How does CMB support the predictions of inflation ?

[lalbatros]

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"?

 

[alexg]

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.

 

[mathman]

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.

 

[salvestrom]

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.

 

[phinds]

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.

 

[George Jones]

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.

 

[Chronos]

Agreed, inflation was proposed to solve some of the problems with the big bang model. It did not arrive on the scene until 1980. Here is some interesting links
http://www4.ncsu.edu/unity/lockers/users/f/felder/public/kenny/papers/inflation.html
http://ned.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver6.html

 

[phinds]

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?

 

[Naty1]

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.

 

[Chalnoth]

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.

 

[Naty1]

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.

 

[Chalnoth]

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.

 

[Naty1]

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.

 

[Chalnoth]

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.

 

[Ryan_m_b]

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

 

[skydivephil]

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.