Electromagnetism moves Desmond's consciousness to sideways timeline

As Simmons' charred body is taken out of the box, Widmore stops to look at him and then proceeds to have his men force Desmond inside. They hit Desmond in the face and then tie him to a chair in the center of the room between the solenoids.

Widmore tells Desmond that he should be fine if everything he's been told about him is true. One guy asks Desmond if he has any keys or changed on him, which he doesn't. Widmore tells Desmond that after this is over, he's going to ask him to make a sacrifice, which prompts Desmond to ask what Widmore knows about sacrifice. Widmore tells Desmond that his son (Daniel) died for the island and that his daughter (Penny) hates him and he's never seen his grandson (Charlie).

Widmore and the other men leave, locking Desmond inside. Desmond freaks out and breaks free from the chair. Inside, Jin demands answers from Widmore. Widmore says Desmond is the only person he knows of that survived a catastrophic electromagnetic event and he needs to know if Desmond can do it again.

Seamus powers up the system, but hesitates in flipping the switch. Widmore comes over and pulls the three levers causing the solenoids in the box to light up. The gauss meter pushes past the maximum reading of 200, the picohertz reaches about 174 and the EMF reading is 242.7958.

Suddenly, as Desmond stands between the solenoids, there is a bright flash and we see the sky shot from the Oceanic 815 window from "LA X." We cut to Desmond standing at the flight status board at LAX.

So Desmond is transported from the main island timeline to the sideways timeline. But what exactly does Widmore have planned on the island if hitting Desmond with a big dose of electromagnetism is just a test for a bigger event later? Presumably, Widmore has heard from someone that Desmond survived the implosion of the Swan Station. Also, what is the sacrifice that Widmore wants Desmond to make? It certainly seems ominous.