In our ever-growing world, we use more and more energy, both as individuals and as societies. Energy production and technological progress go hand in hand. Sometimes, inventions of new methods of generating power, like the steam engine, lead to a boom in growth. Other times, a growing economy builds up the resources to transition to new kinds of energy. We are in the midst of one such transition right now, with solar, wind, and other types of renewable energy creeping up to take the place of fossil fuels. But what about the future? Are there other ways of generating power in large amounts that we have yet to invent?
The answer is a definite yes. Thanks to modern physics, we know of many ways to store and produce energy that are possible, but beyond our current technology or the resources.
Nuclear Fission
Before we go there, I want to nod to an underappreciated method of generating power that modern physics has gifted us, and which already exists: nuclear fission.
Now when many people hear “nuclear,” they think “bombs.” But it’s really referring to the energy stored in the bonds between the protons and neutrons in the nuclei of atoms. If you look at the periodic table of the elements, you will see that all of the elements are numbered from 1 to 118 (as of when this post was published). This number is the number of protons in the atom’s nucleus. There are also neutrons, but those aren’t counted on the periodic table. Since saying “protons and neutrons” can get tiring, when they are referred to together, they are called nucleons.
The energy in the masses of the nucleons and the bonds between them is different for each atom. From Hydrogen, the energy per nucleon goes down, until we reach iron. After iron, the energy per nucleon goes back up. This means that if elements heavier than iron break apart, they release energy. This is called nuclear fission, and we already harness it in nuclear power plants around the world.
Nuclear fission is not very popular, because people associate it with harmful radiation. However, nuclear reactors are actually among the safest ways to generate power. There are an enormous number of safety procedures, many of them redundant, to protect everyone inside and near the plant from radiation, and to prevent meltdowns. The number of people who have died from nuclear reactors in the 70 years they have been around is less than 100.
However, there is a downside. Nuclear power may kill basically nobody today, but the risk goes up over time. This is because when uranium is fissioned, it leaves behind nuclear waste, radioactive material that is dangerous to stand near. Some of this can be used or purified, but some of it just has to be stored away in special warehouses for ten thousand years until it becomes safe. In the meantime, we continue to use more energy, nuclear power plants keep getting built, and the waste keeps piling up. So nuclear fusion has many advantages, and much less risk than people think, but the risks it does have last a long time.
Nuclear Fusion
On the opposite side of the periodic table from fission, we get nuclear fusion. Fusion occurs when two atoms come together to create a larger atom. If the product is iron or anything lighter, energy is released. The sun and stars get their power by fusing hydrogen and some other elements in their cores.
Nuclear fusion requires extreme temperatures and extreme pressures. Our best reactor design is the tokamak, which uses strong magnetic fields to confine super hot hydrogen plasma in a donut shape. However, we have not yet built a tokamak that can generate more energy than is used to heat the plasma, so commercial fusion remains a technology of the future.
Fusion power would be an incredible prize. It is way more energy-dense than any other power source we have tapped into, including fission. It uses hydrogen, which is three times more common in the universe than all of the other elements combined. There is almost no waste; the product at the end is mostly helium, which is about the least harmful substance in the universe. And if something goes wrong and the containment is broken, there is no meltdown. The machine just shuts off.
There is a lot of cynicism in society about fusion power. After all, people have said it is only 20 years away for over 60 years. To the average person, that sounds like no progress has been made. But that is not true; progress has been made, and is still being made today. The problem is that it is hard to predict when research will be finished, because that would require knowing the results ahead of time.
Another reason people are cynical is because fusion seems too good to be true. The fuel for it is everywhere, and it would yield so much energy that compared to the amount we use today it might as well be infinite. It is immensely more friendly toward the environment than fossil fuels or fission. It is such a great positive with so few downsides that it feels too good to be true.
But that kind of thinking is based on human intuition, not on facts. Behind the scenes, fusion research continues to press forward and make progress, and right now there is a tokamak is in the works called ITER, which is designed to produce ten times more energy than it takes. The perception that it is no closer than it has ever been is just an illusion.
What about beyond fusion? Surely in the vast, wide universe there are other power generation options that might become available to us in the far distant future? Why yes, there are.
Solar Satellites
The sun is a giant gravity-powered fusion reactor, and it is putting out enough energy every second to power the entire current world economy for eight trillion (8,000,000,000,000) years.
You read that right. Eight trillion years of human civilization. Every second. Our planet is floating in a sea of practically limitless energy. If only there was a way to go and get it.
In the future, after much technological and economic growth, we might be able to. The idea is to launch satellites into Earth orbit, with giant curved mirrors that focus the sun’s light into a collector, which is hooked up to a laser that would beam the energy to power stations on the Earth’s surface. This will be far more efficient than land-based solar power, because there are no clouds and no night in space, and there is virtually no limit to the number of satellite collectors we could add to the grid.
Now when you think about giant lasers shooting at the Earth, you might worry that they would be used as weapons. However, you need not fear, because there are ways of designing the satellites such that weaponizing them would be impossible. If the output is limited and a sufficiently long laser wavelength chosen, then they won’t be able to hurt anyone or anything.
You can read more about solar satellites at the US Department of Energy website.
Antimatter
So far, we have talked about things that are more or less within the everyday person’s imagination. Now it’s time to take things to the wild parts of physics. In fission and fusion, the energy we get comes from a fraction of the mass getting converted into energy by Einstein’s equation E=mc2. But most of the mass is still there after the reaction. Might there be a way for us to get all of it? The answer, is yes. And it might surprise you to learn that there are more ways than one.
90 years ago, the underappreciated physicist Paul Dirac was playing with one of his equations, when he discovered that there should be particles that are exactly like electrons, but with a positive electric charge instead of negative. Positrons. Since then, we have discovered in lab experiments that there are oppositely charged versions of all particles. These negative doppelgangers of matter are called antimatter. And when particles of matter collide with their antimatter counterparts, they are annihilated, and all of their mass turns into energy. In nuclear fusion, only 1% of the mass gets converted into energy. This means that a matter-antimatter power plant would yield a hundred times as much power!
Unfortunately, because antimatter gets destroyed when it touches matter, it is extremely rare. There isn’t enough around to collect and put into reactors. In fact, the vast majority of the antimatter on Earth is created in particle accelerators, taking the same amount of energy to make as we would get from it. So someday in the far future, rather than being an energy source, we might use antimatter as an ultra-high capacity battery.
A cartridge of antimatter the size of a D-cell would carry about 1/10 the energy of an atomic bomb. And it would very easily explode like one too. You can’t just put it in a bottle, because touching the sides of the bottle would make it go boom. The only way to contain antimatter is to use ultra-precise magnets. Needless to say, if we accumulated enough antimatter to run a power plant with, such a plant would be extremely dangerous. So although it is physically possible, I don’t see us or any future civilization using antimatter as a power source.
Micro Black Holes
As I mentioned earlier, there is another way of getting all of that sweet energy locked away in mass: black holes. Specifically, microscopic black holes. You have probably heard that anything that enters a black hole can never get out. That is true, mostly. However, black holes lose mass very slowly by giving off light in a process called Hawking radiation. Maybe I will try to explain it in a future post, but for now, the important thing is that it exists.
Hawking radiation is usually extremely slow. As in, the slowest process in the universe. But the smaller the black hole, the faster and more powerful the radiation. If you have a black hole, say, the size of a proton (the mass of a mountain), it will put out about the same amount of power as a fission plant, and will last for hundreds of billions of years.
I did my calculations at this handy dandy site.
Of course, there are some questions that arise when we talk about using black holes for anything. First of all is safety. It’s a black hole! Won’t it suck in everything around it and cause lots of destruction? Surprisingly, no. The point of no return is called the event horizon, which is what we mean by the “size” of the black hole. In our case, it is a lot smaller than an atom, making it difficult for anything to get trapped inside. However, anyone closer than 50 meters would feel a force from the black hole equivalent to Earth’s gravity, which means we want to give the black hole a lot of room.
Speaking of which, how are we going to hold the black hole? It is as heavy as a mountain and tinier than an atom, so what is stopping it from falling straight through the table, the floor, and to the center of the Earth? One option is to give it a small electric charge, and have it spiral around in a magnetic field. That magnetic field would require quite a lot more power than our mountain-mass black hole would give off, but we could solve this by making the black hole smaller, which would both reduce its mass and give it a higher energy output. However, there is a better option: build the power plant in space. There is no down in space, so the black hole would just float there, coasting along the gravitational landscape along with the ship that carries it.
Another important question is how we get a black hole of that size. The smallest black holes in nature that we know of are around 3 times the mass of the sun, when enough matter falls onto a neutron star to push it past its Schwarzschild radius. Unfortunately, the rest of the universe will have cooled off and died by the time these black holes’ hawking radiation is enough to use as an energy source.
However, only technology is stopping us from making artificial black holes. Einstein’s General Theory of Relativity showed us that energy has just as much gravity as mass, so if we shoot powerful enough lasers into a small enough point, a black hole will appear. Of course, we need to generate all of that power in the first place, so like antimatter, micro black holes would probably end up more as batteries than power sources. That is, unless life can figure out a way to survive the googols of years until the naturally-occurring black holes are small enough.
Black Hole Spin
There is another way to use black holes for energy generation. Big black holes, in fact, not microscopic ones. This comes from the fact that black holes have spin. What exactly it means for a black hole to have spin is a very complicated topic, so we’ll save it for another day. You can pretend it means the event horizon is revolving around the center, if that makes it easier. The important thing is that there is energy in the spin, and given the right technology and resources we could get to it.
It might surprise you to learn that gravity does not pull objects together. Instead, Einstein showed us in the General Theory of Relativity that space-time is pulled toward the gravitational source, and objects float along with it. It is like a stick floating on a pond with a drain pipe. The drain does not pull the stick toward it. Rather, the stick floats along with the water toward the drain. There is another effect of gravity predicted by Einstein’s equations, which is rare enough that we have never directly observed it. When an extremely massive object like a black hole spins, the rotation pulls space-time around with it. This is called frame-dragging. If regular gravity is like water flowing toward a drain, frame-dragging is like a whirlpool.
When a black hole spins, its frame-dragging is so strong that it creates a region of space outside the event horizon called the ergosphere, where in order to stay still as seen from far away, something has to travel against the black hole’s spin faster than the speed of light. This means that if something dips into the ergosphere without entering the event horizon, it gets a major boost in speed and kinetic energy. This energy comes from the black hole’s rotational kinetic energy, making the black hole’s rotation slow down ever so slightly. Since the object hasn’t passed the event horizon, it can get back out, and we can use its extra kinetic energy for electricity.
The most efficient way to do this would be to build a sphere of mirrors around the black hole, and let light bounce around inside. Every time the light goes through the ergosphere, it picks up some of the black hole’s rotational energy. If there is an opening in the mirror contraption for the light to get out, it becomes an energy fountain. For a visual and entertaining explanation about black hole spin power, check out Kurzgesagt’s video on it.
Unfortunately, extracting a black hole’s rotational energy requires letting some mass fall into the black hole. This is because of something called the Penrose process, which I wish I could explain, but I don’t understand it. The details don’t matter today, though, because it has a bad consequence; the black hole increases in mass, meaning we have to wait longer before it shrinks to sub-atomic size and we can use its Hawking radiation as a power source. It will be a kind of poetic tragedy that the last civilizations in the universe, by taking the energy they need in order to survive, seal away some of the precious energy into a future beyond their grasp. Not to worry, though. Before then, we have billions and trillions and higher-tier-illions of years to figure out how to stick out the long dark purgatory of the black hole era.
In our struggle today to replace fossil fuels with renewables, it's easy to forget that there will be more to the story in the future. As poor countries develop and developed countries get wealthier, our consumption of energy continues to increase exponentially. In another century, we may get vast amounts of energy from space lasers, or from mini-suns we create. Even after all of the stars die, there will still be enough energy to last for a long, long time.
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