From the very moment their existence was theorised, black holes have inspired an almost-unparalleled curiosity in both career scientists and the public at large. They have a mystique to them that appeals to the same senses of awe and wonderment that fuel our love of legends and tall-tales, in that their existence is counterintuitive to our immediate experiences. Naturally, this provides science-fiction with its two eponymous components, but for a long time the emphasis was more heavily placed on the fiction.
However, in the run-up to two of the most major black hole-related breakthroughs in the 2010s – the detection of gravitational waves at LIGO and the direct image of Messier 87 – two films attempted to create the most accurate depictions of black holes ever seen on film: Interstellar (2014) and High Life (2018). While both films are inflected with varying degrees of overly self-serious, fatuous, and tiresome “philosophy” (especially High Life), a more interesting comparison can be drawn from the real-life physics concepts they choose to incorporate into their stories and, of course, how they represent black holes.
We’ll begin with Interstellar. The film brings up two main ideas related to black holes; time dilation (Miller’s Planet) and causal loops (inside the black hole). Gravitational time dilation is the process by which different altitudes in a gravitational potential well age at different rates. Put simply, this means that the greater the gravitational force you experience, the slower time moves for you. This is actually one of the more tangible aspects of general relativity, given that astronauts aboard the ISS and run-of-the-mill satellites are affected by it . However, this effect is absolutely miniscule, unlike on Miller’s Planet (“One hour there is seven years back on Earth”), a rate so high that Kip Thorne, the scientific advisor on Interstellar, later said he struggled to come up with a plausible way that this could be achieved .
Regarding causal loops, this is where things get rather hand-wavy and unphysical. While General Relativity permits some exact solutions that contain “closed timelike curves” (i.e. time travel), this topic quickly devolves into the various time paradoxes that are fun the first time you hear them but soon grow old (unlike that grandfather you just killed). Interstellar avoids this by accepting what is known as “Novikov’s Self-Consistency Principle”, which, in spite of the name, is little more than an opinion that only “self-consistent trips back in time would be permitted”; that is to say, you can’t have any fun with the past by changing it. Also central to the idea of causal loop is that their origin in time cannot be determined. This is precisely what happens in the black hole in Interstellar; the infinite bookshelves cover all the points in time in Murph’s room, while the information he gives himself was exactly what brought him to the black hole in the first place.
Moving on to High Life, the film is (apparently, but that’s not how I remember it) about a crew of death-row prisoners who are sent into space to extract energy from a black hole. Though the method by which the crew will do this is not specified in the film, it could be one of two processes: either the Blandford-Znajek Process or the Penrose Process . The former is based on the idea that a black hole can be considered as a conductor. This idea is derived from the theory that the black hole magnetises the material that it pulls into its orbit, and thus there is a difference in the voltage between the equator and the poles. Hence, by placing electrons near it, said electrons would be accelerated to the point that they radiate gamma-rays, which can then be used for energy.
The latter concept utilises the conservation of momentum to transfer energy to an object. By sending an object into the ergosphere – the part of the black hole whose inner boundary is the event horizon – and having it break apart with one piece going down into the black hole, the other part of the object would shoot out from the ergosphere with more energy than it had going in. Similarly to the Blandford-Znajek Process, this also slows down the black hole.
Finally, we come to the part we’ve all been waiting for: how both films represent their black holes. In Interstellar, the massive rate of spin of Gargantua yields a large and vibrant accretion disk which, as detailed in the film, acts as the “sun” for the various planets orbiting it. Meanwhile, in High Life, the absence of nearby material leaves a much smaller accretion disk. In both cases, the light from the part of the disk on the side of the black hole opposite to the observer can be seen as if it lies on top of the black hole. This is owing to the process of gravitational lensing, whereby the light that isn’t sucked into the black hole is bent by its gravitational pull. It is quite fun to compare these predictions with the actual image obtained in 2019, as they are both amazingly accurate.