do the five realms really exist?

Do the five (sometimes six) realms really exist? It's an interesting question. One reason is that the Buddhist idea of 'worlds' or 'realms' (loka) can be taken both literally (i.e., as external realms of existence) and metaphorically (i.e., as mental states).

They're definitely real in the sense of various pleasant and unpleasant mental states that we mentally take birth into, which is something we can easily observe for ourselves. For example, BuddhaNet's introductory essay, "Introduction to Buddhism," gives a good explanation of the realms in this way:

If ego decides it likes the situation, it begins to churn up all sorts of ways to possess it. A craving to consume the situation arises and we long to satisfy that craving. Once we do, a ghost of that craving carries over and we look around for something else to consume. We get into the habitual pattern of becoming consumer oriented. Perhaps we order a piece of software for our computer. We play with it for awhile, until the novelty wears out, and then we look around for the next piece of software that has the magic glow of not being possessed yet. Soon we haven't even got the shrink wrap off the current package when we start looking for the next one. Owning the software and using it doesn't seem to be as important as wanting it, looking forward to its arrival. This is known as the hungry ghost realm where we have made an occupation out of craving. We can never find satisfaction, it is like drinking salt water to quench our thirst.

Another realm is the animal realm, or having the mind like that of an animal. Here we find security by making certain that everything is totally predictable. We only buy blue chip stock, never take a chance and never look at new possibilities. The thought of new possibilities frightens us and we look with scorn at anyone who suggests anything innovative. This realm is characterised by ignorance. We put on blinders and only look straight ahead, never to the right or left.

The hell realm is characterised by acute aggression. We build a wall of anger between ourselves and our experience. Everything irritates us, even the most innocuous, and innocent statement drives us mad with anger. The heat of our anger is reflected back on us and sends us into a frenzy to escape from our torture, which in turn causes us to fight even harder and get even angrier. The whole thing builds on itself until we don't even know if we're fighting with someone else or ourselves. We are so busy fighting that we can't find an alternative to fighting; the possibility of alternative never even occurs to us.

These are the three lower realms. One of the three higher realms is called the jealous god realm. This pattern of existence is characterised by acute paranoia. We are always concerned with "making it". Everything is seen from a competitive point of view. We are always trying to score points, and trying to prevent others from scoring on us. If someone achieves something special we become determined to out do them. We never trust anyone; we "know" they're trying to slip one past us. If someone tries to help us, we try to figure out their angle. If someone doesn't try to help us, they are being uncooperative, and we make a note to ourselves that we will get even later. "Don't get mad, get even," that's our motto.

At some point we might hear about spirituality. We might hear about the possibility of meditation techniques, imported from some eastern religion, or mystical western one, that will make our minds peaceful and absorb us into a universal harmony. We begin to meditate and perform certain rituals and we find ourselves absorbed into infinite space and blissful states of existence. Everything sparkles with love and light; we become godlike beings. We become proud of our godlike powers of meditative absorption. We might even dwell in the realm of infinite space where thoughts seldom arise to bother us. We ignore everything that doesn't confirm our godhood. We have manufactured the god realm, the highest of the six realms of existence. The problem is, that we have manufactured it. We begin to relax and no longer feel the need to maintain our exalted state. Eventually a small sliver of doubt occurs. Have we really made it? At first we are able to smooth over the question, but eventually the doubt begins to occur more and more frequently and soon we begin to struggle to regain our supreme confidence. As soon as we begin to struggle, we fall back into the lower realms and begin the whole process over and over; from god realm to jealous god realm to animal realm to hungry ghost realm to hell realm. At some point we begin to wonder if there isn't some sort of alternative to our habitual way of dealing with the world. This is the human realm.

The human realm is the only one in which liberation from the six states of existence is possible. The human realm is characterised by doubt and inquisitiveness and the longing for something better. We are not as absorbed by the all consuming preoccupations of the other states of being. We begin to wonder whether it is possible to relate to the world as simple, dignified human beings.

And this psychological interpretation is supported by the suttas themselves. For example, we find passages like these in AN 4.235 (notice the qualifier 'like'):

And what is kamma that is dark with dark result? There is the case where a certain person fabricates an injurious bodily fabrication, fabricates an injurious verbal fabrication, fabricates an injurious mental fabrication. Having fabricated an injurious bodily fabrication, having fabricated an injurious verbal fabrication, having fabricated an injurious mental fabrication, he rearises in an injurious world. On rearising in an injurious world, he is there touched by injurious contacts. Touched by injurious contacts, he experiences feelings that are exclusively painful, like those of the beings in hell. This is called kamma that is dark with dark result.

And what is kamma that is bright with bright result? There is the case where a certain person fabricates a non-injurious bodily fabrication ... a non-injurious verbal fabrication ... a non-injurious mental fabrication ... He rearises in a non-injurious world ... There he is touched by non-injurious contacts ... He experiences feelings that are exclusively pleasant, like those of the Beautiful Black Devas. This is called kamma that is bright with bright result.

As for the literal existence of these realms, I can't say. It's certainly possible, and it's often fun to speculate about them (I've even heard stories of people who could see beings from these others realms); but I think it's more useful to focus on what we can experience for ourselves in the hear and now, and use our practice to try and transcend these mental realms in order to find a true and lasting happiness inside.