When Einstein was doing the math to arrive at the laws of relative motion of electro-magnetic waves, starting from the famous Maxwell equations of electromagnetism, he came across a constant. He called it 'c', for constant.
Later, he noted this constant had units of speed (length/time) and, since he was dealing with electromagnetic waves, he interpreted it as the speed of these waves.
This constant has been measured by university students ever since, multiples times per year and in multiple locations all over the planet.
They have all arrived at the same value, with variable degree of certainty, of course.
None of them have observed a constant shifting of this speed towards a lower speed.... in 100 years, it's always been the same.
Also, a few dedicated teams have been measuring it with increasing accuracy. The presently accepted value can be found at http://physics.nist.gov/cgi-bin/cuu/Value?c
It is considered exact there, because... this is great!...
Not too long ago, the metre was redefined into the length that light spans in 1/299,792,458 seconds.
So, if anyone is willing to claim that the speed of light is changing, then that person will have to acknowledge that the metre is changing, too... O.o
Later, he noted this constant had units of speed (length/time) and, since he was dealing with electromagnetic waves, he interpreted it as the speed of these waves.
This constant has been measured by university students ever since, multiples times per year and in multiple locations all over the planet.
They have all arrived at the same value, with variable degree of certainty, of course.
None of them have observed a constant shifting of this speed towards a lower speed.... in 100 years, it's always been the same.
Also, a few dedicated teams have been measuring it with increasing accuracy. The presently accepted value can be found at http://physics.nist.gov/cgi-bin/cuu/Value?c
It is considered exact there, because... this is great!...
wiki Wrote:The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its value is exactly 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time.[1]
Not too long ago, the metre was redefined into the length that light spans in 1/299,792,458 seconds.
So, if anyone is willing to claim that the speed of light is changing, then that person will have to acknowledge that the metre is changing, too... O.o
