The first time I learnt about the idea of coherence, it was in the context of physics, in high school.
We were learning about light, which I was taught to be an electromagnetic wave; a wave that consists of an electric wave and a magnetic wave oscillating perpendicularly to each other, therefore propelling each other forward. Electromagnetic waves are characterised by having a particular wavelength (the physical length of one cycle of the wave, measured in metres, denoted by the greek letter, lambda, λ) and a frequency (or rate of oscillation, denoted by the letter f). The speed (v) of a wave can be attained by multiplying the frequency by the wavelength, v=fλ.
Albert Einstein postulated that the speed of light is constant in space. This means that as the wavelength of light shortens, the frequency increases. The shorter the wavelength, the faster the wave has to oscillate in order to propel itself forward at the constant speed of light. Which is a stonking three hundred thousand kilometres per second. That’s roughly eight times around the equator of the Earth in one second. So light travels pretty fast. But this is also the same speed that microwaves, radiowaves and X-rays travel. The only difference between all these different kinds of electromagnetic waves is the wavelength and the corresponding frequency.
What this all boils down to is that the colour of light is determined by the wavelength of the corresponding electromagnetic wave.. Red light consist of longer waves, violet light of shorter waves, oscillating at a higher frequency. At least this is what the wave model of the light tells us, which is one way of gaining a rudimentary understanding of light. Like all models, it isn’t completely right, but it also isn’t completely wrong. I’m not going to dive into quantum theory here, which would be exploring a more recent model, where light is considered to be discrete units of energy, or quanta. This would imply that different colours of light correspond to different energy levels. Since pursuing quantum theory would involve at least one thought experiment where a cat is locked in a box with some radioactive material (Schrödinger's Cat), let’s instead continue exploring the wave model of light to understand the idea of coherence.
First light. 2021, Pentax MX, Kodak Image Pro 100.
For light to be coherent, it needs to have two qualities: identical wavelength, and perfect alignment. So for light to be coherent it needs to be the same colour, and originate from the same source, which would have to be a single point in space. In a real life scenario, this can be rather difficult to achieve. The light from a laser, however, is a good approximation of coherent light.
Most of the time, the light we see is actually a mixture of a broad spectrum of different colours, therefore it’s incoherent. There is a mixture of different wavelengths and these waves all criss-cross each other as they travel, sometimes cancelling each other out, other times superimposing. The light from a standard bulb in our home would be an example of incoherent light. Similarly, the light from the sun contains a variety of different wavelengths, or colours and is therefore incoherent.
Morning glow. 2021, Pentax MX, Kodak Image Pro 100.
Now, the other meaning of ‘coherent’, is not in the field of physics, but in linguistics. If someone is coherent, it means they have a clarity of expression. If someone is coherent, they make sense, and the message they wish to communicate to us is clear and easy to understand. Being coherent means being consistent, continuous and sensible.
The author has written a coherent story when the plot can be followed by the audience. It has characters, places and events that are believable, in the context of the fictional world that the author has created.
If our story is coherent, others will find it easy to listen and understand us. Coherent storytelling is where there are a series of images that all seem to fit together.
Some beautiful non-coherent light, looking east from the top of kunanyi. 2021, Pentax MX, Kodak Image Pro 100.
Not being coherent implies gaps which are difficult to bridge. If someone falsely jumps to conclusions, they have lost their coherence. It means they are difficult to follow. The drunkard, stumbling down the street, cursing the lord almighty is one example. The person speaking a language we don’t understand, to us, would also be incoherent. And this is an interesting point. Rarely does the person who is perceived as incoherent actually thinks they are being incoherent themselves.
So how can we know when we are being incoherent? Well usually, there are telltale signs in our audience. Furrowed eye brows, glazed eyes, and various other body language can point to our message being lost in translation. Of course, for us to notice these signs we need to be paying attention. If someone is being incoherent, then there is a good chance that they are not looking out for these signs in the first place.
Some days everything we say comes out right, some days everything we say comes out wrong. That’s just how it goes. Sometimes we are coherent, and sometimes we are not. Some people are coherent less of the time than others, and that is all right. We can’t all be coherent all the time. Just like the light from the sun, we do not consist of a single wavelength. We resonate on various frequencies.
But we are capable of momentary coherence, from time to time.
Forest on lower slopes of kunanyi. 2021, Pentax MX, Kodak Image Pro 100.
PS: I hope the photographs in this post will make for a coherent post, even though they depict incoherent light.