All electromagnetic waves, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays, travel at the same speed in a vacuum, which is approximately 299,792,458 meters per second (or about 186,282 miles per second). This speed is commonly denoted as "c" and is known as the speed of light.
According to the theory of special relativity, proposed by Albert Einstein, the speed of light in a vacuum is the maximum speed that any form of energy or information can travel through space. Therefore, all electromagnetic waves propagate at this ultimate speed.
It's worth noting that the speed of light can be slightly slower when electromagnetic waves pass through different mediums, such as air, water, or various materials, due to interactions with the atoms and molecules of the medium. This results in a reduction in the speed of light relative to its speed in a vacuum, known as the refractive index of the medium. However, in terms of the fastest electromagnetic waves, regardless of the medium, they all travel at the same speed— the speed of light.