To me, the most interesting and important question about the fundamental nature of the universe is whether or not gravity is quantized. For a century our understanding of the universe has been based on the idea that all energy, and perhaps even time and space itself on the smallest scale exists only in desecrate, indivisible units, or quanta. And we have quantum theories of 3 of the 4 forces of nature that agree remarkably well with current experimental results. But, so far there is no workable theory of quantum gravity, and perhaps more importantly no experimental evidence of gravitons, or gravitational quanta. If you are interested here is an excellent article about the current state of experimental findings regarding quantum gravity.
https://www.scientificamerican.com/article/is-gravity-quantum/
https://www.scientificamerican.com/article/is-gravity-quantum/
