A newborn planet orbiting a star just 370 light-years from Earth has been spotted by astronomers using the European Southern Observatory’s Very Large Telescope (VLT) in Chile. Dubbed PDS 70b, the huge planet is the first-ever to be seen orbiting within a disc of planet-forming material. Its discovery could provide important clues as to how systems of planets form around stars.
PDS 70b is a gas giant with a mass that is believed to be several times that of Jupiter. It orbits a very young star called PDS 70, which is about 10 million years old and is surrounded by a dense protoplanetary disc of dust and gas. The disk appears to have a void near its centre, which has probably been cleared by the young planet. Astronomers have known about such voids for decades and have long speculated that they are associated with young planets.
Birthplaces of planets
“These discs around young stars are the birthplaces of planets, but so far only a handful of observations have detected hints of baby planets in them,” explains Miriam Keppler of Germany’s Max Planck Institute of Astronomy in Heidelberg, who led the team that discovered PDS 70b. She adds, “The problem is that until now, most of these planet candidates could just have been features in the disc”.
The discovery inspired a follow-up study that was led by Keppler’s Heidelberg-based colleague André Müller and looked more closely at PDS 70b and how it interacts with the planetary disc. This revealed that the planet is orbiting in the middle of the void at a distance of about 22 au from the star – which in the solar system would put it just beyond Uranus.
The surface temperature of PDS 70b is about 1000 °C and the radius of the planet is 1.4-3.7 times that of Jupiter. According to Müller and colleagues, the upper limit is somewhat greater than expected for the age of the planet – which they estimate to be 5.4 million years. Spectroscopic studies of light from the planet suggest that it has a cloudy atmosphere.
600 young stars
The observations were done using SPHERE, which is a planet-hunting instrument on the VLT that was used by two astronomical survey programmes to study PDS 70. One is called SHINE – which aims to take near-infrared images of 600 nearby young stars in a search for new planets. The other is called DISK, which looks at young planetary systems and protoplanetary discs.
SPHERE detects the faint light from planets by first blocking the much brighter light from the parent star using a coronagraph. Then a series of images is taken of the system over time. The position of the planet will change slightly as it moves in its orbit, while the star will appear stationary. By looking at how the image changes with time, astronomers can extract the light from the planet and reject light from the star.
Only around 20% of highly cited physicists can be classed as “leaders”, with the rest being “successors,” and “toilers”, according to a new bibliometric study. Carried out by Pavel Chebotarev from the Institute of Control Sciences of the Russian Academy of Sciences and Ilya Vasilyev from the Moscow Institute of Physics and Technology, it examined citation statistics for top physicists, mathematicians and psychologists, finding that researchers can be broadly grouped together in these three distinct categories.
The researchers used citation data from Google Scholar, looking at a number of indicators including the yearly and total citations per year a researcher receives as well as the author’s h-index – a measure of a researcher’s productivity and impact of their publications. They then performed cluster analysis to identify groups of researchers that had similar characteristics.
“We wanted to ask whether we can automatically form clusters when describing the recognition that scientists receive by the scientific community and whether that varies from one discipline to another,” Chebotarev told Physics World.
Extended analysis
When looking at the citation data for mathematicians, psychologists and physicists, the authors identified three broad clusters that are “loosely based” on how the citations per year changes over time. Leaders tend to be experienced scientists who are widely recognized in their fields, which results in an annual citation increase. The successors tend to be early-career scientists who have had a surge in their citations in recent years. Toilers, meanwhile, may have a high citation count, but this stays mostly constant and may even drop slightly.
In physics, the researchers found that 48.5% of the 500 physicists analysed classified as toilers with 31.7% as successors and 19.8% as leaders. This compares to 52.0% of mathematicians being toilers with successors and leaders making up 25.8% and 22.2%, respectively. For psychology, 47.7% are toilers with 18.3% being successors and 34% leaders.
The researchers say that they are now going to extend their analysis to other disciplines including literature, genomics and economics.
Some of the nanocluster phenomena quantifiable with the new tool. Merging and splitting may be heretofore unrecognized nanoscale regulatory mechanisms. Credit: Juliette Griffié
Since the advent of super resolution localization microscopy (SMLM), researchers have raced to extend the technique to live cells. However the time required to obtain each image has so far prohibited applying the technique to study dynamics. In order to get access to the nanoscale machinations of proteins in cells, Juliette Griffié and colleagues developed a tool that tracks clusters of molecules from very sparse SMLM data.
The tool works using a Bayesian statistical framework, and increases temporal resolution, allowing them to image fast processes within live cells that were beyond the scope of previous techniques. With it they show they can track how protein clusters allow cells to dynamically segment tasks on a tiny length scale, providing insights into the mechanism of how the cell functions.
Reframing ‘temporal resolution’
Super resolution localization microscopy works by temporally separating flashes of light from fluorophores – molecules that re-emit light after light excitation – which would otherwise overlap. By making the fluorophores switch on and off, the signal from each light flash is separated from other flashes and its centre can be estimated precisely as a single point.
As these points represent the positions of molecules, the techniques really lend themselves to the study of nanoscale phenomena. However to build up a super resolution image, researchers typically sum the points from thousands of individual time frames, and this is what makes building up an image slow. For instance, a meaningful image composed of molecular clusters may require 500 raw frames: the time between each reconstructed frame could be as much as 15 seconds, even with the most applicable fluorescent protein available today mEos3.2 – .
Usually, researchers think of temporal resolution as something to be improved by altering the microscope or the type of fluorophore. Instead Griffié and colleagues focus on using clever analysis techniques to reduce the amount of input data required to reach the true answer.
How does it work?
The algorithm takes a circle around each point, and counts the points within the circle. If the points exceed a threshold, the group is designated a cluster, and descriptors are extracted from it such as size and density. To test thousands of different circle sizes and thresholds, the algorithm uses a Bayesian approach, assessing the quality of the assignments of molecules to clusters against a user supplied model. The method enables a wide range of clustering phenomena to be investigated with different sizes and densities, even in the same cell.
Using this method, the team performed stress tests. If a cluster really contains 50 molecules and is 100 nm in size, what is the minimum number of detected molecules required to register the correct size and density of the nanoclusters in that sector? By performing simulations, the team found that only 20 detected molecules are required per square micron, so fewer raw frames need to be summed together to form a single reconstructed frame. By using further computational tricks such as a sliding window of analysis and reduced proposal generation for adjacent reconstructions, the team were able to achieve sub-second temporal resolution.
To prove that the technique is valuable for studying real molecules, they imaged CD3 zeta, part of the T cell receptor by fusing it to mEOS3.2. As well as size and relative density, other characteristics could be described, such as the movement of the clusters, and their splitting or merging with other clusters. These are newly imaged phenomena on this length scale, and are likely to play a role in the regulation of many proteins on the nanoscale within cells. Griffié and colleagues plan to extend the technique to 3D data.
Full details of the work can be found in the journal Small methods
Analysis: less is more
This paper represents a different way of thinking about localization microscopy. There is a move away from high sampling being the goal by proving that small amounts of input data on size and density can produce consistent answers, which can easily be compared between conditions.
Fluorescent protein engineering may also complement this technique. Multi-blinking, easily replenished or reversibly switchable fluorescent proteins may provide fuller and more constant sampling rates. Also, dependent on the fluorophore, low laser powers can be used to produce fewer localizations with nonetheless the same precision as at high laser power. As well as being able to image faster cellular processes therefore, this software technique may also increase the applicability of SMLM to sensitive primary cells or longer-term imaging. It is likely that techniques based on light sheet microscopy will be able to provide reliable live SMLM data in sensitive cells, enabling whole cell sampling and 3D nanocluster tracking.
The combination of advances in the hardware, advances in fluorescent protein based imaging, and advances in quantification will together provide a more holistic picture of temporally regulated nanoscale happenings. Such phenomena may be widespread in cells but have never been identified on this length scale. They are inherently out of the reach of even the best single-molecule tracking techniques, which only look at single molecules. Whole cluster tracking will be especially important in cells such as T cells, which use heretofore uninvestigable spatial regulation of nanoscale clusters to achieve very fast regulation.
Steven Chu at the 68th Lindau Nobel Laureate Meeting, in Lindau, Germany. (Courtesy: Christian Flemming/Lindau Nobel Laureate Meetings)
“You can observe a lot by watching,” opened physicist and former US Secretary of Energy Steven Chu, at his lecture at the 68th Lindau Nobel Laureate meeting in Germany last week. The quote, by baseball player Yogi Berra, is a nod to the biomolecular and biomedical imaging research that the 1997 physics Laureate now focuses on. Chu presented several new, as yet unpublished findings in the lecture in Lindau.
Based at Stanford University, a major focus of Chu’s lab is rare earth nanoparticle biomolecular probes. Attached to proteins in live cells, these probes emit light when optically stimulated, enabling the molecules to be imaged at high resolution using optical microscopy. Their main application is in basic biology research.
Lighting proteins more brightly
In 2010, Chu’s lab began to develop nanoparticles, after the ones they were using hit a ceiling in brightness and therefore imaging sensitivity. Their new design comprised a 5 nm pure crystal core of sodium yttrium fluoride (NaYF4), surrounded by a shell of the same material, but doped with ytterbium and erbium ions. These, in turn, were enclosed in an inert 28 nm-diameter outer shell. The ytterbium–erbium pairing generates upconversion, where illumination with infrared photons stimulates the emission of shorter wavelength visible light for imaging.
The core-shell-shell structure enabled significantly greater ytterbium doping compared with previously reported nanoparticles comprising a simple doped spheroid. This, in turn, increased upconversion, resulting in dramatically brighter nanoparticles.
In the first tests of the nanoparticles this year, an illumination intensity of 8 W/cm2 resulted in luminescence 150 times brighter than the simple spheroid nanoparticles. These were the first images of an individual nanoparticle of that size using an illumination intensity less than 1 kW. At the sub-watt illumination intensities used in in vivo animal studies, the difference becomes greater still. Here, the researchers estimate that the new nanoparticles are three orders of magnitude brighter.
Tracking proteins in live cells
A valuable application of the rare earth nanoparticles for biologists is the tracking of proteins in live cells as a means to uncover their inner workings.
In a spectacular example also demonstrated by Chu’s lab this year, the nanoparticles were used to track the transport of nerve growth factor along the axon of a live dorsal root ganglion neuron at room temperature. Imaging with a frame rate of 2.5 ms and spatial resolution of 2 nm, even the individual steps taken by the molecules could be discerned.
Consequently, transport to and from the neuron body could be seen. The capability is a valuable one, as retrograde transport has been implicated in neurodegenerative conditions such as Alzheimer’s disease.
Photostability is an important advantage of the rare earth nanoparticles in tracking experiments. Organic dyes, for example, photobleach in seconds, while the rare earth nanoparticles are fully photostable and continue to luminesce for hour to days, enabling longer observation. Unlike quantum dots, the particles also do not blink, enabling uninterrupted observation. In an additional benefit, the particles are non-toxic.
Future applications will include investigations of immune and cancer cell behaviour and the differentiation of stem cells in animals, predicts Chu.
Guiding tumour surgery
The brightly emitting nanoparticles could also benefit patients directly. In new research, Chu’s group is collaborating with surgeons at Stanford on their real-time use during tumour excision. Traditionally, surgeons rely on visual inspections and touch to identify tumour margins, which can result in incomplete excision.
Instead, the collaboration plan to use the nanoparticles combined with cancer-specific antibodies to target and light up the tumour when excited by low-intensity infrared light. Their goal is for the surgeon to eyeball the tumour margins, without a camera, exploiting the intense luminescence of the nanoparticles.
New approaches to ultrasoundimaging
Highlighting a second major area of investigation, Chu described several ongoing projects in ultrasound imaging, the findings of which are still to be published.
Diffraction-limited ultrasound image of a human wrist using a conventional, 15 MHz ultrasound transducer, with transverse resolution of about 90 µm. (Courtesy: Steven Chu, Stanford University)
Speckle is a classic feature of traditional ultrasound images and compound imaging is a well-established strategy to remove it, spatially, by acquiring images from several angles or spectrally using more than one frequency.
In a new step, Chu’s group has combined both types of compounding. In doing so, they demonstrated overall reductions in speckle that are the multiple of improvements provided by the techniques individually. In an example of a wrist in vivo, a six- to eight-fold reduction over conventional ultrasound was obtained using angular compounding with nine angles and spectral compounding using two frequencies. Spectral compounding alone provided only a two- to three-fold reduction.
The researchers have also extended their technique with an algorithm to correct distortions of the scan volume due to patient motion, transducer pressure and weak acoustic lensing effects by the tissue. To do so, they exploited computational methods developed for convolutional neural networks combined with NVIDIA GPU chips that “mapped beautifully” on to the problem.
Currently, the new techniques take around 10 s, but with advances in GPUs, computational times will drop below one second, predicts Chu. At a frequency of 15 MHz, the approach produces diffraction-limited images with a transverse spatial resolution of approximately 90 µm.
Chu’s lab is also developing a nonlinear ultrasound technique that promises significantly greater image contrast than conventional imaging. The approach exploits a difference-frequency of 1 MHz generated when tissue is simultaneously insonated at 5 and 6 MHz.
Potential applications include tumour imaging. In an example, Chu showed preliminary data of a nonlinear image of a glioblastoma brain tumour in a mouse. It showed bright spots matching the location of the tumour, verified by pathology, which were not discernible in a conventional image.
Steven Chu’s full lecture – Recent Advances in Biomolecular and Biomedical Imaging – can be seen below. (Courtesy: Lindau Nobel Laureate meetings)
Electrodynamic spray set up and Taylor cone formation arising from an applied electric potential.
Cell therapy is a promising approach for the treatment of many degenerative diseases. For instance, chondrocytes (cartilage cells) are currently being tested in clinical trials to treat intervertebral disc degeneration, cartilage disease and osteoarthritis. However, the localized delivery of cells still poses some important challenges.
For example, when injecting the cells, most of them can be lost from the affected zone through diffusion to other parts of the body. Meanwhile, the large needles used can cause further damage in the degenerated intervertebral disc. Another limitation is the survival of the cells, which is usually quite low and limits the efficiency of the treatment.
Given these limitations, Conor Buckley and his team from Trinity College Dublin have recently characterized an electrodynamic spray system to encapsulate chondrocytes for delivery to degenerated intervertebral discs (Biofabrication10 035011). To do this, they optimized the conditions to “trap” and deliver the cells and tested their effects on the viability of the chondrocytes.
Conor Buckley (left) and his team at Trinity College Dublin, Lara Kelly (middle) and Jennifer Gansau (right).
How does electrodynamic spraying work?
The researchers used an electrodynamic spray microencapsulation system to “trap” cells in protective microdroplets of alginate, a natural polymer. This technique is based on the application of an electric voltage to a needle while pumping through a polymer solution containing cells. The electric potential in the needle overcomes the surface tension forces of the polymer solution and creates a cone at the end of the needle, called a Taylor cone. From this cone, a jet of microdroplets is ejected and collected, containing cells for further application.
However, multiple variables can influence the formation and properties of such microcapsules. Therefore, the team analysed various processing conditions – such as needle gauge size, electrical charge and pumping flow – to understand how they influence the microcapsules.
Playing with flow, charge and needles
The first stage was to assess how the combinations of the different conditions affected the alginate microcapsules. The researchers found that increasing the voltage and decreasing the needle size decreased the diameter of the particles but resulted in some variability in their size.
Small particle size is a desirable characteristic since it allows use of a smaller needle when injecting the cell-loaded microcapsules into the intervertebral disc, thus decreasing damage to the patient’s intervertebral disc. Moreover, although size homogeneity in the particles could provide positive features such as a more controlled diffusion, the observed slight variation also permits a higher packing density and therefore delivery of denser material.
Increasing the concentration of the polymer increased the particle size, whereas increasing the flow produced more ellipsoidal rather than spherical particles, with no effect on the size. However, increasing the polymer concentration also decreased cell viability, which the authors attributed to the shear forces caused by higher concentrations.
Different particle sizes and shapes arise from different alginate concentrations (scale bar = 1000 μm) and solution flow rates (scale bars = 1 mm; 200 μm).
Based on these results, the researchers chose an operating set up of 10 kV, a 30 gauge (G) needle, 1% alginate and a flow rate of 0.1 ml/min. This parameter set enabled microcapsule injection with a 25G needle, without affecting cell viability, making it suitable for cell delivery.
What about the cells?
Once the set up was optimized, the team next determined how many cells the microcapsules can carry and how this affects their behaviour. They tested three different initial cell densities: 5 million, 10 million and 20 million cells per ml.
They observed that higher densities decreased cell viability, which can be explained by cell-to-cell signalling and/or by the depravation of nutrients due to the high number of cells consuming them. In fact, the low availability of nutrients is a characteristic of the intervertebral disc environment.
Production of glycosaminoglycans (alcian blue) and collagen (picrosirius red) by cells encapsulated in electrosprayed alginate microcapsules.
The researchers also tested whether the cells were producing the main components of the intervertebral disc microenvironment: collagen and glycosaminoglycans (sugar polymers highly present in intervertebral disc and cartilage). They found that chondrocytes in the alginate electrosprayed microcapsules did indeed produce such components, at higher amounts from the high cell density samples, but more efficiently (more collagen/glycosaminoglycan per single cell) at low cell densities.
Moreover, the cells produced these components in a very similar ratio to that found in an intervertebral disc. The authors concluded that the 10 million cell per mL density presented the best balance between viability and intervertebral disc component production.
A minimally invasive cell-delivery system
This study adds important knowledge to the electrodynamic spray microencapsulation technique and may help in the development of further systems employing this powerful approach. The researchers successfully developed a chondrocyte-encapsulation system that preserves the viability of the cells and promotes the deposition of key components of the intervertebral disc microenvironment. In addition, such a system can be delivered through minimally invasive systems, representing a high potential for (though not limited to) intervertebral disc cell therapy.
“Time is nature’s way to keep everything from happening all at once.”
Though the meaning behind this quote could be taken literally, it reads like a joke. Thought to be originally written by the science-fiction author Ray Cummings in 1919, the phrase was used by American theoretical physicist John Wheeler in his chapter of the 1990 book Complexity, Entropy and the Physics of Information.
But Wheeler, who had a way with words, also knew how to be serious about time, and in 1986 he wrote, “Of all obstacles to a thoroughly penetrating account of existence, none looms up more dismayingly than ‘time’…To uncover the deep and hidden connection between time and existence…is a task for the future.”
The shift in tone from treating time as a joke to something deeper is a sign that we do not understand it, though, like fish in the sea, we are immersed in it. Even while expressing our ignorance about time, Wheeler himself had no choice but to self-referentially allude to one of its mysterious aspects – the future. And though he could not explain time, he reminded us that it has human as well as physical meaning when he wrote in that same chapter from 1990: “Heaven did not hand down the word ‘time’. Man invented it…or as Einstein put it, ‘Time and space are modes by which we think, and not conditions in which we live.’ ”
Thinking about time
Wheeler and Einstein are not alone in pondering the nature of time. Philosophers and thinkers have done so for centuries, and no wonder: time both permeates all that we humans do and fascinates us when we consciously consider it. We endlessly speculate about its nature and about the possibilities of manipulating it and travelling through it. These were science-fiction themes even before H G Wells’ classic The Time Machine (1895), and they still remain current, featuring in the 2014 film Interstellar and last year’s Netflix series Dark. The late Ursula Le Guin’s science-fiction novel of ideas The Dispossessed (1974) gives time special attention, with its physicist protagonist Shevek developing a “general field theory of time” to explain both its “sequency” (as Le Guin calls it) or linear evolution, and its relation to cyclic events like the orbiting of a planet around its sun or the repetitive sweep of the hands of an analogue clock.
Time permeates all that we humans do and fascinates us when we consciously consider it. We endlessly speculate about its nature and about the possibilities of manipulating it
In physics itself, scenarios involving relativistic wormholes hint at the possibility of time travel, while tachyons – hypothetical faster-than-light particles – could travel backwards in time or send signals to the past. Although it seems unlikely that wormhole travel can be physically realized, and tachyons have never been detected, real particles going backwards in time have meaning in the diagrams Richard Feynman invented to calculate the behaviour of elementary particles. One of his insights in these useful representations is to show positrons as their antiparticles, electrons, travelling backward in time.
Despite dealing with such exotic notions, physicists have still not been able to produce a full theory of time. Lee Smolin of the Perimeter Institute for Theoretical Physics in Canada even argues in his 2013 book Time Reborn that physics is guilty of “expelling time” by not incorporating its fundamental reality. Nevertheless, physicists have long grappled with defining and using time as they try to explain the universe. Early in Isaac Newton’s seminal Principia (1687), which laid out much of how physics functions today, he defined “absolute, true and mathematical time” that “from its own nature flows equably without regard to anything external”. Along with “absolute” and “immovable” space, to Newton absolute time formed a backdrop for dynamic behaviour and physical reality that, his definitions imply, cannot be affected by human actions.
We abandoned the notion of absolute space in 1887 when Albert Michelson and Edward Morley determined the speed of light to high precision, with results that eliminated the ether, which was previously thought to be the space-filling entity against which motion should be measured. Absolute time was likewise abolished after Einstein re-analysed what it means when we say two events happen at the same time, and then went on to derive special relativity. Now we know that time changes as measured by a moving observer and, according to general relativity, in a gravitational field: if time is a flow, its flow rate can be altered.
Wibbly wobbly timey wimey According to general relativity, time runs slower the closer you are to massive bodies. (Courtesy: Mark Garlick/Science Photo Library)
General relativity has also amplified the role of time in physics. Adding time to the three spatial dimensions through the term ct – the distance light moving at speed c covers in time t – gives a 4D space–time manifold that concisely describes gravity and the universe. This has put time on a par with space, and relativity has also forced us to think more carefully about time. The “twin paradox” – in which a twin who rockets away from Earth at high speed returns younger than her stay-at-home sister – is an exercise in the variability of time and is also an example of time as a physical parameter with deep human effects.
Irreversibly forward
Other features of physical time may connect to our perception of it. The concept of entropy as a measure of disorder that always increases, at least in large systems over long times, has led to its label as the “arrow of time” – a physical progression that, unlike the reversible processes of classical mechanics, irreversibly points “forward” to define the apparent flow of time. That asymmetric one-way road seems integral to the human sense of time; as Feynman succinctly put it in his 1964 lecture at Cornell entitled The Distinction of Past and Future. “We remember the past, we don’t remember the future,” he said. “We have a different kind of awareness about what might happen than we have about what most likely has happened.”
But some subjective experiences of time differ from physical time. Pleasant events seem to pass quickly while unpleasant or boring ones invariably drag, though the measured elapsed time may be the same. These internal experiences depart from the objective measurement of time because of how our consciousness deals with it, as Wells understood. In The Time Machine, the Time Traveller who built that device explains to his friends, saying “There is no difference between time and any of the three dimensions of space except that our consciousness moves along it.”
We do not know if consciousness moves along or through time, or simply provides a vantage point to observe time as it flows; but we do know that the brain does not produce a one-to-one correlation between its evaluation of time and temporal events in the outside world.
The philosopher and cognitive scientist Daniel Dennett from Tufts University in the US has provided a model for this intricate behaviour. In Consciousness Explained (1991) and elsewhere he proposes that the brain and consciousness operate under a “multiple drafts” approach. Instead of a central place in the brain that houses one’s personhood and interprets sensory information – an idea that traces back to René Descartes in the 1600s – consciousness emerges from various functions occurring at different times in different parts of the brain. To bring together these neural events distributed in space and time, Dennett maintains we create a coherent internal narrative that is the “I” of a person, with personality, memory and so on. The scattered behaviour behind consciousness, he adds, guarantees that “the temporal order of subjective events is a product of the brain’s interpretational processes, not a direct reflection of events making up those processes”.
Dennett’s counterintuitive model strongly contrasts with our internal sense of self and is not the only one offered by cognitive scientists. But regardless of the model, the relation between external time – whatever that really is – and our internal time is extraordinarily complex. Reporting on their work about how time and space are perceived by the brain, neuroscientists György Buzsáki and Rodolfo Llinás at New York University comment that “there is no doubt that the terms ‘space’ and ‘time’, as well as other mental constructs, will be part of research for years to come”.
Nature’s clock
Our bodies too experience different aspects of time. Overlaid on our moment-to-moment responses to external events is the circadian rhythm – the approximately 24-hour cycle of physiological activity built into much of life on Earth, from people and animals to plants. In humans, it defines the periods of lowest body temperature, greatest alertness, sharpest rise in blood pressure and deepest sleep. Though the circadian rhythm can be affected by external light and temperature, it arises from internal molecular mechanisms whose exploration led to the 2017 Nobel Prize in Physiology or Medicine for Jeffrey Hall, Michael Rosbash and Michael Young.
The evolutionary benefit of the circadian rhythm is thought to be that it enables organisms to make the best use of light, food and other resources depending on their availability at different times of the cycle. From the viewpoint of our reactions to physical time, this bodily rhythm shows that we respond to its cyclic nature along with its passage. It would be too much to say that the rotation of the Earth around its axis gave birth to time; but the regular alteration between light and dark must have impressed itself upon early humans and helped form our perception of time.
The passage of time hits us hardest as we age. Though now that we understand that time is variable, could we ever slow down the process? From measurements aboard aircraft and from the space satellites in the global positioning system, we know that relativity correctly predicts how time dilates with speed and gravitational field to make a traveller age more slowly. But at the comparatively low speeds and gravitational variation we can reach with today’s technology, the changes are tiny compared to human lifetimes. NASA astronaut Scott Kelly spent over 11 months aboard the International Space Station starting in March 2015, but returned to Earth barely a few milliseconds younger than his identical twin brother astronaut Mark who remained on our planet.
Double trouble Identical twin astronauts, Scott and Mark Kelly, are subjects of NASA’s Twins Study. Scott (right) spent a year in space while Mark (left) stayed on Earth as a control subject. (Courtesy: NASA)
However, the brothers participated in another kind of NASA twin study. With Mark as a control, they underwent extensive medical comparisons to determine how life in space – with its microgravity conditions, increased radiation and psychological stress in unnatural surroundings – affects human health. The test revealed something unexpected as far as Scott’s “telomeres” were concerned. Telomeres are DNA structures at the ends of chromosomes that protect them from damage but shrink as cells reproduce multiple times. This shrinkage seems to be a main cause of cellular ageing but Scott’s telomeres actually lengthened. This observation is probably linked to the months he spent in space, rather than to the milliseconds of relativistic time change. Still, further exploration of differences in human ageing will surely occur in space when we achieve high speeds and changes in gravity, so we should keep in mind the relationship among human biology, time, space travel and relativity.
Everyone’s time
It is hard to envision a more multidisciplinary topic than time and how we perceive and react to it. The great contributions from physics are the development of relativity, which gives time a fuller, more flexible role in the universe; our understanding of time’s arrow; and our remarkable ability to measure time with exquisite precision down to attoseconds while not knowing exactly what it is, with important outcomes for science and technology. A full picture of time, however, also needs neuroscience, biology, linguistics, anthropology, psychology and even literature because of time’s emotional impact. Feynman himself recognized this when he spoke at Cornell of “remorse and regret and hope” that “distinguish perfectly obviously the past and the future”.
Literature too can powerfully distinguish past from future to help us understand what time means to humanity, as in F Scott Fitzgerald’s masterwork The Great Gatsby (1925). In the novel Jay Gatsby is a mysterious figure who started from poor origins. After gaining great wealth he tries to rekindle a deeply felt love affair from his earlier days and enter a new life, but tragically fails to transcend his past and realize his dream. Fitzgerald’s haunting last words turn Gatsby’s story into universal truths about how we strive to grasp time and how, at last, it inevitably slips through our fingers:
“Gatsby believed in the green light, the orgastic future that year by year recedes before us. It eluded us then, but that’s no matter – tomorrow we will run faster, stretch out our arms farther…And one fine morning –
So we beat on, boats against the current, borne back ceaselessly into the past.”
“Urban heat island research is important for the billions of people who live in cities who may be potentially more at risk for heat-related illnesses,” says Anna Scott of John Hopkins University, US. “In a warming world, heat represents a unique but silent risk that urban planners and disaster management officials need to pay attention to. Research into the urban heat islands provides the information that allows decision makers to protect their residents.”
Urban heat islands have been well-documented for several decades. The phenomenon arises as the high concentrations of roads and buildings in cities trap heat more efficiently than the surrounding rural and suburban land, raising temperatures. In recent years, several studies have concluded that as the climate warms, the intensity of urban heat islands – the temperature difference between urban and rural areas – tends to increase.
The need for further research into urban heat island intensity has become critical, according to Scott. Scott and her colleagues recognised that previous studies on urban heat island intensity only considered the effect on individual cities over shorter timescales. To gather more comprehensive data, the researchers used weather data from 54 cities across the US between 2000 and 2015. They calculated the difference between the temperature values recorded at urban and rural weather stations at each location, for both maximum and minimum daily temperatures.
In 38 cities the temperature difference between the weather stations tended to be lower for higher background temperatures, the team found – especially in moister climates. The result held even accounting for extreme heat and variations between different climates.
“Our research shows that during many warmer conditions, temperature differences between cities and rural areas actually decrease because of temperature sensitivity in rural areas,” says Scott. “Many people think the opposite is true, so this has potentially important implications for how governments think about heat in rural areas, which we find can sometimes get left out of the heat-related health discussions because we often focus on urban areas.”
The researchers believe that large-scale trends in weather conditions are responsible for their result, suggesting for the first time that heat mitigation efforts may need to be increasingly focused outside cities.
Scott acknowledges that urban heat island intensity is not the only important parameter when considering the effects of climate change on cities. “Many factors affect thermal comfort, including humidity, which we didn’t consider in this study,” she says. “So, this doesn’t say that climate change won’t affect cities but rather, suggests that rural areas may be more sensitive to warming than previously thought.”
In the future, the insight could be important to consider when making economic projections of climate change and designing methods for relieving and mitigating the effects of heat.
The IceCube Neutrino Observatory may have detected a tau neutrino with an extraordinarily high energy of about 100 PeV, according to a new analysis done by Matthew Kistler at Stanford University and Ranjan Laha at Johannes Gutenberg University Mainz in Germany. The detection was made in 2014 and could provide a glimpse of hitherto unknown astrophysical processes.
Situated at the Amundsen-Scott South Pole Station, the IceCube detector is an array of thousands of light detectors (photomultiplier tubes) embedded throughout a cubic kilometre of Antarctic ice. Occasionally a neutrino will collide with an atom in the ice and produce a charged lepton (electron, muon or tau) that is moving faster than the speed of light in ice. This creates a track of Cherenkov light in the ice, which is picked up by the detector array. By studying the track, IceCube physicists can work-out the energy of the neutrino and its trajectory into the detector.
Neutrinos come in three different flavours (electron, muon or tau) and this dictates what type of lepton is produced in the collision. An important challenge for IceCube physicists is to differentiate between the three leptons, which is not always straightforward.
Long tracks
In June 2014, IceCube saw light from a charged lepton that deposited 2.6 PeV in the detector – an extremely large amount of energy that had never been seen before in the detector. Initially, physicists assumed the event had been initiated by a muon neutrino with an initial energy of at least 10 PeV. Muons had been responsible for most previous tracks measured by IceCube, mostly because these leptons have ideal properties for creating long tracks of Cherenkov light. However, the highest previous muon neutrino energies seen by IceCube were at around 2 PeV – leaving a mysterious gap in energy up to 10 PeV.
Writing in Physical Review Letters, Kistler and Laha argue that it is unlikely that the signal is related to a muon neutrino created by known astrophysical processes. They have also calculated that it is possible that the event could have been caused by a tau neutrino – an elusive particle that was discovered just 18 years ago at Fermilab. Tau leptons are very short-lived, which means that they would normally decay before creating a long track in IceCube. However, Kistler and Laha reckon that a tau lepton created by a neutrino with an energy of about 100 PeV could leave such a track.
New processes
If this proves to be correct, it could open a window to new high-energy astrophysical processes that can create such high-energy tau neutrinos. “Assuming this is the case,” says Laha, “this opens up completely unexpected possibilities, namely that astrophysics should start looking for neutrinos with energy of up to 100 PeV”.
Kistler and Laha plan to study the 2014 event more closely, and also hope to develop new ways to identify different charged leptons based on their individual tracks.
Poor planning on my part and a missed connection meant my travel from Somerset in the UK to the 2018 International Science Journalism School in Erice, Sicily, took a staggering 34 hours. It was already feeling like a pilgrimage when I finally landed in Sicily, but on the last leg by car our final destination came into view to give a hint as to why Erice is such a special place – the ancient town perched atop a mountain was enchantingly shrouded from prying eyes by its very own cloud, the only one in an otherwise clear blue sky.
With its own micro-climate and historical religious significance, an “Erice pilgrimage” may have been a thought that flashed through some of the greatest scientific minds in modern history, given my host for the summer school – the Ettore Majorana Foundation and Centre for Scientific Culture – was founded in 1963 by eminent fundamental physicists to foster ‘science without secrets and without frontiers’. The organization has since attracted dozens of Nobel Prize winners and other titans of physics.
While the likes of Paul Dirac and Richard Feynman were likely hammering out the finer details of quantum theory during their time in Erice, I along with 34 other writers, YouTubers, editors and science communicators of varying flavours had converged on the town to understand how to convey tomorrow’s complex fundamental physics to different audiences.
A hi-tech lecture theatre in the bowels of a converted church was our place of worship for the next four days. For those wanting an update on the latest gravity wave news or what the Large Hadron Collider is doing “post-Higgs”, they got it by the bucketload from Marica Branchesi (Virgo Collaboration) and Guy Wilkinson (LHCb experiment). For others keen to develop their media skills, the likes of Robin McKie from the Observer newspaper and Mario Tedeschini Lalli shared their experiences.
But most inspiring for me was a session by independent award-winning writer Jacopo Pasotti detailing his methods in reportage for the likes of National Geographic, Science and Wired. Having exposed illegal mining in the most biodiverse parts of the Amazon and uncovered hidden science stories that shine a light on tragedies such as the Banda Aceh tsunami, Pasotti was the perfect person to offer a “how-to” guide for any reporter or writer wanting to go beyond regurgitating news – and instead make a difference.
Equally thought-provoking were many of the attendees, whose opinions on the challenges science journalism currently faces in terms of hype, monetizing digital journalism and the role of the journalist in an increasingly crowded media landscape were intelligent and eye-opening during the interactive sessions.
But as with any conference or school, the best stories are told during the coffee breaks. During one of these I got the chance to speak to a young Law student from Ukraine called Daria Zaremba. Her passion for science and frustration at the lack of science reporting in Ukrainian media has led her and a clutch of like-minded students to build PIDZEMKA, the country’s first science-communication digital platform. Meeting people like Daria made my Erice pilgrimage extra special – her determination to report science that informs and inspires the public in the face of overwhelming challenges is a lesson all science journalists should heed.
Weird worlds: the July 2018 issue of Physics World tackles the mysteries of time
Our attempts to understand time is the theme of the new issue of Physics World magazine, which is out now in print and digital format.
The July 2018 issue includes an interview with the Italian-born physicist and author Carlo Rovelli, whose latest book The Order of Time dubs time “perhaps the greatest mystery”.
Sidney Perkowitz examines physicists’ attempts through the centuries to unravel time, while Philip Ball sheds light on exotic materials called “time crystals”.
Jon Cartwright looks at how atomic clocks can determine precisely “when” stock-market transactions take place – in an effort to spot potentially fraudulent transactions, while Robert P Crease wonders why we’re fooled by time.
Finally, we’re delighted to publish our first-ever cartoon by illustrator Eugenia Viti, who takes a wry look at time.
Remember that if you’re a member of the Institute of Physics, you can read the whole of Physics World magazine every month via our digital apps for iOS, Android and Web browsers. Let us know what you think about the issue on Twitter, Facebook or by e-mailing us at pwld@iop.org.
For the record, here’s a run-down of what else is in the issue.
• Horizon Europe plans unveiled – The European Commission is proposing to spend €100bn on science over seven years from 2021, but will the UK see any of the cash now it is quitting the EU? Michael Banks and Michael Allen report
• Newcastle’s new generation – With the first physics students in a decade graduating from Newcastle University this month, Nick Parker and Angela Dyson reflect on what it takes to rebuild and reopen a physics department
• Fusion dreams – James McKenzie wonders if a commercial approach will bring a practical fusion reactor to market faster
• Fooled by time – Robert P Crease wonders if there is a topic murkier than time
• Time examined and time experienced – How we perceive and experience time is fundamental to our lives but we don’t fully understand what is a complex phenomenon. Sidney Perkowitz looks at how scientists and philosophers alike are seeking to
grasp this mysterious and ever-present concept
• Time traders – In today’s markets, every microsecond counts. Jon Cartwright discovers how the UK’s National Physical Laboratory is keeping regulators up to speed
• In search of time crystals – Dreamt up by the physics Nobel laureate Frank Wilczek in 2012, the notion of “time crystals” is now moving from theory to experiment – and could also lead to applications such as a new kind of atomic clock. Philip Ball explains
• The time lord – Carlo Rovelli – the Italian-born physicist and author of the bestselling popular-science book Seven Brief Lessons on Physics – has now published what promises to be another success story. Matin Durrani reviews The Order of Time and questions Rovelli about the motivations behind his new work
• The physicists in the comedy club – Jess Wade reviews The Element in the Room: Science-y Stuff Staring You in the Face by Helen Arney and Steve Mould
• Nuclear futures – Tushna Commissariat talks to Jim Gulliford about a new programme to train early-career nuclear physicists, and what a future in the field looks like today
• Once a physicist – meet Eline van der Velden, who is the two-time award-winning actor, writer and director of the new BBC Three series Miss Holland and founder of Particle6 Productions
• What is time? – An illustration by Eugenia Viti and Ivan Viti
Like the issue? Don’t like it? Did we miss something out? E-mail us at pwld@iop.org to share your thoughts.
