After seeing the Cosmos series by Carl Sagan during my early childhood (for this I consider him one of my greatest teachers even though I didn't actually attend any of his classes), I wondered what could happen billions of years later...

How might the orbit of planet Earth be different if I were to pick up a grain of sand from one beach and deposit it onto another beach on the other side of our planet?  Could this influence our orbit?

Assuming we had computers powerful enough and with enough capacity, would it be possible to predict absolutely everything in the cosmos, our galaxy, our solar system, or even merely our planet and our moon if we knew absolutely everything about every atom throughout the cosmos?

I tend to think so, but I can't say that I know for certain because, how could we be absolutely sure that we knew absolutely everything?