In one of my sci-fi stories, I have a lot of objects/concepts like force fields and balls of light. When describing the appearance of these things, I usually mention the of the size of them, since that can be vital to the scene. (I.e. sometimes the force field is huge, but other times it's the size of a golf ball.)

However, my story is set in a very futuristic time and place, so the world I am describing is very different from the one we live in. (I don't think a game like golf would exist.) However, I'm having a hard time deciding how to describe the sizes of unusual things like force fields and balls of light without referencing basketballs, beach balls, golf balls -- I find myself using a lot of balls, lol. Here's an example of what I'm talking about:

"She opened her palm and produced a force field the size of a golf ball."

I feel like there should be a better way of doing this, without having to reference earthly objects or create clunkiness by giving specific measurements like: "--a force field that was one inch in diameter."

Do you think it would be okay for me to continue referencing earthly objects in a story that takes place on a futuristic, faraway planet? If there's nothing technically wrong with that approach, I would be willing to continue making those comparisons. If not, does anyone have any suggestions of how I can describe sizes of things? Is the approach of giving specific measurements maybe not a bad idea after all? Any advice would be greatly appreciated.

Thanks so much!