A physicist once blew my mind with the following observation. "Mathematicians always get it wrong when you talk about the relationship between position and velocity. You say that velocity is the derivative of position, acceleration the derivative of velocity, etc. And that's all fine, down to 16 decimal places, give or take. Past that, quantum effects become significant. You don't have a clean mathematical identity: perhaps velocity is approximately the derivative of position, acceleration is approximately the derivative of velocity, but below the Planck scale, these quantities aren't even continuous!"

Descartes based his entire concept of the existence of truth on the fact God exists and doesn't hate him. I don't think we have any good arguments for the existence of truth or even consensus reality beyond simple pragmatic acceptance of it as an assumption without evidence.

Not quite true. He used it as proof of gods existence. But his logical premise holds, and has yet to be countered in any meaningful way. Our awareness of our existence proves our existence.

Sure but I wasn't questioning my existence. Only yours and everybody and everything else's. Descartes still would need to believe in God in order to believe in you. It doesn't seem like a particularly good argument.

I was only saying it is a truth. It's a small truth. But truth non-the-less.