Here’s something I never really understood before.

Here’s something I never really understood before. Edwin Hubble is most famous for the idea that galaxies have a redshift proportional to their distance, which gives rise to the idea of the expanding universe since the Big Bang. But the redshift that we measure for galaxies is not a Doppler shift, and you can’t really say that distant galaxies are moving away from us at a certain velocity. Instead, space itself is expanding and that stretches out light waves en route. This cosmological redshift effect looks just like a Doppler shift, so it’s easy to confuse the two, but they’re two unrelated causes that have the same effect.

h/t Sean Carroll for his blog that clarifies this topic in the context of “superluminal expansion” —

4 replies on “Here’s something I never really understood before.”

  1. You know..I know what the doppler effect is and I think I can just about glimmer how it could refer to the other two dynamics you mentioned..but I could be wrong..I prove on a daily basis that the speed of light is quicker than sound…I can look clever until I open my mouth and you hear me speak..then science takes over and reveals me to be the idiot I am. 🙂

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