No, there are several realms in which one can be reborn.
Some people are reborn in heaven, some are reborn in hell, some are reborn as hungry ghosts and so on. Heaven is not a place but a state of existence where one has a subtle body and where the mind experiences mainly pleasure. Some religions strive very hard to be reborn in a heavenly existence mistakenly believing it to be a permanent state. But it is not. Like all conditional states, heaven is impermanent and when one's life span there is finished, one could well be reborn again as a human.
Hell, likewise, is not a place but a state of existence where one has a subtle body and where the mind experiences mainly anxiety and distress. Being a hungry ghost, again, is a state of existence where the body is subtle and where the mind is continually plagued by longing and dissatisfaction.
So heavenly beings experience mainly pleasure, hell beings and ghosts experience mainly pain and human beings experience usually a mixture of both. So the main difference between the human realm and other realms is the body type and the quality of experience.
What decides where we will be reborn?
The most important factor, but not the only one, influencing where we will be reborn and what sort of life we shall have, is kamma. The word kamma means 'action' and refers to our intentional mental actions. In other words, what we are now is determined very much by how we have thought and acted inthe past. Likewise, how we think and act now will influence how we will be in the future.
The gentle, loving type of person tends ot be reborn in a heaven realm or as a human being who has a predominance of pleasant experiences. The anxious, worried or extremely cruel type of person tends to be reborn in a hell realm or as a human being who has a predominance of painful experiences. The person who develops obsessive craving, fierce longings, and burning ambitions that can never be satisfied tends to be reborn as a hungry ghost or as a human being frustrated by longing and wanting.
Whatever mental habits are strongly developed in this life will continue in the next life. Most people, however, are reborn as human beings.
Some people simply go through life under the influence of their past habits, without making an effort to change them and falling victim to these unpleasant results.So we are not determined by our kamma. We can change it.Of course we can. That is why one of the steps on the Noble Eightfold Path is Perfect Effort. It depends on our sincerity, how much energy we exert and how strong the habit is. But it is true that some people simply go through life under the influence of their past habits, without making an effort to change them and falling victim to these unpleasant results. Such people will continue to suffer unless they change their negative habits. The longer the negative habits remain, the more difficult they are to change.
The Buddhist understand this and takes advantage of each and every opportunity to break mental habits that are unpleasant results and to develop mental habits that have a pleasant and happy result. Meditation is one of the techniques used to modify the habit patterns of the mind as does speaking or refraining to speak, acting or refraining to act in certain ways. The whole of the Buddhist life is a training to purify and free the mind. For example, if being patient and kind is a pronounced part of your character in your last life, such tendencies will re-emerge in the present life. If they are strengthened and developed in the present life, they will re-emerge even stronger and more pronounced in the future life. This is based upon the simple and observable fact that long established habits tend to be difficult to break.
Now, when you are patient and kind, it tends to happen that you are not so easily ruffled by others, you don't hold grudges, people like you and thus your experience tend to be happier.
Now, let us take another example. Let us say that you came into life with a tendency to be patient and kind due to your mental habits in the past life. But in the present life, you neglect to strengthen and develop such tendencies. They would gradually weaken and die out and perhaps be completely absent in the future life. Patience and kindness being weak in this case, there is a possibility that in either this life or in the next life, short temperedness, anger and cruelty could grow and develop, bringing with them all the unpleasant experience that such attitudes create. We will take one last example. Let us say that due to your mental habits in the last life, that you came into the present life with the tendency to be short tempered and angry, and you realize that such habits only cause you unpleasantness and so you make an effort to change them. You replace them with positive emotions. If you are able to eliminate them completely, which is possible if you make an effort, you become free from the unpleasantness and so you make an effort to change them. You replace them with positive emotions.
If youare able to eliminate them completely, which is possible if you make an effort, you become free from the unpleasantness that are caused by being short tempered and angry. If you are only able to weaken such tendencies, they would re-emerge in the next life where with a bit more effort, they could be eliminated completely and you could be free from their unpleasant effects.
Not only is there scientific evidence to support the Buddhist belief in rebirth, it is the only after-life theory that has any evidence to support it.
You have talked a lot about rebirth but is there any proof that we are reborn when we die?
Not only is there scientific evidence to support the Buddhist belief in rebirth, it is the only after-life theory that has any evidence to support it. There is not a scrap of evidence to prove the existence of heaven and of course evidence of annihilation at death must be lacking. But during the last 30 years para-psychologists have been studying reports that some people have vivid memories of their former lives.
For example, in England, a 5-year-old girl said she could remember her "other mother and father" and she talked vividly about what sounded like the events in the life of another person. Parapsychologists were called in and they asked her hundreds of questions to which she gave answers. She spoke of living in a particular village in what appeared to be Spain, she gave the name of the village, the name of the street she lived in, her neighbours' names and details about her everyday life there. She also tearfully spoke of how she had been struck by a car and died of her injuries two days later. When these details were checked, they were found to be accurate. There was a village in Spain with the name the five-year-old girl had given. There was a house of the type she had described in the street she had named. What is more, it was found that a 23-year-old woman living in the house had been killed in a car accident five years before.
Now how is it possible for a five-year-old girl living in England and who had never been to Spain know all these details? And of course, this is not the only case of this type. Professor Ian Stevenson of University of Virgina's Department of Psychology has described dozens of cases of this type in his books*. He is an accredited scientist whose 25 years study of people who remember former lives is very strong evidence for the Buddhist teachings of rebirth.
Some people might say that the so-called ability to remember former lives is the work of devils.
You simply cannot dismiss everything that doesn't fit into your belief as being the work of devils. When cold, hard facts are produced to support an idea, you must use rational and logical arguments if you wish to counter them - not irrational and supersitious talk about devils.
You say that talk about devils is superstitions but isn't talk about rebirth a bit superstitious also?
The dictionary defines 'superstition' as - 'a belief whcih is not based on reason, or fact but on association of ideas, as in magic'. If you can show me a careful study of the existence of devils written by a scientist I will concede that belief in devils is not superstition. But I have never heard of any research into devils, scientists simply wouldn't bother to study such things, so I say there is no evidence for the existence of devils. But as we have just seen, there is evidence which seems to suggest that rebirth does take place. So if belief in rebirth is based on at least some facts, it cannot be superstitions.
Well, have there been any scientists who believe in rebirth?
Yes. Thomas Huxley, who was responsible for having science introduced into the 19th century British school system and who was the first scientist to defend Darwin's theories, believed that reincarnation was a very plausible idea. In his famous book 'Evolution and Ethics and other Essays', he says :
In the doctrine of transmigration, whatever its origin, Brahmanical and Buddhist speculation found, ready to hand, the means of constructing a plausible vindication of the ways of the Cosmos to man...Yet this plea of justification is not less plausible than others; and none but very hasty thinkers will reject it on the ground of inherent absurdity. Like the doctrine of evolution itself, that of transmigration has its roots in the world of reality; and it may claim such support as the great argument from analogy is capable of supplying.
Then, Professor Gustaf Stromberg, the famous Swedish astronomer, physicist and friend of Einstein also found the idea of rebirth appealing.
Opinions differ whether human souls can be reincarnated on the earth or not. In 1936 a very interesting case was thoroughly investigated and reported by the government authorities in India. A girl (Shanti Devi from Delhi) could accurately describe her previous life (at Muttra,five hundred miles from Delhi) which ended about a year before her "second birth." She gave the name of her husband and child and described her home and life history. The investigating commision brought her to her former relatives, who verified all her statements.