4 ms·

By saying speed of light, you make the assumption it is the same in any direction or reference frame. This was not known to be true, and is still the subject of

By saying speed of light, you make the assumption it is the same in any direction or reference frame. This was not known to be true, and is still the subject of some question, hence the more modern experiments measuring the speed in a fixed frame to compare to other frames. For example, what is the speed of a bullet? It depends on the observer (as does velocity, but velocity is a more accurate thing to measure for this reason). It so far is experimentally true that the velocity of light has the same magnitude (up to experimental error) in any frame, which was a tremendously crazy result at first, so much so that it forced mankind to give up the notion of constant flow of time, and it forces space and time to "rotate" into each other in a weird manner called space-time. So the velocity of light is the proper term to use in an experiment.

whatshisface 7y ago
>For example, what is the speed of a bullet? It depends on the observer (as does velocity, but velocity is a more accurate thing to measure for this reason). That sentence doesn't make sense to me, velocity is even more sensitive to coordinate change than speed. If you rotate your coordinate system, all the velocities will change but speeds will stay the same. The phrase used in the article was "the velocity of light," which was known to be wrong even back then because light has a different velocity depending on which way it is going.
jayd16 7y ago
But this proves the point that speed should be used. C is the theorized speed of light in all frames. The experimental velocities of light also exist but that shouldn't be what we call C.
twiceaday 7y ago
This doesn't make any sense. If there is an oddity its in saying "THE speed of light." THE is what makes it singular and begs the question "in what direction?" The answer is in any direction. But that doesn't mean direction is not important. If somebody asks you for THE velocity that is a nonsense question. If somebody asks you for A velocity they are asking you for the speed in each direction. Even in 1D, where the units of velocity and speed are the same, these are still not the same concepts because velocity can be negative to signify the direction of "backwards" so there are two possible velocities of light even in 1D.

whatshisface 7y ago

>For example, what is the speed of a bullet? It depends on the observer (as does velocity, but velocity is a more accurate thing to measure for this reason). That sentence doesn't make sense to me, velocity is even more sensitive to coordinate change than speed. If you rotate your coordinate system, all the velocities will change but speeds will stay the same. The phrase used in the article was "the velocity of light," which was known to be wrong even back then because light has a different velocity depending on which way it is going.

jayd16 7y ago

But this proves the point that speed should be used. C is the theorized speed of light in all frames. The experimental velocities of light also exist but that shouldn't be what we call C.

twiceaday 7y ago

This doesn't make any sense. If there is an oddity its in saying "THE speed of light." THE is what makes it singular and begs the question "in what direction?" The answer is in any direction. But that doesn't mean direction is not important. If somebody asks you for THE velocity that is a nonsense question. If somebody asks you for A velocity they are asking you for the speed in each direction. Even in 1D, where the units of velocity and speed are the same, these are still not the same concepts because velocity can be negative to signify the direction of "backwards" so there are two possible velocities of light even in 1D.