<blockquote>
  <p>They say that the observable universe is only 5% of the entire
  equation.</p>
</blockquote>

<p>The observable universe and regular matter are different things.</p>

<p><strong>Regular matter</strong> is the stuff that you and I are made of. Besides regular matter, the Universe is made of dark matter and dark energy. According to some estimates, regular matter is indeed only a few percentage points of the "stuff" in the observable universe.</p>

<p><strong>Dark matter</strong> - it's not clear what it is, but it appears to be matter-like and it interacts gravitationally. It does not seem to interact in any other way; it could be shooting right now through your head and you wouldn't know it. It does not make clumps like regular matter, so it tends to stay in a diffuse state. That's all we know about it, everything else is speculation.</p>

<p><strong>Dark energy</strong> is something that drives and accelerates the expansion of the universe but doesn't seem to do anything else. It is not related to dark matter despite both being called "dark". That's all we know about it.</p>

<p><strong>The observable universe</strong> is the chunk of the Universe that we can see: regular matter, dark matter, dark energy, and the space in between. By definition, the observable universe is everything that we could (theoretically) observe or detect. It's basically everything within a radius of a few dozen billion light years measured from the chair you're sitting on.</p>

<p>Anything placed further than that is outside the observable universe and by definition cannot be observed. Not only that, but it cannot influence us in any way whatsoever - if it could, it would be observable.</p>

<blockquote>
  <p>sort of like how galaxies redshift and slowly face away of out
  existence.</p>
</blockquote>

<p>That's a tricky statement.</p>

<p>The universe expands. Things close to us (on a cosmic scale) are drifting away from us slowly. Things far away from us are drifting apart quickly. Things very far are drifting away very quickly.</p>

<p>Keep going like this and there comes a place where things are drifting away from us at light speed. Beyond this threshold there's nothing for us to see anymore. That's the theoretical outer limit of the observable universe. Anything beyond it is outside the observable universe. In practice you can't quite see that far anyway, to be honest, because at those huge distances it's hard to detect anything, and because at those huge distances you only see very old objects which may not be bright enough yet to be seen (before stars are formed).</p>

<p>It is true that once something is out of the observable universe, it's basically as if it doesn't exist anymore. But that's only true from your frame of reference. From their frame of reference they continue to exist just fine. Both frames are correct, BTW. Disagreements like this one are common in relativity.</p>

<p>So don't say they're fading out of existence, because they may get angry at you. :) Simply say they exit the observable universe.</p>

<blockquote>
  <p>does dark matter/energy increase every year?</p>
</blockquote>

<p>Please be aware that anything that gets out of our observable universe, be it regular matter, dark matter, or dark energy, is lost to us forever. The event horizon (outer limit) of the observable universe does not apply only to regular matter, it applies to everything.</p>

<p>That being said, within the observable universe, we don't really know if the relative percentages of regular matter, dark matter, and dark energy are changing a whole lot.</p>

<blockquote>
  <p>What comes after red shift? Black?</p>
</blockquote>

<p>Red shift does not have a limit. The name seems to suggest it stops at red - but really it doesn't. It's just not a perfect name, that's all.</p>

<p>As things move away from you faster and faster and faster, light coming in from there gets "red shifted" - it simply means the wavelength becomes bigger and bigger and bigger. If light starts out in the color blue, "red shift" just means it becomes green, then yellow, orange, red, infrared, microwave, radio waves... just getting stretched out more and more.</p>

<p>At some point the wavelength gets so big it becomes very hard to detect anything.</p>

<blockquote>
  <p>How do you measure something that has already left the observable
  universe?</p>
</blockquote>

<p>You don't. It's out of OU, it's gone. Completely and forever. Just let it go cause it ain't coming back.</p>

<blockquote>
  <p>does that mean the universe is mostly black because 95% of matter has
  "Blackshifted"?</p>
</blockquote>

<p>The universe is mostly black because there's not enough regular matter (stars, more specifically) in the observable universe to light it up fully. It's just a whole lot of empty space - hence dark.</p>

<p>It is true that in the outer parts of the observable universe objects are so red shifted that it's hard to see them anymore. That's one thing.</p>

<p>The other thing is - once objects are so far that they are moving away from us faster than light speed, it is 100% impossible for us to see them, forever. They are completely outside the observable universe.</p>

<p>So, the night sky is dark because the observable universe is not infinite, and because it's mostly empty. This is the solution to <a href="https://en.wikipedia.org/wiki/Olbers&#39;_paradox" rel="nofollow noreferrer">Olbers' paradox</a>.</p>

CC BY-SA 3.0
2017-01-27T21:54:48.810Z
2017-01-27T22:19:09.737Z
2017-01-27T22:19:09.737Z
Florin Andrei
<p>First off, you need to understand what "<a href="https://en.wikipedia.org/wiki/Redshift" rel="nofollow noreferrer">Redshift</a>" is.  Light that is redshifted means that its wavelength has increased, making it appear more red.  This can come from a variety of sources, including Doppler shifting.  What we're more concerned with here is "cosmological redshift".  As light travels through space, its wavelength increases due to the expansion of space.  We can use a measurement of how much the light has redshifted to calculate the distance to its source.  There is nothing "beyond" redshift, because redshift is just a lengthening of the wavelength.  And nothing is happening to the objects themselves, they just appear to get redder to us.</p>

<p>Next, the definition of the "<a href="https://en.wikipedia.org/wiki/Observable_universe" rel="nofollow noreferrer">observable universe</a>".  Because light travels at a finite speed, it takes a certain amount of time to reach us.  The universe had a beginning in the big bang, meaning that light has only had a certain amount of time to travel.  Therefore we can only see things out to a certain distance.  Light coming from objects further than that has not had enough time to reach us yet, so we can't see them.  That's what we mean by the "observable universe".</p>

<p>Galaxies do not "phase out of existence" because of redshift.  As we look outwards, we're looking at older and older objects.  Because the light takes a certain amount of time to reach us, we're essentially looking back in time.  As time passes, however, we can see more and more because light from further away objects has more time to reach us.</p>

<p><a href="https://en.wikipedia.org/wiki/Dark_matter" rel="nofollow noreferrer">Dark matter</a> and <a href="https://en.wikipedia.org/wiki/Dark_energy" rel="nofollow noreferrer">dark energy</a> cannot be directly observed because they do not interact with light.  They do not absorb it, emit it, reflect it, or anything else.  However, they are still within the observable universe, because the observable universe is basically just the size of the universe.  There are many different theories as to what dark matter and dark energy actually are, but they are not ordinary matter that has been "blackshifted".</p>

CC BY-SA 3.0
2017-01-27T19:21:25.087Z
A bit misleading to say redshift is a distance. Redshift is a wavelength (or frequency) shift in light which can *relate* to distance if that redshift is a Doppler redshift. However a gravitational redshift, for example, does not correspond to distance.
zephyr
CC BY-SA 3.0
2017-01-27T19:34:36.737Z
@zephyr, I understand, but when answering a question like this, it's better to over-simplify than to confuse by providing too much information.  And based on the question, it seems like they were more referring to the cosmological distance redshift.
Phiteros
CC BY-SA 3.0
2017-01-27T20:21:56.823Z
Yes, I agree simplification is good in cases like this, but what you've put is blatantly wrong. Redshift is *not* a measurement of distance. Certain types of redshift (and I now see I mistakenly said it was Dopper when really it is Cosmological) can be used to infer distance if you know other information, but it is wrong to state redshift measures distance. No point in making the topic more confusing by saying half-truths.
zephyr
CC BY-SA 3.0
2017-01-27T20:25:39.643Z
@zephyr In cosmology, we generally refer to redshift as a measure of distance; we say that an object lies at, say, a redshift of 5.  In cosmology, that's the main use of redshift; doppler redshift is not really used.  This redshift value can be readily and easily converted into a distance, so cosmologists just use redshift as distance.
Phiteros
CC BY-SA 3.0
2017-01-27T20:26:41.473Z
@zephyr I added a small clarification that I am specifically referring to cosmological redshift.
Phiteros
CC BY-SA 3.0
2017-01-27T20:38:25.543Z
I know that astronomers use redshift to refer to distance, but my point is that that is technically wrong. If you say to another astronomer, this galaxy is at a distance of z=5, they'll know what you mean. But this is a bad habit of scientists. They say things which are technically wrong, but other scientists know what they mean so they let it slide. You have to be very careful to not use those technically wrong statements when teaching someone inexperienced. Redshift is *not* measure of distance, even in cosmology. It is a measure of a wavelength shift.
zephyr
CC BY-SA 3.0
2017-01-27T21:17:33.853Z
@zephyr Okay, I've edited my answer to make it more specific.
Phiteros
CC BY-SA 3.0
2017-01-27T21:29:02.657Z
Great answer by the way. Didn't mean to give you a hard time, just wanted the best answer for OP.
zephyr
CC BY-SA 3.0
2017-01-27T19:03:55.607Z
2017-01-27T21:16:16.523Z
2017-01-27T21:16:16.523Z
Phiteros
<p>They say that the observable universe is only 5% of the entire equation. The rest of it consists of dark matter and energy. I believe that they are trying to find a way to see something that cannot be seen due to being outside of the observable universe, sort of like how galaxies redshift and slowly face away of out existence. </p>

<p>tl;dr  does dark matter/energy increase every year?</p>

<p>What comes after red shift? Black? If so, then does that mean the universe is mostly black because 95% of matter has "Blackshifted"?</p>

<p>Did I post a question correctly?</p>

CC BY-SA 3.0
2017-01-27T18:04:42.737Z
You're question shows a basic misunderstanding of the fundamental concepts of astronomy. I think you should probably go back a re-read on these topics to be sure you really understand them, then come back with new questions. For example, asking what comes after red shift shows you don't fully understand what red-shifting actually is. Or proposing we cannot see dark matter/energy because it is outside the observable universe indicates you need to read more about these topics.
zephyr
CC BY-SA 3.0
2017-01-27T18:08:05.523Z
You could have just told me what comes after redshift...  If you don't call what is outside the oberservable universe dark matter/energy then what else would it be?
user29434
CC BY-SA 3.0
2017-01-27T18:16:54.150Z
This is my point. Nothing comes after redshift. Redshift is not a thing that something can come after. You have a misunderstanding of what redshift actually is (and dark matter/energy too).
zephyr
CC BY-SA 3.0
2017-01-27T18:31:34.273Z
@zephyr Huh? That doesn't make sense. If light is getting stretched out it doesn't just become nothing. If that's true then you might as well say something is nothing because clearly the sound of a police siren doesn't disappear just because you don't hear it anymore so... What you are saying doesn't make sense. My misunderstanding comes from this contradiction.
user29434
CC BY-SA 3.0
2017-01-28T14:06:31.693Z
There seems to be at least five questions here: "How do you measure something that has left the observable universe? Does dark matter increase? Does dark energy increase. What is after redshift? Is dark matter blackshifted matter." Please ask only one question at a time otherwise this is "too broad". The first two are reasonable (but apparently based on a misconception). The second are unclear, to me. I suggest you try doing some background reading on dark matter first.
James K
<dark-energy><observable-universe>
How do you measure something that has already left the observable universe?
user29434
# How do you measure something that has already left the observable universe?

(Asked by: username_0 on 2017-01-27)

They say that the observable universe is only 5% of the entire equation. The rest of it consists of dark matter and energy. I believe that they are trying to find a way to see something that cannot be seen due to being outside of the observable universe, sort of like how galaxies redshift and slowly face away of out existence.

tl;dr does dark matter/energy increase every year?

What comes after red shift? Black? If so, then does that mean the universe is mostly black because 95% of matter has "Blackshifted"?

Did I post a question correctly?

**Tags:** dark-energy, observable-universe
> **Comments:**
> **username_1**: You're question shows a basic misunderstanding of the fundamental concepts of astronomy. I think you should probably go back a re-read on these topics to be sure you really understand them, then come back with new questions. For example, asking what comes after red shift shows you don't fully understand what red-shifting actually is. Or proposing we cannot see dark matter/energy because it is outside the observable universe indicates you need to read more about these topics.  
> **username_0**: You could have just told me what comes after redshift...  If you don't call what is outside the oberservable universe dark matter/energy then what else would it be?  
> **username_1**: This is my point. Nothing comes after redshift. Redshift is not a thing that something can come after. You have a misunderstanding of what redshift actually is (and dark matter/energy too).  
> **username_0**: @zephyr Huh? That doesn't make sense. If light is getting stretched out it doesn't just become nothing. If that's true then you might as well say something is nothing because clearly the sound of a police siren doesn't disappear just because you don't hear it anymore so... What you are saying doesn't make sense. My misunderstanding comes from this contradiction.  
> **username_2**: There seems to be at least five questions here: "How do you measure something that has left the observable universe? Does dark matter increase? Does dark energy increase. What is after redshift? Is dark matter blackshifted matter." Please ask only one question at a time otherwise this is "too broad". The first two are reasonable (but apparently based on a misconception). The second are unclear, to me. I suggest you try doing some background reading on dark matter first.  

---

## 2 answers

### Answer by username_3 on 2017-01-27. Score: 3

> They say that the observable universe is only 5% of the entire
> equation.

The observable universe and regular matter are different things.

**Regular matter** is the stuff that you and I are made of. Besides regular matter, the Universe is made of dark matter and dark energy. According to some estimates, regular matter is indeed only a few percentage points of the "stuff" in the observable universe.

**Dark matter** - it's not clear what it is, but it appears to be matter-like and it interacts gravitationally. It does not seem to interact in any other way; it could be shooting right now through your head and you wouldn't know it. It does not make clumps like regular matter, so it tends to stay in a diffuse state. That's all we know about it, everything else is speculation.

**Dark energy** is something that drives and accelerates the expansion of the universe but doesn't seem to do anything else. It is not related to dark matter despite both being called "dark". That's all we know about it.

**The observable universe** is the chunk of the Universe that we can see: regular matter, dark matter, dark energy, and the space in between. By definition, the observable universe is everything that we could (theoretically) observe or detect. It's basically everything within a radius of a few dozen billion light years measured from the chair you're sitting on.

Anything placed further than that is outside the observable universe and by definition cannot be observed. Not only that, but it cannot influence us in any way whatsoever - if it could, it would be observable.

> sort of like how galaxies redshift and slowly face away of out
> existence.

That's a tricky statement.

The universe expands. Things close to us (on a cosmic scale) are drifting away from us slowly. Things far away from us are drifting apart quickly. Things very far are drifting away very quickly.

Keep going like this and there comes a place where things are drifting away from us at light speed. Beyond this threshold there's nothing for us to see anymore. That's the theoretical outer limit of the observable universe. Anything beyond it is outside the observable universe. In practice you can't quite see that far anyway, to be honest, because at those huge distances it's hard to detect anything, and because at those huge distances you only see very old objects which may not be bright enough yet to be seen (before stars are formed).

It is true that once something is out of the observable universe, it's basically as if it doesn't exist anymore. But that's only true from your frame of reference. From their frame of reference they continue to exist just fine. Both frames are correct, BTW. Disagreements like this one are common in relativity.

So don't say they're fading out of existence, because they may get angry at you. :) Simply say they exit the observable universe.

> does dark matter/energy increase every year?

Please be aware that anything that gets out of our observable universe, be it regular matter, dark matter, or dark energy, is lost to us forever. The event horizon (outer limit) of the observable universe does not apply only to regular matter, it applies to everything.

That being said, within the observable universe, we don't really know if the relative percentages of regular matter, dark matter, and dark energy are changing a whole lot.

> What comes after red shift? Black?

Red shift does not have a limit. The name seems to suggest it stops at red - but really it doesn't. It's just not a perfect name, that's all.

As things move away from you faster and faster and faster, light coming in from there gets "red shifted" - it simply means the wavelength becomes bigger and bigger and bigger. If light starts out in the color blue, "red shift" just means it becomes green, then yellow, orange, red, infrared, microwave, radio waves... just getting stretched out more and more.

At some point the wavelength gets so big it becomes very hard to detect anything.

> How do you measure something that has already left the observable
> universe?

You don't. It's out of OU, it's gone. Completely and forever. Just let it go cause it ain't coming back.

> does that mean the universe is mostly black because 95% of matter has
> "Blackshifted"?

The universe is mostly black because there's not enough regular matter (stars, more specifically) in the observable universe to light it up fully. It's just a whole lot of empty space - hence dark.

It is true that in the outer parts of the observable universe objects are so red shifted that it's hard to see them anymore. That's one thing.

The other thing is - once objects are so far that they are moving away from us faster than light speed, it is 100% impossible for us to see them, forever. They are completely outside the observable universe.

So, the night sky is dark because the observable universe is not infinite, and because it's mostly empty. This is the solution to [Olbers' paradox](https://en.wikipedia.org/wiki/Olbers'_paradox).


---

### Answer by username_4 on 2017-01-27. Score: 3

First off, you need to understand what "[Redshift](https://en.wikipedia.org/wiki/Redshift)" is. Light that is redshifted means that its wavelength has increased, making it appear more red. This can come from a variety of sources, including Doppler shifting. What we're more concerned with here is "cosmological redshift". As light travels through space, its wavelength increases due to the expansion of space. We can use a measurement of how much the light has redshifted to calculate the distance to its source. There is nothing "beyond" redshift, because redshift is just a lengthening of the wavelength. And nothing is happening to the objects themselves, they just appear to get redder to us.

Next, the definition of the "[observable universe](https://en.wikipedia.org/wiki/Observable_universe)". Because light travels at a finite speed, it takes a certain amount of time to reach us. The universe had a beginning in the big bang, meaning that light has only had a certain amount of time to travel. Therefore we can only see things out to a certain distance. Light coming from objects further than that has not had enough time to reach us yet, so we can't see them. That's what we mean by the "observable universe".

Galaxies do not "phase out of existence" because of redshift. As we look outwards, we're looking at older and older objects. Because the light takes a certain amount of time to reach us, we're essentially looking back in time. As time passes, however, we can see more and more because light from further away objects has more time to reach us.

[Dark matter](https://en.wikipedia.org/wiki/Dark_matter) and [dark energy](https://en.wikipedia.org/wiki/Dark_energy) cannot be directly observed because they do not interact with light. They do not absorb it, emit it, reflect it, or anything else. However, they are still within the observable universe, because the observable universe is basically just the size of the universe. There are many different theories as to what dark matter and dark energy actually are, but they are not ordinary matter that has been "blackshifted".

> **Comments:**
> **username_1**: A bit misleading to say redshift is a distance. Redshift is a wavelength (or frequency) shift in light which can *relate* to distance if that redshift is a Doppler redshift. However a gravitational redshift, for example, does not correspond to distance.  
> **username_4**: @zephyr, I understand, but when answering a question like this, it's better to over-simplify than to confuse by providing too much information.  And based on the question, it seems like they were more referring to the cosmological distance redshift.  
> **username_1**: Yes, I agree simplification is good in cases like this, but what you've put is blatantly wrong. Redshift is *not* a measurement of distance. Certain types of redshift (and I now see I mistakenly said it was Dopper when really it is Cosmological) can be used to infer distance if you know other information, but it is wrong to state redshift measures distance. No point in making the topic more confusing by saying half-truths.  
> **username_4**: @zephyr In cosmology, we generally refer to redshift as a measure of distance; we say that an object lies at, say, a redshift of 5.  In cosmology, that's the main use of redshift; doppler redshift is not really used.  This redshift value can be readily and easily converted into a distance, so cosmologists just use redshift as distance.  
> **username_4**: @zephyr I added a small clarification that I am specifically referring to cosmological redshift.  
> **username_1**: I know that astronomers use redshift to refer to distance, but my point is that that is technically wrong. If you say to another astronomer, this galaxy is at a distance of z=5, they'll know what you mean. But this is a bad habit of scientists. They say things which are technically wrong, but other scientists know what they mean so they let it slide. You have to be very careful to not use those technically wrong statements when teaching someone inexperienced. Redshift is *not* measure of distance, even in cosmology. It is a measure of a wavelength shift.  
> **username_4**: @zephyr Okay, I've edited my answer to make it more specific.  
> **username_1**: Great answer by the way. Didn't mean to give you a hard time, just wanted the best answer for OP.  

---

