Light Speed & Expanding Galaxies: A Cosmological Mystery

In summary: Keep in mind that the galaxies themselves cannot exceed the 186,000 speed limit. It's the space between galactic clusters that is expanding at that velocity and beyond and thus creating insurmountable distances between us and them and making their present light forever undetectable for us. In summary, galaxies are not expanding, but space between them is expanding at a faster speed, and this is why some galaxies are currently unobservable.
  • #1
binbots
170
3
If galaxies aer expanding fast than the speed of light how are we able to see them. At the moment this expansion surpassed the speed of light shouldn't these galaxies dissappear or remain unchanged visually?
 
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  • #2
Galaxies are not expanding.

Do you mean moving away from us due to the expansion of the universe? You can see galaxies that appear to be moving away from us faster than the speed of light for much the same reason you can hear an object moving away from you faster than the speed of sound. The speed of light is not dependent on the speed of the moving galaxy.

There is a limit, though, based on the universe expanding so fast the distance is increasing faster than the light moves.
 
  • #3
binbots said:
If galaxies aer expanding fast than the speed of light how are we able to see them. At the moment this expansion surpassed the speed of light shouldn't these galaxies disappear or remain unchanged visually?

Certain galaxies might be presently unobservable because they are receding from us at faster than light speed due to cosmological expansion. But the light of others might still be streaming on its way toward us and so we see them as they were prior to reaching that superluminal velocity. Keep in mind that the galaxies themselves cannot exceed the 186,000 speed limit. It's the space between galactic clusters that is expanding at that velocity and beyond and thus creating insurmountable distances between us and them and making their present light forever undetectable for us.

Also, we are talking about areas of space where gravity doesn't cancel out cosmological expansion.
Galactic clusters containing from as few dozen to millions of galaxies are not internally affected by that expansion. In fact, within these clusters, galaxies collide and merge. Some. like our Magellanic clouds which orbit our Milky Way are satellites of other galaxies. Andromeda, the largest member of our own galactic cluster is presently approaching us and seems destined to collide with our our galaxy in the far future. The the distancing is between super clusters of galaxies where gravity cannot predominate.

BTW
By unobservable I mean that the light being emitted by them now will never reach us.
 
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  • #4
Receeding galaxies merely redshift into obscurity, they will never suddenly 'disapperar' from view.
 
  • #5
so they will eventually fade away?
 
  • #6
Yes, according to current models.
 

1. What is the speed of light?

The speed of light is a fundamental constant in physics, denoted by the symbol "c". In a vacuum, it has a fixed value of approximately 299,792,458 meters per second (m/s).

2. How does the speed of light impact our understanding of the universe?

The speed of light is a crucial factor in understanding the size and age of the universe. It is the fastest possible speed in the universe and plays a role in the concept of time dilation, which affects how we perceive time in different areas of the universe.

3. What is the expansion of the universe and how does it relate to light speed?

The expansion of the universe refers to the continuous growth of the space between galaxies. This expansion has been observed by scientists and is thought to be accelerating. The speed of light is a limiting factor in how far we can see into the expanding universe, as light can only travel a certain distance in a given amount of time.

4. How is the speed of light related to the Big Bang theory?

The Big Bang theory proposes that the universe began as a singularity and has been expanding ever since. The speed of light plays a crucial role in this theory, as it is thought that in the early stages of the universe, the expansion was so rapid that light could not keep up, leading to the formation of the observable universe we see today.

5. Can the speed of light be surpassed?

According to our current understanding of physics, the speed of light is the maximum speed at which anything can travel in the universe. It is considered a fundamental constant and has been consistently observed and measured to be the same in all frames of reference. However, there are ongoing scientific research and theories exploring the possibility of faster-than-light travel, but it remains a mystery and a subject of debate.

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