Are galaxies moving faster than the speed of light?

[Drakkith]

So I was thinking...if an object is moving THROUGH space, as opposed to WITH space, then wouldn't the CMB be noticeably anisotropic?

 

[alexg]

So I was thinking...if an object is moving THROUGH space, as opposed to WITH space, then wouldn't the CMB be noticeably anisotropic?

It is. The temperature variations are small, but they're there.

http://www.astro.ucla.edu/~wright/CMB-DT.html

Yea, 100 posts.

 

[phinds]

So I was thinking...if an object is moving THROUGH space, as opposed to WITH space, then wouldn't the CMB be noticeably anisotropic?

The anisotropy of the CMB is tiny because the motion THROUGH space is tiny. A MUCH larger effect would be due to the fact that areas that we see as CMB could only have been in casual distance of each other (and thus be at very nearly the same temperature) if it is true that there was this incredible inflation that occurred from (I forget the exact figures) something like 1E-47 to 1E-33 after the singularity when the universe expanded by a factor of something like 10E80. All very incomprehensible stuff to me but if you posit it as real then it DOES explain a number of things including what would otherwise be an unexplainably tiny anisotropy of the CMB.

 

[bapowell]

There is a relatively large anisotropy that results from our motion through space relative to the CMB -- it's called the CMB dipole. Higher-order anisotropies, however, are independent of our motion and result from primordial inhomogeneities. These are the ones that we study to understand the composition and evolution of the universe; the dipole is ignored.

Is this what you had in mind Drakkith?

 

[Chalnoth]

So I was thinking...if an object is moving THROUGH space, as opposed to WITH space, then wouldn't the CMB be noticeably anisotropic?

Others have provided good answers here, but I thought I'd add in a little caveat.

There is no absolute distinction between moving "through" or "with" space. Space itself has no absolute motion. The CMB rest frame is only a convenient choice of rest frame when doing cosmology. It is not an absolute frame.

Interestingly, the movement of galaxy clusters with respect to the CMB changes how the cloud of hot gas within those clusters interacts with the CMB. So we can, in principle, measure the movement of these galaxies with respect to the CMB simply by examining their brightness. In practice this is fantastically difficult because it turns out that the spectrum of this deviation in brightness is exactly the spectrum of the CMB itself, so I'm not sure that we've ever had a confirmed example of the kinetic SZ effect (that's the name of this effect).

 

[Drakkith]

Awesome, thanks all.

 

[RUTA]

Others have provided good answers here, but I thought I'd add in a little caveat.

There is no absolute distinction between moving "through" or "with" space. Space itself has no absolute motion. The CMB rest frame is only a convenient choice of rest frame when doing cosmology. It is not an absolute frame.

Interestingly, the movement of galaxy clusters with respect to the CMB changes how the cloud of hot gas within those clusters interacts with the CMB. So we can, in principle, measure the movement of these galaxies with respect to the CMB simply by examining their brightness. In practice this is fantastically difficult because it turns out that the spectrum of this deviation in brightness is exactly the spectrum of the CMB itself, so I'm not sure that we've ever had a confirmed example of the kinetic SZ effect (that's the name of this effect).

http://www.spacedaily.com/reports/D...niverse_formation_into_sharper_focus_999.html

 

[Chalnoth]

http://www.spacedaily.com/reports/D...niverse_formation_into_sharper_focus_999.html

Ahh, interesting. Here is the source paper, in case anybody is interested:
http://arxiv.org/abs/1203.4219

The detection at 3.8 sigma isn't that significant for a new detection, but it does seem fairly likely to be correct.

 

[phinds]

There is no absolute distinction between moving "through" or "with" space. Space itself has no absolute motion.

Point taken. I use "with space" to discuss the motion of distant galaxies that recede due to the "dark energy" accelerating expansion, even though I realize that it is more appropriate to just say that they are getting farther apart, not "moving with space".

 

[Krunchyman]

The fact that galaxies move faster than the speed of light is the reason why we could potentially use hypothetical Alcubierre drives to accelerate objects faster than light speed.

 

[Chalnoth]

The fact that galaxies move faster than the speed of light is the reason why we could potentially use hypothetical Alcubierre drives to accelerate objects faster than light speed.

Doesn't work. No galaxy moves faster than a light ray moving past it. Nothing can.

 

[phinds]

The fact that galaxies move faster than the speed of light is the reason why we could potentially use hypothetical Alcubierre drives to accelerate objects faster than light speed.

Nonsense. You would be well served to study some physics before making such statements.