Train Experiment in Rotation

[jkg0]

Suppose one constructs a thought experiment similar to the famous light beam bouncing around a train car. In this experiment a laser and mirror are attached to the surface of a rotating disc such that the beam is sent through the center of the disc. From my understanding of the train experiment, to an observer on the disc the light would appear to pass through the center of the disc.

But to an observer outside of the disc the light would have to move to hit the appropriate mirrors and would appear to avoid the center of the disc.

Is this a reasonable understanding? Or do the reference frames vary by radius from the center of the disc such that on the edge of the disc the beam would appear to move through the center but as one approached the center the beam would appear to avoid it?

[JesseM]

Light is only constrained to travel in straight lines at constant speed c in inertial frames (the rest frames of observers moving at constant speed and direction--any change in speed or direction is a form of acceleration, and the observer will know he's accelerating because he experiences G-forces, like the 'centrifugal force' felt by rotating observers). In a rotating frame this is no longer the case, so your inference here is not correct:
From my understanding of the train experiment, to an observer on the disc the light would appear to pass through the center of the disc.

[cragar]

k I don’t know this might be a little off topic But isn't there a thought experiment by Einstein He imagines and elevator going up really fast and a hole is drilled in the side of the
elevator and the light coming in hits lower on the other side or appears to bend.

[JesseM]

k I don’t know this might be a little off topic But isn't there a thought experiment by Einstein He imagines and elevator going up really fast and a hole is drilled in the side of the
elevator and the light coming in hits lower on the other side or appears to bend.
Yes, this is a thought-experiment showing the equivalence between being at constant height in a gravitational field and accelerating in deep space (or equivalently, between freefall in a gravitational field and inertial motion in deep space). See this article (http://www.einstein-online.info/en/spotlights/equivalence_principle/index.html) for some more on the equivalence principle, and this one (http://www.einstein-online.info/en/spotlights/equivalence_deflection/index.html) for some animations showing how, if the light is supposed to move in a straight line in a freely-falling elevator, it must travel on a curved path for an observer at a fixed height in a gravitational field. You can also turn this around to show that if light travels in a straight line as seen by an inertial observer in deep space, then it must travel on a curved path for an observer in an accelerating room in deep space, which according to the equivalence principle is equivalent to being at a constant height in a gravitational field...see the second animation on this page (http://www.phy.syr.edu/courses/modules/LIGHTCONE/equivalence.html):

http://www.phy.syr.edu/courses/modules/LIGHTCONE/anim/equv-m.gif

[cragar]

i see ya that clears it up.