A spoiler-free discussion.
The Flash, seen here utilizing the Cosmic Treadmill
With The Flash movie heavily speculated to contain a narrative that opens up the DCEU multiverse, there are many facets to discuss in regards to this topic on how director Andy Muschietti will attempt to make the introduction of the multiverse canonical to the greater DCEU franchise. The trailers for the film have already teased us with having two Batmans, one played by Ben Affleck and the other portrayed by none other than Michael Keaton himself from Batman 1989, a Supergirl played by Sasha Calle, and a second Flash played by Ezra Miller himself.
With all these goodies for our viewing pleasure, it does make us wonder as to how exactly The Flash will go about creating or opening up an alternate universe using his powers. Based on the information circulating around the internet, it is rumored that the film borrows heavily from the Flashpoint story arc in the comics. In it, The Flash essentially opens up the multiverse when he tries to prevent his mother’s murder. That is all well and good as a storyline from our perspective, but what concerns us is the tool that the superhero will need to use in order to make this happen: The Cosmic Treadmill.
For those unfamiliar to The Flash source material, the Cosmic Treadmill is a specialized time-traveling device created by The Flash in order to travel through time and to alternate universes. The time-traveling device was first introduced in 1961, and has since remained canon for when Barry Allen or any of the other members of the Flash Family require it to travel anywhere beyond their own capabilities.
As interesting as it may be to witness the powers of the Cosmic Treadmill in the pages of a comic book, the inclusion of such a device within the film could be considered clunky if not handled accordingly. After all, the device looks and works almost identically to a regular treadmill, safe for being powered by cosmic rays and possessing radioactive properties attached to a cosmic ray clock.
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If the device is to be included in the upcoming film, it would need to be introduced in a plausible manner that would pique the interests of audiences to accept its outlandish concept and hopefully not have it elicit a negative effect instead, such as the laughable invisible jet in the Wonder Woman 1984 film.
That being said, based on what we have witnessed thus far, The Flash in Zack Snyder’s Justice League did not need the power of the Cosmic Treadmill to go back and time and stop the Unity from happening. Therefore, we believe the writers for the upcoming The Flash film could certainly find a creative way to forego the Cosmic Treadmill in order to tell their story, but that certainly remains to be seen.