Can someone explain about the “axis of evil” in space please?
The Axis of Evil is an observation about the Cosmic Microwave Background that has some troubling implications for some of the foundational assumptions of astrophysics. It is most likely not real–probably a mistake in the measurements or some other error or bias–but it’s not *definitely* not real because we haven’t yet figured out what that mistake is.
At the foundation of astrophysics is the assumption that, broadly speaking, any one area of the Universe is pretty similar to any other area. This allows us to draw conclusions about space and physics based on things we observe very far away (or draw conclusions about far away things from nearby observations). Given this, we expect that the Cosmic Microwave Background (a sort of microwave-spectrum glow that permeates the Universe and is left over from its very early stages) is largely the same everywhere. It’s not *precisely* the same everywhere: there are hot spots and cold spots and what-have-you; but if you average things out it tends to all look the same.
Except that it doesn’t, quite. Under certain kinds of data analysis one half of it appears just slightly cooler than the other half. Even more troubling: the line of division between these two halves roughly aligns with the rotational plane of our own Solar System, something that is very unlikely to occur by chance.
So *if the Axis of Evil is a real phenomenon* it suggests that we have to be more careful about drawing conclusions between different parts of the Universe *and* that our position in the Universe is somehow privileged, which opens up a great many cans of worms.
Most of our understanding of the universe relies on the assumption that if you zoom out enough, the universe is roughly the same everywhere. The axis of evil is a hot and a cold spot* on nearly opposite sides of the CMB. These spots differ enough that we don’t feel super comfortable calling them normal statistical variation. But if they are anything other than normal statistical variation, then that central assumption of cosmology falls apart, leaving us with a universe that we don’t, and possibly can’t, understand.
*hot and cold being relative to the rest of the CMB