"Let the genie out of the bottle" is a commonly used idiom, which signifies the release of a powerful force or the beginning of an irreversible process. However, when it comes to expressing this idea in different ways, there are several other phrases and expressions that can be used. Some of the synonymous phrases include "open the floodgates", "unleash havoc", "ignite a firestorm", "set off a chain reaction", "open Pandora's box", "stir up a hornet's nest", "start a snowball effect", "pull the trigger", and "release the hounds". All of these phrases convey the idea of initiating a powerful force that cannot be easily contained or controlled.