Hi, I am Paulus and new to this forum. I have read some of the articles of this forum and I really like it. Still I have some issues that I like to sort out for some time and I hope some some of you can.
First we know that the speed of light in a vacuum is constant by definition. But what formula (not only observation) is the basis for calculating the speed of light. Why is C not 200.000 or 400.000 in stead of 300.000 km/p/sec? Or is there only observation?
As I believe that a true vacuum does not exist. Can it be so that the speed of C is determined by the properties of spacetime or is it just the other way around?
See ya!
Hi Paulus,
"But what formula (not only observation) is the basis for calculating the speed of light."
In the late 19th century, Maxwell formulated his famous equations, from which one can derive that electromagnetic fields in vacuum propagate at a speed given by:
1 / sqrt ( <font face="symbol">e</font><sub>0</sub><font face="symbol">m</font><sub>0</sub> )
where <font face="symbol">e</font><sub>0</sub> and <font face="symbol">m</font><sub>0</sub> are constants which appear in a natural way in the Maxwell equations (they describe "how well" electric fields and magnetic can propagate in a medium, or in this case, vacuum). These constants can be measured through a variety of ways, but when you plug in the numbers, you find that the speed at which electromagnetic waves propagate through vacuum is exactly equal to the already previously measured speed of light. Since light also exhibited some electromagnetic properties, it was then concluded that light was nothing more but an electromagnetic wave, which travelled at a speed predicted by Maxwell's equations.
"Can it be so that the speed of C is determined by the properties of spacetime or is it just the other way around?"
Uuuuhhh... though question. I would say they are not related. If the speed of light would be 100 km / h instead of 300.000 km / s, there would just as well be a spacetime. It would be a strange world to live in, but it would exist :).
Bye!
Crisp
James R
08-16-03, 08:58 AM
Paulus:
The speed of light is, as you say, constant <b>by definition</b> these days.
The value of c is exactly 299792458 metres per second.
The reason it has this value and not (say) 300,000,000 metres per second is because we <b>choose</b> to define a metre as the distance travelled by light in exactly 1/299792458th of a second.
Why do we choose that definition? To keep the definition of the metre very close to what it was before it was defined by the speed of light.