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# Physics/Definition of basic physical quantities' units

Question
Good morning.
Well, my dear Sir the question is as follows:
" We know that 1m is defined as the distance traveled by light in 1/299792458 s. Why was such a difficult number chosen? What if they defined it as the distance traveled in 1/300000000 s?"
I am prepared to swear that this is no homework question!

Sincerely yours,
AB.

The speed of light was originally a measured quantity based on the meter and the second.  Then it became a defined constant in terms of the actual speed of light and the international standard for the second.  This is now the definition of the meter.  To keep it as close to consistent with the previous meter as possible, this definition was retained (the speed to within one meter/second).  This was done in 1983, I'm not sure exactly why they didn't just use 1/300000000 of a second, but it must have made some prior measurement incompatible with the new definition.

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.