# Next step in inflation theory ?

1. Jan 19, 2014

Hi Guys,
After data release of Planck satellite , at least about early universe cosmology, nothing new except few( i.e Dipole asymmetry of the CMB temperature fluctuations ) in comparison to WMAP results was found. As a case existence of non Gaussianity at the level of squeezed limit has been ruled out. On the one hand cosmologists may find that inflationary scenario is on the true line to describe the early universe , specially single field models.On the other hand , it seems that our almost single data of early universe ( Cosmic Microwave background) has been finished! No more satellites for more precise observation of CMB is needed since more pixels doesn't have early universe information and late time effects destroy them in small angles. So, does it mean that the early universe cosmology ( i may compare it with String theory at 2000) suffers from lack of observational data? and what will happen to it? Please let me know your opinions Guys!

2. Jan 28, 2014

### Mordred

Interesting question, the earliest data we can directly see is the CMB. As far as data before the CMB that is shrouded in as light from that time period cannot reach us. The plasma gases prior to the polarization stage prevents such detections. For example we cannot detect the cosmic neutrino background as of yet. This detection method if we can accomplish such may allow us to directly detect further back in time. So that is one aspect of future cosmic discoveries we can hopefully look forward to

3. Jan 28, 2014

### bapowell

There are hopes (maybe far cry, but hopes still) of a future satellite specialized to measure CMB polarization (WMAP and Planck can both measure polarization data, but they are not optimized to measure B-modes for example). Ground-based telescopes are currently working to detect B-modes as well, which will be a vital data source for sorting out early universe inflation and phase transitions. Proposed space-based laser interferometers (like BBO and DECIGO) have hopes of detecting primordial gravitational waves.

Large scale structure data also likely has more to say. The 21 cm line from neutral hydrogen should help cosmologists measure the power spectrum on much smaller scales than the CMB (down to scales $k \sim 100$ Mpc$^{-1}$; for reference the CMB together with large scale structure surveys like Sloan probe scales $10^{-4}$ to $0.1$ Mpc$^{-1}$.) Lastly, there's recent interest in studying CMB distortions: the deviation of the thermal spectrum of CMB photons from a Planck distribution due to the dissipation of fluctuations. Future distortion probes like PIXIE might have the ability to measure the power spectrum on even smaller scales, between $50$ and $10^4$ Mpc$^{-1}$.

So, it's not all about CMB measurements -- there's lots more out there. Part of the fun of contemporary cosmology is discovering new ways of shedding light on early universe physics.

4. Jan 30, 2014

Another question! Why does some physicists like Hawking let themselves to say that the Cosmology(Or early universe Cosmology) has become to end!
Cry!!!!!!!!!!!

5. Jan 30, 2014

bapowell , but observations of the late time universe say less than z~10 , has little information of early universe. In my opinion our trust should be more on early universe detections like gravitational waves. I really ask GOD to let us find them!!! :)

6. Jan 30, 2014

### bapowell

The 21 cm line from neutral hydrogen can be measured back to z ~ 10, but my understanding is that the interest is not in the physics of the reionization era, but in measuring the primordial power spectrum on relatively small scales. Of course, there is a good amount of contamination of the primordial signal in any measurement based on evolved structures, but I mention it simply as a potential way to observe an otherwise uncharted window of the spectrum.

7. Jan 30, 2014

### Chronos

Gravitational waves are, IMO, the holy grail of cosmology. Nothing like hearing it right from the source. A neutrino telescope would not be a bad second. Extracting detailed information from either potential detection method looks like a challenge. That's the beauty of science. There always seems to be another way to skin the cat.

8. Jan 31, 2014

Chronos , But I think lack of data from early universe and moreover impossibility to repeat the experiment is a
deep and important difference between early universe Cosmology and other branches of physics!

9. Jan 31, 2014

### Mordred

Although we cannot observe beyond the CMB. What we do see at the CMB confirms our current understandings of the early universe physics. The extremely consistent temperatures of the CMB confirms a rapid inflation as such uniformity can only be obtained by the universe rapidly expanding faster than temperature variations could occur.
The other supportive evidence is observing the correct mixtures of Hydrogen and lithium. This supports early universe baryogenesis and nucleosynthesis.
In regards to early universe physics. Much of our understanding derives from observations on Earth such as nuclear reactors and the LHC.
This makes sense as in order to understand the early universe baryogenesis, we need a good understanding of high energy particle physics. Knowing what temperatures allow which particle to react and combine has allowed us to get better estimates of the energy states required for each early universe epoch (stage) to occur.

Given that we cannot see beyond the CMB its rather impressive that the hot big bang predictions came so close to what we observe at the CMB. Luckily their is experiments we can do on Earth that will increase our understanding of the high energy states beyond the CMB. Improvements in Earth experiments will improve our understanding even if we find that we can never observe beyond the CMB.

Last edited: Jan 31, 2014
10. Jan 31, 2014

Mordred , The level of certainty in the theories of early universe is highly different in comparison to particle physics , condensed matter or other precise and repeatable eras of physics. Nothing bad , I do not say : Ok, stop the thinking and do not make models and theories , my opinion is that we should be aware of that uncertainty , who knows may be LambdaCDM may fail to explain dark energy and dark matte we must prevent ourselves to think that : Ok, that is the last theory! As sometimes scientist like Hawking unfortunately have said.

11. Jan 31, 2014

### bapowell

Indeed, studying the universe is a different science from particle physics, but that doesn't mean that we don't have good understanding of where uncertainties -- both theoretical and observational -- lie. LCDM is a concordance model only -- it is the most parsimonious framework that adequately describes the observations. It likely isn't the most successful model of the cosmos that we'll ever come up with -- we need to keep collecting data and learning as much as we can about the universe. Only until we've exhausted our capability to do that will we settle on the best concordance model that science can furnish.

Last edited: Jan 31, 2014
12. Jan 31, 2014