• Question: What is the speed of light?

    Asked by anon-267491 on 9 Nov 2020. This question was also asked by anon-267534.
    • Photo: Sam Geen

      Sam Geen answered on 9 Nov 2020:

      c, which is the letter physicists use to describe the speed of light, is 299 792.458 kilometres per second – it’s fast!

      Here’s a joke: Why are ships so fast? They travel at c

    • Photo: Daisy Shearer

      Daisy Shearer answered on 9 Nov 2020: last edited 9 Nov 2020 11:16 am

      The speed of light (in a vacuum) is 299,792,458 metres per second. We call this value ‘c’ and it’s what is used in the famous equation: E=mc^2

      Einstein thought that this is the ‘universal speed limit’ so nothing can move faster than this. But some physicists think that this speed limit can be broken in quantum mechanical systems because of something called ‘entanglement’ where information can be instantaneously exchanged between two entangled particles, even if they’re on opposite sides of the universe!

      In other mediums like glass and water, light moves more slowly than this and we describe this using a parameter called the ‘refractive index’.

    • Photo: Jesse Dykes

      Jesse Dykes answered on 11 Nov 2020:

      About 3 x 10^8 – Or a foot a nanosecond, which is a convenient number to keep in mind when you’re firing laser over distance

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