Tag Archives: inflation

cosmology, Uncategorized

Cosmic Accelerating Expansion? Really?

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.

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cosmology

Bubble Collisions

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.

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cosmology

More CMB Weirdness

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. Four stages of collision detectionThe 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

Circles in the CMBAnother 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.
Pre-Big-Bang event

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.

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cosmology

I Love This Picture

A Picture of The Whole Shebang

Timeline of the Universe (credit NASA WMAP)

It is a 3D timeline from the big bang to now. The diameter represents the size of the universe or more precisely the scale factor of the universe. It is hard to imagine but the universe did not start from a single point and explode into growing ball of gas. I know that’s what they imply when you listen to the TV pop science shows but the universe is everywhere, right? There is no center either. Its just that space happened all at once with all its bits in several dimensions and it started to expand in all those dimensions all at once.

The rate of expansion is illustrated in this picture, really fast at the beginning and then it slowed down. Now, as we have recently learned, it is starting to speed up again. So what does the diameter of the bell illustrate? In the beginning the bits of the universe were close together, now they are further apart. The diameter of the bell is proportional to how far each bit is from the next. This is called the scale factor. The outward expansion is just the scale factor growing at an accelerating rate. If nothing else changes things the bell will look like a trumpet pretty soon.

Something else cool about this picture is that it shows what we see in the WMAP and now the Planck images, the early microwave glow of the big bang. Using the satellites we capture photons from 13 billion years ago so they see what things looked like back then. The amazing thing about the image is that it is so uniform. In an explosion you’d expect to see billows, and clumps and gaps. But we don’t see much of that in the cosmic microwave background (CMB). This means the universe must have expanded very quickly indeed. Maybe faster than the speed of light (in fact almost certainly). That is why the first part of the bell gets big so quickly, the scale factor was growing so fast that each bit of the universe was moving away from every other at faster than the speed of light. The bits weren’t moving, it was space getting bigger, fluffier.

The interesting implication of this faster than light expansion, physicists call it inflation, is that some matter may be out there that we cannot see, past the edge of the observable universe. And that is the subject of the previous post, dark flow caused by ominous clumps of stuff outside our ability to see.

That is round about 390 words so there must be more in the picture but it is late and I will close with the other 610 left unwritten—for now.

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Tracking Dark Flow

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.

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cosmology

Is Cosmic Inflation Wrong?

Cosmic Inflation attempts to explain why the universe is so uniform by positing that the universe may have expanded faster than the speed of light, at least for a time.  It is a very successful theory which allows us to think of the forces as having not changed with time.  But what if Gravity itself has changed with time?  What if the early universe had little or no gravity and later, through a sort of phase change (like water turning to ice) gravity was switched on?  Could that be an alternative way to explain the state of the universe today and if so how might it have happened?  Those are the questions that Brian Greene, Kurt Hinterbichler, Simon Judes, and Maulik K. Parikh try to address in a new arXiv paper.

The basic premise is that things are uniform now in the universe and if the universe had expanded at a constant rate with gravity acting all the time the laws would predict a more lumpy universe.  Cosmic inflation questions whether the universe expanded at a constant rate.  If the early universe expanded faster that the speed of light then the clumping effect of gravity would have been frozen out for a time.  Then when expansion slowed down the effect would become more pronounced.  As an alternative the new paper questions whether gravity was uniformly powerful the whole time.  If a gas is unaffected by gravity the gas will distribute uniformly in space but when gravity is added the gas atoms will eventually form into clouds, condense into stars, and collapse into black holes.  The new paper suggests that gravity itself might have been weaker for a time, leading to less clumping.

We tend to imagine our surroundings on geological or cosmological time scales as being governed by gradual change.  If things do change the changes must certainly be brought about by constant laws. We think of the speed of light and the strength of the forces as being constant.  But as we are able to see at greater time scales we have found over and over that things we thought were constant do change—stars die, galaxies form, hot rocks flows like water, and the universe expands at an accelerating pace.  There are a growing number of people asking whether the laws of nature also change.  Until we ask this we aren’t done looking at the possibilities so I was excited to read the paper.

Luboš Motl lambasts the idea here.

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