Cosmic microwave background and a reference frame

[BarbaraDav]

Dear Friends

A fleet of spaceships is given, each equipped with a differential microwave radiometer,
just like COBE was, whose detectors are antipodeanly pointing (this way one should catch
blue shifted radiation and the other one red shifted). Could their acquisitions be used to
establish a reference frame locally (!) motionless respect the cosmic microwave background ?
Supposing a such reference frame does exist, is there any reason to think it's an inertial one ?

Best wishes.

Barbara Da Vinci
Rome

 

[Dale]

A fleet of spaceships is given, each equipped with a differential microwave radiometer,
just like COBE was, whose detectors are antipodeanly pointing (this way one should catch
blue shifted radiation and the other one red shifted). Could their acquisitions be used to
establish a reference frame locally (!) motionless respect the cosmic microwave background ?

Yes.

Supposing a such reference frame does exist, is there any reason to think it's an inertial one ?

Well, in GR the idea of inertial and non-inertial reference frames doesn't really exist any more.

 

[Mentz114]

is there any reason to think it's an inertial one ?

Interesting. The nearest thing to an inertial frame in GR is a freely-falling frame. If one of your ships should adjust itself to be stationary in the CBR frame, and can maintain that without using its engines then for that ship the CBR frame may be inertial.

In other words, if the CBR frame coincides with the local FF frame, then it is inertial. Because of the irregular distribution of matter in the local universe, it's not likely to happen. Perhaps in one of the great voids where all matter is very, very far away, this coincidence would be more likely.

 

[BarbaraDav]

Please, what's "FF frame" ?

 

[Dale]

local FF = "local free falling" (i.e. a local frame centered on an inertial observer)

 

[BarbaraDav]

I see. Thanks !