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I know this is probably a silly question but i'm not sure I understand why it is special that radiation is cooler on one side of our solar system than the other. It seems like it would indicate that the "temperature" of the observable universe might have a direction to it, but why does it mean our location might be special?

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    $\begingroup$ Exactly what does this have to do with an axis of evil? $\endgroup$ – ZeroTheHero Sep 6 '18 at 18:22
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    $\begingroup$ @ZeroTheHero news to me: en.wikipedia.org/wiki/Axis_of_evil_(cosmology) $\endgroup$ – JEB Sep 6 '18 at 18:31
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    $\begingroup$ @JEB the things you learn on PSE! $\endgroup$ – ZeroTheHero Sep 6 '18 at 19:13
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    $\begingroup$ Interesting. Never heard of the term "Axis of evil". Edited the title to make it clear that "Axis of evil" is a term used in cosmology and not a flippant term introduced by the OP. $\endgroup$ – Samuel Weir Sep 6 '18 at 20:02
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A blueshift in the radiation on one side of us and a redshift on the opposite side could indicate that we're moving relative to the cosmic microwave background "rest frame" (since redshifts and blueshifts are generated by motion). Though this doesn't make any particular location special, it does identify a particular "special" inertial reference frame: the one in which you are at rest relative to the cosmic microwave background. Given that one of the fundamental precepts of special relativity is that all inertial reference frames are equivalent, this may initially seem surprising. See Is the CMB rest frame special? Where does it come from? for a more involved discussion on this frame.

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  • $\begingroup$ I guess that was my confusion, it doesn't seem to indicate anything about our location being "special" $\endgroup$ – Yogi DMT Sep 6 '18 at 19:04
  • $\begingroup$ well it talks about aligned quadrupole and octopole moments. Would those be translationally invariant? I suppose the dipole alignment isn't, unless you use comoving coordinates. $\endgroup$ – JEB Sep 6 '18 at 20:51

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