If the motion in universe is relative, when you turn yourself 360 degree, stars move faster than light speed?
I learned that universe space has no axis, and any motion is relative. I still do not understand this. Suppose you turn your body by 360 degree in one second. A distant star (say, 1million light years from earth) travel about 6 millions light years by circling around you in one second. This is way way faster light speed (about 400 millions times faster than light speed). Yet nothing can be faster than light speed. Why does this contradiction happen?
Anonymous2009-04-05T21:03:20Z
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Good thinking, based on misconception.
the speed of light limit is the statement that light travels at C. When you look at the distant star and you turn, the light moves across your field of view not the sky.
Suppose the 1 m LY star and you are sending messages by laser using the old dot dash system. You send "hello", A million years later the star men send back "nice to meet you" another million years goes by and your great great ....great grand children get the message. No matter how many times you spun in your grave, the light and the message were limited to speed of light. Does that help?
Relative to the star, YOU moved. The motion of the stars relative to any other body (other than you) remained constant.
To be little more technical, if you want to talk about the movement, you must first define a reference body. This can be anything... like the Earth. You move relative to this reference body. Star's perceived movement is also defined relative to the Earth. Relative to this reference body, the motion of star remained constant where as you moved...
Not all motion is relative. Only uniform motion (or in General Relativity, freely falling motion) is relative. We know that it is you, not the stars, that is turning, because an accelerometer (a mass on a spring) attached to you would read nonzero (stretch the spring), and accelerometers attached to the stars would not.
Moreover, General Relativity nevertheless allows you to design a coordinate system in which you, whirling, are at rest. In such a coordinate system, it is perfectly legal for the stars to travel faster than c. Indeed, they must, and it would be a violation of relativity for a very distant star to be at rest in that frame. The restriction on c is local to the observer. That rule changes for distant bodies outside of the observer's locally flat reference frame. For instance: distant galaxies whose recession velocities exceed c.
If you choose to have such a non-inertial reference frame, all bets are off. SS--you have the right idea (i'll upthumb you for it), but the calculation isn't going to be quite as simple as that. You need GR to track what goes on in a non-inertial reference frame--when your reference rotates, you have enormous centrifugal forces at long distances, so the GR corrections will be substantial. But ultimately, yeah, you're right that when you work it out the speed should be less than c.
The universe is infinite. To understand this first you need to imagine the shape of the universe in all dimensions.
First lets look at what infinity would look like in a 1 dimensional universe (able to only move forward or backward). To us that would look like a circle but to something that con only move in 1 dimension it is infinitely huge because the circle never ends. Now what if something could only move in two dimensions? Say forward/backward and left/right. The infinite shape is a sphere. See a pattern? Infinity in a 1 dimension universe is a 2d image. In a 2d universe the shape is a 3d.
But because we can move in 3 dimensions forward/back, left/right, and up/down our universe is 3d we need to be able to imagine a 4th dimension.
It is said that only true geniuses can actually visualize what our infinite universe looks like. So to fully understand the question you asked and the answer to it we would need to understand the shape of the universe. I am not a genius, so I can't give you a perfect answer.