In my book I have a genius ice-cream truck driver who harnesses the power of a black hole by storing in his ice-cream truck. Here is how he should be able to do it: first he has found a way to crystallize light and create a cube of light inside his ice-cream truck surrounding, and feeding, the black hole. Second he easily has a way of resupplying that light using super high technology solar panels. But what I want to know is could it be possible ,assuming he is a super genius even by like stereotypical alien standards, for him to do it? Also would the black hole move or grow and if so how could he, using amazing technology, keep it the same size and in the same place?

  • 7
    $\begingroup$ If you are crystallizing light, then you are allowed to make up anything else you like! $\endgroup$ – Willk Apr 26 '17 at 18:20
  • 1
    $\begingroup$ I suggest to drop the solar panels. You won't ever have enough power from them (even if they are a 100% efficient) to power a black hole, if they need to be carried around in a ice-cream truck. Just create some handwavium fuel instead - made up physics is preferable to bad physics! $\endgroup$ – T. Sar Apr 26 '17 at 18:24
  • 2
    $\begingroup$ The purpose of 'black hole drives' is to convert the mass-energy thrown into the black hole into Hawking radiation,and thus convert mass into energy. If you use energy collected by solar panels to feed the hole, there is no energy gain. (but there is energy loss, since the containment systems, and the radiation colecting systems are not 100% efficient.) $\endgroup$ – b.Lorenz Apr 26 '17 at 18:29
  • 4
    $\begingroup$ Any black hole small enough to be carried by an ice cream truck would evaporate so rapidly as to be indistinguishable from a nuclear explosion. $\endgroup$ – Joe Kissling Apr 26 '17 at 18:47
  • 3
    $\begingroup$ Something you might want to explore is whether you actually want to deal with the science of black holes, or if you just want to use the term as "technobabble" to explain a bunch of plot devices you use during the story. You'll want to approach them differently. The former may require a great deal of redesign of your story to fit into real physics, while the latter gives you the freedom to accomplish your goals without pesky reality getting in the way. $\endgroup$ – Cort Ammon Apr 26 '17 at 21:18

First he has found a way to crystallize light and create a cube of light inside his ice-cream truck surrounding, and feeding, the black hole.

There's really no need to "crystallize light"... whatever that means, unless you mean the low calorie drink which wouldn't make a good fuel, it's low calorie! Doesn't matter because conversation of energy says it's the same energy either way, crystallized or not.

Why you need to throw that light into a black hole, I'm not sure. Just use the energy from the light directly.

A black hole as an energy source, like in a black hole starship, doesn't use energy falling into the black hole, but rather the energy of the black hole evaporating; its Hawking radiation. The smaller the black hole, the faster it evaporates, the more energy you get. A 1e–18 m black hole will produce about 160 Pettawatts for a few years. It is, in effect, a very, very, very, very, very, very dense battery whose energy output increases as it gets smaller. Unfortunately for your ice cream truck, and anything under it, the black hole weighs 600 million kg.

Any smaller and it will evaporate too fast with too much energy. At a mere 200,000 kg it will last 1 second and emit the equivalent of 5 megatons of TNT. That's not good for kids.

Second he easily has a way of resupplying that light using super high technology solar panels.

Let's talk basic conservation of energy to get a limit on what's possible. How much energy can get from a solar panel, or just a skylight if all you need is light? No matter how super the technology, you're limited by how much energy is available.

Assuming a bright, sunny day at low latitudes, you can get about 6 kWh/m2 out of the whole day. That will, of course, fluctuate between day and night, but let's assume you have some sort of perfect storage mechanism. I'll also assume all your technology is 100% efficient with no wastage.

An ice cream truck is going to be about as big as a large van, I'll use the 2017 Ford Transit XLT Passenger Wagon as a model. It's something like 5m long and 2m wide giving you 10m2 of roof to play with. 10m2 at 6 kWh/m2 gives you about 60 kWh per day to play with. What can you do with that?

It's an ice cream truck, so it needs a freezer. This 18 ft3 commercial ice cream freezer uses 116 Watts, or about 2.8 kWh over a whole day. That eats about 5% of your available energy.

Is it enough power to drive the truck? Let's assume you've replaced the whole engine and drivetrain with a very efficient electric one. I'll use the Tesla Model X SUV as a model. It has 90 kWh battery which can push it about 400 km.

On your 60 kWh that's 266 km. Your van weighs about double, that will roughly halve the range, so 133 km. The Tesla has far, far, far better aerodynamics, 0.24 drag coefficient vs 0.39 for a van. And the Tesla has a smaller front that plows through the air, roughly 3.5m2 vs 4m2. Multiply the drag coefficient by the area to get the drag area, or CdA which is a big factor in fuel efficiency. The Tesla Model S is about 0.84 vs 1.56 for the van. The van has roughly double the drag area of the Tesla, roughly halving efficiency again: 65 km.

So we're talking 65 km range on a full day of sunlight which is probably enough to get around your route, run the freezer, and an audio system to play annoying music with. Not much else.

In contrast, 25 gallons of gasoline in the tank is about 95 liters. Gasoline has a density of 726g/L giving you about 68 kg of gasoline. Gasoline is one of the most energy dense, non-radioactive substances at 46 MJ/kg or 13 kWh/kg. The 68 kg of gasoline in a typical van's 25 gallon tank has 884 kWh or over 10 times the energy you can get from the Sun in a day. This is why cars use gasoline, it's very energy dense, and it's very quick to refuel; and why electric cars use batteries, they're energy dense and can be quickly recharged. Solar panels alone are limited by the available sunlight and your surface area to capture it.

You're probably better off with using a hybrid and supplementing your power with solar panels. Do something more exciting with your black hole and crystallized light.

| improve this answer | |
  • 1
    $\begingroup$ +1, but. You have not taken into account the unique property of light to acquire massive amounts of energy from the the quantum zero-point vacuum when undergoing a phase change from liquid to solid; this more than compensates the energy required to liquefy it from its normal radiative state. In fact, crystallized light is able to extract so much energy from the quantum vacuum (depending on how slowly and carefully the crystallization process is performed) that, assuming the use of nurturing monochromatic pink light, a baby black hole can easily be grown into a big powerful athletic black hole. $\endgroup$ – AlexP Apr 26 '17 at 21:32
  • $\begingroup$ @AlexP On the contrary, Crystal Light is low calorie and thus can't contain much energy. But maybe pink lemonade is better for powering black holes. ;) $\endgroup$ – Schwern Apr 26 '17 at 21:35
  • $\begingroup$ "Unfortunately for your ice cream truck, and anything under it, the black hole weighs 600 million kg" Well it did weigh 600 million kg. Now it weights about 6e24 kg and is orbiting the sun in place of the Earth :) $\endgroup$ – kingledion Apr 26 '17 at 23:55
  • $\begingroup$ @kingledion No, such a small black hole would have very little gravity (about as much as a supertanker). And it would be putting out more mass-energy than it could absorb. That's why it's a useful power source. $\endgroup$ – Schwern Apr 27 '17 at 0:27

Not the answer you're looking for? Browse other questions tagged or ask your own question.