How does CMB support the predictions of inflation ?

In summary: The amazing uniformity of the CMB (1 part in 100,000) implies directly that there was an effective connection (interaction ability) among parts of the universe that could not possibly have ever been in that kind of proximity unless inflation had happened, since it is the only thing that can explain how they WERE so close together but are now so far apart.The CMB was observed and explained theoretically without inflation long before inflation became mainstream science. The observed non-uniformity of the CMB, not the uniformity, is a prediction of inflation.In summary, the observed qualities of the CMB were a prediction of inflation. The theory explains the uniformity of the CMB as the result of an interaction
  • #1
lalbatros
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2
How does CMB support the predictions of "inflation"?

Could explain to the novice I am, how does the CMB observation support the predictions of "inflation"?
 
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  • #2


The black body spectrum of the CMB was predicted exactly by the theory. The error bars are so small they're points on the graph.
 
  • #3


alexg said:
The black body spectrum of the CMB was predicted exactly by the theory. The error bars are so small they're points on the graph.
The spectrum shows that the universe started 13.7 billion years ago with the big bang. The spatial distribution is isotropic - which needs inflation to explain.
 
  • #4


In keeping with Feynman's description of the scientific method: The CMB was what they guessed would be out there, so finding it lends credability to the theory. This is the general idea, the above posters give more precise information about the finer details of what was expected and found.

I guess the direct answer is the observed qualities of the CMB was a prediction of inflation. Ticking a major box like that tends to get scientist to start finding ways to test other predictions.
 
  • #5


lalbatros said:
Could explain to the novice I am, how does the CMB observation support the predictions of "inflation"?

Previous responses are good and correct, but perhaps a more direct answer would be this:

The amazing uniformity of the CMB (1 part in 100,000) implies directly that there was an effective connection (interaction ability) among parts of the universe that could not possibly have ever been in that kind of proximity unless inflation had happened, since it is the only thing that can explain how they WERE so close together but are now so far apart.
 
  • #6


The CMB was observed and explained theoretically without inflation long before inflation became mainstream science. The observed non-uniformity of the CMB, not the uniformity, is a prediction of inflation.
 
  • #8


George and Chronos, thank you for this correction.

I HAD gotten that straight in my head, but here I reverted to my earlier incorrect understanding. Guess I'm just tired tonight, or maybe senile?
 
  • #9


CMB observation is CONSISTENT with inflation model predictions. But apparently so is the Ekpyrotic [cyclic] Universe model predictions of Neil Turok and Paul Steinhardt.

I just did a search and there are several good discussions about "inflation"...

here is one (I hadn't seen) :

https://www.physicsforums.com/showthread.php?t=514186&highlight=Ekpyrotic+Universe

I posted some months ago about planned CMB tests which it is hoped might distinguish between the big bang and cyclic models...If I can find the material I'll post it here tomorrow.
 
  • #10


lalbatros said:
Could explain to the novice I am, how does the CMB observation support the predictions of "inflation"?
Well, many answers, but I don't think any of them got to the heart of the issue.

The real piece of evidence is that the differences in temperature in the CMB are nearly scale independent (once you take the physics of how the CMB was emitted into account). The physics is a little bit complicated, but hopefully I can explain the basics.

If you have a system that starts out with different scales all having (nearly) the same typical amplitude at t=0 and then evolve that system forward in time, you get an interference pattern: the waves of some wavelengths tend to cancel, while the waves of other wavelengths tend to bunch up. This is most easily visualized in the power spectrum, a function of how much temperatures on the CMB differ as a function of wavelength:
http://lambda.gsfc.nasa.gov/product...nyear/powspectra/images/med/dl7_f01_PPT_M.png

(long wavelengths are on the left side of the plot, with short wavelengths on the right)

The key prediction of inflation that stands out incredibly brightly is this interference pattern: a series of peaks in the power spectrum. And crucially the way in which the different peaks change with wavelength is precisely the change predicted by inflation. Of course, theorists have come up with other ideas to explain both this interference pattern and how it changes with scale. Inflation, however, was the first model and remains the simplest.
 
  • #11


CAn't find my earlier post, but I have Steinhardt and Turoks book, THE ENDLESS UNIVERSE,: here are some excerpts starting on pages 204-210:

...The energy density of the universe during the phase when the long wavelength gravitational waves are generated is miniscule compared with the inflationary case...second, the gravitational waves produced in the universe are not scale invarient...the result is a spectrum of gravitational waves that cannot be confused with the inflationary prediction...
...so far (WMAP) measured patterns are pure E-mode consistent with both inflationary and ekpyrotic predictions...

It turns out the concentration of these ruled out some inflationary models, others pass. Hawking bet that the European Space Agency Planck Satellite would be able to make the precision measurements required to rule against the cyclic model. Apparently if B-mode polarization is detected this means some inflationary models pass a last and final test...and the cyclic model would not.
 
  • #12


Naty1 said:
It turns out the concentration of these ruled out some inflationary models, others pass. Hawking bet that the European Space Agency Planck Satellite would be able to make the precision measurements required to rule against the cyclic model. Apparently if B-mode polarization is detected this means some inflationary models pass a last and final test...and the cyclic model would not.
We'd have to get really really lucky for B-modes to be large enough to be detected by the Planck satellite.
 
  • #13


Regarding Planck satellite: Steinhardt and Turok mention maybe ten or so follow on experiments after Planck that were planned about the time of their book...2007...and they also mention that it was believed at that time that in principle there was no reason that such B waves could not be detected...

I like the idea of an alternative theory to rival consensus thinking, but a cyclic universe without a start is not all that satisfying.
 
  • #14


Naty1 said:
Regarding Planck satellite: Steinhardt and Turok mention maybe ten or so follow on experiments after Planck that were planned about the time of their book...2007...and they also mention that it was believed at that time that in principle there was no reason that such B waves could not be detected...

I like the idea of an alternative theory to rival consensus thinking, but a cyclic universe without a start is not all that satisfying.
Yeah, there are a bunch of balloon and ground-based experiments that may be able to detect the B-mode signal within the next few years. We'll see.

There is some talk about designing a next-generation CMB satellite, but that is going to be a much longer, much more involved process.
 
  • #15


Polite moderation notice: Please keep the discussion to the relationship between the CMB and inflation. Off topic posts will be deleted.
 
  • #16


I think Turok made a smart bet with Hawking, not becuase i think inflation is wrong and cyclic is correct as Turok claims. But from what I've read Planck is the first sattelite to have a chance to measure the B mode but most people think it probably won't be senstive enough.
Turok's cyclic comrade in arms, Steinhardt did author a very good article on what predictions each model makes:
http://www.phy.princeton.edu/~steinh/dense8.pdf
I think its a bit more balanced article than his later Sciam piece.
 

1. How does the Cosmic Microwave Background (CMB) provide evidence for inflation?

The CMB is the remnant radiation from the Big Bang, and it contains valuable information about the early universe. Inflation theory predicts that the universe underwent a period of rapid expansion in the first fraction of a second after the Big Bang, leaving behind a distinct pattern of fluctuations in the CMB. These fluctuations match the predictions of inflation, providing strong evidence for its validity.

2. How does the shape of the CMB support the predictions of inflation?

The CMB is incredibly uniform, with only small variations in temperature across the entire observable universe. Inflation theory predicts that the universe should have expanded at an exponential rate, smoothing out any irregularities and producing this uniformity in the CMB. This is exactly what we observe, providing further evidence for inflation.

3. Can the CMB help us determine the rate of inflation?

Yes, the CMB contains information about the rate of inflation. By studying the fluctuations in the CMB, scientists can calculate the rate of expansion during inflation and compare it to predictions from inflation theory. This allows us to test and refine our understanding of inflation and the early universe.

4. What other evidence supports the predictions of inflation besides the CMB?

In addition to the CMB, there are several other observations that support the predictions of inflation. These include the large-scale structure of the universe, the distribution of galaxies, and the amount of dark matter in the universe. All of these pieces of evidence fit together with the predictions of inflation, providing a strong case for its validity.

5. Are there any alternative explanations for the uniformity of the CMB besides inflation?

While inflation is currently the most widely accepted explanation for the uniformity of the CMB, there are some alternative theories. These include the possibility of a pre-Big Bang era or a cyclic universe model. However, these theories do not have as much evidence supporting them as inflation does, making it the leading explanation for the uniformity of the CMB.

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