"I'm still wondering what you're doing."
Martha sat on the jumpseat, watching the Doctor play with complex calculations and geometries on the TARDIS viewscreen. In response, he gave her a smile that was probably meant to be mysterious, but just looked cheeky on his face.
"Oh, you'll see," he grinned. "You'll see."
From Martha's limited experience in mathematics and physics, he was working on some type of higher-dimensional physics that could be used only in the fourth dimension. She told him so, and he looked surprised.
"Funny thing, you're absolutely right!" he told her. "We'll make a physicist out of you yet, Martha Jones."
Slightly boldened by this compliment, she moved over to stand next to him. "And what's this?" she asked, jabbing at a sheet filled with scribbles and swirls. "Is it some type of algebra used for working out equations for sixth dimensions?"
He frowned. "Er, no. That's the space I use for checking if my pen's working."
She looked downcast. He patted her on the back. "Don't worry. You'll get there."
Martha laughed. "So, what exactly are you working on?"
"Oh, it's a problem that would usually take scientists centuries to work out!" He leaned in conspiratorially. "I've been working on it."
She retreated to the jump seat again. "You just said it'd take centuries, though."
He looked extraordinarily pleased with himself. "I did! Luckily for us, though, the TARDIS has a built in quantum computer. And I can now tell you, without a doubt, that white holes do exist!"
He spread his arms out wide, apparently waiting for a reaction. He got none. Martha just stared at him with a puzzled expression.
"Do you mind telling me," she said carefully. "what exactly is a white hole?"
He nodded. "You do know what a black hole is, right?"
"It's a hole that sucks in everything around it?"
He tapped his fingers against the console. "Well, simply, yes... anyway, a white hole is the exact opposite of that! Instead of sucking in everything surrounding it, it pushes out a constant stream of light and energy. It's only a theory in your time, but there's proof that it is real now."
"You found one?" Martha realized.
He gave her a cheeky grin. "Yup!" He pulled a lever. "Allons-y!"
The gears spun into motion.
"Where're we going?" Martha asked, holding onto the railing. The Doctor just grinned and winked.
The trip didn't take very long at all, and soon the Doctor was throwing open the doors. She walked over to join him, and breathed in sharply. "Wow."
It was breathtaking. A hole in time and space, blowing out colors and matter. It looked like a massive, glittering dust cloud that never stopped. The whole spectrum could be seen, and colors that Martha never had even thought existed were there.
"These, Martha Jones," the Doctor proclaimed loudly. "are the colors of the universe!"
She could think of nothing to say to that, so she just hugged him instead.
The white hole kept blowing out a cacophony of matter.
"Want to listen to it?" the Doctor asked after a moment. Martha stared, thunderstruck.
"You can listen to a white hole?"
In answer, he pressed a button on the console. After a moment, silvery chiming whispers echoed though the room. It was beautiful. Almost what you'd have expected fairies to sound like. It was the sound of the universe singing. And it was beautiful.