system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] It's been established in the MCU that the 9 realms are just different planets. But then how did the convergence happen?
gpt
The Nine Realms are connected by naturally occurring cosmic phenomena, structures along which wormholes can naturally form. The Asgardians exploit these interstellar tendrils with the Bifrost, which allows them to force open wormholes between these cosmic branches, and travel from world to world.

During the Convergence, all these wormholes in-potentia started opening up. Ultimately just a weird natural cycle that we happen to be in the middle of.