What Evidence Exists for the Universe Before the Cosmic Microwave Background?

[laymanB]

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?Thanks

 

[phinds]

... is the idea of energy being in an infinitely dense point in the past

This is a total misconception (a VERY common one) that is universally propagated by the pop-sci industry and not by actual physics. It's called a "singularity" but that word does not mean a point in space or anything concrete at all, it just means "the place where the math model breaks down and we don't know WHAT is/was going on".

 

[Drakkith]

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?

There's no directly observable evidence from before the CMB at this time because light prior to the emission of the CMB couldn't get through the plasma that filled the universe. It's possible that a sufficiently sensitive neutrino detector could be used to see past the CMB, but given the fact that neutrinos rarely interact with matter, it seems we won't have one any time soon, if ever.

Most of our information from the state of the universe prior to the CMB is from theoretical models and inferences from observations of the properties of the CMB itself.

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?

There's been no model that I've ever heard of that takes the CMB as the start of the universe. That wouldn't seem to make any sense. The standard model of cosmology easily incorporates a hot, dense, and expanding plasma which gradually cooled over time until it cooled far enough to allow recombination and the emission of the CMB. The physics of the process are well understood and don't start to break down until you wind the clock back so far that the density of this plasma approaches infinity.

Also, note that inflation is different from expansion. While inflation results in a rapidly expanding universe, the expansion of the universe after inflation ended is what we usually call "expansion" and is a different process driven by different causes.

 

[PeterDonis]

What is the evidence and data for the period before the cosmic microwave background (CMB) in the early universe?

Much of it is in the detailed properties of the CMB--how its intensity and frequency varies in different parts of the sky. Other lines of evidence are the relative abundances of the light elements and our knowledge of the Standard Model of particle physics.

A quick summary is here:

https://en.wikipedia.org/wiki/Lambda-CDM_model

Has there been another model proposed that takes the CMB as the starting point instead?

No. The CMB can't be a starting point, because the energy that went into it had to come from somewhere.

 

[phinds]

@laymanB you might like "The First Three Minutes" by Stephen Weinberg.

 

[Chronos]

A neutrino detector called PTOLEMY at the Princeton Plasma Physics Laboratory [PPPL] is slated to start running later this year [2017]. It is expected to be capable of detecting relic neutrinos believed to have been released one second after the big bang. It should reveal a wealth of information about the infant universe and the standard model of particle physics. Looks like a fertile nesting site for future Nobel prizes. See http://research.princeton.edu/news/features/a/?id=16405 for futher details. Combined with the launch of the JWST in 2018, we clearly live in very interesting times for science. The principle behind PTOLEMY is that tritium is an effective neutrino detector. For further discussion on neutrino detection these may be of interest; https://arxiv.org/abs/1503.05866, https://icecube.wisc.edu/outreach/neutrinos, http://www.dw.com/en/the-katrin-tri...scale-for-the-tiniest-of-particles/a-36044018.

 

[Chalnoth]

The CMB is one of our primary sources of evidence for the behavior of the early universe. It is a snapshot of the universe at roughly 300,000 years of age, and it has a number of interesting statistical properties that allow us to make statements about the makeup of the universe and what sorts of things might have happened before that time. For example, the Planck satellite's observations constrain the normal matter density to about 1% and the dark matter density to about 2%.

There is also evidence from the primordial abundance of light elements. In the first few minutes, a number of light elements were produced in very specific quantities (roughly 75% hydrogen, 25% helium, and trace amounts of everything else). This is because the expansion at the time was so fast that there was very little time after nuclear fusion started to when the universe cooled too much for it to continue. Very detailed measurements of the abundances of the light elements can provide evidence of the expansion rate in the very early universe, and places constraints on a variety of beyond-standard-model physics proposals.

Measuring the Cosmic Neutrino Background, as mentioned by Chronos above, would be another way to examine the early universe. Sadly, however, due to the extreme difficulty in detecting low-energy neutrinos, my naive suspicion is that it will be a long, long time before we get anything more than, "The primordial neutrino density is X" as a result of this kind of experiment. Observing this density definitely wouldn't be irrelevant, as it would place further constraints on theoretical models. But it would be a far cry from the clear image of the CMB that we have currently.

 

[newjerseyrunner]

It is predicted that there should be gravity waves from just after the big bang. It was announced that such waves were discovered in 2014, but was determined a year later that they were mistaken. In theory, those waves should be there, we just haven't been able to observe them yet.

 

[Chalnoth]

It is predicted that there should be gravity waves from just after the big bang. It was announced that such waves were discovered in 2014, but was determined a year later that they were mistaken. In theory, those waves should be there, we just haven't been able to observe them yet.

To clarify a little bit: there were some quick responses to the original paper that casted it into doubt (as in, within a few months). It was never considered a solid result from the start, and multiple papers were released over the course of the year confirming that what they actually measured was from the dust in our galaxy, not primordial B modes, and that once the dust was corrected for there was no longer any remaining evidence for primordial B mode polarization (yet).

Also, it isn't completely clear from the theory that the primordial B modes should be observable. The "bouncing cosmology" models don't have any, and many inflation models have a wide parameter space where the primordial B modes are too small to measure. It would be nice if we could measure them, but they are by no means guaranteed to be large enough to measure.

 

[nikkkom]

It is predicted that there should be gravity waves from just after the big bang. It was announced that such waves were discovered in 2014, but was determined a year later that they were mistaken. In theory, those waves should be there, we just haven't been able to observe them yet.

IIRC these detections are also derived from CMB, so in some sense, they attempt to infer some earlier-than-CMB data only indirectly.
Direct detection of such weak gravity waves would be extremely difficult, much harder than even neutrinos from CvB.

 

[phinds]

IIRC these detections are also derived from CMB, so in some sense, they attempt to infer some earlier-than-CMB data only indirectly.

My understanding is that the CMB only has to do with the surface of last scattering, which has nothing to do with gravity waves. The gravity waves in question are from earlier. I don't know if they exist or not but if they do they have nothing to do with the CMB.

Direct detection of such weak gravity waves would be extremely difficult, much harder than even neutrinos from CvB.

Agreed.

 

[nikkkom]

My understanding is that the CMB only has to do with the surface of last scattering, which has nothing to do with gravity waves. The gravity waves in question are from earlier.

Yes. But BICEP experiment does not detect gravity waves. It detects polarization of the CMB. Then the data is used to make inferences about gravity waves.

 

[newjerseyrunner]

Right, I was also under the impression that they derived the data from B modes in the CMB, but those structures are due to things that happened long before it was created.

 

[phinds]

Yes. But BICEP experiment does not detect gravity waves. It detects polarization of the CMB. Then the data is used to make inferences about gravity waves.

Ah. I missed that. Thanks.

 

[laymanB]

Yes. But BICEP experiment does not detect gravity waves. It detects polarization of the CMB. Then the data is used to make inferences about gravity waves.

Do they think that the inferences based on the polarization signals in the CMB are not very strong and therefore need more direct data from the gravitational waves from the inflationary stage?

 

[laymanB]

There is also evidence from the primordial abundance of light elements. In the first few minutes, a number of light elements were produced in very specific quantities (roughly 75% hydrogen, 25% helium, and trace amounts of everything else). This is because the expansion at the time was so fast that there was very little time after nuclear fusion started to when the universe cooled too much for it to continue. Very detailed measurements of the abundances of the light elements can provide evidence of the expansion rate in the very early universe, and places constraints on a variety of beyond-standard-model physics proposals.

This does seem to be an independent data point for evidence before the CMB, thanks. Is the thinking here that apart from the homogeny (maybe not the right word) of the CMB implying inflation, that if inflation did not take place then there would have been more time for a greater percentage of heavier elements to form before the plasma cooled?

 

[laymanB]

I know that they say the equations break down when the density of the plasma approaches infinity near time 0 but nothing in physics makes the density of the plasma at the Planck time impossible? Physics allows for all the energy that is to become all the energy and matter in the universe to occupy such a small space? Am I even asking the question correctly? Can I speak of the plasma at the Planck time as actually occupying space or is the space-time fabric part of the plasma so density doesn't mean the same thing as measuring the density, of say Earth, in space today?

 

[PeterDonis]

nothing in physics makes the density of the plasma at the Planck time impossible?

We don't know; the Planck scale is many orders of magnitude away from what we can probe experimentally. Based on what we currently think we know of quantum gravity, the Planck scale is where we expect our current models, which are all based on a continuous spacetime manifold, to break down. But we have no way of testing that belief at present.

 

[phinds]

I know that they say the equations break down when the density of the plasma approaches infinity near time 0 but nothing in physics makes the density of the plasma at the Planck time impossible? Physics allows for all the energy that is to become all the energy and matter in the universe to occupy such a small space? Am I even asking the question correctly? Can I speak of the plasma at the Planck time as actually occupying space or is the space-time fabric part of the plasma so density doesn't mean the same thing as measuring the density, of say Earth, in space today?

I may be misinterpreting you but you SEEM to be asking if it is physically possible for all the matter that is to expand into the current universe to exist in a space of one Planck Length (diameter?). The universe may have been infinite in extent at one Plank Time, and in any event it was not some tiny volume the size of one Plank length diameter.

 

[nikkkom]

I know that they say the equations break down when the density of the plasma approaches infinity

Equations of Standard Model are not breaking down at Planch density and energy; however, they don't include gravity (iow: they ignore it).
We are almost certain that at Planck energy, gravitational effects start being significant.
Therefore, what SM equations say is no longer relevant - we need to extend the model to include quantum theory of gravity.
And we don't have that theory yet.

 

[Chalnoth]

This does seem to be an independent data point for evidence before the CMB, thanks. Is the thinking here that apart from the homogeny (maybe not the right word) of the CMB implying inflation, that if inflation did not take place then there would have been more time for a greater percentage of heavier elements to form before the plasma cooled?

Inflation really doesn't have any impact on primordial nucleosynthesis. But models of dark matter, attempts to add additional neutrinos, or various "fifth force" proposals can impact the production of light elements in the early universe.

Inflation primarily purports to explain two things:
1. Why the universe is nearly spatially-flat.
2. Why the universe is uniform in space across the observable universe (locations on the CMB separated by more than about a degree haven't had enough time to communicate with one another according to the classical big bang, so how did they know to be at nearly the same temperature?).

The main experimental prediction made by inflation is that it will produce a nearly (but not exactly) scale-invariant spectrum of density perturbations, which is precisely what we measure on the CMB.