You know more than your past self knew. Your future self will have more experiences than your current self. Is that enough to make them different people?
Occasionally, it can be helpful to consider your future self a different person from your present self.
“That’s not my problem,” you might think to yourself. “That’s my future self’s problem.”
Similarly, if there is one person you can be sure that you are smarter than, it is you from the past. You have all the knowledge and experience that that person had, plus whatever you have learned or experienced since then.
But is that enough to define a different person?
Obviously, your past self, present self, and future self have some commonalities. The decisions that your past self made led to the current you, and what you do now will set the stage for who you will become.
In addition, you all share the same DNA, have the same parents, went to the same high school, and so on. You share a temporal existence.
However, your body, and everything around you, is constantly in flux. Each breath you take is slightly different in composition, the food you eat from meal to meal varies, your microbiome is always changing, and so on.
As the saying goes, you can never step in the same river twice — all the water changes from moment to moment, as it rushes downstream and is replaced with the water coming after.
Is it the same with your body? As cells live, divide, and die, to be replaced by new cells, are you the same when most, or all, of your cells are replaced?
When you think about the person you used to be, or the person you will become, do you consider that a different person? Or are they all just you, with some minor tweaks and changes?