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Sunday, August 10, 2008

Dark Energy :The most direct signal of dark energy?


Dark energy
In physical cosmology, dark energy is an exotic form of energy that permeates all of space and tends to increase the rate of expansion of the universe.[1] Dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for 73% of the total mass-energy of the universe.

Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously,[2] and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space, are usually also included in the cosmological constant. The cosmological constant is physically equivalent to vacuum energy. Scalar fields which do change in space can be difficult to distinguish from a cosmological constant, because the change may be extremely slow.

High-precision measurements of the expansion of the universe are required to understand how the expansion rate changes over time. In general relativity, the evolution of the expansion rate is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today.

Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. Dark energy has been used as a crucial ingredient in a recent attempt[3] to formulate a cyclic model for the universe.

It makes up some three-quarters of the mass–energy content of the universe and it’s responsible for cosmic acceleration, but that’s about all we know about dark energy. So what should we make of a bold claim for the “most direct” signal of dark energy yet? roots out all the answers.

So who’s making the claim?
A group of astrophysicists led by István Szapudi at the University of Hawaii. They have analyzed the glow of microwave photons emanating from space to see how the size of massive galaxy “superclusters” changes over time. If our universe is flat — and observations suggest this is indeed the case — Einstein’s theory of gravity predicts supercluster size should stay the same. However, the Hawaii researchers have found that the superclusters are being stretched apart — the hallmark of repulsive dark energy.

This doesn’t happen everyday, especially for theorists like us who mainly deal with abstract mathematical concepts
István Szapudi, University of Hawaii
How do they analyze the photons?
The microwave photons in question, known as the cosmic microwave background (CMB), have permeated the entire cosmos since matter and radiation first “decoupled” some 380,000 years after the Big Bang. In fact, the glow of the CMB is so regular that astrophysicists can use it to illuminate the dynamics of large structures like galaxy clusters and superclusters. Taking data from a galaxy catalogue called the Sloan Digital Sky Survey, Szapudi’s team plot the location of superclusters on a map of the CMB. They can then compare how the CMB map looks in regions where there are superclusters with regions where there is empty space, or supervoids.

How does the comparison show that the superclusters are being stretched?
In the same way you gain gravitational potential energy as you walk up a hill, a photon gains energy when it is fronted by the huge jump in gravity of a supercluster. One might think that the photon loses the same energy when it leaves the other side. However, if the supercluster is stretched as the photon is passing through, the photon will experience a smaller change in gravity when it leaves than when it arrived. In other words, the photon will get to keep a token of its extra energy. Szapudi and his colleagues look out for these slightly more energetic photons by monitoring temperature. The difference isn’t big — only about a millionth of a Kelvin.
Is Szapudi’s team the first to see this extra energy?
No. The phenomenon is called the Integrated Sachs–Wolfe (ISW) effect, and the idea of using it to look at the dynamics of superclusters was first proposed by cosmologists Rob Crittenden and Neil Turok while they were at Princeton University in 1995. Since then a handful of astrophysicists have taken up the challenge, including teams led by Bob Nichol and Crittenden of Portsmouth University in the UK, Enrique Gaztanaga of the Institute of Space Sciences in Spain and Nikhil Padmanabhan of Lawrence Berkeley Laboratory in the US. In the past few years these teams have detected the ISW effect with increasing confidence.

2008 is the coming of age for the Integrated Sachs–Wolfe effect
Bob Nichol, Portsmouth University
Is Szapudi’s team now even more confident?
Well, it’s not so much the statistical confidence that’s a big deal — they claim to detect the ISW effect at just above four sigma (or 99.9995% certainty), which is in the same league as other confidence values reported this year. The important aspect of the Hawaiian researchers’ work is that they have focussed their attention on a single sample of the biggest superclusters and supervoids. The result is a cleaner, less noisy signal that is more trustworthy. In the words of Szapudi: “…We were ecstatic. It is a very subtle and small effect, and this was the first time we could actually see it, which is very different from detecting it from more abstract statistics.”

So why is it the most direct signal of dark energy?
There are many ways to infer dark energy, but almost all rely on large-scale effects and, arguably, unproven assumptions. For example, cosmic acceleration (and hence dark energy) was originally discovered in 1998 by looking at the receding light of distant supernovae, yet the precise mechanism behind a supernova explosion itself is unknown. Few doubt the dark-energy interpretation of those supernovae observations now, of course, but that’s mostly because they have been corroborated time and time again using other techniques. Observations of the ISW effect are part of that corroboration also, but are “direct” in the sense that they relate to the growth of individual structures.

Photon temperature of voids (left) versus clusters (right)
What’s been the reaction to the work?
Szapudi for one is pleased. After he had convinced himself that the results were real in February this year, which was about the time of his 42nd birthday, his team offered him a jelly birthday cake in the shape of a hot and cold spot in the CMB (see figure above). Celebrations aside, Nichol of the Portsmouth group thinks the Hawaiian team has presented “perhaps the most complete analysis” of the ISW effect to date. Nichol also describes 2008 as the “coming of age” of the ISW effect because groups working on the ISW effect now agree over the strength and reliability of the data.

So what’s next for the ISW effect?
Until more precise galaxy surveys come out, which will probably be sometime next decade, all’s pretty much done and dusted from the astrophysicist’s point of view. Theorists, however, can have endless fun examining the analyses by Szapudi and others to try and get a better grip on the nature of dark energy. Current opinion seems to be veering in favour of a “cosmological constant” which manifests as a vacuum energy, although there are several other options. One is that Einstein’s theory of gravity — general relativity — is not 100% complete and needs to be tweaked to account for cosmic acceleration. The ISW effect is particularly good for testing such “modified gravity” theories because it looks specifically at the apparent strength of gravity on large scales.

Physic Ventures budjet, tops off first healthcare fund at $159M


The US has slashed funding for the International Linear Collider (ILC) by 75 % as the budget for 2008 has been finally agreed between the Republican Bush Administration and Democratic Congress. The new budget legislation, which US president George W Bush is expected to sign by 31 December, will see up to 200 scientists at the Fermi National Accelerator Laboratory (Fermilab) lose their jobs. Funding for the international ITER fusion experiment, which is about to be built in France, has also been cut.

After 11 months of debate between the political parties, the budget compromise left the Department of Energy’s Office of Sciences, which funds much of American physics, with $4.02 bn for the financial year which began this October – a rise of 2.6 % compared to 2007 and $504 million below the Administration’s original request. “The appropriation falls so far short of the request that there will be painful cutbacks in laboratory plans,” says Kei Koizumi, a budget analyst at the American Association for the Advancement of Science.

Fusion hit hardest

High-energy physics will bear the brunt of the cuts, falling by 8.5 % to just $688 m. Research into nuclear fusion takes an even larger hit falling by 10.2 % to $287 m compared to last year .

The cuts, announced at extremely short notice, have immediate and significant impact at Fermilab. The lab learned to their astonishment that they will have just $310 m to spend this financial year from an expected $372 m. The budget process has even specified which Fermilab programmes will receive the bulk of the cuts – the most prominent being the 75 % cut for the ILC, which is set to be the next big experiment in particle physics after the Large Hadron Collider at CERN. Funding will fall from $60 million to just $15 million. But as Fermilab has spent roughly that much since the start of the financial year on the project, further spending on the ILC is effectively zero. Funding for the initial construction of the NOvA neutrino experiment at Fermilab has also been cut. “It’s a devastating blow,” said Fermilab’s director Pier Oddone.

Lay-offs and unpaid leave

Oddone moved fast to deal with the situation. At a meeting of the entire lab on 20 December, he announced that he would lay off 200 members of the 1,900-member Fermilab staff. Since severance payments will eat up some of the savings, Oddone announced that staff will have to take 2 days of unpaid leave per month. In making those decisions, Oddone has a two-fold goal: To ensure that the Tevatron accelerator continues to chase the Higgs boson until its scheduled closure in 2009, and to guarantee that Fermilab will continue to make significant contributions to elementary particle physics after that date. “We have a rugged plan to deliver results that matter,” says Fermilab spokesperson Judith Jackson.

The ILC is not the only international venture to suffer in the budget. The US contribution to the International Thermonuclear Experimental Reactor (ITER) also falls to zero compared with a requested amount of $160 million, although the budget includes $10.72 m for American R&D on the project. The budget document adds a warning that “funding may not be reprogrammed from other activities within Fusion Energy Sciences to restore the U.S. contribution to ITER.”

The effect on ITER’s progress may be relatively small. “I don't expect much of a delay,” Koizumi says, “because the other international partners are paying for most of the construction, and it's already facing some delays.” However, cutting ITER’s funding has one virtue: allowing three American fusion facilities – the DIII-D in San Diego, the Alcator C-Mod at the MIT plasma science and fusion center, and the National Spherical Torus Experiment at the Princeton Plasma Physics Laboratory, to be funded at close to their requested levels.

The new budget legislation has put American physicists into a grim mood. A year that started with great hope of increased funding is ending on a note of near despair coming just days after the UK announced that it plans to pull out of the ILC altogether.

Physic Ventures, a San Francisco venture firm that invests in companies focused on healthcare and sustainable living for consumers, has finished raising its first fund of $159 million.

So far, Physic has put money into five companies, including sleep-inducing chocolate maker Dreamerz Food, the interactive exercise company Expresso Fitness and eco-friendly plastic producer Novomer.

Managing director Will Rosenzweig said that where traditional life science investors put money into things like drugs that are reimbursed by health-care providers, Physic will invest in products over which consumers have more decision power. A complete map of potential investment areas can be found here.

Physic started off in April 2007 with a $125 million commitment from consumer goods giant Uniliver, which was later reduced to take on investments from institutions, pension funds and strategic investors.

The firm seeks to exploit synergies between its strategic investors, like Unilever and healthcare giant Humana, and its various portfolio companies. Dreamerz Food products, for example, are carried in Pharmaca stores — another Physic investment.

Previous reports indicated that Physic had raised $190 million; Rosenzweig says the fund was oversubscribed to that amount, but the investment was cut back, and Unilever’s portion reduced to about half of the total.

The patch for critical Internet flaw may be flawed itself


Up until Matasano mistakenly let the cat out of the bag about the DNS forgery attack that Dan Kaminsky found, lots of experts were downplaying the problem as old and known. Once the details were released, those same folks agreed, that yes, the problem Kaminsky found was that bad. Since Kaminsky gave his presentation about the DNS vulnerability (along with two blog posts explaining Why So Serious and a Summary), a lot of noise is being made about the impacts

researcher has reported there are gaping holes in the patch for the DNS flaw that threatened the foundations of the Internet.

Just a month ago, Dan Kaminsky told the world that the Internet’s Domain Name Server system for routing Internet users to the proper addresses for web sites could be compromised. He had organized a months-long effort to create a patch to fix the problem. But not it appears the patch doesn’t do the job, according to a story in the New York Times. It confirms Kaminsky’s own warning that the patch was a stopgap measure and that there were worse things coming out.

Evgeniy Polyakov, a physicist, said that he figured out a flaw in the patch for DNS, which is like the Internet’s telephone book, in just ten hours of work. He posted the news on his blog. Kaminsky said at Black Hat this week that the threat of the flaw was wider than he announced on July 8. That’s because there are a series of common Internet functions — such as sending a new password to a user who has forgotten it — that depend on the accuracy of DNS addresses. (Our interview with Kaminsky).

Meanwhile, companies such as Secure64, which makes a secure operating system, are advocating a shift from DNS to a more secure form of the addressing system, dubbed DNSSEC. But it will likely take a long time for such an infrastructure shift to be implemented.

The patch is still better than no patch at all.

:”The question is, if you are in a boat, which would you rather have - a gaping hole letting water flood in, or a pinhole?,” said Brian Dickson, a DNS expert, in an email. “Hint: With a pinhole leak, you have the option of bailing water out of your boat until help arrives… with a gaping hole, not so much.”

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