If you traveled to the past how much could you recreate from memory?

Very little, I am sure. My memory sucks.

I could remember a lot of things we (collectively) know about, such as scientific discoveries and medical advances, but I’m not one of the ones who know about them.

However, I could recall a lot about a few things. Probably. I don’t know, maybe not. Come to think of it, I’d probably be a flop as a time traveler.

If I went back to ancient Greece or Rome, I could dazzle them with the decimal number system and by solving problems using algebra. Of course, I would have to learn the language first. Without knowing the language, I might be able to use an abacus to show how to translate a number represented on the abacus into decimal notation. As far as being able to do anything of immediate practical value, I would not have a clue. Maybe I could explain how a lightning rod works.