The discussion revolves around the effects of traveling near the speed of light on cosmic background radiation (CMBR), particularly focusing on the potential blue-shifting of the radiation and implications for motion relative to the CMBR. The scope includes theoretical considerations, implications for interstellar travel, and the nature of reference frames in physics.
Participants express multiple competing views regarding the implications of CMBR behavior and the concept of preferred frames of reference. The discussion remains unresolved on several points, particularly regarding the interpretation of anisotropy and the implications for motion through space.
There are limitations in the discussion, including assumptions about the nature of comoving bodies and the implications of velocities relative to the CMBR. The discussion also reflects a dependence on definitions of terms such as "preferred frame" and "anisotropy."
Does this mean we're not either?PAllen said:It is also how we know that the sun is not a comoving body. We see anisotropy of the CMB. Modeling earth’s motion around the sun, we know that the sun would not see CMB isotropy. Nor would the milky way galaxy as a whole. Nor would the local group of galaxies.
Of course. I thought that was too obvious to state, e.g. if the milky way was comoving, the Earth could not be. Actually I said we, on earth, see anisotropy. That, by definition, means we are not comoving.Grasshopper said:Does this mean we're not either?
Yes.Grasshopper said:Does this mean we're not either?
Google said:about 627 km/sec
PAllen said:Of course. I thought that was too obvious to state, e.g. if the milky way was comoving, the Earth could not be. Actually I said we, on earth, see anisotropy. That, by definition, means we are not comoving.
[post originally said isotropy instead of anisotropy]
Good. Because that would be an insane coincidence.jbriggs444 said:Yes.
One can Google (one moment while I do). "speed of Earth relative to cmb" and get an answer ofEdit: One can also Google for "speed of Earth relative to sun in km/s" and see that our velocity with respect to the sun is only about 30 km/sec. So no, we can't just wait six months and wind up momentarily at rest relative to the CMBR. Our velocity relative to the Milky Way is only about 220 km/sec. So we can't wait for half of a galactic year (100 million years or so) and expect that to work either.
"Preferred" in the sense of being picked out by a particular symmetry in the distribution of stress-energy, yes.David Lewis said:If the wavelength of background microwave radiation is the same in all directions, does that imply a preferred frame of reference?
Like the local rest frame of the surface of the Earth is a preferred frame for Earthbound physics, yes. The formulae are the same in any frame, but terms often simplify or drop out in the frame where most of the mass is at rest.David Lewis said:If the wavelength of background microwave radiation is the same in all directions, does that imply a preferred frame of reference?