# Inflation "cooled Universe from 10^27 to 10^22 kelvins" why?

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• nikkkom
In summary, the inflationary phase of the universe is thought to have lasted for a period of time, but the exact duration is uncertain. Some theories propose that it could have lasted for billions of years. During this phase, the universe rapidly expanded and particles were diluted to zero density. After this, the false vacuum decayed, creating a new hot and dense state. This is thought to have led to the "normal Big Bang" scenario. The final temperature of this inflationary patch is estimated to be around 10^22 K, based on the work of physicist Alan Guth in his paper "Phase transitions in the very early universe". However, there is still debate and uncertainty surrounding the exact details of the inflationary phase.
nikkkom
I've seen numerous descriptions of inflationary phase a-la "The universe was supercooled from about 10^27 down to 10^22 kelvins".

However, I do not understand what is the basis for such estimation. We do not even know with any certainty how long the inflationary phase lasted. For one, "eternal inflation" theories even say that it may be lasting something like billions of years.

If it lasted even "only" a few seconds, the inflationary vacuum expansion surely diluted all preexisting particles to zero density. Thus, temp in this case should not be 10^27 or 10^22 K. It should be zero.

Then decay of the false vacuum does create a new hot and dense state. _Now_ it can be at ~10^22 K (if you know a paper where it is estimated to be about this temp to match observations, please post a link).

So, to me, the sequence of events in inflation theories should be:
[whatever] -> temp and density rapidly falls, possibly even to zero -> decay of vacuum, reheating to high temp (10^22K?) -> "normal Big Bang" scenario.

Please give an appropriate source for this statement.

My Google-fu finds that it originated from "Phase transitions in the very early universe" by Guth.

Tried to find it online, no luck so far.

I believe the final temperature in the Guth statement refers to the inflationary patch post-reheating. After the super-cooled phase transition completes, the latent heat is released, reheating the system. Not certain about this, though.

This reference might be helpful: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.44.631

## 1. What is an "inflation cooled Universe"?

An inflation cooled Universe refers to the early stages of the Universe, specifically during the first 10^-32 seconds after the Big Bang. During this time, the Universe underwent a period of rapid expansion, known as inflation, which caused it to cool down from extremely high temperatures to around 10^22 kelvins.

## 2. How does inflation explain the uniformity of the Universe?

Inflation is believed to have smoothed out the irregularities in the density of matter and energy in the Universe, resulting in a more uniform distribution. This is because during inflation, the Universe expanded faster than the speed of light, causing any initial irregularities to be stretched out and become relatively insignificant.

## 3. What evidence supports the theory of inflation?

There are several pieces of evidence that support the theory of inflation. One is the observation of the cosmic microwave background radiation, which is a leftover remnant from the early stages of the Universe and shows a high degree of uniformity. Another is the large-scale structure of the Universe, which suggests that the initial irregularities were smoothed out by inflation. Additionally, the theory of inflation accurately predicts the ratio of different types of particles in the Universe.

## 4. What happened to the Universe after the inflation period?

After the inflation period, the Universe continued to expand and cool down. As it cooled, particles were able to come together and form atoms, leading to the formation of stars, galaxies, and eventually, the complex structures we see in the Universe today.

## 5. Why is understanding the inflation cooled Universe important?

Understanding the inflation cooled Universe is crucial because it helps us explain the current state of the Universe and its development over time. It also provides valuable insights into the fundamental laws of physics and the origins of the Universe. Additionally, studying the inflation period can help us learn more about the nature of dark matter and dark energy, which are still mysteries in modern physics.

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