<blockquote>
  <p>It is said that due to the CMB radiation our universe has been expanding?</p>
</blockquote>

<p>No. It's the the other way round. The CMB is the result of the expansion of space. In the initial stages after the birth of the universe, there was hot plasma everywhere and light could not travel much farther. The universe was opaque at that time. But slowly as the Universe cooled and atoms began to form, light could travel farther. This light got redshifted due to the expansion of space and can be now detected as the CMB radiation. It's in the microwave region of the spectrum and just above absolute zero(about 2.7 K). </p>

<blockquote>
  <p>What do we mean by Dark Energy?</p>
</blockquote>

<p>After Hubble's discovery, we came to the conclusion that the Universe is expanding. We expected the expansion to slow down as time progresses but what we observed as that the expansion was accelerating and is still doing so. Physicists and cosmologists did not have any explanations for this and so it was named "Dark Energy". Dark in the sense that it is unknown.</p>

CC BY-SA 3.0
2014-08-07T02:42:24.780Z
Actually, the Universe's expansion is accelerating *NOW*. It was not always like this. We are now in a period of accelerated expansion.
Py-ser
CC BY-SA 3.0
2014-08-08T15:00:15.523Z
Welcome! If you want to know more about modern cosmology, see [this](http://www.amazon.com/Introduction-Modern-Cosmology-Andrew-Liddle/dp/0470848359/ref=sr_1_1?ie=UTF8&qid=1407509779&sr=8-1&keywords=an+introduction+to+modern+cosmology+andrew) book and if you are looking for an easy to understand book see [A Brief History of Time](http://www.amazon.com/Brief-History-Time-Stephen-Hawking/dp/0553380168/ref=sr_1_1?s=books&ie=UTF8&qid=1407509931&sr=1-1&keywords=a+brief+history+of+time) by Stephen Hawking.
Yashbhatt
CC BY-SA 3.0
2014-08-08T15:01:52.183Z
@Py-ser What evidence do we have that the expansion was not accelerating just after the Big Bang?
Yashbhatt
CC BY-SA 3.0
2014-08-10T07:20:34.090Z
@user52076 If you are satisfied, please think about accepting the given answer.
Arne
CC BY-SA 3.0
2014-08-11T06:39:31.197Z
@Yashbhatt, I think it is uniquely observational:  [link](http://www.guidetothecosmos.com/images/Newsletter_AccelUnivNobel-lores.jpg).
Py-ser
CC BY-SA 3.0
2014-08-14T17:40:45.700Z
@Py-ser So, dark energy comes into play after the expansion had hit the lowest point?
Yashbhatt
CC BY-SA 3.0
2014-08-15T01:47:19.093Z
@Yashbhatt, I don't think it is correct to state it this way, but yes, observationally speaking dark energy starts to rule in the "modern" Universe. I guess, it is a matter of balance among the energy contributions from Friedmann equations.
Py-ser
CC BY-SA 3.0
2014-08-06T10:24:30.897Z
2014-08-06T10:24:30.897Z
Yashbhatt
<p>It is said that due to CMB radiation our universe has been expanding? Firstly what lead the universe to expand? What do scientists mean by dark energy? Will energy convert into matter?</p>

<universe><expansion><cosmic-microwave-background>
What is CMB radiation doing to the universe?
user52076
# What is CMB radiation doing to the universe?

(Asked by: username_0 on 2014-08-06)

It is said that due to CMB radiation our universe has been expanding? Firstly what lead the universe to expand? What do scientists mean by dark energy? Will energy convert into matter?

**Tags:** universe, expansion, cosmic-microwave-background


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## 1 answers

### Answer by username_1 on 2014-08-06. Score: 3

> It is said that due to the CMB radiation our universe has been expanding?

No. It's the the other way round. The CMB is the result of the expansion of space. In the initial stages after the birth of the universe, there was hot plasma everywhere and light could not travel much farther. The universe was opaque at that time. But slowly as the Universe cooled and atoms began to form, light could travel farther. This light got redshifted due to the expansion of space and can be now detected as the CMB radiation. It's in the microwave region of the spectrum and just above absolute zero(about 2.7 K).

> What do we mean by Dark Energy?

After Hubble's discovery, we came to the conclusion that the Universe is expanding. We expected the expansion to slow down as time progresses but what we observed as that the expansion was accelerating and is still doing so. Physicists and cosmologists did not have any explanations for this and so it was named "Dark Energy". Dark in the sense that it is unknown.

> **Comments:**
> **username_2**: Actually, the Universe's expansion is accelerating *NOW*. It was not always like this. We are now in a period of accelerated expansion.  
> **username_1**: Welcome! If you want to know more about modern cosmology, see [this](http://www.amazon.com/Introduction-Modern-Cosmology-Andrew-Liddle/dp/0470848359/ref=sr_1_1?ie=UTF8&qid=1407509779&sr=8-1&keywords=an+introduction+to+modern+cosmology+andrew) book and if you are looking for an easy to understand book see [A Brief History of Time](http://www.amazon.com/Brief-History-Time-Stephen-Hawking/dp/0553380168/ref=sr_1_1?s=books&ie=UTF8&qid=1407509931&sr=1-1&keywords=a+brief+history+of+time) by Stephen Hawking.  
> **username_1**: @username_2 What evidence do we have that the expansion was not accelerating just after the Big Bang?  
> **username_3**: @username_0 If you are satisfied, please think about accepting the given answer.  
> **username_2**: @username_1, I think it is uniquely observational:  [link](http://www.guidetothecosmos.com/images/Newsletter_AccelUnivNobel-lores.jpg).  
> **username_1**: @username_2 So, dark energy comes into play after the expansion had hit the lowest point?  
> **username_2**: @username_1, I don't think it is correct to state it this way, but yes, observationally speaking dark energy starts to rule in the "modern" Universe. I guess, it is a matter of balance among the energy contributions from Friedmann equations.  

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