The speed of light was first determined by a Danish astronomer named Olaus Roemer who came up with the first number on this day in the year 1676. Google in the Doodle dedicated to the event depicts Roemer going back and forth from the telescope. Earlier in the year 1638, even Galileo tried discovering the speed of light. He made two persons stand on hilltops which were at a distance of a few kilometres. The basic idea was that each of them would flash the lamps they were given as a response to the other. But light travels too fast to determine its speed just by a few kilometres apart. It needed inter-planetary determinations. Roemer on his path to the discovery kept observing planet Jupiter while it eclipsed its moon called Io for many times and kept a track of time lapses between the eclipses. The moon Io was discovered by Galileo himself. Roemer found out the speed by studying the eclipses and how time light takes in a relation of a planet or its orbit.
The exact speed of light is known to be 299,792,458 metres per second, but that number wasn’t reached until the year 1975, after years of really close. That is when the General Conference on Weights and Measures suggested the official figure. The speed of light in Physics is known by the letter ‘c’ which is called a ‘universal physical constant’. It means that its value can never change. Even Albert Einstein’s famous theory of relativity is based on the premise that speed of light in vacuum does not change, and this is a basis of on which modern Physics has been built. Recently, however, some scientists from Imperial College, London found that the speed of light was fast when the Universe was formed. If it actually has slowed down, then it changes many concepts of Physics that we study right now.
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As of now, according to Einstein, no particle can travel faster than the speed of light. It is only possible in fiction, till a scientist comes and changes the basic fundamentals of Physics by making anything travel faster. Till then, it is safe to assume that the speed determined by Olaus Roemer is not going to change much.