![]() ![]() It’s also like in fluid mechanics, where there’s a velocity field that gives the velocity of the fluid at every point (like a wind velocity map for the weather). This idea of a field is basically just like in electromagnetism, with its electric and magnetic fields. But one can also think of it as just saying that gravity is associated with a field that has a certain strength or value at every point. General Relativity is often discussed in terms of the geometry of spacetime. I won’t be able to do it perfectly, and might lapse unwittingly into physics-speak from time to time, but here goes… But for the sake of writing a general blog post, I’m going to try to do without these, while still, I hope, correctly communicating what’s known and what’s not. There are lots of complicated issues-that are probably most easily explained using some fairly mathematically sophisticated concepts (Riemann tensors, covariant derivatives, spacelike hypersurfaces, Penrose diagrams, etc. But if something is possible to do, perhaps some more-advanced civilization out there in the universe has already done it-but we likely couldn’t recognize evidence of it without having more idea of what’s possible.īut before we can get to speculating about black hole technology, we’re going to have to talk a bit about what’s known about black holes, General Relativity and gravitation. It seems inconceivable that we ourselves will ever get to try out anything like this for real-unless we find a way to locally make tiny stable black holes. ![]() But as a kind of celebration of the detection of gravitational waves I thought it might be fun to try fast-forwarding a long way-and seeing what one can figure out about technology that black holes could make possible. And perhaps our universe just isn’t big enough for the question to be sensible. So what about black holes? Given how hard it’s been to detect our very first pair of black holes, it might seem almost irreverent to ask. It’s remarkable to look through the list of chemical elements, or a list of physics effects that have been discovered, and to realize that-though it sometimes took a while-almost all those that can be readily realized on the time and energy scales of today’s technology have found real applications. We have to take the raw material that our universe provides, and somehow find ways to organize it for purposes we want. It’s always the same story with technology. But what if somehow we could get our hands on our very own black holes, and maybe even lots of them? What could we-or, for that matter, any putative extraterrestrials-do with them? What kind of perhaps extremely exotic structures or technology could eventually be made with them? And no doubt now-quite amazingly-we’ll get evidence for a steady stream of others around the universe. OK, so we’ve observed one pair of black holes, a billion light years away. But as of a little more than a week ago I’m finally convinced that black holes exist, just as General Relativity suggests. For a long time I myself was a bit skeptical about black holes-and for example about whether true General-Relativity-style ones would actually form in real physical processes. But we’ve now just got some spectacular new evidence of how far the theory can be taken. General Relativity is surely not the whole story of how spacetime and gravity work. I’ve followed General Relativity and gravitation theory for more than 40 years now-and it’s been inspiring to see how the small community that’s pursued it has progressively increased its theoretical prowess, and how the discussions I saw at Caltech in the late 1970s finally led to a successful detector of gravitational waves. ![]() ![]() And a little more than a week ago-in a triumph of theoretical and experimental science- it was announced that just such gravitational radiation had been detected. Like that if two black holes merge, there should be a burst of gravitational radiation generated, with a particular form. And there have been all sorts of predictions. Millions of lines of algebra have been done along the way (often courtesy of Mathematica and the Wolfram Language). And in fact even after 100 years we’re still just at the beginning of the process. The equation that Albert Einstein wrote down for the gravitational field in 1915 is simple enough:īut working out its consequences is not. ![]()
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