In Star Wars Rebels, Season 4 Episode 13: "A World Between Worlds", it is revealed that
the Jedi Temple on Lothal hides a portal to another dimension between life and death, time and space.
But how does the Emperor
open his own portal to this dimension?
Mere scenes earlier, the Emperor is shown talking to Minister Hydan,
who is trying to figure out what the Lothal Jedi temple is all about and how to access it. The Emperor gives him permission to continue exploring.
The Minister knows
there is some kind of portal related to the Mortis gods, he just doesn't know how to open it.
is able to open the portal,
And is then forced to flee into it when Stormtroopers discover him. Then minutes later, the Emperor is shown
opening his own portal and communicating with Ezra.
How did the Emperor know
about this dimension, let alone how to open his own portal to it so quickly?
The Emperor seems to have trouble stepping through on his own, he needs a connection to Ezra
which he uses some kind of Force-controlled Flames to reach Ezra, but Ahsoka (who Ezra pulls out of time following her fight with Vader on Malachor) cuts him off with her lightsaber, forcing him back to his side of the portal.
Seems a little fishy to me, just to drive the plot.