What if I told you that “instability fingers” were a thing?
They appear all across the universe, in fact, and in your salad dressing, too, as you start to mix the ingredients properly.
Wait! What?
Imagine vinegar on olive oil – water on fat that is. Then you take a chop stick and pierce through the water into the oil fast enough. Essentially, what you are doing is to make the lighter fluid (water) push into the heavier fluid (oil). If you were to film the whole thing in slow-motion you would more likely than not even see what is called “instability fingers”:

The underlying physical process is called Rayleigh-Taylor instability. It’s difficult maths, but an important thing to get right. See, instabilities like this can happen, too, in mushroom clouds (volcanoes and bombs) or supernova explosions like the one photographed by the Hubble telescope at the very top of this article. Understanding these instabilities helps us understand both technology and nature.
Still, it’s very difficult to handle properly and we give it a silly name. Aren’t we awesome?
Is there a theory for every phenomena of the universe?
Yes and no. Quantum physics and general relativity explain 99% of it – basically. There are a lot of other theories and models that go into more detail of certain aspects of it all. In the example here, fluid dynamics can be used to do the calculations. At the same time, it’s all still very complicated, so there are a lot of things we don’t know. “What is consciousness?” e.g. is not necessarily a philosophical question, but a very real one.