We Could Harness Black Holes to Eavesdrop on Alien Civilizations, Oxford Physicist Says

5 min readHere’s what you’ll learn when you read this story:Scientists now have multiple lines of evidence that black holes exist. For example, we have images of an accretion disk of matter outside the event horizon.Aside from better understanding them, we could even use black holes as cosmic tools one day. They might provide extreme gravitational slingshots for interstellar travel, or even ultra-powerful computation, for example.And if advanced aliens are using black holes as computers, their radiation signatures might be detectable, which could open the door to learning new physics.Arguably the most extreme objects in the universe, black holes have fascinated us since John Michell, an English astronomer, first proposed their possibility in 1783. He speculated that the gravitational pull of a massive star could be so strong that its escape velocity would exceed the speed of light. This idea gained a firm mathematical footing thanks to the German physicist Karl Schwarzschild, who—while fighting in the First World War in 1916—used Einstein’s newly discovered general theory of relativity to derive the radius of a black hole. This is now known as the Schwarzschild radius or the event horizon. Nothing crossing the event horizon can ever escape from the black hole, not even light. (Hence the name, coined by the American physicist John Wheeler in the 1960s.)Then, Robert Oppenheimer, of atomic-bomb fame, wrote a paper with his student Hartland Snyder, in which they outlined the process by which a massive star would collapse into a black hole. With this 1939 work, the theory surrounding black holes was firmly established, but there was still no evidence for their existence. For starters, one can’t take a picture of a black hole because it does not emit light. This presents us with a problem, since most of our astronomy relies on detecting light and using it to figure out the properties of objects emitting it.Yet, today, we have three different kinds of evidence that black holes exist. But it’s even more astonishing that we’re considering the possibility of using them to send our technology light-years into the future.So how do we know that black holes are really out there? The three kinds of evidence are all indirect. First, astronomers have created images of an accretion disk outside the event horizon, formed from matter the black hole is swallowing. This is not exactly a photograph, but a best-guess image derived from radio telescope data, which is based on x-ray emission from the infalling matter. Secondly, we have detected gravitational waves from merging black holes. We are confident this merging is what generated the waves, because the properties of the process perfectly match the theory. (Several Nobel Prizes are behind this discovery.) Thirdly, black holes strongly affect nearby objects such as stars, and we can deduce by measuring the motion of such stars that they must have an invisible, strongly gravitating neighbor.Now we have plenty of theoretical and experimental evidence that black holes exist, but could they be useful to us technologically? Amazingly, the answer is yes. We could, for instance, use them for interstellar travel. All of our current space travel is based on the idea of “planetary slingshots.” When we send probes around the solar system, we use the gravitational pull of other planets to speed them up. This requires careful calculation of the trajectory so that the probe approaches from behind, say, Jupiter, which then drags it along into its own trajectory, only to finally launch it in the desired direction. Now, if we had two black holes orbiting one another, this would give us a more powerful slingshot. Of course, this requires us to first reach a black hole, and the closest one (according to current observational evidence) is about 1,500 light-years away! Either that, or we need to be able to engineer our own black holes…But if we could engineer black holes ourselves, an even more exciting technological possibility would be to use them as computers. Given that black holes can pack more information than any other known object, they seem ideal for this purpose. According to the Israeli physicist Jakob Bekenstein, the theoretical bound says that one bit of information can be encoded in the Planck area of a black hole horizon, which makes a black hole able to hold 10 to the power of 69 bits of information per square meter of the event horizon. Compare this scale with the best current computers, which can hold up to one trillion bits of information. On top of that, the bit-flip rate, which tells us how quickly we could compute with black holes, is as high as 10 to the power of 33 operations per second per joule, as physicist Seth Lloyd calculated—and this again is orders and orders of magnitude better than current computers).So we prepare matter in the right state, as far as information is concerned. It then forms a black hole, during which process the computation is performed. So how do we read out the answer, given that nothing can come out of a black hole? It was here that Stephen Hawking surprised us in 1974 by showing that if black holes were quantum objects (as well as gravitational), they could emit radiation (known as Hawking radiation). In fact, the information that went into a black hole would then be transformed, but its total amount would always be preserved. No information would be lost inside a quantum black hole. This implies that we would just have to wait for the black hole to evaporate, and the measurement of this radiation would then constitute the output of our computation.Admittedly, we are far from being able to do this. We don’t even understand black holes theoretically yet, let alone know how to engineer them artificially. But we can’t exclude the idea that there is a more advanced alien civilization out there in the universe that already knows how to use black holes as supercomputers. If this were so, the fascinating thing is that we might be able to detect their presence, as the Georgian physicists Gia Dvali and Zaza N. Osmanov recently suggested. Agencies like the CIA can eavesdrop on us by monitoring the heat output from our houses; this would reveal the sequences of 0s and 1s our computers produce since a bit value of 1 is usually energetically more costly than a bit value of 0. In the same way, we could detect extraterrestrials, since information processing via black holes produces a radiation signature distinct from that of any other natural source.This would be a double blessing: not only would we have discovered that there is other intelligent life in the universe, but by reading their computations, we might learn new physics and how to use it to design much more powerful gadgets.Vlatko Vedral is a professor of physics at the University of Oxford, known for both his theoretical and experimental work on quantum information, including developing a novel way of quantifying entanglement and applying it to macroscopic physical systems. When not studying the fundamental nature of reality, Vlatko enjoys drawing, wakeboarding, and playing his electric guitar "up to 11." He is the author of the 2010 book Decoding Reality, as well as the latest "Portals to A New Reality." Born in Serbia, he now lives in Oxford.