…the right answer being “Yes! But they’re really hard to actualise.”
…Shawn refines previous work on just how high an exhaust velocity can be achieved by an antimatter-matter pion-rocket. Previous estimates were surprisingly low – Ulrich Walter computed a mere 0.2084 c, while Robert Frisbee computed ~0.33 c. Westmoreland gets a more hopeful 0.5804 c for a pure pion exhaust, and somewhat higher for basic pion-rocket plus thermalised gamma-rays re-radiated as collimated heat.
…some of Louis’ work on merging Quantum and GR Theories. Hawking radiation is the most relevant result of our best efforts to merge the two and Louis is one hard worker amongst many trying to crack this particular physics puzzle. If he achieves the goal then we’ll have a better idea of how to actualise black-hole star-ships.
Photon-rockets, particularly gamma-ray photons, are inherently high-energy affairs. Raw light requires 300 MW for every measly newton of thrust and Hawking radiation from low-mass black-holes may be the only way we know of converting raw mass into energy on the scale needed. A gamma-ray reflecting material or metamaterial would make the task much easier, but at present such a substance is “unobtainium”.
So what if we did have such? In that case we would need to focus about a million TONS of pure energy into a space small enough to cause it to gravitationally implode into a black-hole. For comparison the Sun puts out about 4.3 million tons of energy per second, but fuses 610 million tons of hydrogen to do so. Not an easy task then if we tried to do so with a super-hydrogen bomb. Coherent gamma-rays are needed, focussed on an infinitesimal target at a gargantuan energy production scale.
Once we have such a black-hole its energies will be of the right frequency to make more black-holes, but of insufficient power. Some kind of “gamma-ray battery” or “capacitor” will be needed to accumulate energy. Enclosing the gammas in a gamma-ray reflecting sphere might do, but the pressure would be unimaginable.
Consider: a photon perfectly reflected off a mirror imparts twice its incident momentum to the mirror. A single kilogram of energy is 90,000 trillion joules, all of which bouncing around would impart ~600 MN of reaction force per bounce on the enclosing volume. Multiply by 1 billion to get our needed energy supply and that’s 6E+17 newtons of reaction for each bounce of the contained photons. Divide by 3 if there’s no directional bias and that gives the average total force experienced by the walls in any direction. The speed of light divided by the linear dimensions of the volume gives the number of bounces per second. Multiply that by 6E+17 N. A mirror ball 3 km across, would experience 100,000 bounces per second, thus the total force is 2E+22 N. A pressure of ~28.3 billion bars.
We’d need some pretty impressively strong stuff to manage that! Of course the outward pressure declines with the inverse cube of the enclosure’s diameter, thus making it a more manageable ~28.3 thousand bars when ~300 km across. Considering the scale of the energies involved that’s manageable!