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I have been looking online and in other resources for some answers to no avail. Thought I would sign up on astrophysics forums to find the answer.

What is the evidence and data for the period before the cosmic microwave background (CMB) in the early universe? In other words, is the idea of energy being in an infinitely dense point in the past simply just the most parsimonious explanation of winding back the clock from the expanding universe from 380,000 years to 0 (or Planck time)? Or is there observational and gathered data from the time prior to the CMB to validate that something was actually taking place prior to 380,000 years?

Has there been another model proposed that takes the CMB as the starting point instead? Or does the data nullify looking for another model apart from Big Bang and cosmic inflation?

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Or is there observational and gathered data from the time prior to the CMB to validate that something was actually taking place prior to 380,000 years?

The CMB itself contains information of what happened before the photons decoupled. The modeling before those 380.000 years depends on the CMB data.

Its high homogeneity ( 10^-5 fit to black body radiation curve) forced the current Big Bang model, because thermodynamics cannot be used to explain it, due to the light cone differences of various regions of the universe then. Thus the inflation model was incorporated in the standard Big Bang model, by introducing at the place of the singularity an effective quantization of gravity which homogenized the available energies leaving seeds that would later develop into the small CMB inhomogeneities, and the clusters of galaxies etc. This is the inflation period.

enter image description here

In between the inflation period and the CMB decoupling an extended standard model of particle physics is used to describe the process of hadronization etc.

The hope is that when gravitational waves can be scanned as was attempted with the BICEP2 experiment, one will be able to probe and verify this model, or change it.

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    $\begingroup$ There is no physics model of Beyond the Standard Model, which your extended standard model refers to. BSM is an area of research, not a model of anything we know beyond the standard model. For hadronization it's mainly QCD, within the SM for the most part except the preponderance of matter to antimatter,while we have no answer for. And also importantly, gravitational waves were discovered in 2014, by the LIGO collaboration. $\endgroup$ – Bob Bee Mar 12 '17 at 6:26
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    $\begingroup$ @BobBee Well, the assumption of unification of the three forces and zero masses at that time for all particles is an extension of the standard model, not verified in accelerator experiments . ( we are on the way after establishing the Higgs). I was thinking of the fine structure given by BICEP2. I will edit. $\endgroup$ – anna v Mar 12 '17 at 6:33
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    $\begingroup$ @laymanB if you look at the picture above, yes, at least from the inflation stage. $\endgroup$ – anna v Mar 12 '17 at 17:16
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    $\begingroup$ Polarizationin the CMB can happen by secondary interactions of the CMB photons as they are traveling to the detection, which is why the original BICEP2 publication of gravitational wave detection was watered down to limits by the dust found by PLANCK. They are now on BICEP3, trying to separated the secondary effects cfa.harvard.edu/CMB/bicep3/science.html . see this for bicep2 arxiv.org/abs/1502.00612 $\endgroup$ – anna v Mar 12 '17 at 18:33
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    $\begingroup$ @laymanB. As Anna says, yes. In her picture. Why is that so? Changes in curvature, which around the Big Bang was changing rapidly, cause gravitational radiation as long as the changes are not spherically symmetric (i.e., a monopole), or axially symmetric (dipole). The simplest terms depends on the time derivatives of the quadrupole moment. An example is a barbell rotating around any axis other than its axis of symmetry. As in Anna's the BICEP2 claims were not valid, and they are trying for more accuracy. It would not be direct detection of g waves which would provide lots more information $\endgroup$ – Bob Bee Mar 12 '17 at 21:17
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One of the main planks of evidence supporting the big bang model is the concordance of the inferred primordial abundances of helium and deuterium with the model predictions.

This primordial nucleosynthesis took place between about a second and a few minutes after the big bang. In the standard model, the primordial He and D abundances can be explained by a single parameter - the baryon to photon ratio. The same baryon to photon ratio can be independently measured from the CMB. All of the physics described by primordial nucleosynthesis requires that the universe was much hotter and denser than it was at the time of the formation of the CMB. Otherwise no nuclei would form and all the neutrons in the universe would have decayed to protons. That these abundances can be simultaneously predicted withing the same temperature-time relationship and the same baryon-photon ratio as given by the CMB is a triumph for the big-bang model.

A point of controversy is the primordial lithium abundance, which may be out of kilter by a factor of two. This may be a genuine problem, requiring alterations to the BB model, or it may be a lack of understanding of the physics of old stars in which the primordial Li abundance is estimated (see Discrepancy problem in lithium? ).

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  • $\begingroup$ What elements are thought to have existed after nuclear fusion ceased at the three-minute mark using the image above from @anna v? $\endgroup$ – laymanB Mar 12 '17 at 16:37
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    $\begingroup$ @laymanB Hydrogen, Helium(4), Helium-3, Deuterium, Lithium, and traces of Beryllium and Boron. $\endgroup$ – Rob Jeffries Mar 12 '17 at 17:13
  • $\begingroup$ If the inflationary phase never took place, would we expect to see a different ratio of primordial elements? More heavy elements? $\endgroup$ – laymanB Mar 14 '17 at 15:44
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    $\begingroup$ @laymanB There maybe some non-standard physics (e.g. certain types of dark matter relics) produced by inflation that open up extra degrees of freedom and that change the overall abundance mixture slightly (this is one class of explanation for the "lithium problem"). But certainly no way to produce heavier elements. $\endgroup$ – Rob Jeffries Mar 14 '17 at 16:53

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