Are galaxies moving faster than the speed of light?

In summary, it has been noted through the Doppler Effect that some of the furthest galaxies seem to be moving away from us faster than the speed of light. However, because relativity forbids objects from moving through spacetime faster than light, this is only apparent. If we were to move at the speed of light, time would be zero and >c time would be <0. Therefore, going 'backwards in time' is an option.
  • #36
So I was thinking...if an object is moving THROUGH space, as opposed to WITH space, then wouldn't the CMB be noticeably anisotropic?
 
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  • #37
Drakkith said:
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.
 
  • #38
Drakkith said:
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.
 
  • #39
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?
 
  • #40
Drakkith said:
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).
 
  • #41
Awesome, thanks all.
 
  • #42
Chalnoth said:
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
 
  • #44
Chalnoth said:
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".
 
  • #45
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.
 
  • #46
Krunchyman said:
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.
 
  • #47
Krunchyman said:
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.
 
<h2>1. What is the speed of light?</h2><p>The speed of light is a fundamental constant in physics, denoted by the letter "c". It is approximately 299,792,458 meters per second in a vacuum.</p><h2>2. Can anything travel faster than the speed of light?</h2><p>According to the theory of relativity, nothing can travel faster than the speed of light. This is a fundamental principle in physics and has been supported by numerous experiments and observations.</p><h2>3. How do we measure the speed of galaxies?</h2><p>The speed of galaxies can be measured using the Doppler effect, which is the change in frequency or wavelength of a wave due to the relative motion between the source and observer. By measuring the redshift or blueshift of light emitted from galaxies, we can determine their speed and direction of motion.</p><h2>4. Are galaxies really moving faster than the speed of light?</h2><p>No, galaxies are not moving faster than the speed of light. The expansion of the universe is causing the space between galaxies to stretch, which can make it appear as though they are moving faster than the speed of light. However, this does not violate the principle that nothing can travel faster than the speed of light.</p><h2>5. What implications does this have for the future of the universe?</h2><p>The fact that galaxies appear to be moving away from each other at speeds faster than the speed of light suggests that the expansion of the universe is accelerating. This has implications for the future of the universe, as it may continue to expand indefinitely and eventually lead to a "heat death" where all matter and energy are evenly distributed and no longer able to sustain life.</p>

1. What is the speed of light?

The speed of light is a fundamental constant in physics, denoted by the letter "c". It is approximately 299,792,458 meters per second in a vacuum.

2. Can anything travel faster than the speed of light?

According to the theory of relativity, nothing can travel faster than the speed of light. This is a fundamental principle in physics and has been supported by numerous experiments and observations.

3. How do we measure the speed of galaxies?

The speed of galaxies can be measured using the Doppler effect, which is the change in frequency or wavelength of a wave due to the relative motion between the source and observer. By measuring the redshift or blueshift of light emitted from galaxies, we can determine their speed and direction of motion.

4. Are galaxies really moving faster than the speed of light?

No, galaxies are not moving faster than the speed of light. The expansion of the universe is causing the space between galaxies to stretch, which can make it appear as though they are moving faster than the speed of light. However, this does not violate the principle that nothing can travel faster than the speed of light.

5. What implications does this have for the future of the universe?

The fact that galaxies appear to be moving away from each other at speeds faster than the speed of light suggests that the expansion of the universe is accelerating. This has implications for the future of the universe, as it may continue to expand indefinitely and eventually lead to a "heat death" where all matter and energy are evenly distributed and no longer able to sustain life.

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