The discussion centers on the effects of cosmic background radiation (CMBR) frequency shifts when a spaceship travels near the speed of light. It is established that the CMBR experiences blue-shifting to x-rays and gamma rays due to relativistic effects. The conversation highlights that the Earth, the Milky Way, and the local group of galaxies are not comoving with the CMBR, as evidenced by the observed anisotropy of the CMB. The velocities of the Earth relative to the CMBR (approximately 627 km/sec) and the Sun (about 30 km/sec) are noted, emphasizing that waiting for a moment of rest relative to the CMBR is not feasible.
PREREQUISITESAstronomers, physicists, and students of cosmology interested in the implications of relativistic travel and cosmic background radiation effects on interstellar navigation and understanding the universe's structure.
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?