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Home » Page 547

Fluids only get so runny as physicists put a universal lower limit on viscosity

Viscosity is an everyday phenomenon recognizable in the difference between slow-pouring liquids like honey and runny substances like water. Yet the complex molecular interactions that create viscosity make it very hard to calculate theoretically. Now, a pair of physicists in the UK and Russia has taken up the challenge and derived a simple formula that puts a lower limit on the viscosity of all materials. That formula, they say, reflects the quantum-mechanical nature of molecular interactions and involves two fundamental physical constants – Planck’s constant (ħ) and the proton-to-electron mass ratio.

Viscosity acts like a kind of internal friction between adjacent layers of a moving fluid. When water flows through a pipe, for example, there is friction between the faster flowing molecules in the centre of the pipe and slower moving molecules nearer the pipe walls. A calculation of the viscosity of a material from first principles must consider the substance’s molecular composition and structure as well as the temperature and pressure of the system. In fact, viscosity varies over 19 orders of magnitude – from very low values for helium gas to extremely high values for liquids near the glass transition.

Undeterred, Kostya Trachenko of Queen Mary University of London and Vadim Brazhkin of the Russian Academy of Sciences’ Institute for High Pressure Physics near Moscow set out to find an equation that would establish a lower bound on viscosity across all fluids. Their work relies on viscosity’s variation with ambient conditions – the fact that at a given pressure any fluid will have a minimum value at a certain temperature.

Exchanging momentum

For liquids, as the temperature goes up, the constituent molecules vibrate more and weaken the cohesive interactions between them – leading to a loss of viscosity. But in a gas the opposite happens. Because layers exchange momentum through collisions, a higher temperature leads to greater viscosity. So a fluid’s viscosity will be lowest at the transition between liquid-like and gas-like states.

To work out the minimum viscosity of any fluid, Trachenko and Brazhkin considered what happens to a gas as it cools down. They reasoned that during the cooling process the mean-free path of the gas molecules decreases but does not drop below a minimum value roughly equal to the distance at which significant interactions between molecules kick in. That assumption led to a formula for the minimum viscosity in terms of three molecular properties – mass, vibration (Debye) frequency and inter-particle spacing.

The researchers confirmed their calculations by obtaining the same formula after starting with a liquid and working up to higher temperatures. They also found that by inserting suitable values for the three variables their formula yielded minimum viscosities for a range of different fluids broadly in agreement with experimental results – those viscosities lying between about 10-4-10-5 Pascal-seconds. However, to arrive at a formula involving only fundamental constants they had to carry out a few more steps.

First, they worked out an expression for what is known as the “kinematic viscosity” – the ratio of a fluid’s viscosity to its density. The duo set the inter-particle spacing as equal to the Bohr radius (the “radius” of a hydrogen atom) and fixed the cohesive energy between molecules in a liquid to be the Rydberg energy (the energy needed to ionize a hydrogen atom). This allowed them to express kinematic viscosity in terms of ħ, molecular mass and electron mass.

Final flourish

Then, as a final flourish, they invented a new quantity that they call “elementary viscosity” – the product of kinematic viscosity and molecular mass. They found that the lower bound on this quantity – when the molecule in question is a single atom of hydrogen and its mass therefore equal to that of the proton – is an expression involving just ħ and the proton-to-electron mass ratio (as well as π). Numerically, they point out, it is roughly equal to ħ.

“Viscosity is a complicated property varying strongly for different liquids and external conditions,” says Trachenko. “Yet our results show that the minimal viscosity of all liquids turns out to be simple and universal.”

Indeed, the pair’s calculations come close to matching the values obtained with experimental data – the lowest elementary viscosities from empirical data for molecular hydrogen and helium being about 3.5 ħ and 1.5 ħ respectively. Heavier water, meanwhile, has a minimum of about 30 ħ. They also point out that their formula is consistent with the uncertainty principle – which sets a minimum value of ħ for a particle constrained within the Bohr radius.

Quark-gluon plasma

In addition, they say, the result chimes with lower bounds on viscosity previously obtained by using quantum field theory to work out the properties of what is known as a quark-gluon plasma – an exceptionally hot soup of unbound fundamental particles thought to have existed in the very early universe.

On a more practical note, Trachenko reckons that their work might help scientists develop new low-viscosity fluids for use in chemical, industrial or biological processes – such as supercritical fluids for dealing with complex waste. The lower bounds on viscosity, he says, could be useful theoretical targets, while aiming any lower would mean wasting resources.

Not everyone is convinced, however. Thomas Schäfer of North Carolina State University in the US says that the pair’s formula might be a good estimate for what he calls “typical fluids”. But he reckons that assumptions about length being on the scale of the Bohr radius and time being tied to the Debye frequency may not always hold true. In ultra-cold Fermi gases, he says, such as laser-cooled atoms of lithium or potassium, the length and time scales “are quite different”.

The research is reported in Science Advances.

Multidimensional physics you can do at home, gingerbread radiation therapy, making glow-in-the-dark plants

Yesterday I helped my daughter with her GCSE physics homework, and I was rather pleased that I remembered that V=IR and P=IV. While we had great fun working out the properties of various electrical appliances, some of you might want to do more hands-on physics at home.

You are in luck because the Institute of Physics (IOP) is releasing a series of videos called “Do try this at home”. My favourite video so far is presented by the IOP’s Lucy Kinghan and is about warping a 2D landscape (a piece of paper) into 3D and accomplishing something that had appeared impossible. Watch her demonstration above – I have to admit I am still scratching my head about how she did it.

If warping space is not your cup of tea how about baking your favourite piece of physics kit? Lotte Fog, a medical physicist in Australia, has made a “gingerbread LINAC” complete with a gingerbread patient receiving radiation therapy. If you are inspired to bake your own apparatus, be sure to send us a photo at pwld@ioppublishing.org.

Making a glow-in-the-dark plant is probably beyond the capability of most scientists at home. But if you are really keen to try, Karen Sarkisyan, Ilia Yampolsky and an international team have used DNA from a bioluminescent mushroom to create plants that glow much brighter than previously possible (see above video).

I don’t know about you, but I bet we have a few bioluminescent mushrooms lurking at the bottom of the fridge. You can read more about these amazing plants in a scientific paper called “Plants with genetically encoded autoluminescence”.

Quantum computers vastly outperform supercomputers when it comes to energy efficiency

Researchers in the US have created a new energy-based benchmark for quantum advantage and have used it to show that noisy intermediate-scale quantum (NISQ) computers use several orders of magnitude less energy than the world’s most powerful supercomputer when doing a specific task.

As quantum computers become larger and more reliable, the question of whether a quantum computer can perform calculations beyond the reach of even the most powerful conventional supercomputer is becoming increasingly relevant. This ability has been dubbed “quantum advantage” or “quantum supremacy” and it marks the point where quantum computers move from being scientific curiosities to useful devices.

However, measuring quantum advantage is difficult as illustrated by the debate that ensued after Google claimed advantage for its Sycamore NISQ device in September 2019. Google scientists said that Sycamore could solve a specific problem in a mere 200 s, while estimating that a powerful supercomputer would take a whopping 10,000 years to perform the same task. But one month later, physicists at IBM argued this was a gross overestimate and a supercomputer could complete the task in just 2.5 days – essentially negating the claim of advantage.

Fragile qubits

Quantum computers show enormous promise because they can – at least in principle – use the laws of quantum mechanics to perform some calculations much faster than even the most powerful conventional computers. Useful calculations could be done using a relatively small number of quantum bits (qubits) – hundreds or maybe thousands – but creating a quantum computer with more than a few dozen qubits is a difficult task because the quantum states used to create qubits are fragile, short-lived and difficult to control. Devices such as Google’s Sycamore are called NISQs because they have an intermediate number of qubits (Sycamore has 54) and are noisy in terms of imperfect qubit control.

Another challenge for the quantum industry is that there is no agreement on the best qubit technology, with some firms opting for superconducting qubits while others are working on trapped-ion computers. Still other technologies are also under development. As a result, practical quantum computers that solve real-world problems are still a few years away – and benchmarking is essential.

In the meantime, researchers are trying to benchmark the development effort by finding problems that today’s nascent quantum computers can perform more efficiently than the most powerful conventional computers. One task that clearly lends itself to a quantum computer is calculating the output of “random quantum circuits” (RQC). This benchmark was used by Google to make the 2019 claim of quantum advantage. The problem can also be solved by running a “quantum simulator” program on a conventional supercomputer and the crucial question is question is whether the quantum computer solves the problem more efficiently than the most powerful quantum simulator.

Defining efficiency

One sticking point is how to define efficiency, and researchers have usually considered the time taken to solve a problem. In this latest study, Salvatore Mandrà and colleagues at NASA’s Ames Research Center in California, Google and Oak Ridge National lab argue that considering time alone is problematic. Mandrà explains, “A problem that will take you 1 h on a one-core processor will take you 30 min on a two-core processor or 15 min on a four-core processor”.

Instead, Mandrà and colleagues calculated the energy required by both NISQ and conventional supercomputers to solve the RQC problem. They designed a program called qFlex, which they believe to be the most efficient quantum simulator possible. This is demonstrated, explains Mandrà, by the fact that the efficiency of the simulation is almost constant regardless of the details of the problem it is applied to.

The team implemented qFlex on the Electra supercomputer at Ames and on the Summit supercomputer at Oak Ridge – Summit is the world’s most powerful supercomputer. They calculated the energy both supercomputers expended in performing the calculation and compared it to the energy used by a NISQ. The researchers found that their qFlex implementation required 97 MWh to run on Electra and 21 MWh on Summit, whereas the problem could be solved by a NISQ using only 4.2×10−4 MWh. To put those figures into perspective, the average US household uses 11 MWh of electrical energy per year.

“Lots of papers are developing classical algorithms to simulate quantum systems because there’s a lot of quantum systems around and physicists care about how they behave,” says Daniel Gottesman of the Perimeter Institute for Theoretical Physics in Waterloo, Canada, who was not involved in the research. “The specific focus on quantum supremacy is a moment in time that will probably extend for a few years, but after that it will probably be assumed that we have quantum computers that are better than classical computers, and the idea of classical algorithms to simulate quantum computers will become less and less valuable.”

The research is described in Quantum Science and Technology.  

Avoid, track, recycle: solutions to the problem of plastic waste

Cover of May 2020 Physics World
Avoid, track, recycle: Dealing with plastic waste is the theme of the May 2020 issue of Physics World magazine.

Finding ways to reduce, track and recycle the mountains of plastic waste consumed and disposed of each year is the theme of the May 2020 special issue of Physics World, which is now out in print and via the Physics World digital apps for iOS, Android and Web browsers.

The issue was timed to coincide with the start of a new era, in which print copies of Physics World were no longer going to be sent out wrapped in plastic, but in paper (sadly the disruption caused by the COVID-19 pandemic has put those plans on hold).

Paper magazine wrapping is not a perfect solution environmentally, but it has certain advantages, as you can discover in the feature “Physics World unwrapped”, which explores the science of magazine wrapping. You can also read it online here.

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@ioppublishing.org.

For the record, here’s a rundown of what else is in the issue.

• Critical research hit by COVID-19 – Major labs have shut their doors in response to the worldwide lockdown, but a few remain open and in some cases are carrying out critical work related to the COVID-19 pandemic, as Peter Gwynne and Michael Banks report

• Physics in the pandemic – Highlights from your experiences around the world

• Philip Anderson: a legend is lost – The Nobel laureate Philip Anderson was a giant of condensed-matter physics, who was unafraid to speak out against what he saw as the excesses of particle physics. Michael Banks looks back

• That’s a wrap! – Physics World will be switching to a paper wrapper, when the COVID-19 pandemic allows, explains Matin Durrani

• Learning from Black Swan events – With COVID-19 causing thousands of deaths worldwide and a global economic crash, Christopher Lavers says that we should have learned from previous crises

• This is the Critical Point – Having written the Critical Point column in Physics World for 20 years, Robert P Crease still worries that physicists don’t realize why the humanities are so important

• Serendipity inaction – Accidental discoveries lie at the heart of many technological innovations. James McKenzie runs through his favourites

• Physics World unwrapped – Ever wondered why your print copy of  Physics World is still delivered wrapped in plastic? That’s about to change, but as Susan Curtis finds out, abandoning single-use-plastic magazine wrappers is not as straightforward as it sounds

• The search for the missing plastic – There is a huge amount of plastic waste polluting our oceans – but we don’t know where it is. Marric Stephens investigates what scientists are doing to find the missing plastic

• Plastic that doesn’t cost the Earth – The vast increase in unwanted plastic pollution has galvanized scientists and innovators around the world to develop ingenious approaches to reuse, retrieve and recycle plastic. But significant challenges remain, as Anna Demming reveals

• Money from maths – David Appell reviews The Man Who Solved the Market: How Jim Simons Launched the Quant Revolution by Gregory Zuckerman

• Quantum inheritance and the ongoing quest for meaning – Philip Ball reviews Quantum Legacies: Dispatches from an Uncertain World by David Kaiser

• Shedding light on the interfaces – Joe McEntee talks to surface scientist Karen Syres about striking a balance between teaching and research while also building visibility and connection with the scientific community

• Ask me anything – Careers advice from Carole Mundell, Bath University, UK

• Ministry of Recovery and Discovery – Peter Wright on if he ruled the world

NASA satellite missions track 16 years of Earth’s melting ice sheets

Losses from the ice sheets of Antarctica and Greenland in the last 16 years have far outpaced snow accumulation, leading to around 14 mm of sea level rise since 2003, a research team led by the University of Washington has revealed. The findings – based on elevation measurements taken by two NASA laser-ranging satellite missions – may help refine our understanding of how ice sheets are reacting to climate change.

Traditionally, studies of the changing mass of ice sheets have relied on combining measurements from various airborne and satellite-based missions, often only representing limited snapshots of time. In the new study, however, researchers contrasted data from NASA’s 2003–2009 ICESat (Ice, Cloud and land Elevation Satellite) mission with its counterpart ICESat-2 that launched in 2018 – allowing for a detailed comparison of elevation changes at tens of millions of sites, from which the team could estimate ice sheet mass changes over the span of more than a decade.

“If you watch a glacier or ice sheet for a month, or a year, you’re not going to learn much about what the climate is doing to it,” says lead author and Washington polar scientist Benjamin Smith. “We now have a 16-year span between ICESat and ICESat-2 and can be much more confident that the changes we’re seeing in the ice have to do with the long-term changes in the climate.”

The researchers found that from 2003–2019, Greenland’s ice sheet shed an average of 200 gigatons of ice each year, while Antarctica lost around 118 gigatons. For comparison, one gigaton of ice would fill some 400,000 Olympic swimming pools. Of the resulting sea level rise, two-thirds came from Greenland ice losses.

“It was amazing to see how good the ICESat-2 data looked, right out of the gate,” says NASA’s ICESat-2 project scientist Thomas Neumann. “These first results looking at land ice confirm the consensus from other research groups, but they also let us look at the details of change in individual glaciers and ice shelves at the same time.”

Greenland ice changes
The amount of ice gained or lost by Greenland between 2003 and 2019. Dark reds and purples show large rates of ice loss near the coasts; blues show smaller rates of ice gain in the interior of the ice sheet. (Courtesy: B Smith et al/Science)

In Greenland, for example, the team found significant ice losses from the thinning of coastal glaciers – such as Kangerlussuaq and Jakobshavn, which both lost between 4–6 m of elevation each year on average. Ice is being lost both from the surface of the glaciers and ice sheets as a product of warmer summer temperatures, but also from their fronts in places due to the presence of warmer ocean water.

Increased snowfall in Antarctica, meanwhile, appears to be causing a thickening of the ice sheet in the content’s interior – but this is being overwhelmed by melting at the edges of the ice sheet. “In West Antarctica, we’re seeing a lot of glaciers thinning very rapidly,” Smith says. “There are ice shelves at the downstream end of those glaciers, floating on water. Those ice shelves are thinning, letting more ice flow out into the ocean as the warmer water erodes the ice.”

Because the ice shelves are already floating, their loss does not contribute to sea level rise – but such has a knock-on effect. “It’s like an architectural buttress that holds up a cathedral,” explains paper author and glaciologist Helen Amanda Fricker of the University of California, San Diego. “If you take away the ice shelves, or even if you thin them, you’re reducing that buttressing force, so the grounded ice can flow faster.”

In West Antarctica – home to some of the continent’s fastest glaciers – the team found that the Thwaites and Crosson ice shelves are being thinned the most, losing ice at an average of 5 and 3 m each year, respectively.

“I would say that the overall findings offer an evolution rather than a revolution of our understanding of current trends in ice sheet mass loss,” comments Andrew Sole – a glaciologist from the University of Sheffield who was not involved in the present study – explaining that the ICESat data broadly support other recent ice sheet mass balance assessments. However, he added, the precision of ICESat-2 measurements compared with radar allows for more accurate analysis of the steeper ice sheet margins where much of the recent loss of grounded ice has occurred – and will likely help us better understand the processes driving these trends and the balance between melting ice shelves and the glaciers that feed them

The research is described in Science.

Clinical experience on an automated QA platform in a busy multicentre department

Want to learn more on this subject?

Watch now

Iridium Kankernetwerk is a busy oncology department that provides about 5600 radiation-therapy treatments per year across four locations in Belgium. The department was looking to optimize its quality-assurance programme through standardization and automation. In addition, the team wanted to develop an in vivo monitoring programme that would both improve patient safety and meet evolving requirements for radiation treatments.

SUN Nuclear iridium bThe solution of choice is SunCHECK™ Patient from Sun Nuclear. In addition to meeting its departmental goals, SunCHECK has allowed the team to continue reviewing patient plans and performing quality-assurance remotely during these challenging times.

Watch this webinar to hear Evy Bossuyt, a medical physicist at Iridium Kankernetwerk, share her and the team’s experiences.

The webinar includes details of

  • Automation and transit dosimetry: implementing a standardized transit-dosimetry solution in a busy radiation-therapy department;
  • Error detection: using automation and standardization to streamline pre-treatment quality assurance and using in vivo dosimetry to enhance error detection; and
  • Clinical insights: initial experiences from an in vivo programme and insights into possible actions for adaptive planning.

Want to learn more on this subject?

Watch now

Evy BossuytEvy Bossuyt is a medical physicist at Iridium Kankernetwerk. Iridium Kankernetwerk includes several hospitals in the Antwerp region of Belgium (including GZA hospital group, ZNA hospital group, UZA, AZ KLINA, AZ Nikolaas, AZ Monica, and AZ St Jozef), with 11 linear accelerators in total. The network includes a staff of 14 medical physicists and five physics assistants, and provides about 5600 radiation-therapy treatments each year.

Sun could be in midlife doldrums, survey of stellar activity reveals

The Sun appears to be far less active than other similar stars, an international team of astronomers has discovered. Timo Reinhold at Max Planck Institute for Solar System Research  and colleagues made the unexpected discovery after studying long-term data gathered by the Kepler Space Telescope. Their findings could give astronomers a broader perspective on evolution of the Sun and could mean that our star is in a midlife lull at the moment.

Centuries of observations of the Sun show that the numbers of sunspots changes in reliable, time-varying cycles. More sunspots mean more magnetic activity at the surface of the Sun and more violent events like mass ejections – which can cause solar storms on Earth that can disrupt some technologies. Other main-sequence stars like the Sun are also expected to have similar variations, but until now little was known about how they compared to the Sun.

Spots on other stars are too small to resolve from Earth, however their movements on the surface of a star cause periodic variations in its brightness that can be observed – and this can be used to calculate magnetic activity. For Reinhold’s team, this effect provided a unique opportunity to compare the Sun’s activity with that similar stars using NASA’s Kepler Space Telescope.

Time-varying brightness

Over four years, the instrument measured the time-varying brightness of 150,000 main-sequence stars as it searched for exoplanets. At the same time, ESA’s Gaia spacecraft measured the motions and positions of stars across the galaxy with similarly impressive accuracy.

By combining and analysing these datasets, Reinhold and colleagues identified 369 stars with similar temperatures, masses, ages, chemical compositions, and rotational periods as the Sun. They found that despite these similarities, most of the stars displayed far higher levels of brightness variation that indicate average activity levels around five times higher than that of the Sun. The team noted that this discrepancy could have arisen since the brightness variations of some Sun-like stars may be too subtle for Kepler to detect, eliminating them from their analysis and boosting the average.

Alternatively, this average could be indicative of Sun-like stars, which suggests that the Sun could have gone through similar periods of higher activity in the past. This idea is in line with other research that suggests that towards the middle of their lifetimes, main-sequence stars could shut down their activity cycles while maintaining their rotational speeds. Reinhold’s team now hope to explore these ideas in more detail through upcoming measurements by instruments including TESS and PLATO; potentially leading to new insights into how the Sun will evolve in the future.

The research is described in Science.

Physics in the pandemic: ‘I’m looking forward to a more balanced blend when this is over’

As a patent attorney, my working life revolves around helping entities protect and exploit their intellectual property (IP). For me, and with my background, that involves interacting with physicists and engineers at start-ups, spin-outs, universities, research bodies and global corporations. Normally, I would look to meet these people in person whenever it made sense, whether that meant popping to a local science park or flying to the US. I always like (liked?) that social interaction: it fits my personality and the way I like to do things.

There’s quite a bit of variety in how IP firms are run. Some have slick electronic systems, but some are still paper-heavy. It’s an old-school profession in some ways. In our case, my team of attorneys and support staff would nearly always be in the same office here in Manchester. Although prepping and filing patent applications, responding to examination reports, and so on is almost 100% electronic, the physical interaction you get in an office environment makes it easier to engender a strong team spirit. Also, it’s just sometimes easier to have a chat about X, Y, or Z without having to draft an e-mail or make a call.

When the pandemic began to affect us, we had to change very quickly. For my team, that meant going from an office-based environment to 100% home working, with electronic workflows, for everyone, in about 24–48 hours. Some of these decisions took seconds to implement, whereas they would normally have taken many meetings (and sometimes meetings about those meetings), and months or years, to roll out. It was quite refreshing to be able to make such changes, without impacting client work, and all whilst making the team more efficient. I have no doubt at all – at all – that nearly all those changes will be permanent, even if we could go back to the office tomorrow.

Uncertainty, squared

It’s an interesting time for our clients too, and that naturally has an impact on us. Some clients have carried on with little or no change, at least in terms of their IP strategy and tactics. Some have even increased their drive in that respect. Others? Perhaps less so. There are clearly lots of factors in play, tied to funding, commercial outlook, access to R&D facilities and functions and so on. Of course, physical meetings have now gone, but we were already meeting lots of clients using video conferencing. For events, we, like many others, are flipping to 100% electronic delivery methods. I’ve done my first podcast, for example – another thing we’d thought about doing for years, and finally did within weeks of the lockdown.

Another – more trivial – change is that I’ve quickly become used to not wearing shoes, or chinos, or worrying about appearances as much. For example, I’m one of the people who has shaved their head. This was partly practical, partly cathartic: my hair was already thinning (perhaps for five or 10 years, some might say), so this pandemic-enforced lockdown was a good time to be brave/stupid about it.

Despite these benefits, though, I miss people. Don’t get me wrong: I absolutely love the fact that I have 1.3 million apps at hand for dialling A, calling B, pestering C, and chatting with D. But it’s not quite the same. While I’m a technical and logical thinker, I am also an emotional and sociable person, and I’m looking forward to a more balanced blend when this is over – one where I work from home a bit more, but still interact as much as I can “in real life”. Travel and sports are big things for me and my family, and I want those back in our lives. We are not very materialistic, and I genuinely just want to get out again, to see the world with my wife and kids. It’s made me realize, more than ever, just how lucky we are – or were – to be able to do that.

The other thing I’m finding difficult is the lack of certainty. In general, I am very efficient and structured at work (and sometimes at home), but when things are uncertain, I sometimes struggle to contextualize what’s going on and what’s coming next. With the pandemic, we have an uncertain event, and uncertain timings – uncertainty squared. Amongst all this uncertainty, I’m trying to focus on keeping clients happy and well-served, while also keeping my family safe and well. As lockdown measures ease, people will begin to have more certainty in terms of how to run their businesses and manage their lives. Even if there isn’t necessarily good news in the short term, I think this certainty will bring more stability, and that will reduce stress levels.

The carrot and the stick

I hope there will be some positives to come out of all this. In fact, I’ll be bolder: I predict there will be loads. For many, home working brings massive flexibility and a more balanced approach to life. I’ve loved exploring my local area a bit more (in a restricted, socially-distanced way), and appreciating what we have, or had, and will (I hope) have again. I’ve no doubt that we will use our local area and its facilities far more after all this, and I know I’m not alone. Look at traffic levels, air quality, pollution – all massively better. I imagine a good few mayors or civic leaders around the world will be thinking “working from home solves a lot of our city’s problems, no?”

Finally, without trying to be too deep, the pandemic has made me realize how a big carrot (or stick) can make people change their entrenched views and actions. If you’d told us on 1 Feb 2020 that we’d need to work from home by 3 Feb 2020, I think we’d have laughed you out of the office. But just a month or so later, we did pretty much that, with no impact to our clients. That’s amazing, and it’s certainly made me think about the big issues we face as a country, or even a planet. Could we do the same sort of thing (perhaps over a slightly longer period!) with fossil fuels, climate change, social care, education? A big carrot or big stick (maybe a bit of both) can make us change very quickly, and for the better – that is, if we need to, or want to. Why not try applying this to some of the world’s other problems?

Breeding butterflies with stunning structural colour, how COVID-19 is affecting the provision of radiation therapy

In this episode of the Physics World Weekly podcast we chat about how a serendipitous collaboration involving the co-founder of the Shady Oak Butterfly Farm in Florida and an evolutionary biologist in California has shed light on how structural colour evolves in the buckeye butterfly.

We also report back from an online event in which experts from around the world compared notes on how COVID-19 restrictions in hospitals are affecting how radiation therapy is being provided to cancer patients.

Test your knowledge of Nobel-prize physics trivia with this quick quiz

1 How many women have so far won a Nobel Prize for Physics? A. Two B. Three C. Four D. Five

2 Which order did Marie Curie win her two Nobel prizes in? A. Chemistry, Chemistry B. Chemistry, Physics C. Physics, Chemistry D. Physics, Physics

3 How old was William Lawrence Bragg when he became the youngest person to win a Nobel Prize for Physics? A. 22 B. 25 C. 28 D. 31

4 How old was Arthur Ashkin when he became the oldest physics Nobel laureate? A. 90 B. 93 C. 96 D. 99

5 Which of these physicists has never won a Nobel Prize for Physics? A. Steven Chu B. Stephen Hawking C. Stefan Hell D. Steven Weinberg

6 What happened to Roy Glauber’s Nobel medal in 2010? A. Sold for money B. Stolen by burglars C. Thrown in the bin D. Lost in the woods

7 Which physicist almost decided turn down the offer of a Nobel prize? A. Paul Dirac B. Albert Einstein C. Werner Heisenberg D. Erwin Schrödinger

8 On what day of the week is the Nobel Prize for Physics normally announced? A. Tuesday B. Wednesday C. Friday D. Sunday

9 For how many years are the deliberations of the Nobel Committee for Physics kept secret after a particular prize has been awarded? A. 25 B. 50 C. 75 D. 100

10 What informal event do Nobel laureates get invited to in Stockholm after picking up their medals? A. Dog Ball B. Frog Ball C. Hog Ball D. Warthog Ball

Stuck on the questions? The answers are below.

IOPSciNotes Sponsor LogoSponsored by IOP SciNotes™ – an IOP Publishing peer-reviewed, open access journal dedicated to rapid publications of shorter research outputs. Currently all publication charges are waived so articles are free to publish. Visit iopscience.org/iopsn to learn more.

1. B 2. C 3. B 4. C 5. B 6. B 7. A 8. A 9. B 10. B

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