The final word (yet) of quantum mechanics on light is that it has a dual nature – it is both a wave and a particle. Verily, the human mind is in discomfort with this, primarily, because it lacks a clear mental picture. In Hindu scriptures, instances abound, where similar dualistic concepts are conjoined – “Non-being then existed not nor being existed” – Hymn of Creation – Rig Veda X 129. Such a meek correlation, however, is not the point of this post. What is first attempted is to understand why making a science of light is difficult and then, to realize that this inherent difficulty was understood by the writers of Kena Upanishad. ( केन उपनिषद् )
The scientist makes observations (using appropriate tools) of the phenomenon he intends to study. Based on these facts, he generalizes and comes up with a principle. Any science rests on these perceptions, also called axioms. The Archimedes principle rests on the observation that objects weigh less in fluids. You and I have to take a weighing machine and observe it for ourselves to be certain of it. The photo-electric effect pivots on the observation of (backward) current when light (of sufficiently high intensity) is incident. The instruments for perceptions are our five senses. No matter how fine-tuned the microscope is, ultimately, it is with our eyes that we observe a sample. Hence, we can make a science of a phenomenon, provided, we are somehow able to make observations of its nature. This is especially true in cases where direct sensual perception is not possible. For example, magnetic (electric) force, though beyond our senses, is manifest in the motion of a magnet (electric charge) - inferential judgements.
The problem with light:
If we want to make observations on light by visual perception, the question is, with what will we observe light? Light itself is what enables us to make observations. Without light illumining the lab, how can we make any visual observations in the first place? Light, which facilitates visual observation, if used to observe itself, has in one instance revealed itself as a particle and in another as a wave (depending on the type of experiment – double slit or photoelectric). The reality is that light is much more than both a wave and a particle.
Kena Upanishad ( केन उपनिषद् )
The difficulty with light, elucidated above, is only a specific instance of the discussion in Kena Upanishad. The idea is in a ‘germ’ form, i.e. it is generalized. Below outlined are verses relevant to the discussion:
"That which cannot be expressed by speech, but by which speech is expressed-That alone know as Brahman, and not that which people here worship." (I. 5)
“That which cannot be apprehended by the mind, but by which, they say mind is apprehended -That alone know as Brahman, and not that which people here worship.” (I. 6)
“That which cannot be perceived by the eye, but by which, the eye is perceived -That alone know as Brahman, and not that which people here worship.” (I. 7)
“That which cannot be heard by the ear, but by which the hearing is perceived -That alone know as Brahman, and not that which people here worship.” (I. 8)
“That which cannot be smelt by the breath, but by which the breath smells as an object -That alone know as Brahman, and not that which people here worship.” (I.9)Note:
- Hymn of Creation - translated by A.A. Macdonell.
- Translation of Kena Upanishad from "The Upanishads" by Swami Nikhilananda, Advaita Ashrama.