If something cannot be experienced and cannot be exactly defined, then we should not speculate about it. That is, we should only speculate about something that can either be experienced or exactly defined. An example of something that can be experienced but not exactly defined is gravity. Gravity does not have an exact definition as of yet other than the mere explanation of the force that we experience. Of course, the explanation of the force might definition of it, but it is far from exact. We are only explaining what happens, not what it is. Even with this, we experience it and therefore can speculate about it. That is, I can see if I let go of a pen that I am suspending in the air, it will fall to the ground because of the force of gravity.

As for, something that we can exactly define, yet cannot experience, are triangles. Triangles can be exactly defined as ‘a polygon with three sides’ and from this definition, we can speculate about the nature of triangles. For example, we can know, through speculation, that a triangle's corners have a total of 180 degrees. But with all this said, there is no way for us to experience a real triangle in itself.

This is all to say, that to speculate about something, we either need to be able to experience it or have an exact a priori definition of it.

With this said, it does not seem the case that we should speculate about something that we can neither experience nor have an exact definition for since there is nothing to speculate about. Heaven is one of these things. We cannot experience heaven ourselves until we get there. Of course, some people claim to have had experience in heaven, but if we wish to speculate about such an experience it would only be about their account of heaven and not about heaven itself. Perhaps they can speculate about it themselves, but this does not mean that people who have not experienced it should speculate about it. For example, if someone explains to you what a chair is like, without you ever having experienced a chair, all you can speculate about is what he said about the chair, not the chair itself.

We also do not have an exact definition of heaven. Of course, we can say that it is paradise, but there is no exact definition of paradise other than vague things like ‘a place where everything is perfect.’ Here we only have a thing that is said to be perfect, but no account of what perfect is in this case.

Therefore, it seems that we should not speculate about heaven because we cannot experience it and do not have an exact definition for it.