What holds the Earth up?
That might sound like a stupid question to our modern sounding ears, but in the past when gravity was considered universally one-way and a flat Earth was the only accepted conception of the universe, it was a big issue as to what was responsible for holding the Earth up. There were some, like the myth-minded Greeks, who supposed it was a god supporting the world like Atlas. Others, like the Egyptians, considered there to be pillars doing the supporting. Some peoples were truly unique, like the Hindus, who thought it was an elephant on a turtle's back swimming in a universal sea which held the Earth up. But let us not dismiss the early Babylonian and Hebrew conceptions which was a flat Earth floating on a cosmic sea.
But in any case, the fact remains that with our modern understanding of the universe the answer to this question which plagued mankind for millennia is: Nothing! Nothing holds the Earth "up" because there's actually nothing pulling it "down." In fact, the answer "nothing" is incorrect because it is answering a question with an incorrect assumption. The answer should truly be "mu." The Earth is _not_ being "held up" at all.
Now given that such a question actually makes no sense, perhaps there are other deep questions that are asked today but also have no real answers because the question is also nonsense.
Consider: What/Who created the Universe? What was the First Cause/Prime Mover? Do these questions even make sense - or are we perhaps making assumptions about the character of our universe which are simply incorrect?