Can the CMB be used as an absolute reference frame?

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Simon Tulloch

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Simon Tulloch  asked the Naked Scientists:
Hi Chris, great show, Im hooked. I have a question:

The cosmic microwave background (CMB) shows a dipole distribution which is normally subtracted from the data to reveal the underlying "wrinkles" that appear in the public relations images (George Smoot´s "face of god"). This dipole distribution means that one side of the sky is slightly hotter than the other and this is usually described as being due to the doppler shifts in the CMB due to the solar systems motion through space. Surely this implies that the CMB provides an absolute frame of reference in space against which velocities can be measured? Einstein showed us that all velocities are relative. How can this apparent paradox be explained?


Simon Tulloch

What do you think?
« Last Edit: 26/03/2011 18:30:02 by _system »


Offline yor_on

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Can the CMB be used as an absolute reference frame?
« Reply #1 on: 26/03/2011 22:02:13 »
There is a difference between choosing a frame to measure yourself against and finding that 'unmoving' frame that permeates the universe. CMB is a radiation that 'moves' at 'c', approximatively as 'hot/cold' in any direction you look. It also has no preferred direction and so becomes indirect evidence for the so called inflationary period when space 'grew instantly'. But it is only radiation, not an 'aether'. I don't think we can use it for measuring a 'absolute' speed, even though it should 'build up' as we accelerate, changing temperature relative us measuring it, although the same can be said of any light measured... You might look at it as a 'frame of reference' that may seem approximately the same 'everywhere' but it's not a 'dimension/aether' 'resisting' motion. Just a form of radiation that seems the same, everywhere we look.

But I've been wondering the same :)
And in a way it seems applicable for measuring at least a relative 'speed', that will give you the approximate same result everywhere, maybe? It's all assumptions as we haven't been 'everywhere' measuring it, sort off. But as good assumptions as we can make it I think

When Einstein thought of 'relative frames' he meant that that there was no frame that you could use as 'the original frame' and even though you might assume that the radiation is the same everywhere, it's never 'at rest'. It's light, mass-less, time-less, without any frame of rest.

The only way to be at rest versus radiation is to become radiation.
Well that's my take for the moment at least :)

Maybe there will be, is, a better answer to your question :)

To prove your 'absolute motion' in the universe you first need to find that 'object' whatever that you can prove to be 'still' relative the universe. I don't think there exist any such 'frames' myself. But for the 'relative speed' CMB, or any light measured, as you accelerates should give you the same sort of blue shift relative the light you measure. So for that kind of 'speed estimate' any light should do (coming from another frame of reference) I think? As long as you're satisfied with measuring the 'energy' relative what you measure that will do very fine, but as for an 'absolute speed' it won't.

« Last Edit: 26/03/2011 22:46:17 by yor_on »
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« Reply #2 on: 08/05/2016 20:31:33 »
Relativity describes the laws of physics, or the rules of the game. The CMB is a player, or an actor on the stage, or a boundary condition. The laws of physics do not define a preferred frame, however the substance (matter & energy) in the universe does--if you think about it, the mass in the universe also defines a center-of-mass.