In English, certain meanings require the phrase "there would have to have been . . " and not "there must have been . . ". I quote this long sentence by the physicist Steven Weinberg so that the context makes clear the need for "There would have to have been": "[in 1977 it was discovered that] the temperature of the microwave radiation [in the universe] is not the same throughout the sky. There are small ripples in the temperature, fluctuations of about one part in a hundred thousand. This was not entirely a surprise. There would have to have been some such ripples, caused by small lumps in the matter of the early universe . . ." How do I translate this into French that means "would have to have been" and not "must have been . ."? il devrait avoir été certaines de ces ondulations . . . il a dû être certaines de ces ondulations . . . . . . or something else?