Occam's Machete: Cosmology

One of the biggest stories in Cosmology over the last two decades has to be the discovery of the accelerating expansion of the universe. It left most scientists gob-smacked but has received no serious criticism since the evidence, mostly taken from type 1-A supernovas, continues to pile up. If the red shift of the 1-A flashes were the only evidence there might be other explanations for the data. Shouldn’t there be some other independent way to verify the expansion data, something that helps validate the explanation?

I love watching for these weird effects and anomalies because, once in a great while they pan out to be the real deal and lead to new science. Enter an international team of researchers led by Masamune Oguri at Kavli IPMU and Naohisa Inada at Nara National College of Technology who have conducted a unique survey of gravitational lensing effects. They calculate the probability of lensing at various times in the past to produce a model. But when the model is fit to the survey data it produces an acceleration very much consistent with the type 1-A red shift measurements. Woohoo, one more vote for Einstein’s Cosmological Constant.

Implicit in most of modern cosmology is the Cosmological Principal, which states the assumption that the universe is isotropic—operates with the same laws and same fundamental constants everywhere. Any observer anywhere in the universe would see, for instance, electromagnetism operate with the same strength. There is a lot of evidence that the principal holds true as far as we can measure it.

About decade ago a survey on one patch of the sky hinted that the measure of electromagnetism’s fine structure constant α may vary over time. Professor John Webb of UNSW and his colleges revisited the study recently with more data from a new source. They find that in one direction of the sky α is greater and in the other it is less than we observe on earth. They do this by studying the absorption spectra of quasars and supply the usual caveats about as yet unknown systemic biases.

If these observations prove out then it means the Cosmological Principal is only an approximation. Just as Newtonian Gravity works well for most calculations and must be replaced with Einstein’s Relativistic Gravity in others. Another implication, since the observations of α vary with direction and fit to a dipole, is that the laws of physics may depend on the observer’s location in space and time.

This study says nothing about other laws of physics but it does make finding a way to measure them across space and time a more interesting endeavor and there are competing theories of everything that would gain a boost from observation of these variations.

IMAGE CREDIT: Appears in published version of the paper, http://prl.aps.org/abstract/PRL/v107/i19/e191101

Much of modern cosmology is built on the idea that the universe is uniform everywhere and in all directions. If it wasn’t uniform that would be a pretty interesting discovery. So far there is precious little evidence that contradicts nearly perfect uniformity at large scales. But it may be very hard to detect non-uniformity. There are several theories about the cosmos beyond our universe that would seem to predict effects we could look for. The telltale signature of some of these theories would be circular anomalies in the CMB and a few have been posted about on this blog here, here, and here.

For example what if the cosmos is filled with many big bangs and our universe is only one bubble in a foam of universes? That is the central question in the idea of Eternal Inflation. A lot of people have thought about the implications of such a model and many have claimed to have seen evidence of such universe collisions. Usually when such claims are made established cosmologists come down hard on the observations as not supported by the data. But how do we decide if an observation is supported or not?

A team comprised of members of the University College London, the Imperial College London, and The Perimeter Institute have tackled the question. They start with the assumption that a hypothetical collision would result in some sort of disk-like structure in a 2D picture of the universe like the WMAP image of the CMB. They then simulate the structure and try to find the most conservative measure for detection. In other words they try to find the 2-sigma rule for detection of a disk. They also define a Bayesian parameter metric for the probability that a detected anomaly is real and not just a trick of chaos. The full paper is here.

This picture shows four of some 10 candidates for possible collision sites in the WMAP data that they found of interest. Two of these sites have been noticed before, one is the famous ‘cold spot’ visible to the naked eye (at least if the naked eye could see microwaves) and another, a hot spot, is described here. Their conclusion is that there is no 2-sigma observation of a disc but that there are some candidates that are never the less significant. Here is a picture of the candidates.

I can’t help thinking that the CMB is a snapshot taken at the time of inflation at the very beginning of the universe when it grew to almost its present size. There are other observations of the universe that reflect effects that have happened since inflation slowed down. For instance speed and direction of movement as in ‘dark flow’ or other observations of behavior seen since the universe emerged from the dark time with the formation of the first stars. I wonder if similar techniques could be applied to that data because if there were a collision during inflation, it would have continuing for the rest of the 13 some odd billion years the universe has been around and should be observable in other ways. Even without using observations of more recent events the authors look forward to applying their techniques to the coming Planck satellite CMB data.

This paper is good for taking a step towards refining how to see order in the chaos and sheds light on how to measure the difference.

Left Handed Galaxy

One of the central ideas in modern cosmology is that the universe is pretty much uniform throughout. You have to look on the large scale to see the uniformity, like at the cosmic microwave background radiation or at the distribution of matter. There are still mysteries like, why is there so much more matter than anti-matter? Seems like they should have been created in equal portions at the Big Bang and proceeded to annihilate each other, leading to a universe with no…us.

In other posts we have seen that there is evidence that much of the matter in the universe is moving in a specific direction in what is called ‘Dark Flow’. Now another interesting question is being tackled. What if you looked at all of the galaxies out there and counted how many have right and left handed spin. The answer seems so obvious that no one really tried until recently and they found a non-obvious answer. There are about 7% more left handed galaxies that right handed, at least in the rather large portion of the sky they checked. Chances are a million to one that this is indeed a significant result and not a mere accident of observation.

The study (described at Physorg.com) was done by professor Michael Longo and a team of five undergraduates who catalogued the rotation direction of tens of thousands of spiral galaxies photographed in the Sloan Digital Sky Survey in an area north of the Milky Way’s pole. This leads to a different question, was the universe born with a spin? And this new data suggest the answer might be yes.

This is not just a cosmetic observation, black holes can have spin, particles can have spin. Spin can be used to extract energy from a system. The implications are only now being considered and all because someone thought to check the obvious answer. I have often thought that one of the greatest of human qualities is curiosity, and a close companion is healthy skepticism, they lead to good things.

I love anomalies, the thrill of thinking that half of what we know is wrong and the other half is suspect. They hold the promise of new discoveries and a newer better understanding of reality. Unfortunately the vast majority of observations in cosmology, which appear to break the rules, do not stand the test of deep scrutiny.

I have written about the Cosmic Microwave Background (CMB) radiation several times, usually in the context of one anomaly or another. Most of them have since been deemed to be questionable. We are talking about tiny variations from the ideal random fluctuations and the sensitivity of the experiments is often pushed beyond its limits. It is not surprising that many conclusions drawn from the data are, well somewhat speculative. That said who would fail to find their possibilities intriguing?

Two new papers have been published describing ripples seen in the CMB. The most recent arXiv post by Stephen M. Feeney, et al, is based on some implications of Eternal Inflation. The model states that our universe banged then inflated quickly and so do other universes. As other universes (or false vacuum bubbles in the jargon) blow up they may slam against ours causing bruises in the CMB. They analyze data from WMAP with special software that looks for the telltale signs of these bruises.

In this image they show an idealized collision, the temperature modulation, a high needlet response, and results of edge detection in the CMB. Using these techniques they have found four candidates for primordial collisions. Check it out here: arxiv.org/abs/1012.1995

Another paper coauthored by the renowned Mathematical Physicist Sir Roger Penrose takes a different starting point for its analysis. Penrose is a proponent of Cyclic Inflation rather than Eternal Inflation. Cyclic Inflation starts from the question of why the beginning of the universe had such low entropy and postulates that at the end of the universe there are only black holes and that they evaporate, somehow removing the entropy from the universe and leaving it in an extremely low entropy state from which another big bang will start the whole rising entropy cycle anew.

He and his collaborator see evidence of concentric circles in the CBM which they imagine may have come about from the merger of ultra massive black holes that existed before the big bang. Check in out here: arxiv.org/abs/1011.3706

The first wave of anomalies (purportedly) seen in the CMB came from analyzing the data with little pre supposition about what the anomalies would look like. We now have at least two examples which start from an existing theory and try to see if there is evidence to support the theory. Both methods are valid but they have to be truly supported by the data and only time and those blessed second guessing trolls who bash through the data looking for mistakes will sort that out. And, of course those trolls will have the Planck data soon. In the meantime we have something to pique our imagination.