Help! Is it plagiarism if my book uses real-world science in it?

Guys I’m freaking out. I was listening to a podcast with this scientist who was talking about something called gravity. I realized that this would make a great idea for a magic system, a world where everything has gravity. I immediately wrote 500 pages.

I was feeling good about myself, but then the podcast ended and the guy mentioned that he will be talking about it in his new book. Needless to say, I was crushed.

I’m freaking out that no publisher will take my story. To be fair, I think I really expanded upon his concept. Is it plagiarism if I still publish?