There are two types of people in this world: The ones who know this is the only universe, and those who believe in other universes.

Other universes mean there is a parallel world to your world, and that world has your doppelganger.

Some people have good doppelgangers who help people and save lives. Others, not so much.

If you have either made or take part in something that includes your doppelganger, you have a stronger chance of making contact with this parallel world, and your doppelganger. And the more you associate about this doppelgangers traits, personality, habits and style, that chance increases higher every level.

YouTubers like Jacksepticeye, Markiplier and Bonnie Kiwi have done this before. Making a video or a post or a picture of them can already trigger a possibility of them opening that world.

Antisepticeye(Jack), Darkiplier(Mark) and Killer Kiwi(Bonnie) are all of their doppelgangers but Mark has many more. As long as you and or society know about this doppelganger, the more in danger you are. And depending on their personality, they'll have a stronger chance to break out of their world and into yours.