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[Phys-l] Aberration and "Einstein's Cat"

From: WC Maddox

Some physics to think about.

An article I read recently stated that Einstein's views on simultaneity (or the lack thereof) may have been motivated in part by the measurement of stellar aberration due to the motion of the Earth around the Sun. Supposedly both Lorentz and Einstein thought that the situation was symmetric and depended only on the transverse part of the relative velocity between Earth and a star. The angles in the two reference frames were related by cos(earth angle) = (cos(star angle) -v/c) /(1-cos(star angle)*v/c). For small v aberration is usually given as sin(telescope tilt angle) = v/c.

Now image that "Einstein's cat" is in a cage on a spacecraft at rest relative to the Sun. A telescope is pointed at a star and tilted to correct for expected aberration due to motion of the star. If the light gets through the scope it shines on a photocell to activate a release mechanism. Does the cat get out or not?

Hint: Think what would happen if you looked at double stars whose components would have different relative velocities.

PS There is an additional effect sometimes called planetary aberration which is a time delay effect due to the finite speed of light. This effect occurs in classical physics but is often ignored.

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