Breakdown of Учёный вряд ли верит, что мы можем мгновенно перемещаться в прошлое.
мы
we
в
in / to (direction)
что
that (conjunction)
мочь
to be able to
Questions & Answers about Учёный вряд ли верит, что мы можем мгновенно перемещаться в прошлое.
Does using вряд ли to express doubt require the subjunctive mood in Russian?
No, it takes the standard indicative mood, which is why we use the regular present tense верит here. Unlike some other expressions of doubt or desire, вряд ли and едва ли just act like adverbs meaning 'it is unlikely that' and do not change the grammatical mood of the verb.
Could we put вряд ли at the beginning of the sentence instead?
You can, but вряд ли generally sits immediately before the specific word that is being doubted. Here, the doubt is specifically about the verb верит (the scientist hardly believes). Placing it before the subject (Вряд ли учёный...) would slightly shift the emphasis to doubt that it is the scientist who believes it, as opposed to someone else.
Both учёный (scientist) and прошлое (the past) have adjective endings. Do they decline like nouns or adjectives?
They decline exactly like adjectives. They are substantivized adjectives, meaning they are adjectives that have taken on the role of nouns. Учёный originally means 'learned', and прошлое means 'past'. You will encounter this structure often in Russian.
Why does the phrase end with в прошлое (accusative) instead of в прошлом (prepositional)?