In Buddhist HEAVEN/PARADISE?
I have been a practicing Buddhist for about 17 years. From the point of view of my being able to give informative answers to questions about Buddhist doctrine, this is both a strength and a weakness. I have reasonably in-depth knowledge concerning my own belief system and practice - the New Kadampa Tradition, which is closely based on the Gelug lineage of Tibetan Buddhism, and draws substantially on the works of classical Buddhist scholars such as Chandrakirti’s Guide to the Middle Way, Shantideva’s Guide to the Bodhisattva’s Way of Life, and Je Tsongkhapa’s Exposition of the Stages of the Path. Whatever knowledge and inner experience I have acquired is based on mainly on the above texts and more specifically on modern commentaries and explanations in English published by Tharpa Publiations, and from oral instructions I have received in study programmes, retreats and classes over the years. The teachings are ultimately based on the Sutras, which are discourses attributed to Buddha, but the Sutras may appear dense, repetitive and obscure to modern readers and it is therefore difficult to put their instructions into practice without the use of later commentaries.
In case you are interested, this site, called The Reading Room, is an ongoing project that aims to provide online catalogue of all texts in the Tibetan Buddhist canon, translated into English:
https://read.84000.co/section/O1JC114941JC12924.html
This also may be of interest as an overview of Tibetan Buddhism:
https://en.wikipedia.org/wiki/Tibetan_Buddhism#Teachings
My knowledge of other traditions is fragmentary as I have not done any systematic study. Different people, whether practitioners or those with a purely scholarly interest in Buddhism, may have varying ideas about what is "authentic". For instance, I understand that Theravada Buddhists do not acknowledge Mahayana Buddhism as part of Buddha's original teachings - from their point of view it is a later development and therefore not "authentic".
But to return to the original question and your follow-up question. My understanding is that according to the law of karma, every action has an effect - it sows a seed on our mental continuum which will later ripen as an experience. This applies to activities of mind as well as those of speech and body. As we are continuously creating actions of mind, speech or body every waking moment, we are necessarily creating the causes for future experiences every waking moment. Virtuous actions create the cause for happy experiences and non-virtuous (or immoral) actions create the cause for unhappy experiences. The effects may come to fruition in our immediate next life, or in a more distant future life – this depends partly upon the state of mind with which we die. Our actions will therefore determine in which of the six realms or modes of existence we are reborn into - these being the human, animal, hungry ghost realms, the hells, the god realm (or heavens) and demi-god realm, and will also determine the specific experiences and quality of life we undergo in that realm. In general, the experiences beings undergo when born as a human, god or demi-god are far pleasanter than the experiences undergone in the other three realms. Of these it is preferable to be born as a human because only humans have the opportunity to devote their lives to virtue and to following spiritual paths. Gods are too distracted by pleasure, demi-gods by jealousy and anger, and the beings in the lower realms either have insufficient mental capacity or are too immersed in suffering. To make our human life meaningful, we should at least strive to create only positive karma, by avoiding immoral actions, and by reducing or eliminating non-virtuous states of mind such as anger. The main causes of a human rebirth are virtuous actions, and developing a strong wish to be reborn human. The cycle of uncontrolled death and rebirth is called “samsara”.
However, all rebirths we undergo, no matter how happy, are contaminated, and are the cause of future suffering. This is because our actions are contaminated by self-grasping ignorance – that is, an innate belief in an inherently existent self or “I”, together with a belief that all other phenomena are inherently existent. Based on our misapprehension of the nature of reality, we create both contaminated virtuous actions and contaminated non-virtuous actions, which are the cause for contaminated rebirths in samsara. The good fortune we experience from, for instance, being born human, with good material conditions, health, security, honour, high status, and so on, is temporary and deceptive. Being born into a state of ignorance, we easily develop non-virtuous minds such as anger, uncontrolled desire, envy and deluded pride, which lead us to commit other harmful actions, and to deplete our merit, or positive karma, faster than we create it. Being born human also means that we inevitably experience the sufferings of birth, aging, sickness and death. To fulfil the higher purpose of our human life, according to Buddhism, we should strive to gain a deep understanding of the true nature of reality through study, analysis and meditation, so as to attain nirvana or enlightenment.
Having attained enlightenment, a person is no longer subject to uncontrolled rebirth but can choose their next place of rebirth, and will also be use their enlightened state to help other beings, either materially or spiritually, including through the use of miracle powers and clairvoyance. A Buddha, a fully enlightened being, may reside in a Pure Land – a place where there is no suffering or contaminated rebirth – but will still be able to produce “emanations” which can be considered as being like avatars, to help beings in samsara. It is said that Gautama Buddha – also known as Buddha Shakyamuni after the aristocratic family into which he was born – actually achieved enlightenment many aeons ago but chose to take rebirth in this world out of compassion as a way of demonstrating the path to enlightenment. According to the Mahayana, there are different levels of enlightenment – the “great enlightenment” achieved by a Buddha, that has been obtained through developing the wish to lead all other beings to the same goal, is more powerful than the lesser enlightenment of someone who has practised the Hinayana path, which consists principally in seeking individual liberation from samsara. An Arhat, someone who has attained enlightenment through the Hinayana path, has freedom from suffering and deluded states of mind, but lacks a Buddha’s omniscience.
No matter how poor or hostile their surroundings appear to human beings, a Buddha, will perceive these surroundings as pure, and although such a person will appear to have a physical body which will also age and sicken, they will not identify with this body and will therefore not be troubled by it.
Finally, please note that on this occasion I am using the terms “nirvana” and “enlightenment” interchangeably, since both involve the extinction of delusion and uncontrolled rebirth. But in some contexts they are used differently – when an enlightened being “passes into nirvana” this can mean that he or she will appear to pass away and stop appearing in the human world.
I hope this helps. It has no doubt raised more questions than it answers, which I am prepared to answer to the best of my ability, but if you have any questions please be patient as I will be at work this week!