Archive for the ‘Peter Woit’ Category

universe

Is our universe merely one of billions? Evidence of the existence of ‘multiverse’ revealed for the first time by a cosmic map of background radiation data gathered by Planck telescope. The first ‘hard evidence’ that other universes exist has been claimed to have been found by cosmologists studying new Planck data released this past June. They have concluded that it shows anomalies that can only have been caused by the gravitational pull of other universes.

“Such ideas may sound wacky now, just like the Big Bang theory did three generations ago,” says George Efstathiou, professor of astrophysics at Cambridge University.”But then we got evidence and now it has changed the whole way we think about the universe.”

Scientists had predicted that it should be evenly distributed, but the map shows a stronger concentration in the south half of the sky and a ‘cold spot’ that cannot be explained by current understanding of physics. Laura Mersini-Houghton, theoretical physicist at the University of North Carolina at Chapel Hill, and Richard Holman, professor at Carnegie Mellon University, predicted that anomalies in radiation existed and were caused by the pull from other universes in 2005. Mersini-Houghton will be in Britain soon promoting this theory and, we expect, the hard evidence at the Hay Festival on May 31 and at Oxford on June 11.

Dr Mersini-Houghton believes her hypothesis has been proven from the Planck data that data has been used to create a map of light from when the universe was just 380,000 years old. “These anomalies were caused by other universes pulling on our universe as it formed during the Big Bang,” she says. “They are the first hard evidence for the existence of other universes that we have seen.”

Columbia University mathematician Peter Woit writes in his blog, Not Even Wrong, that in recent years there have been many claims made for “evidence” of a multiverse, supposedly found in the CMB data. “Such claims often came with the remark that the Planck CMB data would convincingly decide the matter. When the Planck data was released two months ago, I looked through the press coverage and through the Planck papers for any sign of news about what the new data said about these multiverse evidence claims. There was very little there; possibly the Planck scientists found these claims to be so outlandish that it wasn’t worth the time to look into what the new data had to say about them.

“One exception,” Woit adds, “was this paper, where Planck looked for evidence of ‘dark flow’. They found nothing, and a New Scientist article summarized the situation: ‘The Planck team’s paper appears to rule out the claims of Kashlinsky and collaborators,’ says David Spergel of Princeton University, who was not involved in the work. If there is no dark flow, there is no need for exotic explanations for it, such as other universes, says Planck team member Elena Pierpaoli at the University of Southern California, Los Angeles. “You don’t have to think of alternatives.'”

“Dark Flow” sounds like a new SciFi Channel series. It’s not! The dark flow is controversial because the distribution of matter in the observed universe cannot account for it. Its existence suggests that some structure beyond the visible universe — outside our “horizon” — is pulling on matter in our vicinity.

Back in the Middle Ages, maps showed terrifying images of sea dragons at the boundaries of the known world. Today, scientists have observed strange new motion at the very limits of the known universe – kind of where you’d expect to find new things, but they still didn’t expect this. A huge swath of galactic clusters seem to be heading to a cosmic hotspot and nobody knows why.

Cosmologists regard the microwave background — a flash of light emitted 380,000 years after the universe formed — as the ultimate cosmic reference frame. Relative to it, all large-scale motion should show no preferred direction. A 2010 study tracked the mysterious cosmic ‘dark flow’ to twice the distance originally reported. The study was led by Alexander Kashlinsky at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

“This is not something we set out to find, but we cannot make it go away,” Kashlinsky said. “Now we see that it persists to much greater distances – as far as 2.5 billion light-years away,” he added.

Dark flow describes a possible non-random component of the peculiar velocity of galaxy clusters. The actual measured velocity is the sum of the velocity predicted by Hubble’s Law plus a small and unexplained (or dark) velocity flowing in a common direction. According to standard cosmological models, the motion of galaxy clusters with respect to the cosmic microwave background should be randomly distributed in all directions. However, analyzing the three-year WMAP data using the kinematic Sunyaev-Zel’dovich effect, the authors of the study found evidence of a “surprisingly coherent” 600–1000 km/s flow of clusters toward a 20-degree patch of sky between the constellations of Centaurus and Vela.

The clusters appear to be moving along a line extending from our solar system toward Centaurus/Hydra, but the direction of this motion is less certain. Evidence indicates that the clusters are headed outward along this path, away from Earth, but the team cannot yet rule out the opposite flow.

“We detect motion along this axis, but right now our data cannot state as strongly as we’d like whether the clusters are coming or going,” Kashlinsky said.

The unexplained motion has hundreds of millions of stars dashing towards a certain part of the sky at over eight hundred kilometers per second. Not much speed in cosmic terms, but the preferred direction certainly is: most cosmological models have things moving in all directions equally at the extreme edges of the universe. Something that could make things aim for a specific spot on such a massive scale hasn’t been imagined before. The scientists are keeping to the proven astrophysical strategy of calling anything they don’t understand “dark”, terming the odd motion a “dark flow”.

A black hole can’t explain the observations – objects would accelerate into the hole, while the NASA scientists see constant motion over a vast expanse of a billion light-years. You have no idea how big that is. This is giant on a scale where it’s not just that we can’t see what’s doing it; it’s that the entire makeup of the universe as we understand it can’t be right if this is happening.

The hot X-ray-emitting gas within a galaxy cluster scatters photons from the cosmic microwave background (CMB). Because galaxy clusters don’t precisely follow the expansion of space, the wavelengths of scattered photons change in a way that reflects each cluster’s individual motion.

This results in a minute shift of the microwave background’s temperature in the cluster’s direction. The change, which astronomers call the kinematic Sunyaev-Zel’dovich (KSZ) effect, is so small that it has never been observed in a single galaxy cluster.

But in 2000, Kashlinsky, working with Fernando Atrio-Barandela at the University of Salamanca, Spain, demonstrated that it was possible to tease the subtle signal out of the measurement noise by studying large numbers of clusters.

In 2008, armed with a catalog of 700 clusters assembled by Harald Ebeling at the University of Hawaii and Dale Kocevski, now at the University of California, Santa Cruz, the researchers applied the technique to the three-year WMAP data release. That’s when the mystery motion first came to light.

The new study builds on the previous one by using the five-year results from WMAP and by doubling the number of galaxy clusters.

“It takes, on average, about an hour of telescope time to measure the distance to each cluster we work with, not to mention the years required to find these systems in the first place,” Ebeling said. “This is a project requiring considerable followthrough.”

According to Atrio-Barandela, who has focused on understanding the possible errors in the team’s analysis, the new study provides much stronger evidence that the dark flow is real. For example, the brightest clusters at X-ray wavelengths hold the greatest amount of hot gas to distort CMB photons. “When processed, these same clusters also display the strongest KSZ signature — unlikely if the dark flow were merely a statistical fluke,” he said.

In addition, the team, which now also includes Alastair Edge at the University of Durham, England, sorted the cluster catalog into four “slices” representing different distance ranges. They then examined the preferred flow direction for the clusters within each slice. While the size and exact position of this direction display some variation, the overall trends among the slices exhibit remarkable agreement.

The researchers are currently working to expand their cluster catalog in order to track the dark flow to about twice the current distance. Improved modeling of hot gas within the galaxy clusters will help refine the speed, axis, and direction of motion.

Future plans call for testing the findings against newer data released from the WMAP project and the European Space Agency’s Planck mission, which is also currently mapping the microwave background.

Which is fantastic! Such discoveries force a whole new set of ideas onto the table which, even if they turn out to be wrong, are the greatest ways to advance science and our understanding of everything. One explanation that’s already been offered is that our universe underwent a period of hyper-inflation early in its existence, and everything we think of as the vast and infinite universe is actually a small corner under the sofa of the real expanse of reality. Which would be an amazing, if humbling, discovery.

The image at the top of the page shows the most distant object we have ever observed with high confidence, according to Wei Zheng, the leading astronomer of the team at Johns Hopkins University who that noticed the galaxy on multiple images from both the Hubble and Spitzer space telescopes. At 13.2-billion years old, we are technically seeing this galaxy when it was very young, but its light is only reaching Earth now.

http://www.dailygalaxy.com/my_weblog/2013/10/is-our-universe-one-of-billions-new-planck-data-has-anomalies-caused-by-unknown-gravitational-pull-t.html

As a young theorist in Moscow in 1982, Mikhail Shifman became enthralled with an elegant new theory called supersymmetry that attempted to incorporate the known elementary particles into a more complete inventory of the universe.

“My papers from that time really radiate enthusiasm,” said Shifman, now a 63-year-old professor at the University of Minnesota. Over the decades, he and thousands of other physicists developed the supersymmetry hypothesis, confident that experiments would confirm it. “But nature apparently doesn’t want it,” he said. “At least not in its original simple form.”

With the world’s largest supercollider unable to find any of the particles the theory says must exist, Shifman is joining a growing chorus of researchers urging their peers to change course.

In an essay posted last month on the physics website arXiv.org, Shifman called on his colleagues to abandon the path of “developing contrived baroque-like aesthetically unappealing modifications” of supersymmetry to get around the fact that more straightforward versions of the theory have failed experimental tests. The time has come, he wrote, to “start thinking and developing new ideas.”

But there is little to build on. So far, no hints of “new physics” beyond the Standard Model — the accepted set of equations describing the known elementary particles — have shown up in experiments at the Large Hadron Collider, operated by the European research laboratory CERN outside Geneva, or anywhere else. (The recently discovered Higgs boson was predicted by the Standard Model.) The latest round of proton-smashing experiments, presented earlier this month at the Hadron Collider Physics conference in Kyoto, Japan, ruled out another broad class of supersymmetry models, as well as other theories of “new physics,” by finding nothing unexpected in the rates of several particle decays.

“Of course, it is disappointing,” Shifman said. “We’re not gods. We’re not prophets. In the absence of some guidance from experimental data, how do you guess something about nature?”

Younger particle physicists now face a tough choice: follow the decades-long trail their mentors blazed, adopting ever more contrived versions of supersymmetry, or strike out on their own, without guidance from any intriguing new data.

“It’s a difficult question that most of us are trying not to answer yet,” said Adam Falkowski, a theoretical particle physicist from the University of Paris-South in Orsay, France, who is currently working at CERN. In a blog post about the recent experimental results, Falkowski joked that it was time to start applying for jobs in neuroscience.

“There’s no way you can really call it encouraging,” said Stephen Martin, a high-energy particle physicist at Northern Illinois University who works on supersymmetry, or SUSY for short. “I’m certainly not someone who believes SUSY has to be right; I just can’t think of anything better.”

Supersymmetry has dominated the particle physics landscape for decades, to the exclusion of all but a few alternative theories of physics beyond the Standard Model.

“It’s hard to overstate just how much particle physicists of the past 20 to 30 years have invested in SUSY as a hypothesis, so the failure of the idea is going to have major implications for the field,” said Peter Woit, a particle theorist and mathematician at Columbia University.

The theory is alluring for three primary reasons: It predicts the existence of particles that could constitute “dark matter,” an invisible substance that permeates the outskirts of galaxies. It unifies three of the fundamental forces at high energies. And — by far the biggest motivation for studying supersymmetry — it solves a conundrum in physics known as the hierarchy problem.

The problem arises from the disparity between gravity and the weak nuclear force, which is about 100 million trillion trillion (10^32) times stronger and acts at much smaller scales to mediate interactions inside atomic nuclei. The particles that carry the weak force, called W and Z bosons, derive their masses from the Higgs field, a field of energy saturating all space. But it is unclear why the energy of the Higgs field, and therefore the masses of the W and Z bosons, isn’t far greater. Because other particles are intertwined with the Higgs field, their energies should spill into it during events known as quantum fluctuations. This should quickly drive up the energy of the Higgs field, making the W and Z bosons much more massive and rendering the weak nuclear force about as weak as gravity.

Supersymmetry solves the hierarchy problem by theorizing the existence of a “superpartner” twin for every elementary particle. According to the theory, fermions, which constitute matter, have superpartners that are bosons, which convey forces, and existing bosons have fermion superpartners. Because particles and their superpartners are of opposite types, their energy contributions to the Higgs field have opposite signs: One dials its energy up, the other dials it down. The pair’s contributions cancel out, resulting in no catastrophic effect on the Higgs field. As a bonus, one of the undiscovered superpartners could make up dark matter.

“Supersymmetry is such a beautiful structure, and in physics, we allow that kind of beauty and aesthetic quality to guide where we think the truth may be,” said Brian Greene, a theoretical physicist at Columbia University.

Over time, as the superpartners failed to materialize, supersymmetry has grown less beautiful. According to mainstream models, to evade detection, superpartner particles would have to be much heavier than their twins, replacing an exact symmetry with something like a carnival mirror. Physicists have put forward a vast range of ideas for how the symmetry might have broken, spawning myriad versions of supersymmetry.

But the breaking of supersymmetry can pose a new problem. “The heavier you have to make some of the superpartners compared to the existing particles, the more that cancellation of their effects doesn’t quite work,” Martin explained.

Most particle physicists in the 1980s thought they would detect superpartners that are only slightly heavier than the known particles. But the Tevatron, the now-retired particle accelerator at Fermilab in Batavia, Ill., found no such evidence. As the Large Hadron Collider probes increasingly higher energies without any sign of supersymmetry particles, some physicists are saying the theory is dead. “I think the LHC was a last gasp,” Woit said.

Today, most of the remaining viable versions of supersymmetry predict superpartners so heavy that they would overpower the effects of their much lighter twins if not for fine-tuned cancellations between the various superpartners. But introducing fine-tuning in order to scale back the damage and solve the hierarchy problem makes some physicists uncomfortable. “This, perhaps, shows that we should take a step back and start thinking anew on the problems for which SUSY-based phenomenology was introduced,” Shifman said.

But some theorists are forging ahead, arguing that, in contrast to the beauty of the original theory, nature could just be an ugly combination of superpartner particles with a soupçon of fine-tuning. “I think it is a mistake to focus on popular versions of supersymmetry,” said Matt Strassler, a particle physicist at Rutgers University. “Popularity contests are not reliable measures of truth.”

In some of the less popular supersymmetry models, the lightest superpartners are not the ones the Large Hadron Collider experiments have looked for. In others, the superpartners are not heavier than existing particles but merely less stable, making them more difficult to detect. These theories will continue to be tested at the Large Hadron Collider after it is upgraded to full operational power in about two years.

If nothing new turns up — an outcome casually referred to as the “nightmare scenario” — physicists will be left with the same holes that riddled their picture of the universe three decades ago, before supersymmetry neatly plugged them. And, without an even higher-energy collider to test alternative ideas, Falkowski says, the field will undergo a slow decay: “The number of jobs in particle physics will steadily decrease, and particle physicists will die out naturally.”

Greene offers a brighter outlook. “Science is this wonderfully self-correcting enterprise,” he said. “Ideas that are wrong get weeded out in time because they are not fruitful or because they are leading us to dead ends. That happens in a wonderfully internal way. People continue to work on what they find fascinating, and science meanders toward truth.”

From Simons Science News (find the original story here)

http://www.scientificamerican.com/article.cfm?id=supersymmetry-fails-test-forcing-physics-seek-new-idea