The rumors of a Supergirl/Flash crossover refuse to die, so we consider just how it might shake out.

At the Television Critics Association press tour, Supergirl and The Flash executive producer Greg Berlanti was asked, once again, about the potential crossover between the two shows. His other shows comprise what is lovingly known as the Arrow-verse on The CW. And then there is Supergirl on CBS — which, notably, co-owns The CW with Warner Bros. Entertainment.

“Unfortunately, you’re going to get the same answer that I always give, which is that, as a fan, I would love it,” Berlanti said of the potential crossover. “I personally never rule anything out. I would be excited by it. But a lot of things would have to go right, people would have to say yes, for that to happen.”

Berlanti noted “financial hurdles,” “getting everybody to sign off” and time constraints as obstacles for getting the crossover done (presumably) this season.

It’s worth pointing out, however, that Arrow brought in Matt Ryan’s Constantine from the canceled NBC series earlier this season as well, giving precedence to network crossover.

However, perhaps the biggest issue the crossover would run into is that “You haven’t been hearing about Superman [on Arrow/The Flash], and Superman exists in [Supergirl’s] world,” Berlanti said. Not to mention, aliens exist in the Supergirl universe while superpowers are the realm of metahumans in the Arrow-verse. The creative teams have “some thoughts” on how to get around that, though.

As it turns out, so do we.

Alternate Earths

One obvious way for a Supergirl/Flash crossover to work is for the world of Supergirl to be an alternate Earth to the one The Flash inhabits. This season of The Flash has introduced the multiverse, or the concept of parallel universes. A different Flash, Jay Garrick, exists on Earth-2. Earth-2 also has Gorilla City and Atlantis, indicating the Earths can have quite different characteristics — and heroes.

With this in mind, Supergirl‘s world could easily be an alternate world that Barry visits by traveling through a portal. Then again, the multiverse was introduced when Jay came from Earth-2 to Barry’s world through the singularity, so who is to say that Kara couldn’t travel to the world of The Flash?

Wibbly-wobbly, timey-wimey

Another way the crossover could work is if Supergirl is set in the future. That would leave room for Clark to become Superman and Kara to grow into Supergirl. We might then meet an older Barry, or the current Barry could travel into the future, where he meets Kara. So far, Barry has only traveled into the past, but it seems inevitable that he will go forward as well.

Something interesting that may tie into this theory is what Rip Hunter says in the Legends of Tomorrow promo: “I’ve seen Men of Steel die and Dark Knights fall,” indicating a future of the Arrow-verse in which Superman and Batman not only exist but have died — likely at the hand of Vandal Savage.

Some combination of the two

Who is to say it has to only be one of these alternate explanations? Maybe Kara comes from an alternate future of the Arrow-verse.

Unfortunately, Berlanti says they “haven’t had any official conversations with anybody” about getting the ball rolling on a crossover. Maybe next season?

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