That's where a 'mystic' element creeps in. Who manipulates it? If someone controls it, how can they do so without conscious effort? Sure, I suppose I could invent a machine with lights and buttons and circles and arrows on the back that heats particles on a string level. But I want to get closer to the bone on this one.
The question becomes: how much energy does it really take to create a black hole? The more I read and understand the physics the more relative that question becomes. At our place in the scheme of things, that is our size, our velocity, our low energy, it would take a particle accelerator with a circumference the size of Jupiter's orbit to create anything near the Planck energy. That means right now we're safe from creating an energy burst so awesome that it begat the Universe. I can live with that. It also means to invent such a machine in SF requires a jump to future time and technology for my story. But shift into a different paradigm, a different plane of mass/energy, and we could spark it up with much less fuss.
How do we get there from here, you ask? Let me answer with a question: what is the relative density of a thought?
We have no idea what the power our brains really have. We tinker with technology and language while we scrape out an existence on Earth and think we're damn clever. But we haven't scratched the surface of our potential any more than we've scratched through the crust of the planet. A lot of our brain is unused, at least, so we tend to believe. But if we focus on the simple transfer of energy, add a dash of Heisenberg, imagine that thought may relate subjectively to the speed of light, we got us a whole new ball game.
Then the question is: what would a Planck universe look like through such a mind's eye?