Fastest speed possible

The fastest speed possible in the universe is the speed of light. This is achieved only by light and other forms of electromagnetic radiation, ie radio waves, X-rays, infrared radiation etc. The speed of light actually varies depending what it is travelling through. It is fastest when travelling through a vacuum where its velocity is 299,792,458 m/s (983,571,056 ft/sec). This means that, when you look at the Moon, you see it as it was about 1.3 seconds ago, and the Sun around 8.3 minutes ago. Light slows down as it travels through other materials based on the refractive index of the material. For example, in air, the speed of light is reduced to 299,702,547 m/s, and in glass the speed of light is 199,861,638 m/s.