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A cosmologically redshifting puzzle in a box

3 Mar 2009, 01:57 UTC
A cosmologically redshifting puzzle in a box
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In the comments for another blog post about cosmological distances, I suggested a thought experiment that would highlight how the redshift from distant galaxies is not due to a Doppler shift, that is, light from very distant galaxies is not redshifted because of the movement of the galaxies, but rather because the intervening space itself [...]In the comments for another blog post about cosmological distances, I suggested a thought experiment that would highlight how the redshift from distant galaxies is not due to a Doppler shift, that is, light from very distant galaxies is not redshifted because of the movement of the galaxies, but rather because the intervening space itself is expanding:

If someone managed to trap light when the universe first became transparent, about 300,000 years after the Big Bang, inside a perfectly reflecting mirrored box such that the light is contained in perpetuity, what would have happened to the wavelength of the trapped light by now?

We’ll allow ourselves the reasonable assumption that the size of the mirrored box does not change because the electromagnetic, strong, or weak forces that maintain its shape overwhelms any tendency for the box to grow along with the expansion of space.
If ...

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