I want to make the outside of a sphere transparent so that when I’m looking at it, all I see is the inside of the opposite face. If I’m close enough to the sphere that I can only see a small section of the outside then I want to look through that section and see the majority of the inside of the sphere. To do this I just need to make it so the sphere is transparent when viewed from the outside but that the inside face is visible.
Sounds from your description like you want to Cull Front rather than Cull Back in the shader.