Galaxies that are sufficiently far away from our point of view are receding from us due to the accelerated expansion of the universe (supposedly caused by dark energy) and therefore their light is redshifted as it travels towards us.

However, does dark energy or the accelerated expansion of the universe always cause redshift? Or are there situations where light can be blue shifted due to this phenomenon?

I have heard about the Integrated Sachs-Wolfe effect where light is blueshifted as a result of the reduction of a gravitational potential by dark energy as it passes through it. Can you think of another example where light blue shifting is caused by dark energy or the accelerated expansion of there universe?


1 Answer 1


Redshift indicates recession - so if the universe is expanding at an accelerating pace, there should only be redshift.

There should be no blueshifts beyond our local universe (blueshifts in our local universe happen because over small distances, peculiar velocities can dominate over the Hubble flow). If blueshifts are detected at cosmological distances, that would be strong evidence that new physics is necessary. Last I saw, the QSSC predicts such a blueshift, but needless to say that model is very fringe with few people working on it.


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