It’s not every day that you find a Physics book that is both wonderfully thorough and wildly entertaining – but, then again, it’s not every day that Dave Goldberg publishes a book; he’d be quite the busy boy if that was the case. But as writer for the fantastic Ask a Physicist column on io9.com (seriously, check it out), professor and director of undergraduate studies at Drexel University, Slate and LA Times contributor, husband and father – he’s plenty busy already. As an avid reader of Ask A Physicist, I was already familiar with his entertaining writing style – but getting to enjoy it in a full-length book was quite the treat.
Enter The Universe In The Rearview Mirror. Although many recent physics books focus almost entirely on the oddities of quantum mechanics, Goldberg steps outside the now almost tiresome discussions of randomness and Schrodinger’s Cat to enlighten readers on a topic less often discussed, but just as (if not more) fascinating – symmetry. Goldberg’s perusal of symmetry extends far beyond your Elementary School-inspired notions of bilaterally symmetric shapes into questions about the origins, shape and inevitable fate of the universe – among many others!
At most times in Rearview Mirror, Goldberg’s style feels more like a discussion than a book – it’s as if your delightfully nerdy friend from college (the one with a knack for identifying stars, he’s convinced it’s a total turn-on) came over for dinner one night to talk about his favorite topic – the mysteries of the cosmos. Even with the conversational essence, Goldberg is sure to never get bogged down in scientific jargon,instead he frequently relies on allusions and analogies to get his point across.
In the book’s first five pages alone Goldberg makes creative allusions to Star Wars, Angels & Demons, Isaac Asimov, The Incredible Hulk, Twilight , and Star Trek. In the world of science writing since The Big Bang Theory, countless authors have tried to appeal to the “nerdy” sub-genre, but the allusions and comparisons in most books typically seem forced, even irrelevant at times. Perhaps due to his extensive teaching experience, this is never the case with Goldberg’s writing – every allusion is spot-on and fascinating, even Feynman-like at times. Never before had I thought of Lewis Carroll’s Alice jumping down the rabbit hole when discussing a black hole, and now I’ll never be able to think of taking the plunge without doing so.
Throughout the slightly-over-300-page-journey, readers explore fascinating conundrums posed as the subtitle of every chapter, concerning topics like Antimatter (“why there is something rather than nothing”), The Cosmological Principle (“why it is dark at night”) and quantum Spin (“why you aren’t a sentient cloud of helium and what a spoonful of neutron star would do to you”). Although each chapter does seek to answer these questions, the excitement comes from Goldberg’s masterful leadership – he paves the way with insightful analogies and surprisingly digestible descriptions of complex concepts (no equations allowed).
Once the journey is over, readers will not only have a thorough understanding of how symmetry truly shapes our universe, but also a plethora of exciting dinner conversations sure to spice up any date – “Hey, did you know that poker can teach us a lot about entropy?”
This "SWASI" phenomenon is an analogue of the SASI instability occurring in the supernova core, but it is one million times smaller and about one hundred times slower than its astrophysical counterpart. (Image copyrights: Thierry Foglizzo, Laboratoire AIM Paris-Saclay, CEA)
It’s one of the most intense and violent of all events in space – a supernova. Now a team of researchers at the Max Planck Institute for Astrophysics have been taking a very specialized look at the formation of neutron stars at the center of collapsing stars. Through the use of sophisticated computer simulations, they have been able to create three-dimensional models which show the physical effects – intense and violent motions which occur when stellar matter is drawn inward. It’s a bold, new look into the dynamics which happen when a star explodes.
As we know, stars which have eight to ten times the mass of the Sun are destined to end their lives in a massive explosion, the gases blown into space with incredible force. These cataclysmic events are among the brightest and most powerful events in the Universe and can outshine a galaxy when they occur. It is this very process which creates elements critical to life as we know it – and the beginnings of neutron stars.
Neutron stars are an enigma unto themselves. These highly compact stellar remnants contain as much as 1.5 times the mass of the Sun, yet are compressed to the size of a city. It is not a slow squeeze. This compression happens when the stellar core implodes from the intense gravity of its own mass… and it takes only a fraction of a second. Can anything stop it? Yes. It has a limit. Collapse ceases when the density of the atomic nuclei is exceeded. That’s comparable to around 300 million tons compressed into something the size of a sugar cube.
Studying neutron stars opens up a whole new dimension of questions which scientists are keen to answer. They want to know what causes stellar disruption and how can the implosion of the stellar core revert to an explosion. At present, they theorize that neutrinos may be a critical factor. These tiny elemental particles are created and expelled in monumental numbers during the supernova process and may very well act as heating elements which ignite the explosion. According to the research team, neutrinos could impart energy into the stellar gas, causing it to build up pressure. From there, a shock wave is created and as it speeds up, it could disrupt the star and cause a supernova.
As plausible as it might sound, astronomers aren’t sure if this theory could work or not. Because the processes of a supernova cannot be recreated under laboratory conditions and we’re not able to directly see into the interior of a supernovae, we’ll just have to rely on computer simulations. Right now, researchers are able to recreate a supernova event with complex mathematical equations which replicate the motions of stellar gas and the physical properties which happen at the critical moment of core collapse. These types of computations require the use of some of the most powerful supercomputers in the world, but it has also been possible to use more simplified models to get the same results. “If, for example, the crucial effects of neutrinos were included in some detailed treatment, the computer simulations could only be performed in two dimensions, which means that the star in the models was assumed to have an artificial rotational symmetry around an axis.” says the research team.
With the support of the Rechenzentrum Garching (RZG), scientists were able to create in a singularly efficient and fast computer program. They were also given access to most powerful supercomputers, and a computer time award of nearly 150 million processor hours, which is the greatest contingent so far granted by the “Partnership for Advanced Computing in Europe (PRACE)” initiative of the European Union, the team of researchers at the Max Planck Institute for Astrophysics (MPA) in Garching could now for the first time simulate the processes in collapsing stars in three dimensions and with a sophisticated description of all relevant physics.
“For this purpose we used nearly 16,000 processor cores in parallel mode, but still a single model run took about 4.5 months of continuous computing”, says PhD student Florian Hanke, who performed the simulations. Only two computing centers in Europe were able to provide sufficiently powerful machines for such long periods of time, namely CURIE at Très Grand Centre de calcul (TGCC) du CEA near Paris and SuperMUC at the Leibniz-Rechenzentrum (LRZ) in Munich/Garching.
Turbulent evolution of a neutron star for six moments (0.154, 0.223, 0.240, 0.245, 0.249 and 0.278 seconds) after the beginning of the neutron star formation in a threedimensional computer simulation. The mushroom-like bubbles are characteristic of “boiling” neutrino-heated gas, whereas simultaneously the “SASI” instability causes wild sloshing and rotational motions of the whole neutrino-heated layer (red) and of the enveloping supernova shock (blue) . (Images by Elena Erastova and Markus Rampp, RZG)Given several thousand billion bytes of simulation data, it took some time before researchers could fully understand the implications of their model runs. However, what they saw both elated and surprised them. The stellar gas performed in a manner very much like ordinary convection, with the neutrinos driving the heating process. And that’s not all… They also found strong sloshing motions which transiently change to rotational motions. This behavior has been observed before and named Standing Accretion Shock Instability. According to the news release, “This term expresses the fact that the initial sphericity of the supernova shock wave is spontaneously broken, because the shock develops large-amplitude, pulsating asymmetries by the oscillatory growth of initially small, random seed perturbations. So far, however, this had been found only in simplified and incomplete model simulations.”
“My colleague Thierry Foglizzo at the Service d’ Astrophysique des CEA-Saclay near Paris has obtained a detailed understanding of the growth conditions of this instability”, explains Hans-Thomas Janka, the head of the research team. “He has constructed an experiment, in which a hydraulic jump in a circular water flow exhibits pulsational asymmetries in close analogy to the shock front in the collapsing matter of the supernova core.” Known as Shallow Water Analogue of Shock Instability, the dynamic process can be demonstrated in less technicalized manners by eliminating the important effects of neutrino heating – a reason which causes many astrophysicists to doubt that collapsing stars might go through this type of instability. However, the new computer models are able to demonstrate the Standing Accretion Shock Instability is a critical factor.
“It does not only govern the mass motions in the supernova core but it also imposes characteristic signatures on the neutrino and gravitational-wave emission, which will be measurable for a future Galactic supernova. Moreover, it may lead to strong asymmetries of the stellar explosion, in course of which the newly formed neutron star will receive a large kick and spin”, describes team member Bernhard Müller the most significant consequences of such dynamical processes in the supernova core.
Are we finished with supernova research? Do we understand everything there is to know about neutron stars? Not hardly. At the present time, the scientist are ready to further their investigations into the measurable effects connected to SASI and refine their predictions of associated signals. In the future they will further their understanding by performing more and longer simulations to reveal how instability and neutrino heating react together. Perhaps one day they’ll be able to show this relationship to be the trigger which ignites a supernova explosion and conceives a neutron star.
A sequence of images showing the light echo (circled) enshrouding T Pyxidis months after the April 2011 outburst. (Credit: NASA/ESA/A. Crotts/J. Sokoloski, H. Uthas & S. Lawrence).
Some of the most violent events in our Universe were the topic of discussion this morning at the 222nd meeting of the American Astronomical Society in Indianapolis, Indiana as researchers revealed recent observations of light echoes seen as the result of stellar explosions.
A light echo occurs when we see dust and ejected material illuminated by a brilliant nova. A similar phenomenon results in what is termed as a reflection nebula. A star is said to go nova when a white dwarf star siphons off material from a companion star. This accumulated hydrogen builds up under terrific pressure, sparking a brief outburst of nuclear fusion.
A very special and rare case is a class of cataclysmic variables known as recurrent novae. Less than dozen of these types of stars are known of in our galaxy, and the most famous and bizarre case is that of T Pyxidis.
Located in the southern constellation of Pyxis, T Pyxidis generally hovers around +15th magnitude, a faint target even in a large backyard telescope. It has been prone, however, to great outbursts approaching naked eye brightness roughly every 20 years to magnitude +6.4. That’s a change in brightness almost 4,000-fold.
But the mystery has only deepened surrounding this star. Eight outbursts were monitored by astronomers from 1890 to 1966, and then… nothing. For decades, T Pyxidis was silent. Speculation shifted from when T Pyxidis would pop to why this star was suddenly undergoing a lengthy phase of silence.
Could models for recurrent novae be in need of an overhaul?
T Pyxidis finally answered astronomers’ questions in 2011, undergoing its first outburst in 45 years. And this time, they had the Hubble Space Telescope on hand to witness the event.
Light curve of the 2011 eruption of T Pyxidis. (Credit: AAVSO).
In fact, Hubble had just been refurbished during the final visit of the space shuttle Atlantis to the orbiting observatory in 2009 on STS-125 with the installation of its Wide Field Camera 3, which was used to monitor the outburst of T Pyxidis.
The Hubble observation of the light echo provided some surprises for astronomers as well.
“We fully expected this to be a spherical shell,” Said Columbia University’s Arlin Crotts, referring to the ejecta in the vicinity of the star. “This observation shows it is a disk, and it is populated with fast-moving ejecta from previous outbursts.”
Indeed, this discovery raises some exciting possibilities, such as providing researchers with the ability to map the anatomy of previous outbursts from the star as the light echo evolves and illuminates the 3-D interior of the disk like a Chinese lantern. The disk is inclined about 30 degrees to our line of sight, and researchers suggest that the companion star may play a role in the molding of its structure from a sphere into a disk. The disk of material surrounding T Pyxidis is huge, about 1 light year across. This results in an apparent ring diameter of 6 arc seconds (about 1/8th the apparent size of Jupiter at opposition) as seen from our Earthly vantage point.
Paradoxically, light echoes can appear to move at superluminal speeds. This illusion is a result of the geometry of the path that the light takes to reach the observer, crossing similar distances but arriving at different times.
And speaking of distance, measurement of the light echoes has given astronomers another surprise. T Pyxidis is located about 15,500 light years distant, at the higher 10% end of the previous 6,500-16,000 light year estimated range. This means that T Pyxidis is an intrinsically bright object, and its outbursts are even more energetic than thought.
Light echoes have been studied surrounding other novae, but this has been the first time that scientists have been able to map them extensively in 3 dimensions.
An artist’s conception of the disk of material surrounding T Pyxidis. (Credit: ESA/NASA & A. Feild STScl/AURA).
“We’ve all seen how light from fireworks shells during the grand finale will light up the smoke and soot from the shells earlier in the show,” said team member Stephen Lawrence of Hofstra University. “In an analogous way, we’re using light from T Pyx’s latest outburst and its propagation at the speed of light to dissect its fireworks displays from decades past.”
Researchers also told Universe Today of the role which amateur astronomers have played in monitoring these outbursts. Only so much “scope time” exists, very little of which can be allocated exclusively to the study of light echoes. Amateurs and members of the American Association of Variable Star Observers (AAVSO) are often the first to alert the pros that an outburst is underway. A famous example of this occurred in 2010, when Florida-based backyard observer Barbara Harris was the first to spot an outburst from recurrent novae U Scorpii.
And although T Pyxidis may now be dormant for the next few decades, there are several other recurrent novae worth continued scrutiny:
Name
Max brightness
Right Ascension
Declination
Last Eruption
Period(years)
U Scorpii
+7.5
16H 22’ 31”
-17° 52’ 43”
2010
10
T Pyxidis
+6.4
9H 04’ 42”
-32° 22’ 48”
2011
20
RS Ophiuchi
+4.8
17H 50’ 13”
-6° 42’ 28”
2006
10-20
T Coronae Borealis
+2.5
15H 59’ 30”
25° 55’ 13”
1946
80?
WZ Sagittae
+7.0
20H 07’ 37”
+17° 42’ 15”
2001
30
Clearly, recurrent novae have a tale to tell us of the role they play in the cosmos. Congrats to Lawrence and team on the discovery… keep an eye out from future fireworks from this rare class of star!
Time Reborn: From the Crisis of Physics to the Future of the Universe is one of those books intended to provoke discussion. Right from the first pages, author Lee Smolin — a Canadian theoretical physicist who also teaches philosophy — puts forward a position: time is real, and not an illusion of the human experience (as other physicists try to argue).
Smolin, in fact, uses that concept of time as a basis for human free will. If time is real, he writes, this is the result: “Novelty is real. We can create, with our imagination, outcomes not computable from knowledge of the present.”
Physics as philosophy. A powerful statement to make in the opening parts of the book. The only challenge is understanding the rest of it.
Smolin advertises his book as open to the general reader who has no background in physics or mathematics, promising that there aren’t even equations to worry about. He also breaks up the involved explanations with wry observations of fatherhood, or by bringing up anecdotes from his past.
Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time. Image credit: NASA
It works, but you need to be patient. Theoretical physics is so far outside of the everyday that at times it took me (with education focusing on journalism and space policy, admittedly) two or three readings of the same passage to understand what was going on.
But as I took my time, a whole world opened up to me.
I found myself understanding more about Einstein’s special and general relativity than I did in readings during high school and university. The book also made me think differently about cosmology (the nature of the universe), especially in relation to biological laws.
While the book is enjoyable, it is probably best not to read it in isolation as it is a positional one — a book that gathers information scientifically and analytically, to be sure, but one that does not have a neutral point of view to the conclusions.
We’d recommend picking up other books such as the classic A Brief History of Time (by physicist Stephen Hawking) to learn more about the universe, and how other scientists see time work.
The CREAM instrument prior to launch aboard a long-duration balloon. (NASA)
Balloon-based research on cosmic particles that began over a century ago will get a big boost next year — all the way up to low-Earth orbit, when NASA’s Cosmic Ray Energetics and Mass (CREAM) will be sent to the Space Station thus becoming (are you ready for this?) ISS-CREAM, specifically designed to detect super-high-energy cosmic rays and help scientists determine what their mysterious source(s) may be.
“The answer is one the world’s been waiting on for 100 years,” said program scientist Vernon Jones.
Read more about this “cool” experiment below:
Cosmic Ray Energetics and Mass (CREAM) will be the first cosmic ray instrument designed to detect at such higher energy ranges, and over such an extended duration in space. Scientists hope to discover whether cosmic rays are accelerated by a single cause, which is believed to be supernovae. The new research also could determine why there are fewer cosmic rays detected at very high energies than are theorized to exist.
“Cosmic rays are energetic particles from outer space,” said Eun-Suk Seo, principal investigator for the CREAM study. “They provide a direct sample of matter from outside the solar system. Measurements have shown that these particles can have energies as high as 100,000 trillion electron volts. This is an enormous energy, far beyond and above any energy that can be generated with manmade accelerators, even the Large Hadron Collider at CERN.”
Researchers also plan to study the decline in cosmic ray detection, called the spectral “knee” that occurs at about a thousand trillion electron-volts (eV), which is about 2 billion times more powerful than the emissions in a medical nuclear imaging scan. Whatever causes cosmic rays, or filters them as they move through the galaxy, takes a bite out of the population from 1,000 trillion electron-volts upwards. Further, the spectrum for cosmic rays extends much farther beyond what supernovas are believed to be able to produce.
A long-duration balloon carrying CREAM prepares to launch from a location near McMurdo Station (NASA)
To tackle these questions, NASA plans to place CREAM aboard the space station, becoming ISS-CREAM. The instrument has flown six times for a total of 161 days on long-duration balloons circling the South Pole, where Earth’s magnetic field lines are essentially vertical.
The idea of energetic particles coming from space was unknown in 1911 when Victor Hess, the 1936 Nobel laureate in physics credited for the discovery of cosmic rays, took to the air to tackle the mystery of why materials became more electrified with altitude, an effect called ionization. The expectation was that the ionization would weaken as one got farther from Earth. Hess developed sensitive instruments and took them as high as 3.3 miles (5.3 kilometers) and he established that ionization increased up to fourfold with altitude, day or night.
A better understanding of cosmic rays will help scientists finish the work started when Hess unexpectedly turned an earthly question into a stellar riddle. Answering that riddle will help us understand a hidden, fundamental facet of how our galaxy, and perhaps the universe, is built and works.
The phenomenon soon gained a popular but confusing name, cosmic rays, from a mistaken theory that they were X-rays or gamma rays, which are electromagnetic radiation, like light. Instead, cosmic rays are high-speed, high-energy particles of matter.
As particles, cosmic rays cannot be focused like light in a telescope. Instead, researchers detect cosmic rays by the light and electrical charges produced when the particles slam into matter. The scientists then use detective work to identify the original particle by direct measurement of its electric charge and its energy determination from the avalanche of debris particles creating their own overlapping trails.
CREAM schematic
CREAM does this trace work using an ionization calorimeter designed to make cosmic rays shed their energies. Layers of carbon, tungsten and other materials present well-known nuclear “cross sections” within the stack. Electrical and optical detectors measure the intensity of events as cosmic particles, from hydrogen to iron, crash through the instrument.
Even though CREAM balloon flights reached high altitudes, enough atmosphere remained above to interfere with measurements. The plan to mount the instrument to the exterior of the space station will place it above the obscuring effects of the atmosphere, at an altitude of 250 miles (400 kilometers).
“On what can we now place our hopes of solving the many riddles which still exist as to the origin and composition of cosmic rays?”
Two images from the test of a E-Cat device
performed on Nov. 20th 2012. Credit: Levi, Foschi et al.
Cold fusion has been called one of the greatest scientific breakthroughs that might likely never happen. On the surface, it seems simple – a room-temperature reaction occurring under normal pressure. But it is a nuclear reaction, and figuring it out and getting it to work has not been simple, and any success in this area could ultimately – and seriously — change the world. Despite various claims of victory over the years since 1920, none have been able to be replicated consistently and reliably.
But there’s buzz this week of a cold fusion experiment that has been replicated, twice. The tests have reportedly produced excess heat with roughly 10,000 times the energy density and 1,000 times the power density of gasoline.
The names involved are familiar in the cold fusion circles: Italian entrepreneur Andrea Rossi has been claiming for several years that his E-Cat device produces heat through a process called a Low Energy Nuclear Reaction (LENR), and puts out more energy than goes in. In the past, Rossi didn’t allow anyone to verify his device because he claimed his device was an “industrial trade secret.”
But a new paper published on arXiv last week says that seven independent scientists have performed tests of two E-Cat prototypes under controlled conditions, using high-precision instrumentation. Although the authors of the paper wrote that they weren’t allowed to see what was going on inside the sealed steel cylinder reactor, they did write in their paper, “Even by the most conservative assumptions as to the errors in the measurements, the result is still one order of magnitude greater than conventional energy sources.“
The team did two tests:
The first test experiment, lasting 96 hours (from Dec. 13th 2012, to Dec. 17th 2012), was carried out by the two first authors of this paper, Levi and Foschi, while the second experiment, lasting for 116 hours (from March 18th 2013, to March 23rd 2013), was carried out by all authors.
Previously, Rossi and his colleague Sergio Focardi have said their device works by infusing hydrogen into nickel, transmuting the nickel into copper and releasing a large amount of heat.
As expected, the paper – which is not peer-reviewed – and Rossi’s work have both been met with lots of skepticism.
Steven Krivit, writing in the New Energy Times said that the paper by Levi, Foschi et al doesn’t describe any independent test but that authors were just witnesses of a Rossi demonstration.
The folks at the Martin Fleishman Memorial Project website – a group that facilitates the wide-spread replication and validation of things like LENR in an open and scientific manner – say they have an overall positive impression of the paper by Levi and Foschi.
“Our preliminary assessment among the team is that it is a generally good report with no obvious errors or glaring omissions,” they wrote on their website. “It is easily the best evidence to date that Rossi has a working technology, and, if verified openly and widely, this report could be remembered as historic.”
But they also don’t have total confidence in the paper. “It is unfortunate that there are some justified concerns about the independence of the test team, since many of the authors are names that we have seen before in the context of Rossi.” Plus, they are disappointed that none of the authors of the Levi and Foschi paper are willing to present their findings at an upcoming conference.
They also have several other technical questions and criticisms, as do many others.
It’s too soon to say if this latest buzz about cold fusion will amount to anything. Only time and more tests and scrutiny will reveal whether this is anything to get excited about.
What matter and antimatter might look like annihilating one another. Credit: NASA/CXC/M. Weiss
What goes up must always come down, right? Well, the European Laboratory for Particle Physics (CERN) wants to test if that principle applies to antimatter.
Antimatter, most simply speaking, is a mirror image of matter. The concept behind it is that the particles that make up matter have an opposite counterpart, antiparticles. For example, if you consider that electrons are negatively charged, an antielectron would be positively charged.
This sounds like science fiction, but as NASA says, it is “real stuff.” In past experiments, CERN’s particle accelerator has created antiprotons, positrons and even antihydrogen. Properly harnessed, antimatter could be used for applications ranging from rocketry to medicine, NASA added. But we’ll need to figure out its nature first.
Artist's concept of the Hubble Space Telescope viewing ultraviolet light from the jet of the active galactic nucleus of PKS 1424+240. Clouds of hydrogen gas along the line of sight absorb the light at known frequencies, allowing the redshift and distance of each cloud to be determined. The most distant gas cloud determines the minimum distance to PKS 1424+240. Data from the Fermi Gamma-ray Space Telescope, shown on the horizon at the left, were also used for this study. (Image composition by Nina McCurdy, component images courtesy of NASA)
When it comes to sheer wattage, blazars definitely rule. As the brightest of active galactic nuclei, these sources of extreme high-energy gamma rays are usually associated with relativistic jets of material spewing into space and enabled by matter falling into a host galaxy’s black hole. The further away they are, the dimmer they should be, right? Not necessarily. According to new observations of blazar PKS 1424+240, the emission spectrum might hold a new twist… one that can’t be readily explained.
David Williams, adjunct professor of physics at UC Santa Cruz, said the findings may indicate something new about the emission mechanisms of blazars, the extragalactic background light, or the propagation of gamma-ray photons over long distances. “There may be something going on in the emission mechanisms of the blazar that we don’t understand,” Williams said. “There are more exotic explanations as well, but it may be premature to speculate at this point.”
The Fermi Gamma-ray Space Telescope was the first instrument to detect gamma rays from PKS 1424+240, and the observation was then seconded by VERITAS (Very Energetic Radiation Imaging Telescope Array System) – a terrestrially based tool designed to be sensitive to gamma-rays in the very high-energy (VHE) band. However, these weren’t the only science gadgets in action. To help determine the redshift of the blazar, researchers also employed the Hubble Space Telescope’s Cosmic Origins Spectrograph.
To help understand what they were seeing, the team then set a lower limit for the blazar’s redshift, taking it to a distance of at least 7.4 billion light-years. If their guess is correct, such a huge distance would mean that the majority of the gamma rays should have been absorbed by the extragalactic background light, but again the answers didn’t add up. For that amount of absorption, the blazar itself would be creating a very unexpected emission spectrum.
“We’re seeing an extraordinarily bright source which does not display the characteristic emission expected from a very high-energy blazar,” said Amy Furniss, a graduate student at the Santa Cruz Institute for Particle Physics (SCIPP) at UCSC and first author of a paper describing the new findings.
Bright? You bet. In this circumstance it has to over-ride the ever-present extragalactic background light (EBL). The whole Universe is filled with this “stellar light pollution”. We know it’s there – produced by countless stars and galaxies – but it’s just hard to measure. What we do know is that when a high-energy gamma ray photo meets with a low-energy EBL photon, they essentially cancel each other out. It stands to reason that the further a gamma ray has to travel, the more likely it is to encounter the EBL, putting a limit on the distance to which we can detect high-energy gamma ray sources. By lowering the limit, the new model was then used to ” calculate the expected absorption of very high-energy gamma rays from PKS 1424+240″. This should have allowed Furniss’ team to gather an intrinsic gamma-ray emission spectrum for the most distant blazar yet captured – but all it did was confuse the issue. It just doesn’t coincide with expected emissions using current models.
“We’re finding very high-energy gamma-ray sources at greater distances than we thought we might, and in doing so we’re finding some things we don’t entirely understand,” Williams said. “Having a source at this distance will allow us to better understand how much background absorption there is and test the cosmological models that predict the extragalactic background light.”
The international Super Cryogenic Dark Matter Search (SuperCDMS) has detected what may be the particle that's thought to make up dark matter throughout the Universe.
Dark matter: it’s invisible, it’s elusive, it’s controversial… and it’s everywhere — in the Universe, yes, but especially in the world of astrophysics, where researchers have been exhaustively trying to reveal its true identity for decades.
Now, scientists with the international Super Cryogenic Dark Matter Search (SuperCDMS) experiment are reporting the detection of a particle that’s thought to make up dark matter: a weakly-interacting massive particle, or WIMP. According to a press release from Texas A&M University (whose high-energy physicist Rupak Mahapatra is a principal investigator in the experiment) SuperCDMS has identified a WIMP-like signal at the 3-sigma level, which indicates a 99.8 percent chance of an actual discovery — a “concrete hint,” as it’s being called.
“In high-energy physics, a discovery is only claimed at 5-sigma or better,” Mahapatra said. “So this is certainly very exciting, but not fully convincing by the standards. We just need more data to be sure. For now, we have to live with this tantalizing hint of one of the biggest puzzles of our time.”
If this is indeed a WIMP it will be the first time such a particle has been directly observed, lending more insight into what dark matter is… or isn’t.
Notoriously elusive, WIMPs rarely interact with normal matter and therefore are difficult to detect. Scientists believe they occasionally bounce off, or scatter like billiard balls from, atomic nuclei, leaving behind a small amount of energy capable of being tracked by detectors deep underground, particle colliders such as the Large Hadron Collider at CERN and even instruments in space like the Alpha Magnetic Spectrometer (AMS) mounted on the International Space Station.
A stack of crystal germanium CDMS detectors (Fermilab)
The CDMS experiment, located a half-mile underground at the Soudan mine in northern Minnesota and managed by the United States Department of Energy’s Fermi National Accelerator Laboratory, has been searching for dark matter since 2003. The experiment uses very sophisticated detector technology and advanced analysis techniques to enable cryogenically cooled (almost absolute zero temperature at -460 degrees F) germanium and silicon targets to search for the rare recoil of dark matter particles.
This newly-announced detection actually comes from data acquired during an earlier phase of the experiment.
“This result is from data taken a few years ago using silicon detectors manufactured at Stanford that are now defunct,” Mahapatra said. “Increased interest in the low mass WIMP region motivated us to complete the analysis of the silicon-detector exposure, which is less sensitive than germanium for WIMP masses above 15 giga-electronvolts [one GeVa is equal to a billion electron volts] but more sensitive for lower masses. The analysis resulted in three events, and the estimated background is 0.7 events.”
Although Mahapatra says the result is certainly encouraging and worthy of further investigation, he cautions it should not be considered a discovery just yet.
“We are only 99.8 percent sure, and we want to be 99.9999 percent sure,” Mahapatra said. “At 3-sigma, you have a hint of something. At 4-sigma, you have evidence. At 5-sigma, you have a discovery.”
“In medicine, you can say you are curing 99.8 percent of the cases, and that’s OK. When you say you’ve made a fundamental discovery in high-energy physics, you can’t be wrong.”
– Dr. Rupak Mahapatra, SuperCDMS principal investigator, Texas A&M University
Advanced 6-inch silicon detectors developed by Mahapatra’s lab at Texas A&M
The collaboration will continue to probe this WIMP sector using the SuperCDMS Soudan experiment’s operating germanium detectors and is considering using larger, more advanced 6-inch silicon detectors developed at the Texas A&M’s Department of Electrical Engineering in future experiments.
The team has detailed its results in a paper published in arXiv that eventually will appear in Physical Review Letters. Mahapatra will also announce the results today at 12 p.m. CDT in a talk at the Mitchell Institute for Fundamental Physics and Astronomy.
The cameras mounted in the ISS's cupola could serve as the platform for the first-ever quantum optics experiment in space.
With its 180 degree views of Earth and space, the ISS’s cupola is the perfect place for photography. But Austrian researchers want to use the unique and panoramic platform to test the limits of “spooky action at distance” in hopes of creating a new quantum communications network.
In a new study published April 9, 2012 in the New Journal of Physics, a group of Austrian researchers propose equipping the camera that is already aboard the ISS — the Nikon 400 mm NightPOD camera — with an optical receiver that would be key to performing the first-ever quantum optics experiment in space. The NightPOD camera faces the ground in the cupola and can track ground targets for up to 70 seconds allowing researchers to bounce a secret encryption key across longer distances than currently possible with optical fiber networks on Earth.
“During a few months a year, the ISS passes five to six times in a row in the correct orientation for us to do our experiments. We envision setting up the experiment for a whole week and therefore having more than enough links to the ISS available,” said co-author of the study Professor Rupert Ursin from the Austrian Academy of Sciences.
Albert Einstein first coined the phrase ‘spooky action at a distance’ during his philosophical battles with Neils Bohr in the 1930s to explain his frustration with the inadequacies of the new theory called quantum mechanics. Quantum mechanics explains actions on the tiniest scales in the domain of atoms and elemental particles. While classical physics explains motion, matter and energy on the level that we can see, 19th century scientists observed phenomena in both the macro and micro world that could not easily explained using classical physics.
In particular, Einstein was dissatisfied with the idea of entanglement. Entanglement occurs when two particles are so deeply connected that they share the same existence; meaning that they share the same mathematical relationships of position, spin, momentum and polarization. This could happen when two particles are created at the same point and instant in spacetime. Over time, as the two particles become widely separated in space, even by light-years, quantum mechanics suggests that a measurement of one would immediately impact the other. Einstein was quick to point out that this violated the universal speed limit set out by special relativity. It was this paradox Einstein referred to as spooky action.
CERN physicist John Bell partially resolved this mystery in 1964 by coming up with the idea of non-local phenomena. While entanglement allows one particle to be instantaneously influenced by its exact counterpart, the flow of classical information does not travel faster than light.
The orbital pass of the ISS over an optical ground station could be used for quantum communication from inside the Cupola Module, as long as the OGS is not more than 36° off the NADIR direction. Credit: T Scheidl, E Wille and R Ursin.The ISS experiment proposes using a “Bell experiment” to test the theoretical contradiction between predictions in quantum and classical physics. For the Bell experiment, a pair of entangled photons would be generated on the ground; one would be sent from the ground station to the modified camera aboard the ISS, while the other would be measured locally on the ground for later comparison. So far, researchers sent a secret key to receivers just a few hundred kilometers apart.
“According to quantum physics, entanglement is independent of distance. Our proposed Bell-type experiment will show that particles are entangled, over large distances — around 500 km — for the very first time in an experiment,” says Ursin. “Our experiments will also enable us to test potential effects gravity may have on quantum entanglement.”
The researchers point out that making the minor alteration to a camera already aboard the ISS will save time and money needed to build a series of satellites to test researchers’ ideas.
