I Photons being blueshifted when crossing evolving voids?

AI Thread Summary
The discussion centers on the effects of evolving voids on cosmic microwave background (CMB) radiation, particularly through the Rees-Sciama and integrated Sachs-Wolfe effects. It highlights that photons crossing gravitational well potentials are blueshifted, while those crossing voids are typically redshifted. However, some studies suggest that growing voids can lead to a partial cancellation of this redshift, potentially resulting in a net blueshift for photons exiting voids. The inquiry focuses on whether there are scenarios where photons can experience an overall blueshift after traversing voids. This raises important questions about the behavior of light in an expanding universe influenced by cosmic structures.
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Photons being blueshifted when crossing voids due to Rees-Sciama effect...?
I was reading this paper (https://academic.oup.com/mnras/article/288/2/387/960778) where they analysed how CMB radiation is affected by evolving voids in an expanding spacetime (particularly through the Rees-Sciama effect and the integrated Sachs-Wolfe effect).

This effect predicts that photons crossing well potentials would be blueshifted and the ones crossing voids would be redshifted. However, in this paper (and some others: https://arxiv.org/abs/astro-ph/0612347, https://pure.port.ac.uk/ws/portalfiles/portal/6034571/Alvise_Raccanelli_Thesis.pdf) the authors indicate that there can be a partial cancellation of the redshift of photons crossing the voids (or said in another way, that growing voids can blueshift photons).

My question is:

Can there be cases where the photons crossing the voids have a total net blueshift as they get out of them?
 

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