First off, we need to understand what ray tracing actually is. Ray tracing is essentially a method of simulating realistic light in computer graphics. A slightly more detailed explanation is that ray tracing simulates the "path" light takes when it interacts with open spaces and objects. This allows for light to have a "volume" to it — something that you don't necessarily get from generic light sources in video games.
Ray tracing allows for light to interact with its surroundings in a dynamic and natural way. For example, a ray of sunlight shining through an apartment window in Grand Theft Auto V is basically just a block of light. It casts shadows and it moves based on the in-game time of day, but that's about it. With ray tracing, that ray of sunlight "fills" the space that it enters — it's no longer just a block, it's a dynamic shape that changes and interacts with surfaces based on where it's coming from and the angle that it enters the room.
This video showcasing a PC mod for Grand Theft Auto V is a great example of how ray tracing can improve lighting effects in video games:
However, as you'd expect, ray tracing can be quite demanding. Mostly used in film, it's not something that you see in current video games on consoles, but with the power of the PS5, ray tracing will become a lot more commonplace. We're already seeing its application in games such as Ratchet & Clank: Rift Apart, where it's used sparingly in certain scenes to make them more believable.
Mark Cerny, PS5's system architect, is keen to stress that the next-gen console's ray tracing solution isn't a half-heated effort: "There is ray-tracing acceleration in the GPU hardware," he says, clarifying it won't be a simple software-level fix. While ray tracing is certainly being pushed as a next-gen buzzword by companies like Sony, the technology is undeniably impressive.