Gītā is a part of Mahābhārata which defines 4 types of Time, compared
to 2 types of time but Stephen Hawkins in his ‘Brief History of Time’.
Time is perception of change of world. Change is of 3 types defining 3
types of time = Kāla.
(1)Nitya Kāla (Eternal time)-All physical bodies are always decaying.
Changes are irreversible. Whatever has gone cannot come back. So, it
is also called Death (Mŗtyu).
कालोऽस्मि लोकक्षयकृत्प्रवृद्धो (गीता ११/३२)
(2) Janya Kāla (Creative time)-This is related to Yajña which is
creation of useful things in a cycle. Measure of that cycle is unit of
time. There are 9 cycles of creation called 9 sargas. In Bhāgavata
Purāņa, 10 sargas are stated including Avyakta (abstract, formless).
Time of that is Parātpara.
सहयज्ञाः प्रजाः सृष्ट्वा पुरोवाच प्रजापतिः । अनेन
प्रसविष्यध्वमेषवोऽस्त्विष्ट कामधुक् ॥१०॥
एवं प्रवर्तितं चक्रं नानुवर्तयतीह यः ….॥१६॥ (गीता, ३) कालः कलयतामहम् ॥
(गीता, १०/३०)
(3) Akśaya-kāla (conserved time)-This is time of a system which
follows 5 types of conservation laws in physics-mass, momentum,
energy, angular momentum, and parity or charge.
अहमेवाक्षयः कालो (गीता, १०/३३)
(4) Parātpara Kāla-This is time of abstract source of Universe, and is
beyond any perception. It is described in Bhāgavata Purāņa (3/16).
From this abstract 9 levels are created, when forms and changes are
perceived. It is called Day of Brahmā.
अव्यक्ताद्व्यक्तयः सर्वे प्रभवन्त्यहरागमे । रात्र्यागमे प्रलीयन्ते
तत्रैवाव्यक्त संज्ञके ॥ (गीता, ८/१८)
Characteristics of each yuga is also described in Mahābhārata. While
satyayuga is dormant, Tretā is period of production industry (Yajña)
and Dvāpara is of Viplava (revolution, change)-
त्रेतायुगे विधिस्त्वेषां यज्ञानां न कृते युगे। द्वापरे विप्लवं यान्ति
यज्ञाः कलियुगे तथा॥
त्रेतायां तु समस्ता ये प्रादुरासन् महाबलाः।
सन्यन्तारः स्थावराणां जङ्गमानं च सर्वशः॥ (महाभारत शान्ति पर्व २३२/३१,
३४)
Accordingly, period of same period of Svāyambhuva Manu has been called
initial Tretā or Dvāpara according to the activity stated, in same
Vāyu purāṇa. Chart of yuga cycles (3 cycles of 24,000 years) may be
seen in my article ‘Shaka and Samvatsara’ or Panchanga (Hindi) on
scribd/Arunupadhyay-
त्रेतायुगमुखे पूर्वमासन् स्वायम्भुवेऽन्तरे । (वायु पुराण ३१/३)
स्वायम्भुवेऽन्तरे पूर्वमाद्ये त्रेता युगे तथा । (वायु पुराण ३३/५)
अष्टाविंशतिकृत्वो वै वेदा व्यस्ता महर्षिभिः।
प्रथमे द्वापरे व्यस्ताः स्वयं वेदाः स्वयम्भुवा। । (वायु पुराण २३)
-Arun Kumar Upadhyay, Cuttack, 09437034172