Table of contents

Cat litter and radioactive waste – two phrases you wouldn't normally expect in the same sentence.

Pi day is celebrated every 14 March in the US – in recognition of the first few digits of pi, 3.141592653 (the three standing for March and 14 for the day).

How long would it take to fall to the other side of the Earth? This question was first posed in 1966 by physicist Paul Cooper based at Sylvania Electronic Systems, who reckoned that travelling through a "gravity tunnel" would take around 42 minutes.

Fancy a bit of particle-physics electronica? Then make sure you download the latest album from Isle of Wight electronic duo Cosmic Mind Warp.

Physicists in the US and Serbia have created an entangled quantum state of nearly 3000 ultracold atoms using just one photon.

The efficiency of quantum-cryptographic systems could be improved thanks to a new technique that uses "twisted light" to increase the amount of information carried per photon.

Found in deep waters in the western Pacific Ocean, the 20–35 cm-long delicate-looking sea sponge Euplectella aspergillum – also known as Venus's flower basket – has a hidden strength.

Has an advanced alien civilization built a black-hole-powered particle accelerator to study physics at "Planck-scale" energies? And if such a cosmic collider is lurking in a corner of the universe, could we detect it here on Earth?

A new type of extinguisher that uses sound waves to put out fires has been built by two engineering students in the US.

Germany's Max Planck Society is to put all its PhD students on contracts rather than grants, which will benefit overseas students in particular, as Michael Banks reports.

NASA is planning an ambitious mission to a near-Earth asteroid that will involve a robotic craft grabbing a large boulder from the body and moving it into a stable orbit around the Moon, where it will then be studied in detail by astronauts.

Scientists at the European Space Agency (ESA) are hoping that the Philae lander, which successfully landed on a comet last year, will re-establish contact soon as it travels closer to the Sun.

The National Science Foundation (NSF) – one of the biggest funders of research in the US – has released a plan to increase public access to published papers of research funded by the agency.

Scientists in Beijing have received the go-ahead from the Chinese government to start developing one of the world's most powerful synchrotron radiation facilities.

Hiroshi Matsumoto, a plasma physicist and former president of Kyoto University, has become president of the RIKEN network of research labs in Japan.

Female engineering students participate more actively and feel less anxious when working in small groups with a high proportion of women, according to a new study.

It is well known that the annual number of scientific papers is growing rapidly, as journals proliferate and scientists feel the pressure to "publish or perish".

Advances in the physical and mathematical sciences over the last two decades contributed some A$292bn (about £151bn) to the Australian economy each year, according to a report carried out by the Centre for International Economics, an economic consultancy.

The summit of Mauna Kea, a dormant volcano on the island of Hawaii, has long been valued by astronomers for its pristine dark skies and high altitude.

Scientists at CERN's Large Hadron Collider (LHC) have successfully circulated a beam at 6.5 TeV in a step towards collisions at full energy.

The first stone has been laid for the Large Synoptic Survey Telescope (LSST) – a ground-based telescope that will study distant galaxies and nearby asteroids as well as help our understanding of dark energy that is accelerating the expansion of the universe.

Scientists in the US hunting for gravitational waves have received $14.5m from the National Science Foundation to create the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).

Three decades on from winning the 1985 Nobel Prize for Physics for the discovery of the quantum Hall effect, Klaus von Klitzing talks to Michael Banks about the responsibility that comes with winning.

Why we need more scientific literacy among politicians of all persuasions.

Robert P Crease reflects on a decade and a half of writing the Critical Point column for Physics World.

Michael Kang argues that the high price of scientific equipment is choking science – especially in the developing world.

In reply to Margaret Harris' article "Your career questions answered" (Graduate Careers, March pp66–68), which discussed the results of a survey that the Institute of Physics – which publishes PhysicsWorld – conducted on the career aspirations of undergraduate physics students in the UK and Ireland.

In reply to Luke Sibbett's Forum article "Creating better opportunities" (February p17).

In reply to Sidney Perkowitz's feature article "Rooms with a view" (March pp52–56).

In reply to Karen Yates' article "Physics on a coffee break" (Lateral Thoughts, April p52).

In reply to "The laws of light" (March pp44–45).

In reply to Arnold Sikkema's comment on Charles Townes' obituary ("A fine example", Feedback, March p18).

In reply to a review of Math Bytes, Tim Chartier's book about everyday mathematics ("Mathematical doodling", April p43, http://ow.ly/LQ0mL).

In reply to the feature article "Five amazing physics demonstrations" (April pp36–39, http://ow.ly/L4MGO).

By a wonderful stroke of irony, the leaflet pictured here came through my letter box at the same time as the April issue of Physics World.

The deep underground laboratories of the world are no longer the scientific realm of astroparticle physics alone. From Mars rovers to muon tomography, and from radioactive dating to astrobiology, Sean Paling and Stephen Sadler describe the renaissance in the science taking place far beneath our feet.

The deep labs of the world were originally set up in underground sites such as mines or road tunnels to do rare-event astroparticle-physics research.

Perovskite solar cells have quintupled in efficiency in the last five years, making them the fastest growing such type of device. But as Stephen Ornes explains, researchers have yet to overcome one final hurdle: figuring out how to stop them degrading in real-world applications.

Last year's reports that the BICEP2 telescope had uncovered evidence for cosmic inflation turned out to be a false alarm, but researchers in the field have not given up. Matthew R Francis describes how a new generation of telescopes is entering the hunt.

Ever since we first dreamed of life on other planets, science-fiction writers have explored the potential consequences of an interstellar culture clash.

The Conversation's stated aim is to provide "informed news analysis and commentary that's free to read and republish".

Latin America is a diverse continent, interconnected by its common Iberian heritage.

The Sun is – as the old song has it – a mass of incandescent gas, a gigantic nuclear furnace. But it is also much more.

There is a lot of dark matter in the universe.

Most of us have long since grown accustomed to seeing images from the Hubble Space Telescope (HST) on our computers or smartphone screens, but there is still something exceptional about seeing them set out in large glossy pages.

Despite widely reported skills shortages in science, technology, engineering and mathematics, some graduates in these disciplines are finding the job hunt anything but easy. Penny Jackson shares her experiences.

Adrian Liu's work in the emerging field of hydrogen astronomy has won him a string of plaudits, including a Hubble Fellowship from the Space Telescope Science Institute and, most recently, the first ever Origins Project Postdoctoral Prize Lectureship.

Journalist Paul Danahar is the BBC's Americas bureaux chief in Washington, DC. He was previously the BBC's Middle East bureau chief between 2010 and 2013.

The term "meme" comes from the Greek word mimeme ("that which is imitated"), and it denotes an entity (such as an idea or symbol) that propagates from mind to mind within a culture.