It's a wonderful time in physics, because that's the ultimate big open question, and a
lot of competing speculative theories have been proposed in the last 20 years on this, and related aspects, since physics all ties together (we think). For instance, the "multiverse" theories are just some of the competing theories.
Here's a great primer article I think is accessible without a physics degree, but if you have one, it's still worth reading, the writer is that good.
Is Nature Unnatural? | Quanta Magazine
(if you like this one, there are more after it on a similar level of high quality)