Learn Farsi: به فرض اینکه به گذشته بروی، شاید باعث یک پارادوکس بشوی. - Assuming that you travel to the past, you might cause a paradox.

They are triggered by two different words. The first verb, بروی, is in the subjunctive because به فرض اینکه (assuming that) sets up a hypothetical scenario. The second verb, بشوی, is in the subjunctive because it follows شاید (might/maybe), which always requires the subjunctive due to the uncertainty of the action.

Could I use فرضا که instead of به فرض اینکه at the beginning of the sentence?

Yes, you can. Both فرضا که and به فرض اینکه express a supposition and both require the Present Subjunctive for the verb that follows them. Using فرضا که به گذشته بروی is a perfectly natural alternative.

Why does the Farsi sentence use بشوی (you become) instead of a word that directly means to cause?

In Farsi, the concept of causing something is usually expressed with the compound verb باعث شدن (literally: to become the cause). Therefore, to say you might cause a paradox, you say شاید باعث یک پارادوکس بشوی (you might become the cause of a paradox).

What is the literal root of the word گذشته?

It is the past participle of the verb گذشتن (to pass). So گذشته literally means that which has passed, functioning here as a noun for the past. This is a common way Farsi creates nouns and adjectives from verbs.