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>don't know anything about quantum gravity Nobody knows anything about quantum gravity, which is the problem ;) >order of a nanometer As db48x says, syntheti

>don't know anything about quantum gravity Nobody knows anything about quantum gravity, which is the problem ;) >order of a nanometer As db48x says, synthetic black holes aren't going to be much good as power plants, just because it's so darn hard to get them big enough that they can consume normal matter. Let's talk bare minimums. Say the nucleus of an hydrogen atom is about 2.4 femtometers wide. Plugging the numbers into https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati... the mass of a black hole that size is 8.07991 * 10^8 metric tons. That is a lot of laser pulse power to get into a single point just to create the black hole. Wolfram alpha claims it's 2.01718 x 10^25 watthours. The sun radiates 3.828 x 10^26 watts, so we need about a tenth of total solar output for an hour-- assuming we can convert captured solar power into coherent gamma rays with no loss, which there is currently no plausible physical way to do, so we probably need 10 or 100 times as much power. We're beyond future ultratech, and getting into solar engineering. Assuming the black hole is created, which is hard enough, we have further problems. A 2.4 femtometer black hole is still darn hot: it's radiating a total of 545.6 megawatts of light with a peak of 51.3 MeV-- still ultrahard gamma radiation. Our beam of hydrogen ions need to fight past this headwind and into the singularity-- quickly. It's losing 6.054 micrograms per second, which will be hard to deliver as a single row of hydrogen nuclei. Making the black hole bigger in the first place will make it easier to feed... but if you can commandeer a tenth of the Sun's output at will, you don't exactly need domestic power from a black hole.

m_mueller 5y ago
Isn't this rather theorized for interstellar travel anyways? If you can somehow funnel the output of this to push to one side and somehow keep a ship attached to it.. Well you'd reach a nice fraction of light speed.
- kragen 5y ago
  Sure, that's easy enough to do: your ship consists of solar sails orbiting the black hole that spread out when they're on the nose side of the black hole, forming an opaque sphere that's incandescent on the inside, and fold when they're on the tail side, letting both the Hawking radiation and the incandescence shine past them. But being able to convert arbitrary matter to useful energy at 100% efficiency would be a pretty useful thing when you're not just beaming it into space, too. For example, it would make it straightforward to power your black-hole-building machine. However, the trouble with larger black holes like the 2.4-femtometer example is not primarily that they require a lot of mass-energy to produce, but that they last a long time. According to the calculator linked above, it is indeed radiating 545.6 megawatts, which sounds like a lot. But compared to the 808 million tonnes you put into it, it's not very much; it will take you 4.2 trillion years to get back the energy you put in, about 250 times the current age of the universe. (The lifetime calculation on that page is shorter, only 777 billion years, because it's assuming you're allowing the black hole to evaporate rather than feeding it to keep it the same size.) (BTW, actually that was all for a 2.4-femtometer-radius black hole, not a 2.4-femtometer-diameter one.) This is really shitty energy-efficiency from a time-discounted perspective. If you use a conservative 3% yearly discount rate, the time-discounted earnings from your power plant over those 777 billion or 4.2 trillion years are equal to their non-time-discounted earnings over only the next 33.3 years. So from an economic point of view your efficiency is not 100%; it's 7.9e-10%, 0.000000000786% efficient. And that's not even taking into account the costs of building the giant gamma-ray laser. So, for reasonable economic efficiency, you really need to build a black hole with a lifetime of 100 years or less. That means 400,000 tonnes or less, radius of 6.1e-10 nanometers (0.61 attometers) or less, 300 trillion kelvin or more, 102 GeV or more, 2.1 petawatts or more. In nuclear-bomb terms, that's 0.5 megatons per second (still very small compared to the sun's 390 yottawatts or 85 petatons per second), except that it's coming out in 102 GeV photons. That's about the mass of a silver atom, though still very small compared to the Oh-My-God Particle. As skykooler points out, this could complicate the task of feeding the monster. Maybe you could set it to orbiting at a few kilometers per second inside a solid object such as Ceres, so that it occasionally gulps a proton on its way through the body, leaving a trail of rapidly cooling subterranean plasma in its wake. Of course, if all the energy that's coming out has to go in through a nuclear gamma-ray laser, it's not really a power source, just a battery that's conveniently portable and has a built-in rocket engine.

m_mueller 5y ago

Isn't this rather theorized for interstellar travel anyways? If you can somehow funnel the output of this to push to one side and somehow keep a ship attached to it.. Well you'd reach a nice fraction of light speed.

kragen 5y ago
Sure, that's easy enough to do: your ship consists of solar sails orbiting the black hole that spread out when they're on the nose side of the black hole, forming an opaque sphere that's incandescent on the inside, and fold when they're on the tail side, letting both the Hawking radiation and the incandescence shine past them. But being able to convert arbitrary matter to useful energy at 100% efficiency would be a pretty useful thing when you're not just beaming it into space, too. For example, it would make it straightforward to power your black-hole-building machine. However, the trouble with larger black holes like the 2.4-femtometer example is not primarily that they require a lot of mass-energy to produce, but that they last a long time. According to the calculator linked above, it is indeed radiating 545.6 megawatts, which sounds like a lot. But compared to the 808 million tonnes you put into it, it's not very much; it will take you 4.2 trillion years to get back the energy you put in, about 250 times the current age of the universe. (The lifetime calculation on that page is shorter, only 777 billion years, because it's assuming you're allowing the black hole to evaporate rather than feeding it to keep it the same size.) (BTW, actually that was all for a 2.4-femtometer-radius black hole, not a 2.4-femtometer-diameter one.) This is really shitty energy-efficiency from a time-discounted perspective. If you use a conservative 3% yearly discount rate, the time-discounted earnings from your power plant over those 777 billion or 4.2 trillion years are equal to their non-time-discounted earnings over only the next 33.3 years. So from an economic point of view your efficiency is not 100%; it's 7.9e-10%, 0.000000000786% efficient. And that's not even taking into account the costs of building the giant gamma-ray laser. So, for reasonable economic efficiency, you really need to build a black hole with a lifetime of 100 years or less. That means 400,000 tonnes or less, radius of 6.1e-10 nanometers (0.61 attometers) or less, 300 trillion kelvin or more, 102 GeV or more, 2.1 petawatts or more. In nuclear-bomb terms, that's 0.5 megatons per second (still very small compared to the sun's 390 yottawatts or 85 petatons per second), except that it's coming out in 102 GeV photons. That's about the mass of a silver atom, though still very small compared to the Oh-My-God Particle. As skykooler points out, this could complicate the task of feeding the monster. Maybe you could set it to orbiting at a few kilometers per second inside a solid object such as Ceres, so that it occasionally gulps a proton on its way through the body, leaving a trail of rapidly cooling subterranean plasma in its wake. Of course, if all the energy that's coming out has to go in through a nuclear gamma-ray laser, it's not really a power source, just a battery that's conveniently portable and has a built-in rocket engine.