Time
Truthfully, one of the biggest scientific mysteries of humankind is time. Even though it seems straightforward, it’s more complex than that. It’s funny because scientists need more time to study time. But that’s the conundrum. Until they can figure out how to manipulate time, they’ll just have to keep on studying it.

Many questions arise regarding time, and that’s questions as, is time illusory or real? Does time always move forward, or can we manipulate time and make it more backward? Is time travel possible, and could we go into the future and go back into the past? Or must we always stay in the present? We may never get the answers to any of these and will just need to keep on living in the present moment (Science News).