Inflation and density perturbations

In summary, it is possible to estimate the rate of false vacuum decay in the inflationary universe by looking at the density perturbations in the big bang universe, but it is unlikely to yield definitive results. Cosmic bubble collisions could potentially be visible in the CMB, but so far there hasn't been a definitive detection. If such collisions were detected, it could provide useful information about the number of false vacua in our past light cone. However, without such detection, it is probably impossible to determine the rate of false vacuum decay from CMB data. The answer depends on whether the phase transition is first or second-order, as the shape of the potential is directly connected to the characteristics of the density perturbations.
  • #1
Ranku
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Is it possible to estimate the rate of false vacuum decay in the inflationary universe by looking at the density perturbations in the big bang universe?
 
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  • #2
Ranku said:
Is it possible to estimate the rate of false vacuum decay in the inflationary universe by looking at the density perturbations in the big bang universe?
Maybe, but it's unlikely.

There is the outside possibility that cosmic bubble collisions could be visible in the CMB. Here's a blog post about a paper that looks into this possibility:
https://www.earlyuniverse.org/simulating-cosmic-bubble-collisions-in-full-general-relativity/

So far, there hasn't been a definitive detection of the ring-like structure which would signal such a collision, so there probably won't ever be. If we had gotten lucky and could detect a number of these kinds of collisions, that would place limits on the number of false vacua in our past light cone, which might be useful in determining how often they decay. But with no detection, the answer is that it's probably impossible to know from the CMB data.
 
  • #3
Depends. First- or second-order transition?

If the latter, then there is a direct connection between the shape of the potential, i.e. the dynamics of the phase transition, and the characteristics of the density perturbations.
 

1. What is inflation and how does it relate to density perturbations?

Inflation is a theoretical period of rapid and exponential expansion in the early universe, proposed to explain the observed uniformity of the universe. Density perturbations refer to small variations in the distribution of matter and energy in the universe. Inflation is thought to have amplified these perturbations, leading to the formation of structures in the universe, such as galaxies and galaxy clusters.

2. What is the evidence for inflation and density perturbations?

The cosmic microwave background radiation, the leftover heat from the Big Bang, is one of the main pieces of evidence for inflation. The observed pattern of temperature fluctuations in the cosmic microwave background is consistent with the predictions of inflation. Additionally, the distribution of galaxies and galaxy clusters in the universe also supports the existence of density perturbations.

3. How does inflation solve the horizon problem?

The horizon problem refers to the observed homogeneity of the universe on a large scale, despite the fact that different regions of the universe could not have communicated with each other due to the limited speed of light. Inflation solves this problem by stretching the universe so rapidly that all regions were once in close proximity, allowing for the exchange of information and the creation of a uniform universe.

4. What is the relationship between inflation and the flatness problem?

The flatness problem refers to the observed flatness of the universe on a large scale, which is difficult to explain without assuming a fine-tuning of initial conditions. Inflation solves this problem by expanding the universe so rapidly that it appears flat, even if it was not initially.

5. Can inflation and density perturbations be tested or observed directly?

While there is no direct observation or experimental confirmation of inflation or density perturbations, scientists are actively searching for evidence through observations of the cosmic microwave background, gravitational waves, and other cosmological phenomena. Additionally, the predictions of inflation and density perturbations have been verified through various mathematical models and simulations.

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