The study was conducted by Prof. Haim Diamant and Prof. Yael Roichman of the School of Chemistry at Tel Aviv University, together with the research group of Prof. Stefan Egelhaaf at Heinrich Heine University Düsseldorf. The findings were published in the journal Nature Physics.

Using colloids to model the transition

The research focuses on colloidal materials — suspensions of microscopic particles dispersed in a liquid — which are considered an ideal model for studying the glass transition. When particle concentration is low, the system behaves like a regular liquid. But as density increases, the particles increasingly restrict each other’s motion, until the entire system becomes “jammed” and acquires the properties of an amorphous solid, similar to glass.

Tiny particles, big insight

The researchers’ key innovation is the use of particularly small and highly mobile particles embedded within a system of larger particles undergoing the glass transition. While the larger particles gradually lose their ability to move, the smaller particles remain mobile, allowing the team to measure how the surrounding medium changes.

Using advanced microscopy, the researchers measured the coordinated motion of pairs of small particles, examining how the movement of one affects the other, along different directions and at varying distances. The results paint a clear picture: in the liquid state, motion spreads over long distances through the fluid. But as the system approaches the glassy state, this propagation is suppressed, and the system begins to behave like a solid that absorbs momentum instead of transmitting it.

Colloidal Glass

Clear signatures of transformation

The researchers identified three clear signatures of the transition: a pronounced change in how the decay of correlations varies with distance; the emergence of a new characteristic length scale that grows with the material’s viscosity; and even opposing motions between neighboring particles — evidence of the development of resistance to shear, a fundamental property of solids. The experimental findings precisely confirmed theoretical predictions made by the same team several years ago.

Beyond glass: broader implications

The research team notes that, beyond their importance for a deeper understanding of the glass transition, the findings have broad implications. The new method may be used to study gels, soft materials, active systems, and even biological tissues — areas in which it is difficult to pinpoint when a system stops “flowing” and begins to solidify. In this sense, the tiny particles serve as microscopic witnesses to the moment a liquid loses its fluid character.

Prof. Haim Diamant concludes: “The significance of this research lies not only in identifying new signatures of the glass transition, but also in offering a fresh perspective on the phenomenon as a whole. Our findings show that the glass transition is not merely a gradual slowing of particle motion, but is accompanied by a profound change in the way momentum is transmitted from point to point within the material. The use of small tracer particles as hydrodynamic probes opens the possibility of examining the emergence of solid-like properties even before the system actually ceases to flow, and may provide a new tool for studying soft materials and complex systems in which the transition from liquid to solid is difficult to measure.”

A new study conducted by researchers from the Coller School of Management at Tel Aviv University and George Washington University offers a psychological explanation for the phenomenon: online shopping carts containing more 'indulgent' products and fewer basic utilitarian products generate stronger feelings of guilt and wastefulness in the buyer, increasing the likelihood of cart abandonment.

The study was conducted by Prof. Liat Hadar, Prof. Yael Steinhart, and Prof. Yaniv Shani from the Coller School of Management at Tel Aviv University, together with Dr. Gil Appel, an assistant Prof. of marketing at the George Washington University School of Business. Published in the prominent Journal of Consumer Research, the study is based on analysis of large-scale e-commerce data alongside controlled experiments, aiming to examine how psychological considerations influence actual purchase decisions in a digital environment.

What drives abandonment

The main finding is clear: the higher the proportion of 'indulgent' products – meant for pleasure or pampering, relative to practical, basic products, the greater the likelihood of cart abandonment. Indulgent products include, for example, chocolates and sweets, scented candles, luxury personal care products, home décor items, clothes with funny prints, or amusing gadgets. In contrast, basic functional products are items perceived as necessary or useful, such as basic food or cleaning products, sports equipment, work clothes, batteries, water bottles, or storage boxes.

The researchers analyzed two vast e-commerce databases encompassing nearly 15 million items that had been either purchased or abandoned and conducted four controlled experiments. Across all methods and contexts, a consistent pattern was revealed: even after controlling for total cart price, number of items, browsing duration, and user traits, the ratio between indulgent and practical products significantly predicted cart abandonment.

The Research Team

Guilt, justification, and decision-making

According to the researchers, the explanation is not technical but psychological. Carts perceived as 'indulgent' or 'non-essential' – like those consisting mainly of indulgence items - evoke guilty feelings and difficulty in justifying the expense to oneself. This guilt amplifies hesitation and delay, sometimes leading to complete abandonment of the cart. In contrast, the inclusion of utilitarian products, such as basic consumer goods or functional items, creates a sense of balance and reduces guilt, even when the cart also contains indulgent items.

The researchers note that the study generates immediate implications and suggestions for e-commerce websites and their managers. Recommendations to purchase utilitarian products, such as everyday equipment or useful complementary items, may reduce abandonment, even if the consumer does not actually add them. Such recommendations, claim the researchers, change customers' perception of their carts, reducing guilty feelings, and increasing conversion rates.

A small shift with a big impact

Prof. Liat Hadar concludes: “Our findings show that shopping cart abandonment does not stem only from technical considerations such as price or shipping, but from a deeper psychological process of purchase justification and guilt. When the shopping cart is perceived as too indulgent, consumers find it difficult to justify the expense to themselves and sometimes simply choose not to buy. The message for e-commerce companies is that small changes in the cart's composition or in how it is presented, such as recommending useful products, can reduce guilt, improve the shopping experience, and lead to a significant economic impact."

The study was conducted at TAU's Zoological Garden, the I. Meier Segals Garden for Zoological Research on two local mammals, the golden spiny mouse and the common spiny mouse. It was carried out by doctoral student Hagar Vardi-Naim at the George S. Wise Faculty of Life Sciences. The study’s supervisors were Prof. Yariv Wine, head of the Applied Immunology Laboratory at the Shmunis School of Biomedicine and Cancer Research, and Prof. Noga Kronfeld-Schor, head of the Ecological and Evolutionary Physiology Laboratory at the School of Zoology, and Rector of TAU. Both Prof. Wine and Prof. Kronfeld-Schor are also affiliated with the new Environmental School at Tel Aviv University. The research was supported by the Israel Science Foundation. The disturbing findings were published in the journal Environmental Pollution.

Vardi-Naim explains: “Large parts of every mammal's body, including our own, are regulated by an internal biological clock. With a 24-hour rhythm based on the natural light-dark cycle, this biological clock signals to various organs and physiological systems, including the immune system, what they should do at different times of day. For example, the levels of certain white blood cells rise and fall in the blood, and the body produces more/less antibodies at specific times. Such oscillations can enhance the immune response to bacteria or viruses, but for this the body must know the time. Light pollution alters the natural light-dark regime, disrupts the central clock's synchronization with environmental time, and changes these patterns, rendering time almost meaningless.”

Testing the effects of light pollution

The researchers examined the effects of artificial lighting on the immune systems of two related species of small rodents: the golden spiny mouse and the common spiny mouse. Both live in the Israeli desert, sharing the same geographical habitat, but differing in their activity time: while the golden spiny mouse is active during the day, the common spiny mouse is active during night. The animals were taken from the Judean Desert to outdoor enclosures at TAU's Zoological Garden, where some of them were exposed to ALAN.

Vardi-Naim: “We kept the spiny mice in enclosures that simulated natural environmental conditions as much as possible. Half of the enclosures were illuminated at night with white LED, the most common type of lighting used today, at a relatively low intensity that simulates street lighting, while the control group was exposed only to natural light-dark conditions - the sun, moon, and stars.”

When timing breaks down

The researchers measured the percentage of white blood cells (i.e., lymphocytes) in the mice's blood at several points in the 24-hour cycle, and found a pattern similar to the human rhythm, with lymphocyte levels in the blood rising during rest hours, between two and four in the morning. In addition, they discovered a very clear 24-hour lymphocyte rhythm, and found that the amount of antibodies produced in response to an antigen (a substance that evokes the immune system's response, e.g. a virus or vaccine), is time-dependent.

“We saw that animals exposed to an antigen during their rest hours produced far more antibodies than those exposed during their active hours,” adds Vardi-Naim. “Exposure to light pollution, however, completely muddled these rhythms.  Instead of a daily cycle of peaks and lows in the level of lymphocytes and immune response, we observed a complete flattening of the daily patterns. This means that the immune system loses its natural timing, and consequently, its response to infections, environmental stress, or vaccination might be less than optimal, possibly increasing the animals' vulnerability over time.”

A significant rise in mortality

In addition, extensive and rapid mortality was observed among the mice exposed to light pollution, with a 2.35 times higher risk of death compared to the control group. The researchers note that even though the exact cause of death could not be determined, the rise in mortality occurred alongside disruption of immune and endocrine (hormonal) rhythms, suggesting a likely connection between damage to biological timing and reduced survival.

Vardi-Naim emphasizes that the spiny mice in the study are only an example, and that the findings have implications for all living creatures, including humans. “Our results show that ALAN is not merely an aesthetic environmental change, but an active biological factor capable of disrupting critical physiological mechanisms. Chronic exposure to ALAN disrupted the timing of the mice's immune and endocrine systems and impaired their survival under conditions that otherwise simulated the natural environment. We believe that light pollution should be regarded as an environmental health risk with broad implications, not only for wildlife but also for human health and the ecosystem as a whole. Studies show that animals with weakened immune systems can transmit diseases to humans, and it is possible that the human immune system responds in a similar way. The study underlines the need to include biological considerations in lighting policies and to reexamine ALAN scope and intensity in both urban and open spaces.”

Overall, by studying animals that live in conditions close to their natural environment rather than in sterile laboratory settings, this research highlights the value of using wild models to understand how the immune system functions in the real world. Such approaches reveal how environmental changes, including growing light pollution, can affect complex biological systems in ways that are often missed in traditional lab studies. As human activity continues to reshape natural environments, studying immune responses under realistic ecological conditions is essential for understanding how global environmental change may influence the health of wildlife, ecosystems, and potentially humans.