What are the life expectancies (ages) in the different realms of the gods?

Question

In Buddhism, there are a few realms that exist. Does each realm have the same life expectancy, or does it vary from realm to realm?

Answer 1

Even in the human realm the life span is said to vary greatly depending on where the human race is at during any given cycle of rise and decline. The longest lifespan given for humans is 80 000 at its peak, and a mere 10 years at its lowest ebb: DN 26. It's notable that even when it's near its peak, heedful meditators are still depicted as warning each other of how short human life is, and the importance of not wasting one's time: AN 7.70

This might partly be due to their skill in seeing heavenly realms, where the life span is considerably longer. The suttas give some indication of how long.

“Fifty human years are equal to one day & night among the Devas of the Four Great Kings. Thirty such days & nights make a month. Twelve such months make a year. Five hundred such heavenly years constitute the life-span among the Devas of the Four Great Kings. Now, it is possible that a certain man or woman—from having observed this uposatha endowed with eight factors—on the break-up of the body, after death, might be reborn among the Devas of the Four Great Kings. It was in reference to this that it was said, ‘Kingship over human beings is a meager thing when compared with heavenly bliss.’

“A human century is equal to one day & night among the Devas of the Thirty-Three. Thirty such days & nights make a month… One thousand such heavenly years constitute the life-span among the Devas of the Thirty-three. Now, it is possible that a certain man or woman—from having observed this uposatha endowed with eight factors—on the break-up of the body, after death, might be reborn among the Devas of the Thirty-three. It was in reference to this that it was said, ‘Kingship over human beings is a meager thing when compared with heavenly bliss.’

“Two human centuries are equal to one day & night among the Devas of the Hours… Two thousand such heavenly years constitute the life-span among the Devas of the Hours…

“Four human centuries are equal to one day & night among the Contented Devas… Four thousand such heavenly years constitute the life-span among the Contented Devas…

Eight human centuries is equal to one day & night among the Devas Delighting in Creation… Eight thousand such heavenly years constitute the life-span among the Devas who Delight in Creation…

Sixteen human centuries are equal to one day & night among the Devas Wielding Power over the Creations of Others. Thirty such days & nights make a month. Twelve such months make a year. Sixteen thousand such heavenly years constitute the life-span among the Devas Wielding Power over the Creations of Others. Now, it is possible that a certain man or woman—from having observed this uposatha endowed with eight factors—on the break-up of the body, after death, might be reborn among the Devas Wielding Power over the Creations of Others. It was in reference to this that it was said, ‘Kingship over human beings is a meager thing when compared with heavenly bliss.’” AN 3.71

The final figure above would give us a life span of 9,216,000,000 human years.

All the above devas would be on the level of form, and there are higher planes yet, with longer life spans. The problem with making comparisons is that we start to leave the realm of concrete measurements in human years and get into measurements in terms of eons. Here's the Buddha on the length of an eon:

“Long, monk, is an eon. It’s not easy to count as ‘so many years’ or ‘so many hundreds of years’ or ‘so many thousands of years’ or ‘so many hundreds of thousands of years.’”

“But is it possible to give an analogy, lord?”

“It is, monk,” said the Blessed One. “Suppose there were an iron fortress—a league long, a league wide, a league high—full of mustard seeds packed tight, and a man would come along once every hundred years and take from it a single mustard seed. More quickly would that great heap of mustard seed waste away and be consumed by that effort, but not the eon. That’s how long, monk, an eon is." SN 15.6

The term translated as 'league' here is yojana, which is normally considered to be at least 5km.

With that in mind, here are some further descriptions of heavenly life spans:

" The Devas of Brahmā’s Retinue, monks, have a lifespan of an eon... The Ābhassara devas, monks, have a lifespan of two eons... The Subhakiṇha devas, monks, have a lifespan of four eons... The Vehapphala devas, monks, have a lifespan of 500 eons." AN 4.123

That seems to be about as far as we go for devas on the level of form. Then there are the formless realms:

"The life span of the devas of the dimension of the infinitude of space is 20,000 eons... The life span of the devas of the dimension of the infinitude of consciousness is 40,000 eons... The life span of the devas of the dimension of the nothingness is 60,000 eons." AN 3.117

One might expect to find that life spans in lower realms are very short - animals, for instance, typically live shorter lives than humans. The Buddha warns us, however, that stretches of time spent in hell can be very long indeed. Devadatta is perhaps the person to look to for the longest time in hell due to the gravity of his deeds, whom the Buddha declared was confined to hell for an eon: Iti 89

Perhaps the most salient point from the discussion on the duration of life spans is that the time we've each spent wandering through the different realms far, far exceeds even the longest heavenly life span. The Buddha says we've been getting born, dying and suffering for such a long time that it's high time to look for something entirely different: the unborn, the undying, freedom from all stress and pain - nibbāna. As he says to the monk who asks the length of an eon:

...not just one eon has been wandered-through, not just one hundred eons have been wandered-through, not just one thousand eons have been wandered-through, not just one hundred-thousand eons have been wandered-through.

“Why is that? From an inconceivable beginning comes the wandering-on. A beginning point is not discernible, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries—enough to become disenchanted with all fabrications, enough to become dispassionate, enough to be released.”

Answer 2

Different realms have different ages. But none of them lasts forever. There is realm spontaneous rebirth. Some states of existence extend to eons. No matter how long the realm exists it is not worthwhile to call it self.