By Shishir Thadani
Understanding of physical sciences in India evolved over centuries and these theories were very close to the modern scientific theories. For instance, the earliest applications of chemistry took place in the context of medicine, metallurgy, construction technology (such as manufacture of cement and paints) and in textile production and dyeing. But in the process of understanding chemical processes, there also emerged a concomitant interest in attempting to describe the basic elements of matter - what they were composed of, and how they interacted with each other to produce new substances. Natural phenomenon were studied in the context of tides, rainfall, appearance of the sun, the moon and stellar formations, changes in season, weather patterns and agriculture. (For instance, Vedic literature mentions the condensation of water vapor from seas and oceans due to evaporation caused by the sun's heat and the subsequent formation of clouds and rain.) This naturally led to theories about physical processes and the forces of nature that are today studied as specific topics within the fields of chemistry and physics.
In the earliest surviving scientific texts -the Vaisheshikas, basic information on the physical properties of different types of plants and natural substances were recorded and a summary and classification scheme put forth. Intuitive formulations and approximate theories about the composition of matter and physical behavior followed.
Although particle physics is one of the most advanced and most complicated branches of modern physics, the earliest atomic theories are at least 2,500 years old. Virtually every rational school of philosophy had something to say on the nature of elementary particles, and various schools of thought promoted the idea that matter was composed of atoms that were indivisible and indestructible. Later philosophers further elaborated on this notion by positing that atoms could not only combine in pairs (dyads) but also in threes (triads) - and that the juxtaposition of dyads and triads determined the different physical properties of substances seen in nature. The Jains also postulated that the combinations of atoms required specific properties in the combining atoms, and also a separate "catalyst" atom. In this way, the earlier atomic theories became converted into a molecular theory of matter. While many details of these theories no longer stand the test of scientific validity, there was much in these formulations that was conceptually quite advanced and sophisticated for its time.
The development of the Jain molecular theory appears to parallel practical developments in other fields such as medicine or metallurgy where the vital role of catalysts had been observed and carefully documented. Medical texts postulated that proper human digestion and the successful absorption of medicinal pills and potions also required the presence of "catalytic" substances. The requirement of catalytic substances relating to the manufacture of acids and alkalis (relevant to medicinal and surgical applications) had also been documented, as had the role of suitable catalysts in metallurgical processes, and in the manufacture of color-fast dyes.
Atomic/molecular theories were also utilized in explanations of chemical changes caused by heat. Prasastapada proposed that the taijasa (heat) factor affected molecular groupings (vyuhas), thus causing chemical changes. Two competing theories attempted to provide a more detailed explanation of the process (as applied to the baking/coloring of a clay pot through firing):
- the Pilupakavada theory, as proposed by the Vaisesikas held that the application of heat (through fire, for instance) reduced the molecules of the earthen pot into atoms and the continued application of heat caused the atoms to regroup creating new molecules and a different color.
- The Pitharapakavada theory offered by the Nyayikas (of the Nyaya school) disagreed, suggesting that the molecular changes/transformations took place without a breakdown of the original molecules into basic atoms, arguing that if that happened, there would also have to be a disintegration of the pot itself, which remained intact, but only changed color.
An intuitive understanding of kinetic energy appears in the texts of Prasastapada and the the Nyaya-Vaisesikas who believed that all atoms were in a state of constant activity. The concept of parispanda was propounded to describe such molecular/atomic motion, whether it be whirling, circling, or harmonic.
Optics and Sound
The earliest of the rationalists also attempted to provide theories on the nature of light and sound. Cakrapani suggested that both sound and light traveled in waves, but that light traveled at a much higher speed. Susruta posited that it was light arriving from an external source at the retina that illuminated the world around us. The Mimamsakas imagined light to comprise of minute particles in constant motion and spreading through radiation and diffusion from the original source.
The wave character of sound was elaborated on by Prastapada who hypothesized that sound was borne by air in increasing circles, similar to the movement of ripples in water. Sound was understood to have its own reflection - pratidhvani (echo). Musical pitches (sruti) were seen as caused by the magnitude and frequency of vibrations. A svara (tone) was believed to consist of a sruti (fundamental tone) and some anuranana (partial tones or harmonics). Musical theory was elaborated on the basis of concepts such as jativyaktyoriva tadatamyam (genus and species of svara), parinama (change of fundamental frequency), vyanjana (manifestation of overtones), vivartana (reflection of sound), and karyakaranabhava (cause and effect of the sound).
Varahamihira discussed reflection as being caused by light particles arriving on an object and then back-scattering (kiranavighattana, murcchana). Vatsyayana referred to this phenomenon as rasmiparavartana, and the concept was adapted to explain the occurrence of shadows and the opacity of materials. Refraction was understood to be caused by the ability of light to penetrate inner spaces of translucent or transparent materials and Uddyotakara drew a comparison with fluids moving through porous objects - tatra parispandah tiryaggamanam parisravah pata iti.
Astronomy and Physics
Just as the study of Mathematics received an impetus from the study of astronomy, so did the study of Physics. Aryabhatta made pioneering discoveries in the realm of planetary motion. This led to advances in the definition of space and time measuring units and better comprehension of concepts such as gravitation, motion and velocity.
For instance, Yativrasabha's work Tiloyapannatti gives various units for measuring distances and time and also describes a system of infinite time measures. Vacaspati Misra  anticipated solid (co-ordinate) geometry eight centuries before Descartes. In his Nyayasuchi-nibandha, he states that the position of a particle in space could be calculated by assuming it relative to another and measuring along three (imaginary) axes.
The study of astronomy also led to a great interest in quantifying very large and very small units of time and space. The solar day was considered to be made up of 1,944,000 ksana (units of time), according to the Nyaya-Vaisesikas. Each ksana thus corresponded to .044 seconds. The truti was defined as the smallest unit of time i.e. 2.9623*10-4. The Silpasastra records the smallest measure of length as the paramanu i.e. 1/349525 of an inch. This measurement corresponds to the smallest thickness of the Nyaya-Vaisesika school - the trasarenu, which was the size of the smallest dot visible on a sunbeam as it shone into a dark room. Varahamihira  posited that 86 trasarenu were equal to one anguli i.e. three-fourths of an inch. He also suggested that 64 trasarenu were equal to the thickness of a hair.}
The Laws of Motion
The Vaisesikas made the earliest attempts at classifying different types of motion. These were further developed by Prasastapada who described
- Linear motion
- Curvilinear motion (gamana)
- Rotary motion (bhramana)
- Vibratory motion.
He also differentiated motion that was initiated by some external action from that which took place as a result of gravity or fluidity.
He also described motion that resulted from elasticity or momentum, or as an opposite reaction to an external force and noted that some types of actions result in like motion, and others in opposite motion, or no motion at all - the variations arising from the internal and inherent properties of the interacting objects.
Prasastapada also noted that at any given instance, a particle was capable of only a single motion (although a body such as a blowing leaf composed of multiple particles may experience a more complex pattern of motion due to different particles moving in different ways).
Magnetism is referred to by Bhoja  as well as by Sankara Misra later. Udayana recognized solar heat as the heat-source of all chemical changes, and also that air had weight in a discussion of balloons in his Kiranawali. Vallabhacharya  in his Nyaya-lilavati pointed out the resistance of water to a sinking object. Sankara Misra noted the phenomenon of electrostatic attraction after he had observed how grass and straw were attracted by amber. He also recorded some awareness of the concept of kinetic energy and in his Upaskara dwelt on the properties of heat, and tried to relate the process of boiling to evaporation. In the same treatise, he also gave examples of capillary motion citing the ascent of sap from root to stem in a plant and the ability of liquids to penetrate porous vessels. He also wrote about surface tension, and posited sandrata (viscosity) as the cause behind the cohesion of water molecules and the smoothness of water itself.
Raja Bhoja's Somarangana-sutradhara describes many useful mechanical inventions.
Notes & References
- now referred to as photons
- Varahamihira is dated to the 6th century CE
- Aryabhatta lived from 476 to 550 CE
- Tiloyapannatti is tentatively dated between 5th and 6th century CE
- Vacaspati Misra is tentatively dated circa AD 840
- Varahamihira is tentatively dated circa 6th century CE
- Prasastapada is dated to the 7th century CE
- Sridhara lived from 870 CE to 930 CE
- Bhaskaracharya is dated to the 12th century CE
- Bhoja lived circa 10th-11th century CE
- Udayana lived circa 10th-11th century CE
- Vallabacharya is dated to 13th century CE
- Sankara Misra is dated to 15th-16th century CE
- Raja bhoja's Somarangana-sutradhara is dated circa AD 1100
- The Positive Sciences of the Ancient Hindus (Brajendranath Seal)
- Concise History of Science in India (Bose, Sen, Subarayappa, Indian National Science Academy)
- Studies in the History of Science in India (Anthology edited by Debiprasad Chattopadhyaya)
- Causation in Indian Philosophy (Mahesh Chandra Bhartiya, Vimal Prakashan, Ghaziabad)