space telescope, or an electron microscope.

Since Bronowski alluded to this in the early 1970s, many other scientists and popularizers of science have uttered similar sentiments. For instance, the holistic thinker Peter Russell suggests that we should not confuse the map (scientific concepts and theories) with the thing mapped (fundamental aspects of the universe).

¹ Source:

² The entire series also appears in book form, with text matching the TV script. The Ascent of Man: Boston/Toronto, Little, Brown and Company, 1973, pp. 321-367.


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