Question: how fast does light traville????????????????

Paul Coxon answered on 13 Mar 2014:

The speed of light isn’t constant. Its speed depends on what material the light is passing through.

In a perfect vacuum light travels exactly 299,792,458 metres per second – no more, no less. Nothing can beat it. It’s the same no matter who measures it even if they are standing still or moving at 100mph. No one will measure a faster speed – it will always be 299,792,458 metres per second. It’s a sort of universal speed limit throughout the universe. It travels this fast because in a vacuum there are no particles in the way to slow it down.

The speed of light in a vacuum is a very useful quantity, and it appears throughout physics. Because of its fixed definition and unchanging nature, it’s a fundamental physical constant, and we can use the speed of light to define other constants such as the second.

But we can make light slow down by passing it through denser materials. Light in water travels at a mere 225,056,264.1 metres per second. The changing of light’s speed as it passes through different materials is why a straw in a glass of water looks ‘bent’. As it meets the interface between two different materials – such as water-glass, glass-air, it bends (known as ‘refraction’.)

We can slow down light to quite low speeds. In 1999 researchers in the US passed light through super-chilled sodium gas and measured the speed of light at 26.922 metres per second (60mph, which is about as fast as a car.)