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.

Added by Dave Hawksett 23/01/12:

In March 2011 scientists working on the OPERA experiment, in which a beam of neutrinos is sent 730 km through the Earth from CERN (Geneva) to the Laboratori Nazionali del Gran Sasso (Italy), seemed to observe the neutrinos arriving earlier than anticipated. Their initial results showed that these particles had travelled from one lab to another 60.7 billionths of a second faster than light would have covered the same distance in a vacuum. As of January 2012, follow-up experiments do seem to confirm these results, although independent verifications are still under way. If ultimately accepted, it could mean that the speed of light in a vacuum, 299,792,458 m/s, is no longer the fastest speed theoretically possible in the universe.