No, not all light travels at the speed of light in a vacuum, which is approximately 299,792,458 meters per second (or about 186,282 miles per second). The speed of light in a vacuum is considered to be the ultimate speed limit in the universe. However, when light passes through a medium such as air, water, or glass, its speed decreases due to interactions between the photons (particles of light) and the atoms or molecules in the medium.
This decrease in speed occurs because the photons interact with the electric fields of the atoms or molecules in the medium, which temporarily absorb and re-emit the photons. This absorption and re-emission process leads to a slower overall propagation of light through the medium compared to its speed in a vacuum. The degree to which light slows down depends on the specific properties of the medium, such as its refractive index.
So, while light always travels at the maximum speed possible in a vacuum, its speed can be lower when it passes through a medium. The speed of light in a medium is still incredibly fast compared to other everyday objects, but it is not the same as the speed of light in a vacuum.