There were several things he could do to show her. Taking her on the same abrupt journey the Ancient One showed him, traveling through multiple dimensions in an astral form, was out of the question. It was too much to absorb, too soon. But the split between their two very close dimensions? He could show Christine that. Or, at the very least, hear it.
"No matter what, stay calm. If you panic, you'll be back in your body in an instant. And it will hurt all over for a few seconds." Stephen rested his other hand on her shoulder, guiding her back onto the couch until they were both leaning against the back of it, facing one another. The intimacy of this moment wasn't lost on him, and he spared a token moment lost in a memory of long shifts where life and death was always weighing upon their every choice, and with stolen kisses when their colleagues weren't looking. "Turn off your mind, relax and float downstream."
He smiled at her and it was at the precise moment that his hand on her cheek felt like it began humming with gathering energy. With the slightest application of pressure, he suddenly pushed Christine's astral form out of her body. He simultaneously left his own body behind. They floated together until they were standing as two ghosts in front of the shells of their own selves, only two feet away from the couch.
Everything around them looked slightly hazy, the colors a little off as though trying to peek through a technicolor fog. That was not all that was different. In the distance, emanating from every imaginable direction, were sounds that could only be described as crystalline. The noise alternated between a glistening shimmer not unlike innumerable tiny wind-chimes in a soft breeze, to the sound of heavy glacial ice cracking. At irregular intervals, there was a long drawn out cacophony, like several tectonic plates made of glass were slowly scraping against one another.
"That," Stephen said, his voice very faintly echoing, "is the sound of a broken universe."