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Peterdevis
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The speed of light in vacuum is c in all frames, but is it also in comoving frames?
turin said:Does "all" include "comoving?"
hemmul said:I doubt there is no co-moving frame defined for light:
Reference Frame is defined as a material object, which is associated with the axes and so on... but there is no material object moving with c...
Which one then?Peterdevis said:The frame I mend is not the lights frame.
hmm...Peterdevis said:Furthermore a reference frame is a matimatical object non material.
I think I get your question now.Peterdevis said:That's my question!
turin said:I think I get your question now.
c is NOT the same in all frames! It is the same in all inertial frames. A frame, K, moving at c wrt an inertial frame is not itself an inertial frame. Therefore, K does not contain the notion of a constant c.
Not true. The definition of an inertial frame is one in which massive objects move uniformly in straight lines in the absense of forces. It is quite an obscure definition in itself, but can be understood concretely.Eyesaw said:The definition of inertial frames are frames that are moving at constant velocity relative to one another.
Because it is not inertial. It is mathematically valid, but not physically realizable (as far as I know) from the rest frame of a massive object.Eyesaw said:Why should a frame moving at the constant velocity c not be an inertial frame?
I agree. But this is not the state of affairs. After strong resistance by physicists in the 19th and early part of the 20th century (physicist for whom I indeed hold a distant repect) the inertial frame invariance of c has been repeatedly demonstrated. Are the demonstrations absolutely conclusively? Of course not.Eyesaw said:It's irrational to restrict apriori c as a limiting velocity for motion through space.
Did you mean the translated and published work of Einstein, Relativity? If so, I suggest you do the same, while also carefully considering the context. Chapter 9 is by no means intended as a conclusion.Eyesaw said:(Chapter 9 Special RElativity, read carefully).
You didn't like the answer the last time it was explained to you - what is the point of asking again, other than possibly to hijack someone else's thread?Eyesaw said:Why not?
russ_watters said:Peterdevis: C. I'm still not exactly clear on the question though...
selfAdjoint said:Some of the confusion is that comoving frame has a different meaning in SR, leading to the question "comoving wrt what?"
turin said:In your balloon analogy, let's say the balloon is rubber (naturally), and that you draw lines (curves) on it much like those on a globe with ink. Then, the balloon surface (the rubber) would be a 2-D space and the lines (ink) would be our artificial coordinate surfaces. Is this what you're talking about?
turin said:Two flaws with the balloon analogy:
1) As it expands, the rubber only stretches, it does not actually increase. The surface area of the rubber increases, and, from here on, when I refer to the rubber, I will mean the 2-D volume (surface area on the balloon) of the rubber, not the mass or 3-D volume of the rubber. This will make the analogy more consistent.
turin said:2) The rubber seems rather ethereal. I can't think of a way around this while maintaining a meaningful balloon analogy. So, this actually does not address the question, but, it addresses the issue of the expansion and how it affects local measurements.
turin said:Imagine an ant crawling on the surface in a straight line (great circle/geodesic). It would take the ant longer to crawl from one ink line to another if the balloon is expanding than if it is not, but that doesn't mean the ant is going slower, even with respect to the coordinate system. The metric of the coordinate system changes in time.
That's how I see it.Peterdevis said:When i see it right : when the metric change in time, also the measurement of distance change in relation to the coördinates?
The speed of light in a comoving frame is the same as the speed of light in a stationary frame, which is approximately 299,792,458 meters per second.
In a comoving frame, the speed of light remains constant regardless of the motion of the observer, while in a moving frame, the speed of light appears to change due to relative motion.
A comoving frame is a reference frame that is at rest with respect to the average motion of matter in the universe. This means that objects in a comoving frame will appear to be stationary, and the speed of light will remain constant in this frame.
The speed of light in a comoving frame is important in cosmology because it allows us to measure the expansion of the universe. By observing the redshift of light from distant galaxies, we can determine the rate at which the universe is expanding.
No, the speed of light in a comoving frame is not affected by gravity. This is because in a comoving frame, the observer is considered to be at rest, and the speed of light is always constant in this frame regardless of the presence of gravity.