The story of Jocelyn Bell Burnell


Jocelyn Bell at Cambridge’s Mullard Radio Astronomy Observatory in 1968. (Daily Herald Archive/SSPL/Getty Images)

via Timeline

In the winter of 1967, Jocelyn Bell Burnell pored over the near-frozen dials of a radio telescope. Between curses, she breathed on the instruments hoping to thaw them when, suddenly, the telescope’s recording chart sputtered to life and began transmitting a series of regularly spaced ticks.
This was the second time Bell Burnell had observed the puzzling metronomic space signals as a doctoral student working with the Cambridge astronomer Antony Hewish. Initially unsure what could cause such a measured celestial blink, Bell Burnell and her colleagues jokingly called the beating emissions “LGM” for Little Green Men.
The second time the telescope picked up a similar signal, she knew it wasn’t a quirk in the equipment or an extraterrestrial invitation. Bell Burnett had discovered pulsars—and astrophysics would never be the same.
In 1974, however, it was Antony Hewish whose “decisive role in the discovery of pulsars” would be honored with a Nobel Prize. In later years, Hewish would diminish, with defensive bluster, Bell Burnell’s contribution. “It’s a bit like an analogy I make — who discovered America? Was it Columbus or was it the lookout? Her contribution was very useful, but it wasn’t creative,” Hewish told interviewers in 2007.
But Bell Burnell was always more than a lookout. Susan Jocelyn Bell was born in Northern Ireland in 1943 and encouraged by her parents to pursue a clear propensity for understanding things. She and her family protested fiercely when, on the first Wednesday of secondary school, the girls were segregated for training in the art of “domestic science,” while their male peers pored over Bunsen burners and beakers.
She went on to study at the University of Glasgow, where she again found herself defined by her gender rather than her brain. For two years, whenever Bell Burnell entered a lecture hall her male peers whooped, cat-called, and banged their desks. “It was a little isolating. I had to work very much on my own,” she recalled during a TEDx talk in 2013.
After enduring years of the simian ritual, Bell Burnell made haste for Cambridge in 1965 to pursue a PhD studying under the radio astronomer Antony Hewish. Clad in cat-eye glasses, she spent two years constructing a radio telescope of Hewish’s design — a four-acre affair consisting of wires and pylons with galactic radiation receptors. This vineyard-like tessellation was originally built to study quasars — scintillating deep-space objects discovered in the early 1960s.
The first time the telescope’s radio-frequency needle recorded a regularly timed radiation signal, the team was convinced a glitch had befallen their equipment. What aside from human interference or some intelligent messenger could account for the clockwork pulses of energy? The Cambridge researchers were plagued by the Little Green Men mystery for weeks until Bell Burnell detected a second — and later a third and fourth — percussive signal from separate corners of the heavens.
As the probability of detecting multiple galactic dispatches from distant, intelligent civilizations was near zero, the scientists sought a solution consistent with the laws of physics and the scope of the universe. Hewish interpreted the data as the result of neutron stars or pulsars: superdense dead stars that emit radiation from their magnetic poles like strobe lights.
Before Bell Burnell divined the cosmic transmissions, it was believed that when stars died they simply exploded, releasing their energy in volatile displays we call supernovae. But her discovery suggested that a supernova may not lead to the wholesale destruction of a star — that something might stick around. Pulsars, Hewish and Bell Burnell would establish, were the neutron-rich cores of dead stars emitting radio waves as they rotated around a highly magnetized axis. Pandora’s box was open to all sorts of stellar post-mortem possibilities, most notably the theories of a young astrophysicist named Stephen Hawking, whose ravings about black holes were suddenly taken seriously.

Burnell’s pulsar discovery changed the field of astrophysics forever. SXP 1062 (right) is between 10,000 and 40,000 years old. (NASA)

Bell Burnell would go on to receive her PhD in 1968, sans Nobel, despite co-authoring the article in Nature that would lead to Hewish’s nomination. But it wasn’t just the Nobel committee in Stockholm who were guilty of a double standard. Following the discovery of pulsars, Bell Burnell faced casual sexism from the media and public as well.
“When the press found out I was a woman, we were bombarded with inquiries,” she said. “My male supervisor was asked the astrophysical questions while I was the human interest,” she recalled in an interview with the Belfast Telegraph in 2015. “Photographers asked me to unbutton my blouse lower, whilst journalists wanted to know my vital statistics and whether I was taller than Princess Margaret.”
In the years since the discovery of pulsars Bell Burnell has been a vocal critic of the traditional white male power structure that dominates Western scientific thought and academia. When she was appointed the chair of the physics department at Open University in 1991, Bell Burnell was one of only two female physics professors in the U.K. “Throughout my working life, I’ve been either one of very few women or the most senior woman in the place,” she told the TEDx audience.
After obtaining her PhD, Bell Burnell worked part time for many years while raising a family and following the career of a “peripatetic” husband. “I am very conscious that having worked part time, having had a rather disrupted career, my research record is a good deal patchier than any man’s of a comparable age,” she said in a 1996 interview with the Institute of Physics.
Still, Bell Burnell has continued to advance, earning visiting professorships at Oxford and Princeton. She is currently the president of the Royal Society of Edinburgh, Scotland’s national academy of science and the arts.
In public forums, she often repeats the fundamental truth so many people fail to grasp: that the small number of women in STEM in the West is the result of social restrictions and expectations. “The limiting factor,” she points out, “is culture, not women’s brains, and I regret that its still necessary to say that.”


Bouncing ball’s trajectory in general relativity and newtonian gravity


by Paul Mainwood on Quora

This is a conceptually simple and fun piece of work that has been let down by an appalling write-up on
Reading the paper itself, what the authors have done is to put together two fascinating phenomena from 20th Century physics.

  1. At low speeds and with weak gravitational fields, the predictions of Newtonian Physics and General Relativity approach one another, giving rise to dynamics that are so similar that they can be treated as identical.
  2. There are some types of system — chaotic systems — where very small differences can give rise to unexpectedly huge differences in future dynamics.(1)

With these two phenomena written next to one another, there is an obvious path to explore. Why don’t we see if we can come up with a chaotic system whose dynamics can distinguish between the tiny differences between the predictions of GR and NP, even at low speeds and in a weak gravitational field?
And that’s exactly what the authors: Shiuan-Ni Liang and Boon Leong Lan have done, claiming to have found such a desktop system that can distinguish between the predictions of GR and NP when its dynamics becomes chaotic. Fun!
But the write-up of this simple concept veers all over the place, making it sound as though the paper is claiming to contradict General Relativity (it says the opposite). Worse, after happily taking a logically labyrinthine tour through some out-of-context quotes that the authors may have said on the phone, the write-up triumphantly ends with a crashing non-sequitur: “Explore further: Doubly Special Relativity”. (Doubly Special Relativity is a speculative theory with zero connection to anything in the paper.)
So, which one of General Relativity or Newtonian Physics is right? The authors of the paper could not be clearer:

When the predictions are different, general-relativistic mechanics must therefore be used, instead of special-relativistic mechanics (Newtonian mechanics), to correctly study the dynamics of a weak-gravity system (a low-speed weak-gravity system).

(1) Usually in the study of chaotic systems, these small differences are differences in initial conditions: that is, you keep the dynamical laws the same but alter the initial conditions slightly. But you could equally ask what happens if you keep the initial conditions the same and slightly alter the dynamics, which is what they are effectively doing here.

Extragalactic origin confirmed


Cosmic rays — fast-moving, high-energy nuclei — pervade the Universe. We know that the lower-energy variety that we detect on Earth is funnelled by the solar wind. However, higher-energy cosmic rays have an isotropic distribution due to scattering that makes it difficult to identify their source, although they are likely to be generated by high-energy phenomena like supernova explosions and jets from active galactic nuclei. By looking at the ultrahigh-energy end of the cosmic ray spectrum (on the order of exa-electron volts and higher, where cosmic rays are not scattered by solar-scale magnetic fields), the Pierre Auger Collaboration detected an anisotropy in their arrival directions that indicates an extragalactic origin.
Ultrahigh-energy cosmic rays are rare: typically one cosmic ray with an energy > 10 EeV hits each square kilometre of the Earth’s surface per year. The Pierre Auger Observatory in Argentina detects cosmic rays using two combined techniques: telescopes to detect fluorescence from cosmic-ray-generated air showers, and a network of 12-tonne containers of ultrapure water, spread over an area of 3,000 square kilometres. Photomultiplier detectors in the containers observe the faint Cherenkov radiation generated when cosmic-ray-generated muons encounter water molecules. By reconstructing the cone of emission of the muon (analogous to an aircraft’s sonic boom) an incident direction can be derived. By analysing 32,187 cosmic rays detected over 12.75 years, a map of the sky was produced (pictured), showing evidence of an enhancement (5.2 σ significance) in a region away from the Galactic Centre (marked with an asterisk; the dashed line indicates the Galactic plane). The distance of this hotspot from the Galactic Centre (~125°) points towards an extragalactic origin of ultrahigh-energy cosmic rays, reinforcing previous (less conclusive) results from the Collaboration at lower energies.

Paul Woods, doi:10.1038/s41550-017-0304-0

Martian dust blower


by Bart Verberck, Nature Physics 13, 623 (2017) doi:10.1038/nphys4207 (sci-hub)

Your Earthly carpet sweeper won’t do the job in the low-pressure, CO2-dominant atmosphere on Mars. But Catalin Ticoş and colleagues have now shown how to build a Mars-proof dirt broom, which can be used for removing sand and dust from equipment stationed on the Martian surface.
The authors’ experimental setup involved a coaxial plasma gun, capable of producing dense pulsed plasma jets, directed perpendicularly to the area to be cleaned. As a test surface, they used an array of photovoltaic cells, covered with a powder retrieved from volcanic ash, which mimicked Martian surface soil.
Ticoş et al. measured the efficiency of their cleaning method in terms of how the voltage delivered by the cells increased during operation. An analysis of the plasma jets in a CO2 environment at the same pressure as that on Mars’s surface revealed an average plasma plume speed several orders larger than the planet’s typical wind speeds — implying that the plasma broom would indeed succeed in the Martian environment.

Higgs boson’s “little brother” probably never existed


The inflaton has not been seen in the decay of B+ mesons at the LHCb. (Courtesy: LHCb Collaboration, CERN)

The hypothetical inflaton is almost certainly not the particle behind the universe’s rapid expansion soon after the Big Bang. This is according to an international collaboration of physicists working at the LHCb experiment on the Large Hadron Collider (LHC) at CERN, who have been looking for traces of the inflaton in the decay of B+ mesons. Back in 1981, Alan Guth proposed a new model of the early universe to explain why it looks the same in all directions today. He theorized that after the Big Bang the universe initially expanded slowly, allowing time for matter to interact and the temperature to level out. Then, there was a very short, extremely fast expansion of space–time, which happened so rapidly that the universe now appears uniform throughout. For such an expansion to take place, however, there must have been a force field behind it. “A new [force] field always means the existence of a particle that is the carrier of the effect,” explains team member Marcin Chrzaszcz from the Institute of Nuclear Physics of the Polish Acadamy of Sciences (IFJ PAN). For a while, it was thought that this particle was the Higgs boson – however, when it was observed in 2012, the boson was too heavy to be the correct candidate. So theoreticians proposed a new particle called the inflaton, which had the properties of the Higgs boson but a smaller mass. To prove its existence, physicists looked at the decay of B+ mesons, which sometimes decay into K+ mesons and Higgs bosons. According to quantum mechanics, the near-identical nature of the “brother” particles means that they transform and oscillate between each other, so the Higgs boson should then convert into the inflaton. Rather than directly measuring the inflaton or Higgs, the LHCb detects their decay into a muon and antimuon. “Depending on the parameter describing the frequency of the inflaton–Higgs oscillation, the course of B+ meson decay should be slightly different,” Chrzaszcz explains. “We found nothing. We can therefore say with great certainty that the light inflaton simply does not exist.” The work is presented in Physics Review D.


Ticking clocks


by Iulia Georgescu, Nature Physics 13, 529 (2017) doi:10.1038/nphys4169 (sci-hub)

Special relativity assumes that laws of physics are the same in all reference frames, a principle known as Lorentz invariance. This principle has been subject to numerous experimental tests, but no sign of Lorentz violation has yet been spotted: either a reassuring or disappointing revelation, depending on your stance. These results are now reinforced by a new test using a fibre network of optical clocks, which pushes the existing bound on Lorentz violation in experiments measuring time dilation.
Pacôme Delva and colleagues used strontium optical lattice clocks located at the LNE-SYRTE, Observatoire de Paris in France, the National Metrology Institute in Germany and the National Physical Laboratory in the UK and connected via state-of-the-art optical fibre links. Looking at the frequency difference between the clocks, they were able to test whether time dilation varies between the reference frames of the three geographically remote locations. This approach improves on previous tests — including other atomic clock comparison experiments — by two orders of magnitude. Moreover, it is only limited by technical noise sources, so further improvements are certainly possible.

Transparent perfect mirror


by Rachel Won, Nature Photonics 11, 331 (2017) doi:10.1038/nphoton.2017.90 (sci-hubpaper)

Transparent ‘perfect’ mirrors — one-way mirrors that transmit or reflect light completely depending on the direction of view — are useful for security, privacy and camouflage purposes. However, current designs are not perfectly reflective. Now, Ali Jahromi and colleagues from the USA and Finland have demonstrated a new design based on a non-Hermitian configuration — an active optical cavity — that may overcome this limitation. At a critical value of prelasing gain that is termed Poynting’s threshold, all remnants of the cavity’s structural resonances disappear in the reflected signal. At this point, the reflection becomes spectrally flat and light incident on the cavity is 100%-reflected at all wavelengths continuously across the gain bandwidth independently of the reflectivities of the cavity mirrors. Thus, the device at Poynting’s threshold becomes indistinguishable from a perfect mirror. The researchers have confirmed these predictions in an integrated on-chip active semiconductor waveguide device and in an all-optical-fibre system. They note that Poynting’s threshold is, however, dependent on polarization and incidence angle, and that observing the reflection of coherent pulses may reveal the cavity structure via its decay time. Since the concept of Poynting’s threshold is a universal wave phenomenon, it can be exploited in many areas including microwaves, electronics, acoustics, phononics and electron beams.

Space inspires people


Four Eyes of Tatooine by Stefan Lines (created whilst working on his PhD thesis in Dr Leinhardt’s Planet Formation Group at the University of Bristol). This computer generated image, based on data taken from actual super-computer simulations, shows the formation of a planet around a binary star — a so called ‘circumbinary planet’. Tiny unit vectors show the magnitude (colour) and direction (orientation) of the acceleration of millions of tiny rocky ‘planetesimals’ that eventually coalesce to form a planet.

Why do you think space inspires people so much?

I guess that it’s our human nature to explore and we see it, at least most of us can see it, at night and I think that it’s in our nature to ask why things look the way they do, or why a process happens. And since you can look up in the sky and see a bunch of lights, it’s natural to question what that is and want to be able to explain it and go there. So I think it’s just our natural instinct to want to explain what we don’t understand, especially if we can see it.

(Zoë Leinhardtcontinue to read the interview)

Indefinite causality


Causality is a concept deeply rooted in our understanding of the world and lies at the basis of the very notion of time. It plays an essential role in our cognition — enabling us to make predictions, determine the causes of certain events, and choose the appropriate actions to achieve our goals. But even in quantum mechanics, for which countless measurements and preparations have been rethought, the assumption of pre-existing causal structure has never been challenged — until now.
Giulia Rubino and colleagues have designed an experiment to show that causal order can be genuinely indefinite. By creating wires between a pair of operating gates whose geometry is controlled by a quantum switch — the state of single photon — they realized a superposition of gate orders. From the output, they measured the so-called causal witness, which specifies whether a given process is causally ordered or not. The result brings a new set of questions to the fore — namely, where does causal order come from, and is it a necessary property of nature?

via Nature Physics (sci-hub)

Titan brighter at twilight than in daylight


Sketch showing the definition of phase angle

Muñoz, Antonio García, Panayotis Lavvas, and Robert A. West. “Titan brighter at twilight than in daylight.” Nature Astronomy 1, Article number: 0114 (2017) doi:10.1038/s41550-017-0114 (arXiv)

Investigating the overall brightness of planets (and moons) provides insights into their envelopes and energy budgets. Phase curves (a representation of the overall brightness versus the Sun–object–observer phase angle) for Titan have been published over a limited range of phase angles and spectral passbands. Such information has been key to the study of the stratification, microphysics and aggregate nature of Titan’s atmospheric haze and has complemented the spatially resolved observations showing that the haze scatters efficiently in the forward direction. Here, we present Cassini Imaging Science Subsystem whole-disk brightness measurements of Titan from ultraviolet to near-infrared wavelengths. The observations show that Titan’s twilight (loosely defined as the view at phase angles ≳150°) outshines its daylight at various wavelengths. From the match between measurements and models, we show that at even larger phase angles, the back-illuminated moon will appear much brighter than when fully illuminated. This behaviour is unique in our Solar System to Titan and is caused by its extended atmosphere and the efficient forward scattering of sunlight by its atmospheric haze. We infer a solar energy deposition rate (for a solar constant of 14.9 W m−2) of (2.84 ± 0.11) × 1014 W, consistent to within one to two standard deviations with Titan’s time-varying thermal emission from 2007 to 2013. We propose that a forward scattering signature may also occur at large phase angles in the brightness of exoplanets with extended hazy atmospheres and that this signature has a valuable diagnostic potential for atmospheric characterization.