Virtual reality lets students experience a black hole

Imagine this: you board a spaceship, fly to the edge of a black hole and look out of the window. What you see is spectacular, says Bijoy Bera, associate professor at TU Delft. "All kinds of objects and even rays of light are pulled into the black hole. The gravity of a black hole is so strong that nothing can escape from it." Of course, it is science fiction to fly to that black hole. Or is it? What if you could experience this in virtual reality?

Speed of light

Through experimentation, students learned more about relativity theory than through explanation, Bera observed. A few years ago, he therefore developed a virtual reality environment for undergraduate students in which a train travels at the speed of light. “They found it interesting. It also felt a bit like gaming, with the VR headset.”

After this success, Bera wanted to expand the experiment to include the general theory of relativity and black holes. "I don't know much about VR development myself, but I know very well what I want to do with it. So I have to collaborate with programmers."

Turning point

The film Interstellar by Christopher Nolan is praised by physicists for the way it visualises what it’s like to be near a black hole. “That film was a turning point for me: it made me start thinking seriously about this field.” The idea for the film came from renowned astrophysicist Kip Thorne, who was also an executive producer. "For the film, they put the equations of a black hole into a visualisation programme. That seemed like a good starting point to me: if I can show this not only on a screen but also in a VR environment, I have achieved my goal."

Multiple effects due to the bending of light rays can be observed in such images. For example, normally the part of the disk behind the black hole would not be visible, but now we can see both the top and the bottom of the disk - behind - the black hole.
 

Super difficult

Bera sent an email to Thorne, not really expecting a reply, but within a few hours he received a response. "A concise response, but with all the information I needed. He wrote: these calculations are super difficult. We have also published about it; see that and that article." Thorne did not think it would be feasible to turn it into a teaching project.

Complex physics problems

"These are some of the most difficult equations in physics; you have to be able to understand them well. I can follow them myself. But I want to visualise them so that the results don't remain abstract and can also be understood by a layperson. For that, I needed a team experienced in visualising complex physics problems. That is very expensive, mainly because of the time it takes. And you don't have that much money and time in an educational project."

Accessible and open software

A perfect meeting provided the answer when Bera visited the NWO Physics conference early this year. There, Ben de Vries, visualisation expert at SURF and himself an astronomer, gave a demo of the black hole visualisation software he had recently developed. "I heard from researchers that they need accessible and open software that makes calculations in highly curved spacetime," De Vries explained.

"Is this what I think it is?"

For educational purposes, De Vries then further developed curvedpy so that the tool integrates with a custom render engine he built for Blender, an open-source 3D graphics programme. A render engine, also known as a raytracer, is software that calculates how light moves through a 3D environment. The Black Hole Render Engine can do this in the highly curved spacetime of a black hole. The result: you can travel past a black hole and see for yourself what it looks like according to theory. Bera stepped up to De Vries: "Is this what I think it is?" he asked. "That's exactly what I need for my teaching!"

In the image above, the black hole is surrounded by a flat disk. Multiple effects due to the bending of light rays can be observed in such images. For example, normally the part of the disk behind the black hole would not be visible, but now we can see both the top and the bottom of the disk - behind - the black hole. 

Challenges

Since then, they have been working intensively together to develop the software into a VR application that Bera can use for his master's degree. "We only met two months ago, but it feels like we have been working together for a year," says Bera. "It is not yet at the level I want, we are still very much searching and there are many challenges."

Wanted: VR developer

TU Delft has its own VR lab, but it does not have enough expertise in this field. "They are mainly there to support teachers within the TU, and a black hole is not a priority for a technical university. So we are still looking for a VR developer who can implement Ben's calculations in virtual reality. Moreover, these calculations take a lot of computing power. Without SURF's computing facilities and expertise, I could never do this."

Visualisation of the sun rotating around a black hole. The bending of light rays create effects such as multiple images of the sphere (when the sphere is to the side you see a faint second image of the sphere at the other side of the black hole) as well as being able to see the sphere even when it is directly behind the black hole (the sphere is projected into an Einstein ring around the black hole).
 

Fantastic

So it will be at least another year before students can experience this VR experiment in lecture halls, Bera expects. After that, he wants to expand the experiment with different variations. "It would be fantastic if in five years a student can experience what it is like when you dive into a black hole," he says. However, nobody knows what the core of a black hole looks like, so that will be more speculation than simulation." With a chuckle, "In Interstellar, they did manage to do that. But our goal as educators isn’t to show people a sci-fi film; we want students to experience real physics.”

Text: Josje Spinhoven
Images: Ben de Vries, rendered in Blender using the Black Hole Render Engine