Dravyam (द्रव्यम्): The Basic Physical Quantity

भौमं दिव्यमुदर्यमाकरजं च | तत्र भौमं काष्ठेन्धनप्रभवमूर्ध्वज्वलन–स्वभावं, पचन-दहन-
स्वेदनादिसमर्थ-दिव्यम् अबिन्धनं सौरविद्युदादि |

Vaiśeṣika describes terrestrial (bhaumaṁ, भौमं) and celestial (divyaṁ, दिव्यं) as the sources of energy. The other two, viz. abdominal (udaryaṁ, उदर्यं) and mineral (ākarajaṁ, आकरजं) are related to metaphysical quantities. Bhaumaṁ and divyaṁ have been described as heat and light in physics, their properties being temperature and colour, respectively. The invisible causal factors of the motion of iron needle towards magnets and the effects of electricity are also different forms of energy

Ākāśa (Plasma):

Ākāśa is interpreted as the fourth state of matter, namely plasma. According to Vaiśeṣika, the specific property of plasma is the wave aspect. This property is permanent to this state. This state of matter is spread all over the universe, including our planet. In physics, plasma is a mixture of ionized atoms (ions) and free electrons, with a sprinkling of whole atoms, and sometimes even molecules of gas.

Bhūta, Dik, Kāla (The Fundamental Physical Quantities: Mass, Length and Time):

The sixth dravya, space (dik) and the seventh, time (kāla) possess a continuum and conjunctive relation with the matter of any state (bhūta, भूत). Thus, bhūta dik and kāla become the fundamental physical quantities, analogous to those of modern physics. As physics is the science of measurements, they are mass, length, and time. Here mass and time are scalars while length is a vector.

Aṇu (अणु), Dvyaṇuka (द्व्यणुक) and Trasareṇu (त्रसरेणु) (Atom, Molecule and Smallest
Colloidal Particle):

The cosmic creation follows a certain order: from the aṇu is synthesized the dvyaṇuka and from it the trasreṇu is synthesized. According to the modern physics aṇu, dvyaṇuka and trasreṇu or tryaṇuka (त्र्यणुक) can be compared with atom, molecule, and the smallest colloidal particle, respectively. The Praśastapādabhāṣya (प्रशस्तपादभाष्य) describes the sequence in the following way:

परममहत्त्वं अनित्यं त्र्यणुकादेव | तत्रेश्वरबुद्धिमपेक्ष्योत्पन्ना परमाणुद्व्यणुकेषु
बहुत्वसंख्यातैरारब्धे कार्यद्रव्ये त्र्यणुकादिलक्षणे रूपाद्युत्पत्तिसमकालं महत्त्वं दीर्घत्वं च करोति |

According to Vaiśeṣika, individual atom (aṇu) does not possess any property, but as it combines with another atom, a diatomic molecule (dvyaṇuka) is formed, which in turn, combines with other three similar molecules to produce a trimolecule (trasareṇu); only then the properties are perceived. Such a molecule, the constituents of which are three
diatomic molecules forms the smallest unit known as trasareṇu (colloidal particle). These trasareṇus further combine to give the structure of gross bodies and their properties become suitable for direct perception – त्र्यणुकादिलक्षणे रूपाद्युत्पत्तिः

Pīlupākavāda (पीलुपाकवाद) – The Theory of Chemical Reaction:

पार्थिवपरमाणुरूपादीनां पाकजोत्पत्तिविधानम् | घटादेरामद्रव्यस्याग्निना सम्बद्ध-
स्याग्न्यभिघातान्नोदनाद्वा तदारंभकेष्वणुषु कर्माण्युत्पाद्यन्ते तेभ्यो विभागः विभागेभ्यः
संयोगविनाशाः संयोगविनाशेभ्यश्च कार्यद्रव्यं विनश्यति | तस्मिन् विनष्टे स्वतन्त्रेषु
परमाणुष्वग्नि-संयोगादौष्ण्यापेक्षाच्छ्यामादीनां विनाशः पुनरन्यस्मादग्निसंयोगादौष्ण्यापेक्षात्
पाकजा जायन्ते | तदनन्तरं भोगिनाम् अदृष्टापेक्षादात्माणुसंयोगोत्पन्नपाकजेष्वणुषु कर्मोत्पत्तौ
तेषां परस्परसंयोगाद् द्व्यणुकादिक्रमेण कार्यद्रव्यमुत्पद्यते |

– Praśastapādabhāṣya

In chemical reactions (pākakriyā, पाकक्रिया), when change in properties is observed, the properties cannot be restored by general method. The change due to pākakriyā is known as pīlupākavāda or chemical change in modern science. In the process of pākakriyā due to conjunction of heat trasareṇu first breaks down to dvyaṇuka and then to aṇu. Subsequently, new arrangements of dvyaṇuka of a new substance of different properties, which further joins to form trasareṇu, is seen.

According to Vaiśeṣika, the physical properties like smell, taste and colour remain unchanged up to the level of diatomic molecules. Due to the chemical reaction (pākakriyā ), the structure of the substance (gross body) breaks down into atoms, which re-arrange themselves into new combinations. The molecules formed due to this chemical reaction, referred to as the chemical products (pākaprabhāva, पाकप्रभाव), (or pākaja, पाकज), shed the previous properties and gain new properties.

For pākakriyā, the conjunction of tejas (energy) with matter is necessary. In a chemical process of Vaiśeṣikas, these molecules along with similar molecules, after combination, form a gross body having new properties.

Dalton’s theory which has been already modified by Avogadro’s hypothesis, states that:
(i) Substances (elements and compounds) consist of molecules, i.e. ultimate particles capable of separate existence and the molecules are composed of indivisible particles called atoms.
(ii) Molecules of particular substances are similar to one another and possess the same properties and the same mass; but molecules of one substance are altogether different from the molecules of another substance.
(iii) Molecules of an element consist of atoms which are all alike, while molecules of a compound consist of dissimilar atoms.
(iv) When chemical combination takes place between two or more substances, the molecules of each substance are first disintegrated into atoms and then the atoms combine to produce new molecules of a new substance.