physics - Story set inside a sphere

This is a story with a civilisation whose "planet" is the inside of a sphere, like an inverted/hollow world (or Dyson sphere but that's not quite the same thing). The physics in the story is made up.

I think they try digging and the conclusion is that they are surrounded by a large or infinite amount of rock/soil.

Their "sun" is at the centre of the sphere, but it is a fire that goes off at night and relights the next day.

I think they have oceans and continents. And there is flight but it works differently in their world.

It was science fiction (rather than fantasy). In particular, why the "sun" goes out and relights, and how the flight works, were explained.

I read it in the 1990s so it wouldn't have been published after that. I think it was a short story or novella. I don't remember what the plot was though.

Answer

The Straight Dope has a thread with examples of stories set on just about every shape of planet imaginable, including "the inside of a spherical void within infinite solid matter" (post #39) in Ring of Truth by David Lake.

That description and the very limited reviews of the book on the web (Amazon, Goodreads) seem consistent with what I remember.

However, I don't recognise the title, author or cover pictures at all. So I've ordered a copy and will update this to confirm whether it's the right book.

(The hollow sphere idea is mentioned on page 102 of Science Fact and Science Fiction: An Encyclopedia By Brian Stableford, with other examples, but they seem less likely.)

Edit: I've read it now, and it was the book I was thinking of. It is a 192 page sci-fi novel, not a short story. It has some nice alternative physics that seems consistent and somewhat plausible. The fact that they are in a sphere is a plot spoiler.

The characters are not initially aware of the shape of their world and, although there are clues for the reader to guess, it isn't revealed to the characters until the end. The plot follows a prince with wanderlust who is initially tutored with the current state of knowledge about the world and then goes on a quest to find out more. Gravity works by light being repellent (rather than masses attractive) so, for example, you weigh less indoors and at night. However, they use other means to achieve flight.