"Here we go then."
"Are you absolutely sure about this?"
"I am, Starlight. I double-checked the calculations, I had you check them, I had Sunburst check them, I had Starswirl check them, I had Celestia check them, and I even asked Sunset for help with checking them. I'm as sure as I can possibly be that this thing is going to work."
"You said that last time too, and the wall still hasn't finished growing back."
"This time is different."
"How, exactly?"
"If I messed up this time you won't have to worry about the walls, because there won't be a castle left. Why do you think I had everyone else leave the building?"
"You didn't have me leave."
"You can go if you want."
"And miss my chance to see this work? Forget about it, Twilight." Starlight swallowed, uneasy. "Are you really sure about this?"
Twilight swallowed too. "No. But I'm as sure as I can be." Slowly, her horn lit up. "Here we go then."
A small, pulsating orb of light left the tip of Twilight's horn, and very slowly floated towards the round white hoof-sized object suspended in a slim metal harness just a short distance from her. The speck of arcane energy came in contact with the surface of the scale, and seeped into it.
There was a subtle fluttering along the edges of the scale, like water rippling under a breeze. The white colour turned to light, weak at first then brighter and brighter. And the light spread out, like a bubble growing, twirling as it expanded in a sphere of blinding energy, tendrils along its surface flowing out and back in. Like a miniature star, the edge a boiling wall of energy storming and cracking as the sphere grew wider and wider.
Twilight watched it happen, refusing to close her eyes, and as the light was about to reach her she hoped she had at least been only so wrong in her calculations as to not have caused the rest of Ponyville to be wiped out along with her castle.
Then the growing stopped. Moment by moment, the rotation slowed down. The sphere stabilised, about the size of a pony, the surface no longer bubbling and instead occasionally showing some flashes of rainbow colours. Twilight finally breathed again. So did Starlight, far more audibly.
The unicorn walked closer. "Okay. Now what?"
Twilight kept her eyes on the light. "Now we see what's on the other side."
"Oh, right." Starlight put on a smile, and the inner screaming it was masking was palpable. "Are we sure it's safe to go through that thing? To put anything near that thing?"
"Not at all. And there's a chance we'll lose this half of Equestria the moment I touch it." Twilight lifted a hoof and placed it onto one of the outer strands of light slowly spinning around the sphere. The light seemed to break out and reform around her, like a stream of water.
Starlight looked at her, meanwhile dropping her own jaw so far down Twilight almost expected to hear it hit the ground.
The alicorn shrugged. "It was the adrenaline still circling." She looked Starlight in the eyes, and extended her other hoof towards her. "Are you coming with me?"