It's important to first note the obvious: physics didn't change when Einstein came up with his theory of relativity. Where classical mechanics had proven to be

It's important to first note the obvious: physics didn't change when Einstein came up with his theory of relativity. Where classical mechanics had proven to be very accurate, Einstein's relativity had to be in agreement. It could not have been otherwise. It's only where classical mechanics had not been tested (or not been tested with much success) that relativity could diverge. This is something that is often misunderstood by those who dismiss scientific knowledge: accumulated observations and experiments don't end up in the trash. Any new breakthrough theory is first going to have to be in agreement with all of them. That's why classical mechanics is still not only taught at school, but also widely used by engineers to this day: it's extremely accurate (within some bounds).