Why Photons Carry Energy Without Having Mass | Sleepy Scientist Stories

Why Photons Carry Energy Without Having Mass | Sleepy Scientist Stories

The mind-bending reality of quantum mechanics - with Jim Al Khalili

The mind-bending reality of quantum mechanics - with Jim Al Khalili

Solving the secrets of gravity - with Claudia de Rham

Solving the secrets of gravity - with Claudia de Rham

 

Higgs decay to muon–antimuon pairs sheds light on the origin of mass

22 Dec 2025

Significant event Collision data from ATLAS showing a Higgs boson decaying to a muon–antimuon pair (red tracks). (Courtesy: CERN)

A new measurement by CERN’s ATLAS Collaboration has strengthened evidence that the masses of fundamental particles arise from their interactions with the Higgs field. Building on earlier results from CERN’s CMS Collaboration, the observations suggest that muon–antimuon pairs (dimuons) can be created by the decay of Higgs bosons.

In the Standard Model of particle physics, the fermionic particles are organized into three generations, broadly defined by their masses. The first generation comprises the two lightest quarks (up and down), the lightest lepton (the electron), and the electron neutrino.

 

Environmental physics should be on a par with quantum physics or optics

24 Sep 2025

As climate change intensifies, environmental physics must be taught to every physics undergraduate, explains Peter Hughes

Damaging effects. We now live in an increasingly urban world, with cities expanding into megacities that are causing significant environmental damage. (Courtesy: iStock/Daniel Stein)

The world is changing rapidly – economically, geopolitically, technologically, militarily, and environmentally. But when it comes to the environment, many people feel the world is on the cusp of catastrophe. That’s especially true for anyone directly affected by recurring environmental disasters, such as drought or flooding, where mass outmigration is the only option.

The challenges are considerable, and the crisis is urgent. But we know that physics has already contributed enormously to society, and environmental physics can make a huge difference by identifying, addressing, and alleviating the problems at stake. However, physicists will only be able to make a difference if we put environmental physics at the centre of our university teaching.

 

Slow spectroscopy sheds light on photodegradation

09 Dec 2025

Slow spectroscopy. The experiment detected extremely faint, long-timescale signals emitted by luminescent materials. This material is illuminated by a laser, and faint signals that persist long after excitation are not visible to the naked eye. (Courtesy: OIST)

Using a novel spectroscopy technique, physicists in Japan have revealed how organic materials accumulate electrical charge under long-term illumination by sunlight, leading to material degradation. Ryota Kabe and colleagues at the Okinawa Institute of Science and Technology have shown how charge separation occurs gradually via a rare multi-photon ionization process, offering new insights into how plastics and organic semiconductors degrade in sunlight.

In a typical organic solar cell, an electron-donating material is interfaced with an electron acceptor. When a donor absorbs a photon, one of its electrons may jump across the interface, creating a bound electron-hole pair that may eventually dissociate, yielding two free charges from which practical electrical work can be extracted.

 

Physicists take ‘snapshots’ of quantum gases in continuous space

18 Jul 2025 Nohora Hernández 

Say cheese! A dilute quantum gas in a red pancake-shaped trap (left) is quenched into a two-dimensional square lattice to “freeze” the atoms in place (right). It is then possible to take a “snapshot” of their positions by collecting their fluorescence via laser cooling. (Courtesy: Yao, R., et al. Phys. Rev.. Lett. 134 183402)

Three teams of researchers in the US and France have independently developed a new technique to visualize the positions of atoms in real, continuous space, rather than at discrete sites on a lattice. By applying this method, the teams captured “snapshots” of weakly interacting bosons, non-interacting fermions, and strongly interacting fermions, and made in situ measurements of the correlation functions that characterize these different quantum gases. Their work constitutes the first experimental measurements of these correlation functions in continuous space – a benchmark in the development of techniques for understanding fermionic and bosonic systems, as well as for studying intensely interacting systems.

 

Can we compare Donald Trump’s health chief to Soviet science boss Trofim Lysenko?

10 Dec 2025 Robert P. Crease

U.S. Health Secretary Robert F. Kennedy Jr. has led attacks on US science. But can he really, as Robert P Crease wonders, be compared to Stalin’s feared science administrator, Trofim Lysenko?

Shocking comparison Is it fair to regard Robert F Kennedy Jr (right) as a modern-day Trofim Lysenko (left)? (Both images are in the public domain)

The US has turned Trofim Lysenko into a hero.

Born in 1898, Lysenko was a Ukrainian plant breeder who, in 1927, found he could make pea and grain plants develop at different rates by applying the proper temperatures to their seeds. The Soviet news organ Pravda was enthusiastic, saying his discovery could make crops grow in winter, turn barren fields green, feed starving cattle, and end famine.

Despite having trained as a horticulturist, Lysenko rejected the then-emerging science of genetics in favour of Lamarckism, which holds that organisms can pass on acquired traits to their offspring. This meshed well with the Soviet philosophy of “dialectical materialism”, which sees both the natural and human worlds as evolving not through mechanisms but through the environment.

 

Oscar-winning computer scientist on the physics of computer animation

23 Dec 2025 Margaret Harris

This episode of the Physics World Weekly podcast features Pat Hanrahan, who studied nuclear engineering and biophysics before becoming a founding employee of Pixar Animation Studios. As well as winning three Academy Awards for his work on computer animation, Hanrahan won the Association for Computing Machinery’s A.M. Turing Award for his contributions to 3D computer graphics, or CGI.

Earlier this year, Hanrahan spoke to Physics World’s Margaret Harris at the Heidelberg Laureate Forum in Germany. He explains how he was introduced to computer graphics by his need to visualize the results of computer simulations of nervous systems.

 

Leo Cancer Care launches first upright photon therapy system

30 Sep 2025 Tami Freeman

Pioneering with purpose, Leo Cancer Care’s Grace system, currently available for research and discussion purposes only, will deliver X-ray radiation therapy to patients in the upright position. (Courtesy: Leo Cancer Care)

Leo Cancer Care is a trans-Atlantic company that’s pioneering the development of upright radiotherapy – a totally new take on radiation delivery in which the patient is treated in an upright position and rotated in front of a fixed treatment beam. At this week’s ASTRO 2025 meeting in San Francisco, the company introduced its first upright photon therapy system, named Grace, to an enthusiastic crowd in the ASTRO exhibit hall.

Upright treatments have a host of potential advantages over conventional radiotherapy, where patients typically lie on their backs during treatment. Studies have shown that a more natural upright posture can deliver more consistent anatomical positioning and organ stability, and enable more comfortable treatment positions.

 

The fingerprint method can detect objects hidden in complex scattering media

27 Oct 2025

Imaging buried objects Left: artistic impression of metal spheres buried in small glass beads; centre: conventional ultrasound image; right: the new technology can precisely determine the positions of the metal spheres. (Courtesy: TU Wien/Arthur Le Ber)

Physicists have developed a novel imaging technique for detecting and characterizing objects hidden within opaque, highly scattering material. The researchers, from France and Austria, demonstrated that their new mathematical approach, which leverages the fact that hidden objects generate their own complex scattering pattern, or “fingerprint,” can be applied to biological tissue.

Viewing the inside of the human body is challenging due to the scattering nature of tissue. In ultrasound, when waves propagate through tissue, they are reflected, refracted, and scattered chaotically, creating noise that obscures the signal from the object the medical practitioner is trying to visualize. The further you delve into the body, the more incoherent the image becomes.

High-speed 3D microscope improves live imaging of fast biological processes 12 Sep 2025

High-speed 3D microscope improves live imaging of fast biological processes

12 Sep 2025

 

 

High-speed 3D microscope improves live imaging of fast biological processes

12 Sep 2025

Multifocus microscope A new microscope combines diffractive optics with 25 tiny cameras to simultaneously image at multiple depths. (Courtesy: Eduardo Hirata Miyasaki)

A new high-speed multifocus microscope could facilitate discoveries in developmental biology and neuroscience by enabling imaging of rapid biological processes across the entire volume of tiny living organisms in real time.

Images from many 3D microscopes are acquired sequentially by scanning through different depths, which is too slow for accurate live imaging of fast-moving natural processes in individual cells and microscopic animals. Even current multifocus microscopes that capture 3D images simultaneously have either relatively poor image resolution or can only image to shallow depths.

 

Astronauts could soon benefit from a dissolvable eye insert

16 Oct 2025 Tami Freeman

Spending time in space has a significant impact on the human body and can cause a range of health issues. Many astronauts develop vision problems because microgravity causes body fluids to redistribute towards the head. This can lead to swelling in the eye and compression of the optic nerve.

While eye conditions can generally be treated with medication, delivering drugs in space is not a straightforward task.

 

Juno: the spacecraft that is revolutionizing our understanding of Jupiter

11 Sep 2025 Margaret Harris

This episode of the Physics World Weekly podcast features Scott Bolton, who is principal investigator on NASA’s Juno mission to Jupiter. Launched in 2011, the mission has delivered important insights into the nature of the gas-giant planet. In this conversation with Physics World’s Margaret Harris, Bolton explains how Juno continues to change our understanding of Jupiter and other gas giants.

Bolton and Harris chat about the mission’s JunoCam, which has produced some gorgeous images of Jupiter and its moons.

Although the Juno mission was expected to last only a few years, the spacecraft is still going strong despite operating in Jupiter’s intense radiation belts.

 

Hybrid deep-learning model eases brachytherapy planning

19 Dec 2025 Tami Freeman

CTV segmentation test: Target contouring in two example slices of a patient’s CT scan, using BCTVNet and 12 comparison models. Red and green contours represent the ground truth and the model predictions, respectively. Each image is annotated with the corresponding Dice similarity coefficient. (Courtesy: CC BY 4.0/Mach. Learn.: Sci. Technol. 10.1088/2632-2153/ae2233

Brachytherapy – a cancer treatment that destroys tumours using small radioactive sources implanted inside the body – plays a critical role in treating cervical cancer, offering an essential option for patients with inoperable locally advanced disease. Brachytherapy can deliver high radiation doses directly to the tumour while ensuring nearby healthy tissues receive minimal dose, but its effectiveness relies on accurate delineation of the treatment target. A research team in China is using a hybrid deep learning model to address this task.

Planning brachytherapy treatments requires accurate contouring of the clinical target volume (CTV) on a CT scan, a task that has traditionally been performed manually.

 

A generative AI model detects blood cell abnormalities

04 Dec 2025 Tami Freeman

Generative classification. The CytoDiffusion classifier accurately identifies a wide range of blood cell appearances and detects unusual or rare blood cells that may indicate disease. The diagonal grid elements display original images of each cell type, while the off-diagonal elements show heat maps that provide insight into the model’s decision-making rationale. (Courtesy: Simon Deltadahl)

The shape and structure of blood cells provide vital indicators for the diagnosis and management of blood diseases and disorders. Recognizing subtle differences in cell morphology under a microscope, however, requires the expertise of experts with years of training, prompting researchers to investigate whether artificial intelligence (AI) could help automate this onerous task. A UK-led research team has now developed a generative AI-based model, known as CytoDiffusion, that characterizes blood cell morphology with greater accuracy and reliability than human experts.

Conventional discriminative machine learning models can match human performance at classifying cells in blood samples into predefined classes.

 

Real-world quantum entanglement is far from an unlimited resource

19 Dec 2025 Daniele Iannotti 

Different approaches: Two entities, traditionally known as Alice and Bob, can manipulate the quantum states held at their respective laboratories using only local operations and classical communications (LOCC). The picture illustrates the primary distinction between information-theoretic (1) and computational (2) versions of entanglement manipulation. (Courtesy: Leone, L, Rizzo, J, Eisert, J et al. Entanglement theory with limited computational resources. Nat. Phys. 21, 1847–1854 (2025). https://doi.org/10.1038/ CC-BY-4.0 http://creativecommons.org/licenses/by/4.0/.s41567-025-03048-8)

Achieving a profound understanding of any subject is hard. When that subject is quantum mechanics, it’s even harder. And when one departs from ideal theoretical scenarios and enters the real world of experimental limitations, it becomes more challenging still – yet that is what physicists at the Freie Universität Berlin (FU-Berlin), Germany, recently did by exploring what happens to entanglement theory in real quantum computers. In doing so, they created a bridge between two fields that have so far developed mainly in parallel: entanglement theory (rooted in physics) and computational complexity (rooted in computer science).

Ebits, the standard currency of entanglement

In quantum mechanics, a composite system is said to be entangled when its total wavefunction cannot be written as a product of the states of its individual subsystems.

 

Quantum gravity: we explore spin foams and other potential solutions to this enduring challenge

27 Nov 2025 Hamish Johnston

Earlier this autumn I had the pleasure of visiting the Perimeter Institute for Theoretical Physics in Waterloo Canada – where I interviewed four physicists about their research. This is the second of those conversations to appear on the podcast – and it is with Bianca Dittrich, whose research focuses on quantum gravity.

Albert Einstein’s general theory of relativity does a great job at explaining gravity, but it is thought to be incomplete because it is incompatible with quantum mechanics. This is a critical shortcoming because quantum mechanics is widely regarded as one of science’s most successful theories.

Quantum-scale thermodynamics offers a tighter definition of entropy

03 Dec 2025

How it works: When laser light passes through a cavity filled with atoms, part of it can do practical work. In this example, the work is used to charge a quantum battery (top). The remainder of the light is converted into "heat" (bottom). (Courtesy: Enrique Sahagún, Scixel/University of Basel, Department of Physics)

Researchers in Switzerland and Germany have proposed a new microscopic formulation of the second law of thermodynamics for coherently driven quantum systems. The researchers applied their formulation to several canonical quantum systems, such as a three-level maser. The result provides a tighter definition of entropy in such systems and could serve as a basis for further exploration.

In any physical process, the first law of thermodynamics states that the total energy must be conserved, with some converted to practical work and the remainder dissipated as heat. The second law of thermodynamics says that, in any allowed process, the total amount of heat (the entropy) must always increase.

Why You Are Alive: Quantum Biology Explained

Why You Are Alive: Quantum Biology Explained

 

Looking for inconsistencies in the fine structure constant

01 Dec 2025 Isabelle Dumé

The core element of the experiment: a crystal containing thorium atoms. (Courtesy: TU Wien)

New high-precision laser spectroscopy measurements on thorium-229 nuclei could shed more light on the fine structure constant, which determines the strength of the electromagnetic interaction, say physicists at TU Wien in Austria.

The electromagnetic interaction is one of the four known fundamental forces in nature, with the others being gravity and the strong and weak nuclear forces. Each of these fundamental forces has an interaction constant that quantifies its strength relative to the others. The fine structure constant, α, has a value of approximately 1/137. If it had any other value, charged particles would behave differently, chemical bonding would manifest in another way, and light-matter interactions as we know them would not be the same.

“As the name ‘constant’ implies, we assume that these forces are universal and have the same values at all times and everywhere in the universe,” explains study leader Thorsten Schumm from the Institute of Atomic and Subatomic Physics at TU Wien.

 

Physicists use a radioactive molecule’s own electrons to probe its internal structure

04 Dec 2025 Isabelle Dumé

Where the electrons hang out: This image depicts the radium atom’s pear-shaped nucleus of protons and neutrons in the centre, surrounded by a cloud of electrons (yellow), and an electron (yellow ball with arrow) that has a probability to be inside the nucleus. In the background is the spherical nucleus of a fluoride atom, which joins to form the overall molecule of radium monofluoride. (Courtesy: Ronald Fernando Garcia Ruiz, Shane Wilkins, Silviu-Marian Udrescu et al

Physicists have obtained the first detailed picture of the internal structure of radium monofluoride (RaF) thanks to the molecule’s own electrons, which penetrated the nucleus of the molecule and interacted with its protons and neutrons. This behaviour is known as the Bohr-Weisskopf effect, and study co-leader Shane Wilkins says that this marks the first time it has been observed in a molecule. The measurements themselves, he adds, are an essential step towards testing for nuclear symmetry violation, which might explain why our universe contains much more matter than antimatter.

 

‘Patchy’ nanoparticles emerge from new atomic stencilling technique

25 Nov 2025 Isabelle Dumé

Patch as patch can: With atomic stencilling, researchers have made a variety of patterned patchy nanoparticles with new shapes and properties. (Courtesy: University of Illinois/Illustration by Maayan Harel)

Researchers in the US and Korea have created nanoparticles with carefully designed “patches” on their surfaces using a new atomic stencilling technique. These patches can be controlled with incredible precision and could find use in targeted drug delivery, catalysis, microelectronics, and tissue engineering.

The first step in the stencilling process is to create a mask on the surface of gold nanoparticles. This mask prevents a “paint” composed of grafted polymers from adhering to some regions of the nanoparticles.

 

Will this volcano explode, or just ooze? A new mechanism could hold some answers

15 Dec 2025 Isabelle Dumé

Bubbling up: A schematic representation of a volcanic system and a snapshot of one of the team’s experiments. The shear-induced bubbles are marked with red ellipses. (Courtesy: O Roche)

An international team of researchers has discovered a new mechanism that can trigger the formation of bubbles in magma – a major driver of volcanic eruptions. The finding could improve our understanding of volcanic hazards by improving models of magma flow through conduits beneath Earth’s surface.

Volcanic eruptions are thought to occur when magma deep within the Earth’s crust decompresses. This decompression allows volatile chemicals dissolved in the magma to escape as gas, producing bubbles. The more bubbles there are in the viscous magma, the faster it will rise, until eventually it tears itself apart.