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There is not a universal rest frame. There is, however, a galactic rest frame. Because you can look up at the stars, falsely assume that they do not change, and count your rotations that way. However, that method is only as reliable as the premise that the stars don't move, which they do slightly. The Hafele-Keating experiment used a variant of this, ...

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Leaving aside for a moment the comments made by dmckee et al, what matters is the angle of the measurement to the direction of motion. If an ether exists and you make a measurement along the direction of motion then you would get a different result to a measurement made at right angles to the direction of motion. It doesn't matter whether the right angle ...

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Yes. The speed of light is independent from the direction and the reference system. In fact Michelson and Morley did their experiment in different directions and periods of the year in order to work in different earth revolution period, and they found always c.

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A "vertical variation of modern versions of the Michelson-Morley experiment (MMX) with one arm pointed in the vertical direction" experiment has been performed. Watch the following video starting at 0:45. http://youtube.com/watch?v=s9ITt44-EHE "Imagine the Earth as if it were immersed in honey," says Francis Everitt of Stanford University in California, ...

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The way to do problems like this is always to use the Lorentz transformations. Choose some sensible spacetime points in the rest frame $S$ and use the transformations to see what those points look like in the moving frame $S'$. In this case this is what the points look like in $S$: The spacetime points are labelled as $(t, x, y)$ - we'll ignore $z$ since ...

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Light isn't a single vector. It propagates out in all directions, because it is a spherical wave. edit: I stand corrected, but I was trying to imply being able to a light pulse would require some sort of spherical wave reflecting off of particles in air. If in vacuum then you would not see the light ray. In this picture you wouldn't see anything because ...

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Both observers would perceive the light at the same speed. Any observer in any frame of reference anywhere in the universe will see light travel at the same constant speed. In terms of an light under gravity - if the light is approaching the massive object it will have a Doppler blueshift, while if the light is going away from the massive object it will have ...

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General relativity reduces to special relativity locally. What this means is that given an error tolerance $\varepsilon$, you can find an extended region (perhaps just a small one) around any point in spacetime such that the laws of physics as tested only within that region match those of special relativity to within $\varepsilon$. That means if you measure ...

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The short answer has been given a few times in the comments: gravity only bends light, it doesn't speed it up. Of course this statement in and of itself is useless if you want to understand nature. So let's dig a bit deeper. To understand why gravity acts this way, the first step is the equivalence principle. Now, there are several versions of this but we'll ...

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If a ray of light is aimed exactly at the center of a body, then will it get accelerated like a meteor? Short answer: no. However, when falling in a gravity field, the momentum of light increases. Some background... In Newtonian mechanics, the rate of change of momentum of a (massive) particle is proportional to the acceleration: \frac{d\vec ...

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