Conceptual problem

Relativity theory asserts that there is no preferred frame of reference.

But...

What else is the Cosmic Microwave Background (CMB) radiation?

Doesn't this radiation give an universal frame of reference of a
frame that will be always at rest by definition?

If I accelerate in some direction, the CMB will be bluer in that
direction and redder in the opposite direction isn't it?

So I can detect movement respective to that absolute frame
of reference...

Where do I go wrong?

Thanks in advance for your help.

[Mod. note: that's not what 'preferred' means; local physics is not
different in a frame at rest wrt the CMB. This is a FAQ, see
http://www.astro.ubc.ca/people/scott/faq_basic.html -- mjh]

--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

jacob navia wrote:
Relativity theory asserts that there is no preferred frame of reference.

But...

What else is the Cosmic Microwave Background (CMB) radiation?

Doesn't this radiation give an universal frame of reference of a
frame that will be always at rest by definition?

Others have responded, but let me add a couple of points. There are
two terms in your question that are ambiguous: "preferred" and
"reference frame."

Let's start with the second. Normally, a when people use the term
"reference frame" they have in mind several features. One of these
is that if observer A is at rest relative to a reference frame, and if
observer B is at rest relative to the same frame, then observer A is
at rest relative to observer B. For the CMBR frame, this is not the
case: two observers at different locations, each at rest relative to
the CMBR, will *not* be at rest relative to each other, but instead
will observe the distance separating them to increase with time.

So if you take this as part of the definition of a reference frame, the
CMBR provides only a *local* reference frame. This it does. But so,
in my office, do the walls of the room -- I can certainly tell whether
I am at rest or moving with respect to them. To be "preferred," a
reference frame would have to have some interaction with the laws
of physics: the laws would have to be different (presumably simpler)
when described in terms of the preferred frame than when described
in terms of other frames. This is not the case for the CMBR frame,
any more than it is for the walls of my office.

Steve Carlip