Yes 1 plus 1 equals 2.
How is it even possible that we know this?
As Albert Einstein said:
The most incomprehensible thing about the world is that it is at all comprehensible.
Only if we agree what those numerical symbols mean. I'll play Devil's Advocate now. I have no idea what those artificial symbols mean. I don't understand your truth, because your language is inadequate. Worse still, I'm deaf.
Now try to get me to understand the objective truth of the beautiful dawn song of the crissal thrasher.