While the word "universe" would imply that there's only one of them, there has been a lot of speculation about the possibility of a parallel universe. Some people take running into their doppleganger as irrefutable evidence of a the existence of a parallel universe. However, science may have found more concrete evidence of the possibility of a second universe (duoverse?).
The CMB is a light echo from the Big Bang. It is "radiation that fills the universe and can be detected in every direction." It's a relic from the Big Bang and holds many secrets we have yet to unlock - including the Cold Spot.
Previously, scientists though the Cold Spot was a supervoid. A supervoid is a "region with a relatively smaller number of galaxies inside." However, the supervoid theory seems like it might be improbable.
We live in an expanding universe. And as the universe expands, light from far away galaxies redshift. In other words, the photos are moved to longer wavelengths (i.e. redder). By measuring redshift, we can measure distance. And by studying the redshift of the CMB, researchers were able to find out that the galaxies in the Cold Spot were arranged in a regular pattern.
“Now that the possibility of a void looks much less likely, there are other suggestions of what the Cold Spot might be," said Ruari Mackenzie, lead author on a study of the Cold Spot recently published in the Monthly Notices of the Royal Astronomical Society. "These include non-standard inflation, collisions between universes and a dozen other ideas."
"The voids we have detected cannot explain the Cold Spot under standard cosmology," said Mackenzie. "There is the possibility that some non-standard model could be proposed to link the two in the future but our data place powerful constraints on any attempt to do that."
Co-Author Professor Tom Shanks concurs. "This means we can't entirely rule out that the Spot is caused by an unlikely fluctuation explained by the standard model. But if that isn't the answer, then there are more exotic explanations." Sounds like a Twilight Zone episode waiting to happen!
“The results in the paper don't really say anything about the possibility of a multiverse one way or the other,” said Mackenzie. “What we set out to do was test the claim that there was a huge supervoid aligned with the Cold Spot that was so extreme it could have created the CMB Cold Spot, possibly by an effect beyond standard cosmology.”
“It's true our results leave room for these other explanations, but our results don't support any of them. Could the Cold Spot be evidence of a collision between universes? Maybe. Do we have any evidence to claim it is? No. These exotic hypotheses really require more evidence before any of them gain much traction as an explanation," said Mackenzie.
So maybe the Cold Spot isn't the "scar" of when two universes crashed into each other. Science still doesn't have an explanation for what the Cold Spot is. Perhaps one day we'll finally figure out what it is.