I always thought of subspace as an infinite trampoline.
At very large and very small scales, it all gets very strange and ill defined.... in the middle, the equations mostly work out.
Observations in very cold conditions may reveal the exact processes behind particles spontaneously appearing and disappearing in vacuum at quantum scales. They've recently cooled and slowed down plasma, which may lead to developments in fusion:
Matter held not for long... but for long enough
www.theregister.com
I certainly hope they never create any black hole matter on earth though - that could fall in through the middle, punch it's way out the other side over and over again and devour the planet. But if as Musk believes, we all live in a gigantic holographic simulation, it doesn't matter anyway.
Some astromers think that Planet 9 is a very small black hole, which could be very handy for charging ebikes, for lucky inhabitants of an artificial planet built nearby:
Scientists propose a method to determine, once and for all, if any planet-mass black holes are lurking in the outer solar system.
astronomy.com