The last plane of existence where living beings are born according to the result of their kamma is the Arupavacara-bhumi, or the Plane of the Formless. Similar to the Rupavacara-bhumi, the Arupavacara-bhumi is closely connected with the arupa jhana. This jhana can be developed only when a person has experienced all the four stages of rupa jhana.  The practitioner of meditation intending to rise higher in the levels of jhana, gives up the rupa-kammatthana and practices the arupa-kammatthana which will lead him to the attainment of arupa jhana.

There are four stages of arupa jhana which the meditator will attain one by one, as follows:

1. Akasanancayatana: The meditator, having obtained and then abandoned the fourth stage of rupa jhana, applies his mind to the infinity of space (ananta-akasa). He thereby attains the first stage of arupa jhana called akasanancayatana.

2. Vinnanancayatana:He, having obtained the first stage, gives up concentrating on the infinity of space and switches his mind over to the concentration on the infinity of consciousness (ananta-vinnana). He thereby attains the second stage of arupa jhana called vinnanancayatana.

3. Akincannayatana:The meditator, having attained and dwelled in the second stage, gives up concentrating on the infinity of consciousness and switches his mind over to the concentration on the nothingness of consciousness (akincanna). He thereby attains the third stage of arupa jhana called akincannayatana.

4. Nevasannanasannayatana:He, having attained and dwelled in the third stage, gives up concentrating on the nothingness of vinnana or consciousness. His mind then enters a state in which cognition is so extremely subtle that it cannot be said whether it is or not. At this point he is, regarded as having attained the fourth stage of  arupa jhana called nevasannanasannayatana.

A person who has developed any of these four stages of arupa jhana and sustained it up to the last moment of life will, at the breaking up of his body, after death, be reborn in the world of the formless (Arupaloka).  The Arupavacara-bhumi is classified into four realms in accordance with the four stages of the arupa jhana.

One who attains the first stage will be reborn, after death, in the first realm; one who attains the second stage will be reborn in the second realm; one who attains the third stage will be reborn in the third realm and one who attains the fourth stage will be reborn in the fourth realm.

The four realms of the Arupavacara-bhumü bear the same names as the four stages of the arupa jhana, i.e.,

1. Akasanancayatana,
2. Vinna,nancayatana,
3. Akincannayatana and
4. Nevasannanasannayatana.

The Vibhanga of the Abhidhamma gives the following approximate life-periods of the formless gods in the Arupavacara-bhumi: The life-period of the Akasanancayatana gods is twenty thousand kappas; of the Vinnanancayatana gods forty thousand kappas; of the Akincanna-yatana gods sixty thousand kappas; and of the Nevasannanasannayatana gods eighty-four thousand kappas.

The problem now arises as to how long one aeon or kappa is. To this question we find a parable explaining the duration of an aeon in the Pali Pitaka itself. According to the Samyutta-Nikaya it is said that a bhikkhu put to the Buddha a question about the duration of an aeon. The Buddha replied that an aeon is exceedingly long. It is not easy to reckon how long by saying so many years, so many thousand years, so many hundred thousand years.

Suppose there were a mountain of solid mass one yojana (league) wide, one yojana across and one yojana high, and at the end of every hundred years a man were to stroke it once each time with a kasi cloth. That mountain in this way would be sooner done away with and ended than would an aeon (kappa).

The parable quoted above indicates that the duration of an aeon or kappa is immeasurable. The Paramatthajotika explains that an aeon is the span of time counted from the beginning of the world’s evolution up to its destruction. At the end of its cosmic life the world will be destroyed by fire, water or wind.

After its destruction it starts forming again by gradual evolution and it will be again destroyed at the end. The span of time from the beginning to the end of the world is regarded as one kappa. In eight kappas the world will be destroyed seven times by fire and one time by water. The cycle of destruction will repeat itself in this way up to the sixty-fourth kappas and then the world is destroyed by wind. One round of sixty-four kappas is called asankheyya-kappa.

It is said that when the world is destroyed by fire the heavens are destroyed up to the Pathama-jhana-bhumi; when it is destroyed by water the Dutiya-jhana-bhumi is also destroyed; and when it is destroyed by wind the heavens are destroyed up to the Tatiya-jhana-bhumi. Only the Catuttha-jhana-bhumi and the four realms of the Arupavacara-bhumi remain undisturbed by the destructions of the world.

The life-period of the beings in the Arupavacara-bhumi appears to be exceedingly long. It is very difficult even to imagine how long it is. Even one kappa is still immeasurable. There is, therefore, nothing to say about eighty-four thousand kappas which are said to be the span of life in the  Nevasannanasannayatana realm.

But although the life-period in the Arupavacara-bhumi is so long, the beings born there still have to be reborn in other planes of existence when their span of life in that particular realm expires. They may obtain rebirth in other planes of happiness or in the plane of misery, depending on the nature of their previous kamma.

The Rupavacara-bhumi and the Arupavacara-bhumi are collectively called Brahmaloka or the world of Brahma. It should be noted that the formless beings of the Arupavacara-bhumi are just opposite to the Asannasatta of the Rupavacara-bhumi: the formless being is born without form or corporeal body (rupa) while the Asannasatta is born without mental faculties (nama). In the case of the Asannasatta we can imagine a being subsisting in an unconscious state from the beginning up to the end of his life in this realm.

But in the case of the formless beings in the Arupavacara-bhumi, it is very difficult to see how life subsists without a material body. However, the cases of the Asannasatta and the formless beings in the Arupavacara-bhumi demonstrate the two extreme types of kamma that yield results just opposite to each other.

Now, we may conclude that rebirth and planes of existence are closely connected, since to be reborn means to exist somewhere. Buddhism speaks of rebirth and planes of existence in three different ways.

1.Viewed in terms of happiness and suffering, which are the results of good and evil kamma, there are only two planes of existence, viz., the plane of happiness or Sugati-bhumi and the plane of suffering or Duggati-bhumi.

2.Viewed in terms of kamma which brings about rebirth in different planes of existence suitable to its nature, there are three planes, namely, the plane of desires (kamabhava), the plane of form (rupabhava) and the plane of the formless (arupabhava).

3.Viewed from the same ground the Venerable Anuruddhacaraya in his Abhidhammatthasangaha, classifies the planes of existence into four groups, namely, Apaya-bhumi or the plane of misery, Kamasugati-bhumi or the better plane of happiness connected with desires, Rupavacara-bhumi or the plane of form, and Arupavacara-bhumi or the plane of the formless.

All these are the planes of existence where an unemancipated individual is to be reborn again and again in the course of his wanderings in Samsara. To be born here and die here and be born elsewhere, to be born there and die there, to die there and be born elsewhere, is what the Buddhist calls Bhavacakka, the Wheel of Becoming.