The antimatter cannon was the ultimate weapon of mass destruction. It was invented by Mobius with a single purpose, spread antimatter across the multiverse in order to destroy all of the infinite Earths in existence.
On April 28, 2024, the Anti-Monitor used the cannon to begin wiping out the Multiverse. However the Barry Allen of Earth-1 sacrificed himself by running so fast, he reversed the flow of the cannon and made it implode on itself; sacrificing himself in the process by going so fast he incinerated himself.
As a result, at least Earth-1 (the planet) was saved from destruction.
For unknown reasons Cicada's dagger was tied to the Crisis in some way; it's destruction in Spring 2019 somehow accelerated the time to just half a year away.
On December 10, 2019, the cannon was unleashed on the entire multiverse, destroying every Earth until the Flash, Vibe, Killer Frost and Pariah discovered the machine under Central City, with the Flash of Earth-90 powering it. Vibe managed to get Barry off the treadmill, but this triggered a fail-safe that would destroy every Earth immediately. Pariah summoned Black Lightning from Earth-TUD5 to help contain the energy of the cannon and buy time to find a solution. Barry of Earth-1 decided to sacrifice himself by running backwards on the treadmill to cause the wave to recede, the stress of which would kill him. However, Barry of Earth-90 temporarily stole Barry of Earth-1's speed and took his place on the treadmill, succeeding in stopping the wave and saving Earth-1, the last Earth in existence, but disintegrating in the process.
Behind the scenes
- In the DC Comics, the antimatter cannon is the Anti-Monitor's weapon to wipe out the universe. It was powered by concentrated antimatter and the only way to destroy it was for the Flash to continually run around it and sacrificing himself in the process.