Re: Microwave Background Radiation as an absolute frame of reference.

Date: Sun Sep 12 23:27:28 1999
Posted By: Steven Levin, Research Scientist, Astrophysics
Area of science: Astronomy
ID: 933884757.As

Message:

Hi,

The Cosmic Microwave Background radiation (I'll call it CMB from now on) can certainly serve as a frame of reference. As you suggest, we can observe the CMB, and assuming it is uniform, determine our motion relative to it. This measurement has actually been done (see http://aether.lbl.gov/www/science/cmb.html), and we find that the CMB appears about 0.1 % brighter than average in one direction, and about 0.1 % dimmer in the opposite direction. The usual way to interpret this is to take it as an indication that the Sun (and the Earth along with it) is moving relative to the CMB, towards the "bright" direction and away from the "dim" direction. There is, however no way to disprove the possibility that the CMB is simply brighter in one direction than the other. This gets to the heart of your question. The CMB can very definitely be used as a frame of reference, but is it an *absolute* frame of reference ? It certainly seems like a reasonable assumption to treat it that way, and it makes the description of the Universe simpler, but it's still only an assumption.

You can find a lot more interesting stuff about the CMB at these and other web sites:

http://map.gsfc.nasa.gov

http://www.gsfc.nasa.gov/astro/cobe/cobe_home.html

http://aether.lbl.gov

http://astro.estec.esa.nl/SA-general/Projects/

I hope this helps, and I apologize for taking so long to respond. Steve Levin

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DISCLAIMER: Just because I work for JPL/NASA/Caltech doesn't mean anything I say is in any way official. This is just me talking, not NASA, JPL, or Caltech.

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