Occam's Machete: Cosmology

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.

There is a spot in the sky at the edge of the observable universe where galaxies are moving towards something that cannot be observed and is probably beyond the edge of what we can observe. I’ve written several times (here and here) about dark flow since it was observed in 2008 by Kashlinsky and about one possible explanation for it here. In the time since dark flow was originally observed, the Kashlinsky data has been vetted pretty well.

But what is causing it? Kashlinsky thinks that a dense region of the universe exists just outside our observation horizon and imagines that this implies a non-uniformity to the universe, one that is great enough to call into question the Lambda Cold Dark Matter model. This model leads to a very uniform universe caused by early hyper inflation, just after the big bang. The CMB shows a pretty uniform universe in agreement with LCDM. So Kashlinsky is casting doubt on LCDM, basically saying that the universe may be very lumpy we just can’t see the lumps in the CMB from here.

Enter Dai et al who use a fundamentally different method to measure the flow of individual objects. They examine the type 1A supernova data to see if there is a relationship between the very far away novas (those with a high red shift) and their velocity towards the path of dark flow; they find no correlation, which means that the furthest away novas aren’t really moving faster than the closer ones in the path of the flow. Furthermore they find the likely velocity of the flow to be much smaller than the Kashlinsky suggests. Kashlinsky measured an aberrant bulk flow of more than 600 kilometers a second, while Dai et al found only 188 kilometers a second. Dai et al observe that this velocity is very close to that predicted by LCDM.

So what is one to conclude? Well Dai is measuring individual objects to see if there is a generalization to make about their movement and Kashlinsky is looking at the movement of great globs of matter. Also the methods they use are different. The main thing that the new data questions is whether the observations imply LCDM is wrong. Even within LCDM predictions something is going on out there that has yet to be explained very well. So we continue to observe and perchance to speculate…

Image courtesy of universe-review.ca which (though really slow) has an incredible array of photos and illustrations.

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.

How big is the Universe and if there are many, what would happen if they collided? Not a new question and several answers have been proposed (here is one). Another interesting question is why does time move in a single direction? Why does entropy increase? Laura Mersini-Houghton proposes an idea that answers both questions saying that bubble universes form with different arrows of time, eventually adding up to no preferred direction. She even claims to have a way to test this by looking our into the dark for boundaries.

Some have proposed that the Dark Flow may be one of these collisions, and the (now controversial) Great Void may be another. Where bubble universes are pulling and pushing on ours in places. FQXi has given her a grant to pursue the idea.

The year of Entropy continues with a paper referencing Verlinde but describing gravity and dark energy as effects of entanglement entropy. Read it on arXiv.

Something that has alway bothered me is the opinion expressed by moralistic politicians that faith and belief are virtues. Why? Doesn’t the skeptic who searches for evidence and rejects wishful thinking embody real virtue?  Would you be persuaded by someone’s belief that aliens crashed in a volcano and spread to infect all of humanity causing our combined ill-fortunes?  Oh, wait some people do believe that even though most of us would call that belief silly.  It is not backed by evidence and without evidence is not worthy of serious consideration. Which brings me to the quote of the day.

“I don’t ‘believe’ in string theory”, Brian Greene (the popular face of string theory and author of The Elegant Universe) in a Discover interview here.

Of course he goes on to make the distinction between belief and the virtuous pursuit of scientific skepticism in examining string theory. This balance of conviction and skepticism is the hallmark of good science. Greene is clearly a proponent of string theory and has written much about it but he is making a point about thought hygiene that ought to be applied broadly.

So the next time you are asked to vote for a politician who professes “faith” ask yourself if that lack of intellectual rigor is a good thing in a leader.  Faith is generally not a virtue.

Click to download the movie-all 18M of it.

There’s more news on that weird sucking from outside the visible universe.  This was first noted by Alexander Kashlinsky at Goddard Space Flight Center and I wrote about it here.  The team has now tracked the flow to twice the distance reported back in 2008—to 2.5 billion light years away.  This video shows the flow for different distances from the Earth.  Unfortunately they don’t know yet for sure whether the flow is away from us or towards us.  Everyone assumes it is away and there is some data to say that this assumption is true.  At least if it is flowing away from us we can blame it on something outside our light horizon, something really really big.  The galaxy clusters studied are travelling at a million miles per hour.  Read about the new data here.

If Roger Zelazny had written the Amber books today I’m sure he would have had a Courts of Entropy instead of Chaos.  But I digress…

The Holographic Principal states that a 5-D universe can be encoded holographically on a 4-D universe.  Just as a 3-D object can be captured in a flat hologram.   The implications are that the supertring universe of 5 dimensions can be seen by thinking of our own universe as a hologram.  Using this principal some really smart guys (including George Smoot of Nobel fame) proposed on arXiv that dark energy in our universe is only a holographic affect of an entropic force in higher dimensions.

They develop their theory and use it to predict the amount of dark energy we should see in our universe.  Unless there are mistakes in their reasoning, which I cannot judge, the most interesting thing is how close the prediction is to the dark energy seen in the supernova data—you know the data that showed our universe is expanding at an accelerating rate.  The other interesting thing is this how people are beginning to find observable predictions in String/M-theory.

I’m going to have to pay more attention to this Entropy stuff.

BTW Motl has some thoughts on this paper too.

Entropy is big lately.  A new paper on arxiv (The Entropic Lanscape, Bousso and Harnik) uses entropic principles to derive predictions about such things as the cosmological constant and the nature of entropic radiation.  These predictions match well with observations in our corner of the universe and give a framework that applies to any part of the universe, even in other vacua.  This paper relates to examinations of the vacuum lanscape that usually end up relying on anthropic arguments.  In other words things are the way they are because we wouldn’t be here to observe them if they were different.  Bousso and Harnik replace arguments like that with ones that favor the maximiztion of entropy.

Also in a comment to a previous post here Nisheeth points to his arxiv article (The relativity of theory, Nisheeth) where he describes a framework for deriving physical laws from information-theoretic first principles.  He too relies on the maximiztion of entropy.

Lately I’ve seen a several papers describing how one fundamental way of measuring the universe or another is actually emergent from a different way of looking at things.  There are those that claim time does not exist in any fundamental way, we are just looking at things wrong. So what is fundamental?

Entropy.

Understand entropy and gravity emerges.  Understand it in a moving frame and General Relativity emerges.  The idea is published on arxiv (On the Origin of Gravity and the Laws of Newton, Erik Verlinde) and even made it to Slashdot.  Woit surveys other entropy related ideas.

As a computer scientist there is something appealing in the notion that information is fundamental and that all the laws of nature are derived from the way information works.

Update: There is a long post from Verlinde on Motl’s blog here.  It illuminates some of his ideas and explains their history.  If you can stomach Motl’s bullying read the comments too, there are many.