Hey team! CMB photons are always being redshifted by the expanding Universe, but there is also a cool way in which they can get a little bit of blueshift too, or even some extra redshift! Let me introduce you to the Integrated Sachs-Wolfe Effect. If there is some other cool topic in physics you think we should learn about together, leave a comment down below! Until next time, stay safe. Please consider subscribing if you enjoyed the video, and you can also find me on Twitter: https://twitter.com/chrisdpattison