Black Holes, Starships and Antimatter

Some interesting papers by Prof. Louis Crane and his Ph.D student Shawn Westmoreland

Are Black Hole Starships Possible?

…the right answer being “Yes! But they’re really hard to actualise.”

A note on relativistic rocketry

…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.

Categorical Geometry and the Mathematical Foundations of Quantum General Relativity

…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!

4 Responses to “Black Holes, Starships and Antimatter”

  1. […] Crowlspace relays some cool papers on starships and then speculates about photons bashing into mirrors. […]

  2. […] Working with colleague Shawn Westmoreland, Crane has been exploring a different and far more speculative option for upping the energy extraction levels. What about using black holes for propulsion? Specifically, Crane and Westmoreland ask whether Hawking radiation from black holes can power a starship, calculating that a black hole of about a million tons would be just the right size, small enough to generate the needed Hawking radiation, while large enough to survive for the duration of a century-long star crossing. Adam Crowl has written fascinatingly about this in Crowlspace. […]

  3. Shawn Westmoreland says:

    Hello Adam.

    A revised version of my paper “a note on relativistic rocketry” has recently been accepted for publication in Acta Astronautica. One of the anonymous reviewers pointed out that the method proposed in my original preprint – about using thermalized gammas – had serious flaws. It was therefore removed from the final draft and will not appear in the publication.

    • Adam says:

      Hi Shawn
      Good to hear from you. Nice to get an update on the paper too. They’re pretty tough at “Acta Astronautica” – can’t imagine how Louis’s Black Hole rocket would be received. I discovered, by accident, that Louis was trumped by Robert Freitas in his book “Xenology”…

      Total Conversion Drives

      …though, of course, Louis’s quantum gravity theories might modify the figures significantly. Have you seen the recent paper on our Universe springing from a black hole?

      Cosmology with Torsion …by Nikodem Poplawski. Very interesting ideas, potentially neatly synergising with Louis’s.