Friday, September 23, 2016

Without Direction, or Has No Prefered Direction?

This is why popular news coverage of science can often make subtle mistakes that might change the meaning of something.

This UPI news coverage talks about a recent publication in PRL that studied the CMB and found no large-scale anisotropy in our universe. What this means is that our universe, based on the CMB, is isotropic, i.e. the same in all direction, and that our universe has no detectable rotation.

However, instead of saying that, it keeps harping on the idea that the universe "has no direction". It has directions. In fact, it has infinite directions. It is just that it looks the same in all of these directions. Not having a preferred direction, or being isotropic, is not exactly the same as "having no direction".

If you read the APS Physics article accompanying this paper, you'll notice that such a phrase was never used.

I don't know. As a layperson, if you read that UPI news article, what impression does that leave you? Or am I making a mountain out of a mole hill here?


1 comment:

Douglas Natelson said...

A tangentially related question. The fact that there is a net Doppler dipole of the CMB when viewed from the earth implies that there is some particular reference frame that is co-moving with the "center of mass" of the CMB. Does this mean anything? I mean, special/general relativity assumes that there are no preferred reference frames, and there's no reason to think that the laws of physics have anything special to say about that particular frame, except for the fact that it's the one frame where the CMB (which has something to do with all the matter in the universe) really looks isotropic.