WARNING: IF YOU HAVE NOT SEEN THE FLASH TV SHOW, OR ARE NOT CAUGHT UP WITH IT, THEN THERE ARE MAJOR SPOILERS FOR YOU. READ WITH CAUTION.
If you've seen season two of the CW's The Flash, then you probably had this theory in mind. As we see in season two of The Flash, we see Jay Garrick, A.K.A. "The Flash"/ Zoom comes from another Earth. Season two of The Flash starts the DC Multiverse Theory in TV, because if you have seen the episode of CBS's Supergirl, we see The Flash coming through a breach, like the ones Zoom used to get through to Barry's world, to get to Supergirl's. Now, the DC Multiverse Theory states that the Earths in each universe occupy the same space, but vibrate at different frequencies so they don't collide. So, this is where my theory comes in. Could the MARVEL universe be apart of DC's Multiverse. Of course, there are many Earths in DC's Multiverse, along with MARVEL's universe, but they could be occupying the same space but at different frequencies. Now, how could this be possible if DC and MARVEL are rivals? Well:
1. MARVEL probably doesn't know about this theory.
Yes, MARVEL most likely know about the CW making Arrow and The Flash, but they most likely know about the DC Multiverse Theory, but they might not know that The Flash is using the DC Multiverse Theory.
2. DC probably doesn't know about it.
On the other hand from point one, DC probably doesn't know about them accidentally inserting the MARVEL universe into the DC Multiverse. But, we probably spotted this before they did, so... on to the next point.
3. The probably both know about this, and are forming an unlikely partnership.
OK, this one seems pretty unlikely, but hey, if everyone thought Sony wouldn't let MARVEL put Spider-Man in Civil War, then we don't know what's happening behind the scenes at MARVEL and DC. They could be working together, and who knows. There could be a MARVEL DC cross-over comic. Or, The Flash could cross over into MARVEL's New York City, and work with the Avengers, Fantastic 4, the X-Men, or maybe even Spider-Man for an episode. And maybe one of the few teams stated could cross over into The Flash or Arrow.
The universe works in mysterious ways. And so does the DC Multiverse. Could DC and MARVEL put aside their differences and form a partnership? Leave your answer in the poll. Would you like to see a MARVEL DC cross-over? I know I would.