The invisible side of the Universe sends shivers down our spines this Halloween at the Museum of Science and the Cosmos.
The IAC, through the UNDARK project, and the Museum of Science and the Cosmos are organising “The Battle of Dark Matter. Three Theories, One Mystery”, a spine-chilling gathering featuring scientific debate and interactive questions from the audience.
This eerie encounter will take place on 29 October at 17:30 at the Museum of Science and the Cosmos, to mark Dark Matter Day, celebrated internationally on 31 October.
A mysterious web of unanswered questions surrounds the nature of dark matter, a component as essential as it is enigmatic, which helps hold the Universe’s large-scale structures together. Stars, planets, and everything we can observe make up only a small fraction of our Universe, with dark matter and dark energy accounting for the vast majority.
This Halloween, the Instituto de Astrofísica de Canarias (IAC), through UNDARK, Unravelling the Dark Universe from the Canary Islands Observatories, funded by the European Union under the Horizon Europe programme, and the Museum of Science and the Cosmos invite the public to follow the traces of the invisible in “The Battle of Dark Matter. Three Theories, One Mystery”, an event open to all audiences on 29 October at 17:30.
A date to summon curiosity
The alliance between Halloween and dark matter was deliberate. In 2017, Interactions Collaboration, an international network of communications professionals from particle physics laboratories, launched Dark Matter Day on 31 October. The fascination with shadows associated with Halloween offered the perfect setting to introduce the public to a cosmic enigma that has challenged science for decades.
Long before pumpkins and costumes, Halloween’s European roots evoked an unsettling encounter with the invisible. Among its antecedents is Samhain, an ancient Celtic festival particularly associated with Ireland, which marked the arrival of winter and was traditionally linked to a thinning boundary between the living and the spirits. In Spain, All Saints’ Day and All Souls’ Day bring us closer to those who are no longer with us: loved ones who inhabit our memories, giving substance to the invisible just as dark matter holds galaxies together.
In the Canary Islands, this encounter with remembrance has its own tradition: Los Finados, popularly known as “Finaos”. Around All Saints’ Day and All Souls’ Day, families and neighbours gather to remember those who have passed away, sharing stories and anecdotes over chestnuts, walnuts, almonds and figs. Through these stories and recollections, the unseen presence of our loved ones comes alive in our memories. This image invites us to turn towards another mystery, also invisible, that remains hidden in the Universe: dark matter.
In the cosmos, the dark traces of the invisible are investigated through physical effects we can measure.
The gravity of a shadowy, hidden presence
The cosmic enigma begins with a figure: according to the current cosmological model, around 85% of the matter in the Universe is dark matter. It has not been observed to emit, absorb, or reflect light, yet its gravitational influence leaves clues in the motion of galaxies and the bending of light. Like an invisible glue, it helps hold large cosmic structures together, and explain how they formed.
Yet the suspect has still not shown its face. Almost a century after the first evidence emerged, we still do not know what dark matter is made of. To uncover its identity, scientists combine astronomical observations, computer simulations, and experiments searching for signals of its possible constituents. There are plenty of clues on the table, but the case remains open.
Three proposals confront one unsettling mystery
The first to shed light on this darkness will be María Benito Castaño, a researcher at the IAC, who will explain what dark matter is and how we infer its presence. Her research connects astrophysics with particle physics and uses observations of the Milky Way and nearby galaxies to investigate the nature of this elusive component of the Universe.
The battle of arguments will then begin: three researchers will venture into the realm of dark matter with different proposals for interpreting its secrets. Each contribution will open a door to the mystery and show which observations can put the different explanations to the test.
Isabel Santos Santos, a researcher at the Leibniz Institute for Astrophysics Potsdam (AIP, Germany), will champion cold dark matter, one of the pillars of the standard cosmological model. Her research focuses on dwarf galaxies: small cosmic hideouts whose properties may reveal secrets about dark matter. To interrogate them, she compares observations with simulations that recreate the formation and evolution of galaxies.
Jorge Sánchez Almeida, a research professor at the IAC, will explore alternative dark matter models. What if the hidden presence had properties different from those we expect? Lighter particles or different interactions could leave signals capable of challenging the conventional picture. His recent work seeks precisely these clues: patterns of behaviour that could help unmask the physical nature of dark matter.
Guillaume Thomas, a researcher at the University of La Laguna (ULL), will introduce an unsettling plot twist: what if part of the mystery attributed to dark matter required us to revise our description of gravity? In the debate, he will argue the case for modified gravity. A specialist in galactic archaeology, he studies the motion of stars and the remnants of other galaxies to reconstruct the Milky Way’s past.
In this investigation of dark matter, the proposals will face an unforgiving judge: the evidence. Cold dark matter is the reference scenario in contemporary cosmology; examining its limits and testing alternatives helps reveal what each model explains and where unanswered questions still lurk.
The audience joins the spine-chilling battle
Those attending will also be able to follow the trail of dark matter. Using their mobile phones, they will take part in an interactive quiz with prizes from the IAC and vote for the proposal they find most convincing. Each question will offer a new clue to guide them through the shadows of the enigma.
The audience’s verdict will enliven the gathering, although dark matter will not reveal its secrets by majority vote. Theories are tested through observations and experiments: the event offers an opportunity to explore that process from within, share questions and discover which findings could transform the investigation.
This Halloween, the mystery takes on cosmic dimensions. On 29 October at 17:30, the Museum of Science and the Cosmos invites the public to cross the threshold of the visible and follow the ghostly traces of dark matter. Three proposals, a battle of ideas and a Universe that still harbours an unsettling secret.
