Learn Spanish (Latin America): Sin gravedad, eso habría alterado nuestra hipótesis. - Without gravity, that would have altered our hypothesis.

It is formed by combining the conditional tense of the helper verb haber (here, habría to match the subject eso) with the past participle alterado. It translates exactly to "would have altered" and is used to talk about an action that would have happened in the past under different circumstances.

Why use the conditional perfect if there is no si (if) clause in this sentence?

The "if" clause is actually implied by the phrase Sin gravedad (Without gravity). You do not always need a formal si clause to trigger the conditional perfect. Here, Sin gravedad acts as the condition, meaning the exact same thing as "If there had been no gravity" (Si no hubiera habido gravedad).

Why does the sentence use eso instead of ese or esa?

Eso is a neuter pronoun. It is used here because "that" refers to an abstract idea, a situation, or a previously mentioned event, rather than a specific masculine or feminine noun. If "that" referred to a specific feminine noun from a previous sentence like a theory (la teoría), you would use esa instead.

Why does hipótesis use the feminine adjective nuestra, and how do you make it plural?