We can explore impermanence in two ways, at least, and both are useful.
First is the exploration of impermanence in the world of thought, and also in terms of what it brings up in terms of emotions and so on. This may be in the form of high level generalization thoughts such as all is impermanent, and then also explorations within thoughts in more specific ways. I can for instance explore my day or my life, or the life of my parents, or my culture, or human civilization, or the Earth, or the Universe, and specifically see how it all changes over time, including how it all will be gone at some point in the future. This is an exploration of impermanence using thoughts of change, continuity, past and future.
To make it a little more real for me, it is helpful to bring it back to my own life. Everything I have experienced in the past is gone and will never come back in the same way. My life is limited. My days are counted, and there is a specific year, day, hour and minute that I will die, although I don’t know what it is. In a hundred year or so, I and everyone I know will be dead. In less than two hundred years, all memories of me will probably be gone, or at least not kept alive much.
In some thousand years, most of what is happening in my lifetime will be forgotten. In some hundreds of thousands of years, or maybe millions of years, humans will be gone, and everything humans have done will be gone and there will be nobody to remember it. In some millions of years, this Earth will be burnt to a crisp and all traces of human civilization will be gone (unless we went to another solar system in the meantime.) In some billions of years, this whole universe will either collapse into a big crunch, or disperse enough to die a slow heat death. Then, at the very least, will all traces of humanity be completely gone, and there will be nobody left to remember it either.
Also, what happens if I have a vivid, felt-sense of knowing that I will die in ten years? In five years? In a year? In six months? In a month? In a week? Tomorrow? Next hour? Next minute? What comes up for me then? How does it reorganize my priorities? What becomes more important? Less important? How would I live my life then?
This way of exploring impermanence can certainly have an effect, especially in terms of my priorities and what seems important in my life. Trying to impress others seems quite a bit less important, because it will all be forgotten and gone in a while anyway. Living a meaningful life, in a way meaningful for me, becomes more important.
The other way to explore impermanence is through how it shows up here and now, in immediate perception.
Since thought creates a sense of continuity, and also tells us that different experiences are the “same” as previous ones, it is helpful to differentiate the sense fields, to explore sight, sound, sensation, smell/taste and thought distinct from each other. By doing that, it becomes easier to notice how all the sense fields are in constant change. What was here a moment ago is utterly and completely gone, only a thought is left at best, a memory, but this thought is here now, brand fresh and new, even if another thought says it looks a lot like a thought from the past.
Everything arising, in each of the sense fields, is fresh and new. A thought may say that it looks similar to a memory of something that was, but that is a story of the past. What it refers to, both as here now and as something happening in the past, is already gone.
This form of exploration undermines the whole tendency to take stories as anything more than a thought, arising here now.Â Attachment to stories is weakened, revealing everything arising as awakeness itself.