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Bell's paradox has in the past been the topic of quite heated discussions. It is posed in the context of a silk thread connecting two identical rockets whose engines are ignited at the same instant. The paradox has revolved around whether or not the silk thread breaks as viewed by different observers. The answer is that the thread does break but that is does so for apparently different reasons according to different observers.

I am curious what happens if the two rocket engines are replaced by a uniform gravitational field and the rockets are in freefall. I assume that all the observers agree that the thread does not break? Both rockets are in the same inertial frame and cannot even recognise their common acceleration. A stationary observer will surely see the Lorentz contraction of the thread but I'm less sure about how the observer would measure the distance between the two rockets. Also, both rockets are falling into a gravitational well. Does gravitational time dilation play any role in the arguments?

[clarification: at a time instant, t=0, both rockets and the 'stationary' observer have zero relative velocity. The stationary observer is immersed in the same gravitational field as the rockets but remains stationary by virtue of a force that exactly counteracts the gravitational acceleration]

Roger Wood
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A falling rod length-contracts without any stress. When the coordinate speed of the rod is 0.86 * coordinate speed of a light pulse next to the rod, then the length of the rod is half of its rest-length.

Accelerating observer observing a rod, observes the rod length-contracting without any stress. When the coordinate speed of the rod is 0.86 * coordinate speed of a light pulse next to the rod, then the length of the rod is half of its rest-length.

Accelerating observer observing a fast moving rod, observes the rod length-contracting fast without any stress. The rear of the rod moves x percent faster than the front. The absolute speed difference is large when the speed of the rod is large.

Also an observer observing a rod moving fast downwards, observes the rod length-contracting fast without any stress. The rear of the rod moves x percent faster than the front. The absolute speed difference between the rear and the front is large when the speed of the rod is large.

stuffu
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Let's say we "drop" two electrons in an uniform electric field. The distance between electrons does not change as the electrons "fall". For many people that have studied relativity this is just very weird, and impossible to understand. This is the Bell's spaceship paradox.

Let's say we drop two masses in an uniform gravity field. The distance between the masses changes as the masses fall. Now for those aforementioned people this should be just normal, and easy to understand. Right? Or maybe not?

Let's say we drop two masses inside an accelerating rocket. The distance between the masses changes as the masses fall. This is jut normal Lorentz-contraction. Right?

Well anyway, in the first paragraph there was a weird absence of Lorentz-contraction. While in the second paragraph there was a Lorentz-contraction, which was equivalent to the Lorentz-contraction in the third paragraph, as the equivalence principle requires.

stuffu
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