But isn’t rationality purely subjective? That’s kind of my point.
No, it’s not. That’s relativistic thinking, and is itself irrational.
If rationality is subjective, then there’s no reasonable means by which to determine that a course of action is rational because there is no way to ensure that you yourself are being rational. There may be multiple rational courses of action in a given situation, but what is rational and what is irrational are knowable qualities given a set of circumstances.
Your example of stocks isn’t an apt one for the discussion because it involves too many unknowable factors. In situations like that there are multiple potential rational judgments that could be made given the user’s knowledge and other external variables.
The topic at hand deals with only two potentials with a handful of knowable variables.
- One, is there an afterlife? A simple yes or no.
- Two, is the universe going to end? Yes. We may not know the specifics of how, but this iteration of the universe, and everything contained within it, will end.
- Will all individuals eventually die? Yes. No matter how long we may live, when the universe goes we go with it. In most suggested ends of the universe, it will be impossible for life to exist long before the universe itself actually collapses, so there’s no avoiding this one.
So, the only variable factor here is whether or not there is an afterlife.
If there is, then what we do continues on after our deaths, and even after the eventual death of the universe. Our meanings do not stop with our hearts and brains, they continue on in whatever afterlife exists.
If there isn’t, the no matter what we do, or how long we last, eventually the universe will be destroyed and it will all amount to nothing. No matter what meaning we may give a life, the longest that meaning can continue to be remembered / acted upon is the end of the universe, at which point the final outcome will be no different than had that meaning never existed. This renders it all ultimately meaningless.
We ascribe meaning because we must, we have an instinctual understanding that life is not meaningless, that we must have a purpose. That is why your rabbi friend, and pretty much all the atheists/non-believers I know, believe it has meaning. However, if there is nothing external to this reality, no afterlife in which our actions may continue to have impact eternally, then it will all ultimately be meaningless. The fact that people don’t allow themselves to arrive at this conclusion doesn’t disprove it.
Given that we
know life has meaning, then the only rational conclusion is that we also
know that there is something afterwards, even if we’re unwilling to consciously acknowledge that fact.