Thread: Does local spin make a difference in relativity?

I was thinking about a distant object moving from point A to point B at the speed of light but keeping a constant distance away from the observer.

Could the observe observe them moving faster than light? How is that object limited by SRs "nothing can travel faster than the speed of light"?

The thing is what if the observer was rotating slowly to coinside with the object so that the object didnt appear to move with respect ot the rotating observer?

Observer is rotating at the same rate that object is travelling in the direction of the V ( downwards ).

0--------------------------------------------------------V

For the observer it would appear that the object is not moving at all, even though it is travelling through space at the speed of light.

For the observer all of the other stars and everything else around ti would be moving at apparently the speed of light ( but this is really just because the observer is rotating ) .

Does this make sense? If not I can try to draw a picture.

According to relativity in cosmology, you would never have a circumstance where an object is travelling adjacent to you at the speed of light, since the theory demands an expanding universe (everything would be moving away from you, and never sideways).

The rule of never travelling faster than the speed of light is ignored at great distances. Not only is it acceptable for two distant galaxies to be travelling apart faster than light, it is demanded by current accepted theory.

Of course, I disagree with the accepted.

How about in an isolated non expanding universe? Or in a universe where only the "moving" object and the observer" ( and maybe a few other stars for reference ) exist?

Originally Posted by KickLaBuka

According to relativity in cosmology, you would never have a circumstance where an object is travelling adjacent to you at the speed of light, since the theory demands an expanding universe (everything would be moving away from you, and never sideways).

The rule of never travelling faster than the speed of light is ignored at great distances. Not only is it acceptable for two distant galaxies to be travelling apart faster than light, it is demanded by current accepted theory.

Of course, I disagree with the accepted.

Well, yes. The situation you describe is geometrically correct, however unlikely. Strictly on paper, the rotating object "arcs" across its view (in degrees per second), and at some distance (r), an object could be moving the speed of light and cover an "arc length" (s), all while being observed to be stationary overhead of the rotating observer. An object a bit farther away would have to be moving faster than the speed of light in order to remain in a fixed viewpoint over the observer. The geometric name for that would be "similar triangles" or "similar arcs."

this relies too much on the light comming from the "object" to the "observer" which can actually contradict what is actually happening

I believe that the correct answer to this problem requires a reference to General Relativity, inasmuch as a spinning observer is not in an inertial reference frame. A simplified answer is as follows: What relativity says about the speed of light is that it is constant for all observers in a inertial frames, or more generally, that every observer in any frame will calculate the local (to himself) speed of light as having the same value. This does not mean that that observer will measure the same speed of light for light travelling at a remote location. Thus, for example, pursuant to General Relativity, the speed of light in a gravitational field is c at the location of the observer, and is less than c (as seen by that observer) at an altitude below that of the observer, and is greater than c (as seen by that observer) at an altitude above the observer. Therefore it is erroneous to say that a spinning observer should expect all light everywhere to travel at c as measured in his own reference frame. Likewise, it is incorrect for him to suppose that the dynamics of objects will look the same in his frame as they do to other observers.

Originally Posted by Atomic-S

What relativity says about the speed of light is that it is constant for all observers in a inertial frames

Originally Posted by Atomic-S

it is erroneous to say that a spinning observer should expect all light everywhere to travel at c as measured in his own reference frame

"The speed of light is constant in inertial frames" per above.

This assertion does not permit the assertion that the opposite is true--neither to call the former erroneous, nor necessarily relativistic just for rotating--by inertia.

The speed of light is the same in all reference frames--inertial and non-inertial alike. In fact, the speed of light is a defined constant of nature. This would not be possible if the speed changed in accelerated reference frames. By the Equivalence Principle, this would mean that the speed also changed in non-uniform gravitational fields. We all know that the strength of the gravitational field is local. It varies from location to location. A rotating reference frame results in the bending of light beams as seen by an observer in the rotating reference frame. Although the direction of the light would change, its speed would not.

Originally Posted by MisterMe

A rotating reference frame results in the bending of light beams as seen by an observer in the rotating reference frame.

Inaccurate.

Originally Posted by KickLaBuka

Inaccurate.

Why do you believe so?