On Sat, Apr 21, 2012 at 10:40 AM, [email protected] < [email protected]> wrote:
> From 1905 the SRT doesn’t give sleep. > 1. > One postulate of SRT takes vacuum as reference frame. > Another postulate of SRT takes inertial reference frame (s). > No, none of the postulates take the vacuum as a reference frame, which doesn't make sense since a vacuum doesn't have a measurable rest frame (there are no landmarks in a vacuum that could be used to measure the "velocity of the vacuum" relative to anything else). One postulate does talk about the speed of light in a vacuum, but they're still talking about the speed of light as measured in an inertial frame--"in a vacuum" is just there to specify that it's not talking about a light beam moving through some measurable medium like water or air. In one reference frame speed of ‘Electrodynamics Bodies’ is constant. > In another reference frame speed of ‘Electrodynamics Bodies’ is > relative. > Nope, all speeds are measured relative to a particular frame. But in relativity it works out that if you and I are riding in spaceships at rest in different inertial frames (so we are moving relative to each other), and we each measure the speed of the *same* light ray using our own rulers and clocks, we will each find that the ray travels at a speed of 299792458 meters per second relative to ourselves (i.e. as measured in terms of distance/time by rulers and clocks at rest relative to ourselves). This in spite of the fact that in my frame, according to my rulers and clocks, the distance between your spaceship and the light ray is changing at a rate different than 299792458 meters per second (and you will say the same thing about me when you measure with your own rulers and clocks); I will explain the fact that you nevertheless measure the ray to be traveling at exactly 299792458 meters per second in terms of the fact that your rulers and clocks appear to be distorted relative to mine, with your meter-stick appearing shrunk relative to mine, your clock ticking slower than mine, and your "synchronized" clocks appearing out-of-sync in my frame (and again you will say exactly the same thing about my rulers and clocks relative to yours) So, in this sense the speed of light is "constant", because it has the same measured speed of 299792458 meters per second relative to all inertial frames. But the speed can still only be measured relative to a particular frame, and if you make use of a *non* inertial frame (an accelerating coordinate system like "Rindler coordinates", for example), the speed of light relative to that frame's coordinates may be quite different. Jesse -- You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/everything-list?hl=en.
