Random thoughts about random subjects… From science to literature and between manga and watercolours, passing by data science and rugby; including film, physics and fiction, programming, pictures and puns.
I was pleasently surprised and bewildered about this article in the New York Times reporting on a recent paper in the journal Mammalia about fluorescence being observed in platypuses when shining ultraviolet light on them… Yes! Not only are platypuses the most extraordinary collection of oddities from being mammals that lay eggs, webbed feet and duck-like bills as well as being venomous… and now they also fluoresce!
I had intended to post this much ealier on, and certainly closer to the actual announcement of the Nobel Prizes in early October. It has however been a very busy period. Better late than never, right?
I was very pleased to see that the winners of the 2020 Nobel Prize in Physics were a group that combined the observational with the theoretical. Sir Roger Penrose, Reinhard Genzel, and Andrea Ghez are the recipients of the 2020 Nobel Prize in Physics. Penrose receives half the 10 million Swedish krona while Ghez and Genzel will share the other half.
Penrose’s work has taken the concept of black holes from the realm of speculation to a sound theoretical idea underpinning modern astrophysics. With the use of topology and general relativity, Penrose has provided us with an explanation to the collapse of matter due to gravity leading to the singularity at the centre of a black hole.
A few decades after the 1960’s work from Penrose we have Genzel and Ghez whose independent work using adaptive optics and speckle imaging enabled them to analyse the motion of stars tightly orbiting Sagittarius A*. Their work led to the conclusion that the only explanation for the radio source at the centre of the Milky Way’s was a black hole.
In 1916 Karl Schwarzwild described a solution to Einstein’s field equation for the curved spacetime around a mass of radius . Some terms in the solution either diverged or vanished for or . A couple of decades later, Oppenheimer and his student Hartland Snyder realised that the former value corresponded to the radius within which light, under the influence of gravity, would no longer be able to reach outside observers – the so called event horizon. Their work would need more than mathematical assumptions to be accepted.
By 1964 Penrose came up with topological picture of the gravitational collapse described and crucially doing so without the assumptions made by Oppenheimer and Snyder. His work required instead the idea of a trapped surface. In other words a 2D surface in which all light orthogonal to it converges. Penrose’s work showed that inside the event horizon, the radial direction becomes time-like. It is impossible to reverse out of the black hole and the implication is that all matter ends up at the singularity. Penrose’s research established black holes as plausible explanation for objets such s quasars and other active galactic nuclei.
Closer to Home
Although our own galaxy is by no means spewing energy like your average quasar, it still emits X-rays and other radio signals. Could it be that there is a black hole-like object at the heart of the Milky Way? This was a question that Genzel and Ghez would come to answer in time.
With the use of infrared (IR) spectroscopy, studies of gas clouds near the galactic centre showed rising velocities with decreasing distances to the centre, suggesting the presence of a massive, compact source of gravitation. These studies in the 1980s were not definitive but provided a tantalising possibility.
In the mid 1990s, both Genzel and Ghez set out to obtain better evidence with the help of large telescopes operating in the near-IR to detect photons escaping the galactic center. Genzel and colleagues began observing from Chile, whereas Ghez and her team from Hawaii.
Their independent development of speckle imaging, a technique that corrects for the distortions caused by Earth’s atmosphere enabled them to make the crucial observations. The technique improves the images by stacking a series of exposures, bringing the smeared light of individual stars into alignment. In 1997, both groups published their measurements stars movements strongly favouring the black hole explanation.
Further to that work, the use of adaptive optics by both laureates not only improved the resolutions obtained, but also provided the possibility of carrying out spectroscopic analyses which enabled them to get velocities in 3D and therefore obtain precise orbits.
The “star” object in this saga is the so-called S0-2 (Ghez’s group) or S2 (Genzel’s group) star. It approaches within about 17 light-hours of Sagittarius A* every 16 years in a highly elliptical orbit.
To find the smallest of the small, it pays to dream big. The American physicists Rainer Weiss, Kip Thorne and Barry Barish shared the 2017 Nobel Prize in Physics today for their leading roles in the https://www.quantamagazine.org/gravitational-waves-discovered-at-long-last-20160211/,” tiny ripples in space-time set in motion by faraway cataclysms such as the collisions of black holes. The existence of gravitational waves was predicted a century ago by Albert Einstein, who assumed they would be far too weak to ever detect. But Weiss, Thorne, Barish and the late Scottish physicist Ronald Drever spent decades building a hypersensitive experiment that did just that, recording contractions and expansions in the fabric of space-time less than one-thousandth the width of an atomic nucleus.
“It’s really wonderful,” Weiss said after learning of the prize this morning. “But I view this more as a thing that is recognizing the work of about 1,000 people, a dedicated effort that’s been going on for, I hate to tell you, as long as 40 years.”
In the 1960s, Thorne, a black hole expert at the California Institute of Technology who is now 77, came to believe that collisions between the invisible monsters he studied should be detectable as gravitational waves. Meanwhile, across the country at the Massachusetts Institute of Technology’s https://www.quantamagazine.org/rainer-weiss-remembering-the-little-room-in-the-plywood-palace-20170615/,” Weiss, now 85, came up with the concept for how to detect them. They, along with Drever, founded in 1984 the project that became the Laser Interferometer Gravitational-Wave Observatory (LIGO). More than three decades later, in September 2015, LIGO’s two giant detectors recorded gravitational waves for the first time.
“This was a high-risk, very-high-potential-payoff enterprise,” Thorne told Quanta last year.
After LIGO’s breakthrough success, he and Weiss were seen as shoo-ins to win a physics Nobel. The committee chose to give half of the award to Weiss and split the other half between Thorne and Barish. (Drever, who died in March, was ineligible as the prize is not awarded posthumously, and the gravitational-wave discovery did not make the deadline for consideration last year.)
Barish’s recognition by the Nobel committee was harder to predict. He “was the organizational genius who made this thing go,” Thorne told Quanta. Barish, a Caltech particle physicist who is now 81, replaced the talented but discordant “troika” of Drever, Thorne and Weiss as leader of LIGO in 1994. Barish established the LIGO Scientific Collaboration, which now has more than 1,000 members, and orchestrated the construction of LIGO’s detectors in Louisiana and Washington state.
Left to right: Kip Thorne, Rainer Weiss and Barry Barish.
From left to right: Courtesy of the Caltech Alumni Association; Bryce Vickmark; R. Hahn
Weiss, Thorne and Barish — all now professors emeritus — and their LIGO collaborators have kick-started a new era of astrophysics by tuning in to these tremors in space-time geometry. As they radiate past Earth, gusts of gravitational waves alternately stretch and squeeze the four-kilometer-long arms of LIGO’s detectors by a fraction of an atom’s width. With princess-and-pea sensitivity, laser beams bouncing along both arms of the L-shape detectors overlap to reveal fleeting differences in the arms’ lengths. By studying the form of a gravitational-wave signal, scientists can extract details about the faraway, long-ago cataclysm that produced it.
Just last week, for example, LIGO announced its fourth and latest gravitational-wave detection. Its two detectors, along with a new detector in Europe called Virgo, registered the signal from two enormous black holes 1.8 billion light-years away. After circling each other for eons, the pair finally collided, radiating three suns’ worth of energy into space in the form of telltale gravitational waves.
“That would be one of the most fascinating things man could do, because it would tell you very much how the universe started,” said Weiss shortly after the announcement. “Gravitational waves, because they are so imperturbable — they go through everything — they will tell you the most information you can get about the earliest instants that go on in the universe.”
This article was updated on October 3, 2017, with additional details from the Nobel Prize announcement. It was also corrected to reflect that Rainer Weiss is now 85.
Yesterday the 2016 Nobel Prize in Physics was announced. I immediately got a few tweets asking for more information about what these “exotic” states of matter were and explain more about them… Well in short the prize was awarded for the theoretical discoveries that help scientists understand unusual properties of materials, such as superconductivity and superfluidity, that arise at low temperatures.
The prize was awarded jointly to David J. Thouless of the University of Washington in Seattle, F. Duncan M. Haldane of Princeton University in New Jersey, and J. Michael Kosterlitz of Brown University in Rhode Island. The citation from the Swedish Academy reads: “for theoretical discoveries of topological phase transitions and topological phases of matter.”
“Topo…what?” – I hear you cry… well let us start at the beginning…
Thouless, Haldane and Kosterliz work in a field of physics known as Condensed Matter Physics and it is interested in the physical properties of “condensed” materials such as solids and liquids. You may not know it, but results from research in condensed matter physics have made it possible for you to save a lot of data in your computer’s hard drive: the discovery of giant magnetoresistance has made it possible.
The discoveries that the Nobel Committee are highlighting with the prize provide a better understanding of phases of matter such as superconductors, superfluids and thin magnetic films. The discoveries are now guiding the quest for next generation materials for electronics, quantum computing and more. They have developed mathematical models to describe the topological properties of materials in relation to other phenomena such as superconductivity, superfluidity and other peculiar magnetic properties.
Once again that word: “topology”…
So, we know that all matter is formed by atoms. Nonetheless matter can have different properties and appear in different forms, such as solid, liquid, superfluid, magnet, etc. These various forms of matter are often called states of matter or phases. According to condensed matter physics , the different properties of materials originate from the different ways in which the atoms are organised in the materials. Those different organizations of the atoms (or other particles) are formally called the orders in the materials. Topological order is a type of order in zero-temperature phase of matter (also known as quantum matter). In general, topology is the study of geometrical properties and spatial relations unaffected by the continuous change of shape or size of figures. In our case, we are talking about properties of matter that remain unchanged when the object is flattened or expanded.
Although, research originally focused on topological properties in 1-D and 2-D materials, researchers have discovered them in 3-D materials as well. These results are particularly important as they enable us to understanding “exotic” phenomena such as superconductivity, the property of matter that lets electrons travel through materials with zero resistance, and superfluidity, which lets fluids flow with zero loss of kinetic energy. Currently one of the most researched topics in the area is the study of topological insulators, superconductors and metals.
Here is a report from Physics Today about the Nobel Prize announcement:
David Thouless, Duncan Haldane, and Michael Kosterlitz are to be awarded the 2016 Nobel Prize in Physics for their work on topological phases and phase transitions, the Royal Swedish Academy of Sciences announced on Tuesday. Thouless, of the University of Washington in Seattle, will receive half the 8 million Swedish krona (roughly $925 000) prize; Haldane, of Princeton University, and Kosterlitz, of Brown University, will split the other half.
This year’s laureates used the mathematical branch of topology to make revolutionary contributions to their field of condensed-matter physics. In 1972 Thouless and Kosterlitz identified a phase transition that opened up two-dimensional systems as a playground for observing superconductivity, superfluidity, and other exotic phenomena. A decade later Haldane showed that topology is important in considering the properties of 1D chains of magnetic atoms. Then in the 1980s Thouless and Haldane demonstrated that the unusual behavior exhibited in the quantum Hall effect can emerge without a magnetic field.
From early on it was clear that the laureates’ work would have important implications for condensed-matter theory. Today experimenters are studying 2D superconductors and topological insulators, which are insulating in the bulk yet channel spin-polarized currents on their surfaces without resistance (see Physics Today, January 2010, page 33). The research could lead to improved electronics, robust qubits for quantum computers, and even an improved understanding of the standard model of particle physics.
Vortices and the KT transition
When Thouless and Kosterlitz first collaborated in the early 1970s, the conventional wisdom was that thermal fluctuations in 2D materials precluded the emergence of ordered phases such as superconductivity. The researchers, then at the University of Birmingham in England, dismantled that argument by investigating the interactions within a 2D lattice.
Thouless and Kosterlitz considered an idealized array of spins that is cooled to nearly absolute zero. At first the system lacks enough thermal energy to create defects, which in the model take the form of localized swirling vortices. Raising the temperature spurs the development of tightly bound pairs of oppositely rotating vortices. The coherence of the entire system depends logarithmically on the separation between vortices. As the temperature rises further, more vortex pairs pop up, and the separation between partners grows.
The two scientists’ major insight came when they realized they could model the clockwise and counterclockwise vortices as positive and negative electric charges. The more pairs that form, the more interactions are disturbed by narrowly spaced vortices sitting between widely spaced ones. “Eventually, the whole thing will fly apart and you’ll get spontaneous ‘ionization,’ ” Thouless told Physics Today in 2006.
That analog to ionization, in which the coherence suddenly falls off in an exponential rather than logarithmic dependence with distance, is known as the Kosterlitz–Thouless (KT) transition. (The late Russian physicist Vadim Berezinskii made a similar observation in 1970, which led some researchers to add a “B” to the transition name, but the Nobel committee notes that Berezinskii did not theorize the existence of the transition at finite temperature.)
Unlike some other phase transitions, such as the onset of ferromagnetism, no symmetry is broken. The sudden shift between order and disorder also demonstrates that superconductivity could indeed subsist in the 2D realm at temperatures below that of the KT transition. Experimenters observed the KT transition in superfluid helium-4 in 1978 and in superconducting thin films in 1981. More recently, the transition was reproduced in a flattened cloud of ultracold rubidium atoms (see Physics Today, August 2006, page 17).
A topological answer for the quantum Hall effect
Thouless then turned his attention to the quantum foundations of conductors and insulators. In 1980 German physicist Klaus von Klitzing had applied a strong magnetic field to a thin conducting film sandwiched between semiconductors. The electrons traveling within the film separated into well-organized opposing lanes of traffic along the edges (see Physics Today, June 1981, page 17). Von Klitzing had discovered the quantum Hall effect, for which he would earn the Nobel five years later.
Crucially, von Klitzing found that adjusting the strength of the magnetic field changed the conductance of his thin film only in fixed steps; the conductance was always an integer multiple of a fixed value, e2/h. That discovery proved the key for Thouless to relate the quantum Hall effect to topology, which is also based on integer steps—objects are often distinguished from each other topologically by the number of holes or nodes they possess, which is always an integer. In 1983 Thouless proposed that the electrons in von Klitzing’s experiment had formed a topological quantum fluid; the electrons’ collective behavior in that fluid, as measured by conductance, must vary in steps.
Not only did Thouless’s work explain the integer nature of the quantum Hall effect, but it also pointed the way to reproducing the phenomenon’s exotic behavior under less extreme conditions. In 1988 Haldane proposed a means for electrons to form a topological quantum fluid in the absence of a magnetic field. Twenty-five years later, researchers reported such behavior in chromium-doped (Bi,Sb)2Te3, the first observation of what is known as the quantum anomalous Hall effect.
Exploring topological materials
Around 2005, physicists began exploring the possibility of realizing topological insulators, a large family of new topological phases of matter that would exhibit the best of multiple worlds: They would robustly conduct electricity on their edges or surfaces without a magnetic field and as a bonus would divide electron traffic into lanes determined by spin. Since then experimenters have identified topological insulators in two and three dimensions, which may lead to improved electronics. Other physicists have created topological insulators that conduct sound or light, rather than electrons, on their surfaces (see Physics Today, May 2014, page 68).
Haldane’s work in the 1980s on the fractional quantum Hall effect was among the theoretical building blocks for proposals to use topologically protected excitations to build a fault-tolerant quantum computer (see Physics Today, October 2005, page 21). And his 1982 paper on magnetic chains serves as the foundation for efforts to create topologically protected excitations that behave like Majorana fermions, which are their own antiparticle. The work could lead to robust qubits for preserving the coherence of quantum information and perhaps provide particle physicists with clues as to the properties of fundamental Majorana fermions, which may or may not exist in nature.
After closely following comet 67P/Churyumov-Gerasimenko for 786 days as it rounded the Sun, the Rosetta spacecraft’s controlled impact with the comet’s surface was confirmed by the loss of signal from the spacecraft on September 30, 2016. One the images taken during its final descent, this high resolution view looks across the comet’s stark landscape. The scene spans just over 600 meters (2,000 feet), captured when Rosetta was about 16 kilometers from the comet’s surface. Rosetta’s descent to the comet brought to an end the operational phase of an inspirational mission of space exploration. Rosetta deployed a lander to the surface of one of the Solar System’s most primordial worlds and witnessed first hand how a comet changes when subject to the increasing intensity of the Sun’s radiation. The decision to end the mission on the surface is a result of the comet’s orbit now taking it to the dim reaches beyond Jupiter where there would be a lack of power to operate the spacecraft. Mission operators also faced an approaching period where the Sun would be close to line-of-sight between Earth and Rosetta, making radio communications increasingly difficult.
Really thrilled to continue seeing the American Museum of Natural History series Shelf Life. I blogged about this series earlier on in the year and they have kept to their word with interesting and unique instalments.
In Episode 6 we get to hear about micropaleontology, the study of fossil specimens that are so tiny you cannot see them with the naked eye. The scientist and researchers tell us about foramnifera, unicellular organisms belonging to the kingdom Protista and which go back to about 65 million years. In spite of being unicellular, they make shells! And this is indeed what makes it possible for them to become fossilised.
Interestingly enough these fossils allow us to used them as ways to tell something about ancient climate data. As Roberto Moncada pointed out to me:
According to our expert in the piece, basically every representational graph you’ve ever seen of climate/temperatures from the Earth’s past is derived from analyzing these tiny little creatures.
The Tiniest Fossils are indeed among the most important for climate research!