# Is cosmic background radiation absolute [duplicate]

Now that we don't have permeating Ether anymore, why don't we consider the omnipresent Cosmic background radiation in place of it? and measure Speeds with respect to the CMBR? In that way an object moving through the space, can be said to have at least a 'kind-of' absolute velocity w.r.t Background radiation? I.O.W is that radiation stationary?

## marked as duplicate by John Rennie, Kyle Kanos, Brandon Enright, Jim, dmckee♦Apr 19 '14 at 19:13

• Two key words: microwave radiation. Since it is light, it's speed is...? (and no, it's certainly not stationary!) – David H Apr 19 '14 at 4:36
• Thanks...you mean CMBR also always travels at light speed? – user3409697 Apr 19 '14 at 4:41
• It most definitely does. See the link in my comment above for more info on microwave radiation. – David H Apr 19 '14 at 4:52

The above data is the is the anisotropy of temperature of the Cosmic Microwave Background (CMB) as measured by NASA U2 airplanes in the 1970s.

The anisotropy is due to the redshift and blueshift of the Earth moving 300 kilometers per second or 1,080,000 kilometers per hour relative to the frame of the CMB, in the direction of the + at the center of the red region of the plot. This is mostly due to the peculiar motion of the Milky Way toward the Great Attractor.

This anisotropy is usually subtracted out in the data you see nowdays, but it is still there in the raw data.

So, yes, the CMB is used as a standard frame of reference. Even though all light moves at the same speed in a vacuum, there is redshift and blueshift of the CMB due to motion relative to its frame.

Note: in the plot red means hotter and blueshifted, blue means cooler and redshifted.

• You should be very clear that an identifiable, agreed-upon base frame is in no way a "special" or "privileged" frame. Being able to pick a frame that every one (or at least every one for a long distance around) can agree upon does not break relativity. – dmckee Apr 19 '14 at 14:44
• @dmckee Greorge Smoot won the 2006 Nobel prize in physics for CMB work, and his group states in the link of my answer "This would seem to violate the postulates of Galilean and Special Relativity but there is a preferred frame in which the expansion of the Universe looks most simple. That frame is the average rest frame of the matter and CMB and from that frame the expansion is essentially isotropic." I'll stay neutral and let you two work it out :) – DavePhD Apr 19 '14 at 14:59
• @dmckee In Smoot's Nobel lecture he said "modern efforts to find violations of Special Relativity look to this reference frame as the natural frame that would be special". I would say he's open to the possibility that the CMB is a special frame. – DavePhD Apr 19 '14 at 21:14
• The article you linked about the Great Attractor says we're moving away from it, not toward it. – B T Aug 11 '14 at 2:21
• @BT Yes, overall, including expansion of the universe, we are moving away from the Great Attractor. Only subtracting out the expansion of the universe, to yield the "peculiar velocity", is motion toward the attractor. – DavePhD Aug 18 '14 at 15:47