<p>I...think you've got it backwards? Slow-roll inflation is alive and well, unlike models which involve tunneling between two vacua. The model of inflation first proposed by Alan Guth back in 1980 was a tunneling model. But it had a serious problem: it didn't <em>reheat</em>. Tunneling from a false vacuum to a true one (or a lower-energy false one) wouldn't release any radiation. And we need that radiation, because we <em>are</em> that radiation, cooled down and condensed after nearly 14 billion years of expansion. The solution was slow-roll inflation: as you mentioned in your question, rolling down the potential well releases a great deal of energy, which in turn leads to the wide variety of matter and radiation in the universe today. Slow-roll inflation also does a nice job of predicting the tiny density fluctuations in the early universe that seeded the formation of all the structures in the universe. Wikipedia has <a href="http://en.wikipedia.org/wiki/Inflation_%28cosmology%29#Early_inflationary_models">more on all of this</a>.</p>

<p>A small disclaimer: there's a lot of inflationary models out there in the literature (there's a hilarious partial list in footnote 3 of <a href="http://arxiv.org/abs/1006.0275">this excellent paper by Yadav and Wandelt</a>), and for all I know, one or more of them involve vacuum decay. But the dominant paradigm for inflation today is definitely slow-roll.</p>

CC BY-SA 3.0
2013-11-21T17:10:13.933Z
Thanks for this nice answer, these explanations are indeed the other way round from what I have heared or read ... What I do not yet see right now is why the "latent energy" released by some kind of a vacuum transition (the difference between the two values for the cosmological constant constants) can not be turned into radiation (= photons?) apart from other stuff ... Will have to look deeper at the reheating problem a bit.
Dilaton
CC BY-SA 3.0
2013-11-21T06:59:41.517Z
2013-11-21T06:59:41.517Z
freelanceastro
<p>In slow-roll inflation models, the early inflation of the universe is driven by the flat non-zero part of the inflaton potential, and it ends as the ball rolls down the cliff and the potential energy released leads then to the formation of matter.</p>

<p><img src="https://i.sstatic.net/ylJYx.gif" alt="enter image description here"></p>

<p>However, as I have heard such slow-roll models are no longer deemed realistic today in inflationary cosmology, instead other models where the end of the inflation is explained by quantum tunneling of the universe from a state with higher vacuum energy density to another state with lower vacuum energy density are considered for example.</p>

<p><img src="https://i.sstatic.net/ljdEY.jpg" alt="enter image description here"></p>

<p>Why (from a physical point of view) are slow-roll inflation models no longer considered to be realistic, what are their disadvantages? What can models that explain (the end of) the early inflation by a tunneling transition between to vacua explain or describe, that slow roll models can not do?</p>

CC BY-SA 3.0
2013-10-15T14:24:51.827Z
@UV-D I certainly could find some references ..., I first learned about these things in Lenny Susskind's online cosmology course.
Dilaton
CC BY-SA 3.0
2013-10-15T18:40:14.893Z
@TildalWave I have cleaned up the comments about the on-topicness of this post. The discussion about where cosmology and theoretical astrophysics, as well as astrophysics in general, fall in our scope has moved to [Meta](http://meta.astronomy.stackexchange.com/questions/136/how-much-is-astrophysics-cosmology-and-theoretical-astrophysics-on-topic).
called2voyage
<cosmology><cosmological-inflation><early-universe>
Inflation cosmology: slow-roll inflation versus tunneling between two vacua
Dilaton
# Inflation cosmology: slow-roll inflation versus tunneling between two vacua

(Asked by: username_0 on 2013-10-15)

In slow-roll inflation models, the early inflation of the universe is driven by the flat non-zero part of the inflaton potential, and it ends as the ball rolls down the cliff and the potential energy released leads then to the formation of matter.

![enter image description here](https://i.sstatic.net/ylJYx.gif)

However, as I have heard such slow-roll models are no longer deemed realistic today in inflationary cosmology, instead other models where the end of the inflation is explained by quantum tunneling of the universe from a state with higher vacuum energy density to another state with lower vacuum energy density are considered for example.

![enter image description here](https://i.sstatic.net/ljdEY.jpg)

Why (from a physical point of view) are slow-roll inflation models no longer considered to be realistic, what are their disadvantages? What can models that explain (the end of) the early inflation by a tunneling transition between to vacua explain or describe, that slow roll models can not do?

**Tags:** cosmology, cosmological-inflation, early-universe

> **Comments:**
> **username_0**: @UV-D I certainly could find some references ..., I first learned about these things in Lenny Susskind's online cosmology course.  
> **username_1**: @TildalWave I have cleaned up the comments about the on-topicness of this post. The discussion about where cosmology and theoretical astrophysics, as well as astrophysics in general, fall in our scope has moved to [Meta](http://meta.astronomy.stackexchange.com/questions/136/how-much-is-astrophysics-cosmology-and-theoretical-astrophysics-on-topic).  

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## 1 answers

### Answer by username_2 on 2013-11-21. Score: 9 | Accepted answer

I...think you've got it backwards? Slow-roll inflation is alive and well, unlike models which involve tunneling between two vacua. The model of inflation first proposed by Alan Guth back in 1980 was a tunneling model. But it had a serious problem: it didn't *reheat*. Tunneling from a false vacuum to a true one (or a lower-energy false one) wouldn't release any radiation. And we need that radiation, because we *are* that radiation, cooled down and condensed after nearly 14 billion years of expansion. The solution was slow-roll inflation: as you mentioned in your question, rolling down the potential well releases a great deal of energy, which in turn leads to the wide variety of matter and radiation in the universe today. Slow-roll inflation also does a nice job of predicting the tiny density fluctuations in the early universe that seeded the formation of all the structures in the universe. Wikipedia has [more on all of this](http://en.wikipedia.org/wiki/Inflation_%28cosmology%29#Early_inflationary_models).

A small disclaimer: there's a lot of inflationary models out there in the literature (there's a hilarious partial list in footnote 3 of [this excellent paper by Yadav and Wandelt](http://arxiv.org/abs/1006.0275)), and for all I know, one or more of them involve vacuum decay. But the dominant paradigm for inflation today is definitely slow-roll.

> **Comments:**
> **username_0**: Thanks for this nice answer, these explanations are indeed the other way round from what I have heared or read ... What I do not yet see right now is why the "latent energy" released by some kind of a vacuum transition (the difference between the two values for the cosmological constant constants) can not be turned into radiation (= photons?) apart from other stuff ... Will have to look deeper at the reheating problem a bit.  

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