Are the following sentences correct?
We don't know how the word was used in the 13th century, unless we could go back in time.
We don't know how the word was used in the 13th century, unless we went back in time.
Clearly, going back in time is currently an impossibility, so "unless we go back in time" doesn't seem correct. ESL grammar books haven't discussed the hypothetical (counterfactual) use of "unless" and this hypothetical use with a factual main clause.
I'd appreciate your help.