if they shatter or change, the 'wall' would stop stop letting stuff in(or out) and the force would stop moving
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Okay, let's see...
If they meet, and you say that they do, (and that they are unstoppable), then
something happens.
We're talking about a tangible object and actual momentum. If not, please clarify. We might have to change our description of the wall and the force.
After the collision, they shatter or change. Unless now you wish it to be understood that the wall will "open" in some fashion and let the force pass through. Or does the force discover that it can go in more than one direction after all? Is it capable of evolution/adaptation? A change will have occurred regardless.
Even if the supposedly unstoppable/unbreakable wall and force meet and
everything stops. Change will have taken place--or it will in a universe that is like what we know of ours. We may not be around any more to take note of said change, but a change occurred leading to the new Nirvana or Nothingness.
There may be other details you haven't shared yet. And if there is an actual answer to this "unanswerable question," it may just have to be tossed into the category of "unknown"until further information is made available.
But if that's the case, (if the answer can never be known), why bother asking?
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It's still an interesting question unless the only purpose for asking is to see how many folks crash against the wall of "unknown."
(I kinda liked the doorway to Nirvana idea!)
Counterbalance