The Vaisheshika School defined motion in terms of the non-instantaneous movement of the physical atoms. Light rays were taken to be a stream of high velocity fire atoms. These atoms can exhibit different characteristics depending on the speed and the arrangements of these particles. The Buddhists Dignaga (5th century) and Dharmakirti (7th century) developed a theory of light being composed of energy particles. This was very much similar to the modern concept of photons.
From ancient times, Indian philosophers believed that except ether or space, all other elements were physically palpable. Hence they comprised of small and minuscule particles of matter. They believed that the smallest particle which could not be subdivided further was paramanu (can be shortened to parmanu), a Sanskrit word.
Paramanu is made of two Sanskrit words, param meaning ultimate or beyond and anu meaning atom. Thus, the term "paramanu" literally means 'beyond atom.' This concept at an abstract level indicated the possibility of splitting atom, which is now the source of atomic energy. The term "atom" however should not be conflated with the concept of atom as it is understood today.
Kanada, a 6th century, Indian philosopher was the first person who went deep systematically in such theorization. Another Indian, philosopher Pakudha Katyayana, who was a contemporary of Buddha, also propounded the ideas about the atomic constitution of the material world.
All these were based on logic and philosophy. As a result, they lacked any empirical basis for want of commensurate technology. Similarly, the principle of relativity (not to be confused with Einstein's theory of relativity) was available in an embryonic form in the Indian philosophical concept of 'sapekshavada.' The literal translation of this Sanskrit word is theory of relativity.
These theories have attracted attention of the Ideologists. As a matter of fact, even veteran Australian Ideologist A. L. Basham have eventually concluded that they were brilliant imaginative explanations of the physical structure of the world. Also, to a great extent, agreed with the discoveries of modern physics.
From the Vedic times, around 3000 B.C. to 1000 B.C., Indians (Indo-Aryans) had classified the material world into four elements. These four elements were Earth (Prithvi), fire (Agni), air (Maya) and water (Apa). To these four elements was added a fifth one viz. ether or Akasha.
The root to the concept of atom in ancient India is derived from the classification of material world in five basic elements by ancient Indian philosophers. According to some scholars these five elements or Pancha Mahabhootas were identified with the various human senses of perception; earth with smell, air with feeling, fire with vision, water with taste and ether with sound. Whatever the validity behind this interpretation, it is true that since very ancient times Indians had perceived the material world as comprising these 5 elements.