Cosmological Inflation: Theory and Observations

In summary, the paper discusses how quantum mechanical fluctuations during the inflationary era produce macroscopic density fluctuations that are imprinted on the CMB. These fluctuations can be used to probe the early universe.
  • #1
wolram
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arXiv:0810.3022 [pdf, other]
Title: Cosmological Inflation: Theory and Observations
Authors: Daniel Baumann (Harvard), Hiranya V. Peiris (Cambridge)
Comments: 18 pages, 12 figures. Invited review to appear in Advanced Science Letters Special Issue on Quantum Gravity, Cosmology and Black Holes
Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
In this article we review the theory of cosmological inflation with a particular focus on the beautiful connection it provides between the physics of the very small and observations of the very large. We explain how quantum mechanical fluctuations during the inflationary era become macroscopic density fluctuations which leave distinct imprints in the cosmic microwave background (CMB). We describe the physics of anisotropies in the CMB temperature and polarization and discuss how CMB observations can be used to probe the primordial universe.
 
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  • #2
Is this paper theorizing or eleborating on some form of eternal inflation? Or is there some consideration of the possibility that entropy can be reversed in parches? Does it suggest that there can be tracing of inflation's history or is the history lost in a maze of fluctuating rates and patches of inflation, but all in the direction of final entropy?
 
  • #3
Force1 said:
Is this paper theorizing or eleborating on some form of eternal inflation? Or is there some consideration of the possibility that entropy can be reversed in parches? Does it suggest that there can be tracing of inflation's history or is the history lost in a maze of fluctuating rates and patches of inflation, but all in the direction of final entropy?

To me it suggests one should play with some numbers ( numbers from the washing machine),
And come up with a macrscopic white wash, nice, so long as there is not too much starch.
 
  • #4
Lol, that doesn't seem like an endorsement. Where do you stand?
 
  • #5
Inflation is a convergent theory - i.e., is supported by multiple, unrelated observations. But, like most other cosmological theories, it can only take you back so far into the early universe.
 
  • #6
Yes. But there is Big Bang Theory with inflation and there is eternal inflation :), the arrow of time, etc. In the OP, the abstract mentions, "a particular focus on the beautiful connection it provides between the physics of the very small and observations of the very large". Does it suggest that the micro world and the macro world have similarities in how they function only on vastly different scales? If so I would be interested in that full text. Is there a PDF file availavble?
 
  • #7
Force1 said:
Yes. But there is Big Bang Theory with inflation and there is eternal inflation :), the arrow of time, etc. In the OP, the abstract mentions, "a particular focus on the beautiful connection it provides between the physics of the very small and observations of the very large". Does it suggest that the micro world and the macro world have similarities in how they function only on vastly different scales? If so I would be interested in that full text. Is there a PDF file availavble?

The paper is, presumably (I've only read the abstract) discussing how quantum mechanical early time perturbations in the scalar field driving inflation produce macroscopic density fluctuations imprinted on the CMB.

The pdf is available here: http://arxiv.org/abs/0810.3022
 
  • #8
cristo said:
The paper is, presumably (I've only read the abstract) discussing how quantum mechanical early time perturbations in the scalar field driving inflation produce macroscopic density fluctuations imprinted on the CMB.

The pdf is available here: http://arxiv.org/abs/0810.3022
Thank you. Now that I read the abstract again I see that you are right.

It would be interesting to know if paper takes a position on the cause of the initial expansion and inflation or at least what lead to the perturbations? It seems clear that the anisotropy would require perturbations and the large scale of the anisotropy would point to them early during inflation.
 
  • #9
It does take a position on the post big bang universe, it does not posit any precursor conditions - which is very mainstream.
 
  • #10
Yes, it is very mainstream. But in my minds ear I can hear Daniel Baumann (Harvard), and Hiranya V. Peiris (Cambridge) talking by satellite phone and Dan saying, "Hey Hirny, don't you think we should mention that the infinitesimal perturbations came from preconditions? And Hirny saying, "Shut your mouth, fool" :).
 
  • #11
I think not, but that is merely an opinion.
 

1. What is cosmological inflation and why is it important in understanding the early universe?

Cosmological inflation is a period of rapid expansion in the very early universe, where the size of the universe increased exponentially in a fraction of a second. This theory was proposed to explain certain observed features of the universe, such as its uniformity and large-scale structure. It is important because it helps us understand the initial conditions of the universe and provides a framework for other theories, such as the Big Bang theory.

2. What evidence do we have for cosmological inflation?

One of the strongest pieces of evidence for cosmological inflation comes from the cosmic microwave background (CMB) radiation. This is a remnant of the radiation from the early universe and is observed to be remarkably uniform across the sky. Inflation predicts this uniformity, as it suggests that regions of the universe that were previously in contact were stretched apart during the inflationary period. Additionally, observations of the large-scale structure of the universe also support the idea of inflation.

3. How does the inflationary model explain the flatness problem of the universe?

The flatness problem refers to the observation that the universe appears to be very flat, or close to a Euclidean geometry, despite the fact that it should have curved significantly over billions of years. Inflation addresses this problem by proposing that the universe underwent a period of rapid expansion, which would have smoothed out any curvature and resulted in the observed flatness.

4. Can cosmological inflation be tested or observed?

While we cannot directly observe the inflationary period, there are several ways in which we can test the predictions of inflation. Observations of the CMB and large-scale structure provide evidence for inflation, but scientists are also looking for other signatures, such as gravitational waves, which may have been produced during inflation. Additionally, ongoing experiments, such as the Large Hadron Collider, may provide further evidence for the inflationary model.

5. Are there any alternative theories to explain the early universe besides inflation?

Yes, there are several alternative theories that have been proposed to explain the early universe, including the Steady State theory and the Ekpyrotic model. However, inflation remains the most widely accepted and supported theory due to its ability to explain many observed features of the universe. Other theories are still being researched and tested, and it is possible that new evidence may emerge in the future to support a different model.

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