Is the CMB a Distorted Image of the Early Universe?

[Doctor]

Hi,

I have been doing a coarse lately and am currently studying refraction. And it got me thinking about refractions effects on the Cosmic Microwave Background. If the cmb is light from the early universe then I think it would be ridiculous to assume that this light has traveled through nothing but vacuum from the point it was emitted. And over such a large distance even the slightest bend in the light could make a huge difference in an objects perceived location. Could the CMB just be a scrambled picture of the early light from the universe were none of the objects are were they appear to be? And if so could any research done using it be potentailly misguided?

 

[Bill_K]

Doctor, One could imagine that the universe was permeated with a gas of some sort that would distort the CMB. However it would show up in many other ways such as spectral lines.

Also if something was present that had a "scrambling" effect on the CMB, it would have a similar effect on the images of distant galaxies, and this is not evident.

 

[phinds]

... picture of the early light from the universe were none of the objects are were they appear to be?

There WERE no "objects" at the time of the Surface of Last Scattering other than perhaps atoms. It was just coming out of being nothing but a hot dense plasma.

 

[Bill_K]

There WERE no "objects" at the time of the Surface of Last Scattering other than perhaps atoms. It was just coming out of being nothing but a hot dense plasma.

Inhomogeneities.

 

[phinds]

Inhomogeneities.

Yes, I understand that, but I don't think of inhomogeneities in plasma as "objects". Too vague. Besides, I didn't get that that was what the OP had in mind, though he may have.

 

[Orodruin]

Things such as gravitational lensing do affect the CMB, but not at a level strong enough to change the conclusions. In fact, gravitational lensing induce so-called B-modes at small scales in the CMB polarization (in contrast to those predicted by primordial gravitational waves, which seem to be quite popular at the moment and would appear on larger scales).

 

[Chronos]

There was a paper on arxiv recently, http://arxiv.org/abs/1405.7860, that discussed the possible effects of gravitational lensing on CMB measurements.

 

[Chalnoth]

Hi,

I have been doing a coarse lately and am currently studying refraction. And it got me thinking about refractions effects on the Cosmic Microwave Background. If the cmb is light from the early universe then I think it would be ridiculous to assume that this light has traveled through nothing but vacuum from the point it was emitted. And over such a large distance even the slightest bend in the light could make a huge difference in an objects perceived location. Could the CMB just be a scrambled picture of the early light from the universe were none of the objects are were they appear to be? And if so could any research done using it be potentailly misguided?

Yes, the CMB is distorted! But the distortions are shockingly small. There are three primary sources of distortion:

1. The integrated Sachs-Wolfe effect. This comes about as a result of dark energy. If there were no dark energy, then gravitational potential wells (e.g. clusters of galaxies) have a tendency to remain stable through time. But if there's dark energy, then they become more shallow. So if a photon enters this well, and the well becomes more shallow, then it doesn't need as much energy to climb out as it gained going in, then it ends up with a net gain of energy. The reverse happens for voids. On small scales, this effect cancels out, because there are lots and lots of small gravity wells (small, in this case, is a galaxy cluster). But on large scales, this effect adds a bit to the variation of the CMB. The effect dies out pretty rapidly at smaller scales and is quite tiny for scales smaller than about 6 degrees on the sky. But it does add a noticeable bump at larger scales.

2. The Sunyaev–Zel'dovich effect. This comes about because clusters of galaxies contain huge amounts of ionized gas. In fact, something like 90% of the normal matter mass of galaxy clusters lies in this ionized gas that permeates the entire cluster. The temperature of this gas is set by the strength of the cluster's gravitational potential well. That is, if you think of this gas as starting far away from the cluster at zero temperature, and gaining energy as it falls into the cluster, you'll get approximately the current temperature of the gas. And this temperature is massive: it's so high that this gas shines brightly in x-rays. As CMB photons travel through such clusters of galaxies, the much higher temperature of the cluster gas, on average, tends to give the photons a little "kick". So when there is a galaxy cluster between us and the CMB, the CMB light that makes it through that cluster has fewer low-frequency photons and more high-frequency photons than the CMB elsewhere.

3. Gravitational lensing. Clusters of galaxies also bend light, and this leads to a distortion of the CMB on very small scales. The impact is most pronounced in polarization, where it mixes up the polarization signal.

 

[bapowell]

Just to point out: the term CMB "distortions" has a specific meaning in the literature, referring to spectral distortion (deviations of the photon spectrum from a black body), not inhomogeneities or "scrambling". Just pointing this out in case the OP continues to research this question.