I’ve been a believer in entropic gravity for a long time and believe it’s due to quantum foam. In a region of space with nothing in it the quantum foam in that space would be perfectly uniformly random. With mass and energy the state of the space would be biased and less random. This creates an entropic gradient. Further this doesn’t just explain gravity but explains why the space between galaxies seems to demonstrate negative energy and space expansion. I’m glad to see more research into the idea of entropic gravity as it’s IMO a more reasonable explanation than most other gravity theories I’ve heard.