Polytheism was a common form of religion in ancient times. People believed that different gods lived and controlled various parts of nature (ie the sun, the moon, thunderstorms), and praying to these gods gave them a sense that they had control over their lives.
In modern and scientifically advanced societies, polytheism is not regularly practiced. It seems that the most prominent religions today either circle around one omniscient god (Christianity, Judaism, Islam) or no god at all (atheism, Buddhism). My reasoning behind this is that we have scientific evidence that explains most of the natural processes to us (like the water cycle, the rotation of the earth around the sun, etc.), but the one question we can't answer is where we came from, hence the one god that created everything.
I need a reason why a scientifically advanced future society would begin to worship multiple gods again. Does anyone have any good ideas for why this would happen?
NOTE: My original idea is something that veers from the current Catholic idea of saints. Each saint is a patron of something different, and people pray to them to pray to God on their behalf. Maybe sometime in the future, this idea gets warped and people begin to pray to the saints as individual gods?
I am not completely satisfied with this idea though, and would love to hear other ideas.
NOTE 2: Kingledion pointed out that Hinduism is a modern religion that is semi-polytheistic. From my vague understanding of Hinduism, the belief is that there is one god that takes on many forms (see here). I suppose I was looking for a truly polytheistic religion and not some blend between monotheism and polytheism.