The fastest known object in the universe is light itself. Light travels through a medium called a vacuum at its maximum possible speed, which is approximately 299,792,458 meters per second, often rounded to 3.0 x 10^8 meters per second or approximately 186,282 miles per second.
In a vacuum, there are no particles or other matter to interact with or slow down the propagation of light. This allows light to travel at its maximum speed, often referred to as the speed of light. In other transparent media, such as air, water, or glass, light can still travel, but its speed is slower than in a vacuum due to interactions with the atoms or molecules of the medium. The speed of light in different media is determined by the refractive index, a property that describes how much the light is slowed down or refracted as it passes through the medium.