Emma is one of my regular guest bloggers. I feel really thrilled about the possibility to post one educating post of this great blogger once a month over the next couple of months. Thank you so much, Emma, for sharing these great posts with us! If you would like to check out the previous guest posts, this amazing blogger wrote for me, head over here.
How about a dose of theoretical astrophysics to brighten our day? Or, should I say, darken? For what I’m about to tell you revolves entirely around the physics of black holes, and they aren’t called “black holes” for nothing. Nothing, not even light, can escape their immense gravitational pull. More frightening is the discovery that a monstrous black hole lies at the center of every large galaxy, including ours, the Milky Way.
But what if a light-devouring monster such as a black hole could be used to benefit humankind? After all, the reason black holes are undetectable is that no form of radiation can escape their event horizon. That means that no form of radiation we can see by reaches our eyes and telescopic instruments. But it also means that the radiation gets trapped in the black hole. And radiation means not only light, but also heat.
What could we use heat for? Well, kitchen appliances and cars, for starters. If you want to get into 21st-century technology, I would extend that list to computers and tablets, solar panels and lightbulbs such as low-pressure sodium and LEDs. And of course, we can’t forget rockets, campfires, stars, and even our own Earth, which is hot enough at its core to produce infrared radiation. Most of this heat we get from energy captured from our star, but one day in the future, our sun will lose its heat source. The hydrogen fuel powering its nuclear fusion will run out, the sky will grow cold and, if Earth survives at all, humankind will be plunged into perpetual winter. Our descendants’ only chance of survival will be to find other power sources. They will first exhaust the resources of Earth, then the solar system, and eventually all the stars in all the galaxies in the visible universe. When they have nothing left to burn, they will cast their gaze on the only remaining store of energy—black holes.
For some time, black holes have seemed to defy physics. We could not puzzle out how the force of gravity works beyond the event horizon, a sphere of no return where the gravitational field becomes infinite and anything that strays inside is doomed. But luckily for the scientists on our backwater planet, the laws of physics are universal and apply to anything and everything. And we’d managed to figure out how gravity worked inside, until the legendary Stephen Hawking proved us wrong. He showed that black holes leak small amounts of radiation, called Hawking radiation, and this radiation leakage causes black holes to eventually grow old and die.
For theoretical physicists planning to mine energy from black holes, Hawking’s prediction served as a beacon of hope in the dark jungle of space. But how to we get the energy that black holes leak? Energy emitted from a black hole, unless on a precisely straight trajectory, ends up tugged back inside the black hole. One suggestion has come in the form of a space elevator, a futuristic structure made famous by science-fiction author Arthur C. Clarke in his novel The Fountains of Paradise. If the building material was strong enough to support both its own weight and the elevator box of energy, a rope extending from Earth to a black hole could ferry Hawking radiation to Earth.
The difficulty lies in finding a suitable material. Steel is not nearly strong enough. A segment of steel suspended from space must not only bear the weight below it, but also its own weight, and that means making the steel thicker. Long before it reached the geostationary point, the steel would have to be impractically thick. Then, of course, there is the carbon nanotube, a new revolution in materials science. Carbon nanotubes are long strips of carbon 1,000 times stronger than steel, and excellent candidates to build an extraterrestrial space elevator, but the physics tests they pass here on Earth would be insurmountable barriers within the gravitational field of a black hole.
Perhaps future technology will yield more hopeful results. After all, the Iron Age followed the Bronze age, and carbon nanotubes will someday follow steel. So, too, might we expect that materials scientists will invent stronger and stronger and lighter and lighter materials. But no matter what, those materials will be bound by the laws of Einstein’s famous equation relating mass to energy—E = mc2. And that equation sets a limit on the strength of materials just as the speed of light limits how fast we can ever propel ourselves.
But we haven’t reached that limit yet. And so we continue forth!