What Does the Cold Spot in the CMB Reveal About Parallel Universes?

[Gravitons]

Whats this all about the cold spot found on the WMAP satellite's photo of cosmic microwave background radiation? To explain this there's even been a possibility of a parallel universe's gravitational effect causing this cold spot?

 

[bcrowell]

How about giving us the source of your information? It's been known for a long time that the CMB has hot and cold spots. Therefore there must be something more about this than what you're saying, or else it wouldn't be anything new.

 

[Chalnoth]

Whats this all about the cold spot found on the WMAP satellite's photo of cosmic microwave background radiation? To explain this there's even been a possibility of a parallel universe's gravitational effect causing this cold spot?

Basically, the "cold spot" just isn't far enough away from the expected variations for there to be much reason to believe it's anything different than normal variation.

 

[Chronos]

http://www.newscientist.com/article/mg19626311.400 reported
' "It [the CMB cold spot] is the unmistakable imprint of another universe beyond the edge of our own," says Laura Mersini-Houghton of the University of North Carolina at Chapel Hill. It is a staggering claim. If Mersini-Houghton's team is right, the giant void is the first experimental evidence for another universe.'
This claim is countered by a number of other studies - e.g.,
No evidence for the cold spot in the NVSS radio survey
Authors: Kendrick M. Smith, Dragan Huterer
(Submitted on 18 May 2008)
Abstract: We revisit recent claims that there is a "cold spot" in both number counts and brightness of radio sources in the NVSS survey, with location coincident with the previously detected cold spot in WMAP. Such matching cold spots would be difficult if not impossible to explain in the standard LCDM cosmological model. Contrary to the claim, we find no significant evidence for the radio cold spot, after including systematic effects in NVSS, and carefully accounting for the effect of a posteriori choices when assessing statistical significance.
Comments: 7 pages, 3 figures, MNRAS submitted
Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Journal reference: Mon.Not.Roy.Astron.Soc. 403:2,2010
DOI: 10.1111/j.1365-2966.2009.15732.x
Cite as: arXiv:0805.2751v1 [astro-ph]
.

 

[Dotini]

So the CMB cold spot could be:

1) Noise in the measurement process. <-- My choice.
2) Primordial temperature fluctuation.
3) A huge void between us and the CMB.
4) A wormhole or Einstein-Rosen bridge to another universe.
http://en.wikipedia.org/wiki/CMB_cold_spot

If you fancy #4, you might enjoy this link, which multiplies one interesting mystery by another: http://www.technologyreview.com/blog/arxiv/23410/

Respectfully submitted,
Steve

 

[bapowell]

Doubtful it would be noise in the instrument, since this should be isotropic Gaussian white noise. More likely it is a larger than average primordial fluctuation.

 

[Tanelorn]

Can the presence of a large body of matter block the CMBR from reaching us and thus produce a cold spot?

 

[bapowell]

Can the presence of a large body of matter block the CBMR from reaching us and thus produce a cold spot?

No, there are definitely photons reaching the detector from the location of the big cold spot, and their temperature is of the same order of magnitude as the other cold spots.

 

[Tanelorn]

Ok so the intensity (ie. amplitude) is constant in every direction (is this correct?), but the center frequency of the black body radiation varies by a tiny percentage. It must be difficult to measure the center frequency so accurately when the shape of the radiation has such a rounded top?

 

[Chalnoth]

Ok so the intensity (ie. amplitude) is constant in every direction (is this correct?), but the center frequency of the black body radiation varies by a tiny percentage. It must be difficult to measure the center frequency so accurately when the shape of the radiation has such a rounded top?

If you look at the way it works, the difference in temperature is approximately linearly-related to the amount of flux you get in anyone detector. So first they calibrate the detectors off of the dipole (which is much brighter than the galaxy across most of the sky), and since the CMB dipole is a fluctuation with CMB spectral scaling, anything else which has CMB spectral scaling will also raise/lower its temperature proportional to how much it is raised/lowered by the dipole.

Of course, the relationship isn't exactly linear, but it is quite close enough for the range in temperature deviation for the primary CMB anisotropies.

 

[Tanelorn]

I feel like I should be getting this, but I am not. It should be right up my alley, so to speak, which is a bit disconcerting.

Forgetting the detectors for the moment, we are trying to measure the black body temperature variation in different directions of the sky. This is equivlent to variation in the frequency of the black body radiation. Is this correct?

Now the detectors appear to comparing intensity from different directions, how does this tell us the frequency and thus temperature?

 

[Chalnoth]

I feel like I should be getting this, but I am not. It should be right up my alley, so to speak, which is a bit disconcerting.

Forgetting the detectors for the moment, we are trying to measure the black body temperature variation in different directions of the sky. This is equivlent to variation in the frequency of the black body radiation. Is this correct?

Now the detectors appear to comparing intensity from different directions, how does this tell us the frequency and thus temperature?

Each detector only sees the flux in one particular frequency band. Increasing the temperature increases the flux an individual detector sees. And the amount it increases the flux is approximately proportional to the amount of temperature increase (as long as the temperature increase is small compared to the average temperature level...which it is).

 

[bapowell]

I'll add that scanning the sky in several different frequency bands is vital to performing foreground subtractions, since galactic processes, for example, occur at different frequencies than the CMB.

 

[Tanelorn]

So each detector is actually a bank of several narrowband detectors, each tuned to detect the amplitude of a particularly wavelength. How many different wavelengths are being detected simultaneously?

Is it correct that for the detector to be able to make very accurate relative measurements of different points in the sky that there are two banks of these detectors each looking in different directions simultaneously? Do they switch these rapidly into a common receiver perhaps with a double down conversion before being sampled?

How much of the sky is each detector measuring ie. beam width? Presumably they use some kind of high gain, very highly directional horn antenna?

We are talking about the WMAP instrument here correct?

 

[Chalnoth]

So each detector is actually a bank of several narrowband detectors, each tuned to detect the amplitude of a particularly wavelength. How many different wavelengths are being detected simultaneously?

Well, no, each detector is a single detector. They have horns which only allow photons within a certain range of wavelength to pass. Then all of the photons that are able to make it to the bottom of the horn dump their energy into the detector, which is read off as a voltage.

Bear in mind that WMAP only detects photons in five different wave bands, so it isn't actually very good at estimating the temperature spectrum. It just depends upon the slight differences in flux at a given frequency across the sky.

Is it correct that for the detector to be able to make very accurate relative measurements of different points in the sky that there are two banks of these detectors each looking in different directions simultaneously? Do they switch these rapidly into a common receiver perhaps with a double down conversion before being sampled?

I believe that's how it works. That's the basic idea with Planck, though one detector in Planck is looking at the sky, whereas the other is looking at a 4K reference source. With WMAP, it actually has two back-to-back telescopes looking at different parts of the sky.

How much of the sky is each detector measuring ie. beam width? Presumably they use some kind of high gain, very highly directional horn antenna?

It varies based upon frequency. With WMAP, the beam varies from just under a degree to around a quarter of a degree in resolution.

 

[Tanelorn]

Thanks Chalnoth,

Re: "Then all of the photons that are able to make it to the bottom of the horn dump their energy into the detector, which is read off as a voltage."

What I am not getting is if the 5 different wavelength photons are all summed at the same detector producing a single voltage then the frequency information is lost.


Also it seems like I may have been under a misapprehension for a very long time.
I thought that the CMBR image was showing different temperatures, which I thought meant different photon wavelengths.
How can temperature be determined from the number or intensity of the photons?

 

[Chalnoth]

Thanks Chalnoth,

Re: "Then all of the photons that are able to make it to the bottom of the horn dump their energy into the detector, which is read off as a voltage."

What I am not getting is if the 5 different wavelength photons are all summed at the same detector producing a single voltage then the frequency information is lost.

Oh, I think you misunderstood me. There are different sets of detectors for different wave bands, at 23GHz, 33GHz, 41GHz, 61GHz, and 94GHz. The 23GHz detector, for instance, doesn't only measure photons at exactly 23GHz, but actually captures photons from about 19GHz to about 25GHz. That's what I've been talking about.

Also it seems like I may have been under a misapprehension for a very long time.
I thought that the CMBR image was showing different temperatures, which I thought meant different photon wavelengths.
How can temperature be determined from the number or intensity of the photons?

See law[/url]. Temperature impacts not only the frequency of radiation, but also the amount that is emitted.

Because previous experiments (in particular FIRAS) measured the average temperature of the CMB so incredibly accurately, we can simply use differences in flux to determine the small temperature differences at different parts of the sky.

 

[bapowell]

I thought that the CMBR image was showing different temperatures, which I thought meant different photon wavelengths.
How can temperature be determined from the number or intensity of the photons?

It is showing different temperatures. A gas of photons in equilibrium at a certain temperature T have wavelengths distributed according to a black body: http://en.wikipedia.org/wiki/Black_body" . The CMB is the closest thing that nature has to a black body, and so even a perfectly uniform CMB with temperature T would consist of photons across a range of frequencies.

 

[Naty1]

This possible dark spot causation sounds awfully like the one being attributed to "dark flow" that I asked abnout here:

https://www.physicsforums.com/showthread.php?t=513878

I wonder if the separate teams have connected yet??

 

[Tanelorn]

Ok thanks guys the WMAP detectors are a lot clearer now as well as a better understanding of the way temperature is determined.

Just to be sure, Flux is another way of saying intensity, or numbers of photons, correct?

Flux can also be affected by other things though correct? eg. a galaxy between us and the CMBR. Could we be seeing variation due to this and falsely attributing this to temperature variation? Also wouldn't dispersion over 13.7B years of traveling tend to want to flatten out any initial photon temperature variation?




Naty, they should be able to determine if the directions match.

 

[Chalnoth]

Ok thanks guys the WMAP detectors are a lot clearer now as well as a better understanding of the way temperature is determined.

Good!

Just to be sure, Flux is another way of saying intensity, or numbers of photons, correct?

Well, it's the combination of the number of photons, the energy per photon, and the area over the sky from which those photons came.

Flux can also be affected by other things though correct? eg. a galaxy between us and the CMBR. Could we be seeing variation due to this and falsely attributing this to temperature variation?

Well, right. This is why CMB experiments make use of data at multiple frequencies: other sources of radiation have very different dependence upon frequency, and so with multiple frequencies we can distinguish between them.

Also wouldn't dispersion over 13.7B years of traveling tend to want to flatten out any initial photon temperature variation?

What dispersion? The speed of light is identical for all wavelengths, so I'm not sure what you're talking about.

 

[Tanelorn]

Re: Dispersion: This is the bending of different frequencies of light where you might think one frequency came from one direction, different to the original direction. However I suspect something like this isn't going to effect the temperature map of the sky very much.

What I really meant was divergence, where a light beam spreads or disperses over distance. Here the distances are truly vast, so could something like dispersion cause an error in the temperatures seen across the sky? Perhaps making the measured temperatures across the sky look less variable than they really were when the photons were first emitted?

 

[Chalnoth]

Re: Dispersion: This is the bending of different frequencies of light where you might think one frequency came from one direction, different to the original direction. However I suspect something like this isn't going to effect the temperature map of the sky very much.

What I really meant was divergence, where a light beam spreads or disperses over distance. Here the distances are truly vast, so could something like dispersion cause an error in the temperatures seen across the sky? Perhaps making the measured temperatures across the sky look less variable than they really were when the photons were first emitted?

Ah, well, that's not an issue here because the CMB isn't a coherent beam of light. It's light that was emitted everywhere in every direction. So there's no divergence of the beam to speak of, because there's no beam in the first place.

Edit: But by the way, that isn't dispersion. Dispersion is what happens when the speed depends upon the frequency, which it doesn't here.

 

[Tanelorn]

Chalnoth, as I said I meant divergence, where a light beam spreads or disperses over distance.

In this case the distances are truly vast, so could something like dispersion cause an error in the temperatures seen across the sky?
Perhaps making the measured temperatures across the sky look less variable than they really were when the photons were first emitted?

 

[Chalnoth]

Chalnoth, as I said I meant divergence, where a light beam spreads or disperses over distance.

In this case the distances are truly vast, so could something like dispersion cause an error in the temperatures seen across the sky?
Perhaps making the measured temperatures across the sky look less variable than they really were when the photons were first emitted?

Yeah, that's what I was referring to in my first statement. There is no sense of divergence, because there is no beam in the first place. Divergence is only a sensible thing to talk about when you have a focused beam of light. In this case, however, the CMB is better thought of as a nearly-uniform gas of photons that expands along with the universe.

 

[Tanelorn]

Chalnoth, but doesn't that then provide some relief from having to explain the temperature uniformity with a rapid phase of inflation? Or is the near uniform gas of photons not sufficient alone?

 

[Chalnoth]

Chalnoth, but doesn't that then provide some relief from having to explain the temperature uniformity with a rapid phase of inflation? Or is the near uniform gas of photons not sufficient alone?

I don't understand what you're thinking here. The "cold spot" is simply consistent with our current models of the early universe. There isn't any good reason to believe there is anything special going on here.

 

[Dotini]

The "cold spot" is simply consistent with our current models of the early universe.

Exactly how is it simple that the cold spot is consistent with early universe models? If it were consistent, why would it be the subject of various articles and papers?

The authors of the wiki article seem to doubt ALL current explanations of the cold spot, don't they?

Very respectfully yours,
Steve

 

[Chalnoth]

Exactly how is it simple that the cold spot is consistent with early universe models? If it were consistent, why would it be the subject of various articles and papers?

Because it's a slight statistical outlier. It's well within bounds for current models, but many people are attracted to such small signals, in the hopes of finding something.

I actually think it's a little bit foolish in this case. It is a decent enough strategy for finding new things when there is a situation where we can significantly improve measurement uncertainty, and in improving measurement uncertainty we can determine whether or not it's real. The problem is that these anomalies in the CMB, such as the cold spot, are already about as accurately-measured as they are likely to ever be, and still the statistics aren't strong enough to say that there is definitively something screwy going on. So I think the scientists that are taking a leap here are exercising somewhat poor judgement.

 

[Tanelorn]

I don't understand what you're thinking here. The "cold spot" is simply consistent with our current models of the early universe. There isn't any good reason to believe there is anything special going on here.

Chalnoth, I wasnt referring to the cold spot here, just how there was a need during inflation for all parts of the universe to be in thermal equilibrium with each other in order to explain the uniform CMBR temperatures that we see today. I recall the speed of sound was mentioned. So what I was asking was if divergence of the CMBR radiation also equalises the CMBR temperatures anyway, then maybe that helps relax or reduce the need for the temperature to be so equal or flat or uniform during the inflation stage. Maybe I am not using the right terms.