The speed of light in a vacuum stands at “exactly 299,792,458 metres per second“. The reason today we can put an exact figure on it is because the speed of light in a vacuum is a universal constant that has been measured with lasers; and when an experiment involves lasers, it’s hard to argue with the results. As to why it comes out somewhat conspicuously as a whole number, this is no coincidence- the length of metre is defined using this constant: “the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.” Prior to a few hundred years ago, it was generally agreed or at least assumed that the speed of light was infinite, when in actuality it’s just really, really, really fast- for reference, the speed of light is just slightly slower than the fastest thing in the known universe- a teenage girl’s response time if Justin Bieber were to say on Twitter, “The first to reply to this tweet will be my new girlfriend.” The first known person to question the whole “speed of light is infinite” thing was the 5th century BC philosopher Empedocles. Less than a century later, Aristotle would disagree with Empedocles and the argument continued for more than 2,000 years after.
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Via Chuck Sherwood, Senior Associate, TeleDimensions, Inc