You are assuming there is an edge. Your image is of a universe expanding into space. That is NOT what happens in the Big Bang scenario. Instead, it is space itself expanding. There is no space outside of the universe. It is simply that the space is expanding: distances are getting larger over time.
Butting in...I agree, but what you said still doesn't make sense...there is no practical way to understand the whole Universe as an object of our contemplation that is not riddled with problems of self-reference. If something is getting bigger then it must have "room" to grow.
Mathematically this might make sense but then we have to understand whether math is the ground of being or not.
And I see no reason to think that is the case. You aren't making the distinction between the universe and things inside of the universe. Each thing inside the universe could be caused and the universe itself not.
And again...please excuse me...Experience teaches us that no natural system is closed. It always arises out of another layer of activity even as it contributes to a layer of activity "above" it. The Universe itself, based on our vast scientific knowledge, is probably an outgrowth of some sort of activity outside of the Universe. As a part of that Universe our awareness is naturally limited to our ability to be aware. The Self-Awareness of the Universe within us is, as with any other natural phenomenon, not perfect.
The idea of "Nothing" is a clue to our mythic understanding of the idea of "Everything". Any such complimentary pairs of opposite concepts (such as Nothing-Everything) have the "stink" of the neural basis of human knowledge on them. It is as if our knowledge depended on a neural architecture that makes use of mutually inhibitory neurons associated with each end of the polarity in the pair of opposites themselves. And in nature, no pair of complimentary opposite qualities manifest as a pure expression of either extreme. There is no perfect darkness (virtual particles) nor perfect light (particle-wave duality). No top speed for matter (no matter can go the speed of light) and no perfect point of stillness (special theory of relativity).
The idea that there is a perfect Nothing that is not pregnant with potential or that there is anyway to know the whole of Everything except as being somehow causally born out of something unknown is counter to our understanding of nature and our neural modeling of reality.
We see the Universe through brain colored glasses and those glasses create pairs of complimentary opposites through dynamic neural activity of mutually inhibitory neural interconnections. We can't really see reality any other way.