The starting point seems simple, but it is enough to open up a succession of scales that challenge our imagination: understanding what things are made of and the limits of human knowledge regarding the Universe. At the April session of the “Explain it like I’m 5” initiative, held at Alameda campus of Instituto Superior Técnico, Universidade de Lisboa, Pedro Abreu, a professor at Técnico and a researcher at the Laboratory of Instrumentation and Experimental Particle Physics (LIP), guided participants on a journey between the ‘infinitely large’ and the ‘infinitely small’.

The session began with what “is closest and most familiar”. The Sun, taken as a reference point in the sky, served to introduce the concept of scale and put perceptions into perspective. “The Sun seems very large to us because it is close to Earth, but in the context of our galaxy, it is just one star among many others, some of which are much larger”, explained the researcher, highlighting the relationship between size and distance. From this point, the discussion expanded to galaxies, described as “collections of stars”, and to the evolution of scientific knowledge, which, about a century ago, demonstrated that the Universe extends beyond the Milky Way.

To observe the ‘infinitely large’, Pedro Abreu turned to history and technology, recalling the moment when Galileo Galilei pointed a telescope to “see the sky”, marking the beginning of modern astronomy. “Telescopes are, at their core, tools that allow us to ‘zoom in’ on the Universe and see farther into space and time”, he explained.

The transition to the ‘infinitely small’ was achieved through a reversal of scale. “If telescopes help us see the very large, microscopes allow us to explore the very small”, Pedro Abreu continued. Among examples drawn from the daily scientific life at Técnico, he mentioned electron microscopes capable of revealing chromosomes, viruses, or DNA fragments. “Everything we know is made of atoms”, he added, also introducing another scale of matter.

“Science advances precisely because of unanswered questions”

As the observable scale shrank, new tools and new challenges emerged. The researcher described particle accelerators as “giant microscopes” that allow us to study the interior of protons and neutrons, which are the constituents of the atomic nucleus. When the talk turned to the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) in Switzerland, the audience responded with amazement, exclaiming, “So big!” as they learned about the accelerator’s impressive length of 27 kilometers.

“This is how we gain a better understanding of what matter is made of and what the fundamental forces of nature are”, he emphasised. “By inducing collisions at very high energies, we are able to reproduce, on a microscopic scale, conditions similar to those that existed in the early moments of the Universe”. When these collisions occur, particles fragment and give rise to others, allowing us to observe fundamental constituents, such as quarks and gluons, and understand the interactions that bind them.

Between the “very large” and the “very small,” the session also addressed what remains to be understood. “Despite everything we already know, only about 5% of the Universe is composed of matter that we can describe in terms of atoms”, he noted. The rest corresponds to so-called “dark matter” and “dark energy”, whose nature remains unidentified. “We know they exist because of their effects, but we don’t know what they are. It is one of the great challenges of modern science”, concluded the experimental particle physicist.

“Science advances precisely because of unanswered questions”, emphasised Pedro Abreu. He set a challenge for the younger participants: “We, researchers, don’t know all the answers yet. But if you want to understand these questions better and help answer them in the future, the next step is to come study Physics at Técnico”.

On the way out, conversations continued beyond the auditorium. Between stars, atoms, and particles, the initial question unfolded into a universe of unanswered questions. The session ended without a definitive answer, but with clearer ideas: understanding the Universe requires a simultaneous exploration of its extremes.

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The “Explain it like I’m 5” initiative has already held seven sessions this year, introducing younger audiences to various scientific fields studied at Técnico. The series concludes on May 13, 2026, at 10 a.m., with the session “Why are soap bubbles round?” – Hugo Tavares (CAMGSD).

Previous talks:

8 October 2025, 10 a.m. – “How does a satellite work?” – João Paulo Monteiro (ISR-Lisboa)

News published on the Técnico website: “How does a satellite work?”: Técnico opened its doors to the curiosity of young children

12 November 2025, 10 a.m. –  “How does a laboratory that fits in the palm of your hand work?” – Vânia Silvério (INESC-MN)

News published on the Técnico website: “A laboratory that fits in the palm of your hand: children discover micro-scale science at Técnico”

10 December 2025, 10 a.m. – “What happens to toilet water?” – Ricardo Santos (LAIST)

News published on the Técnico website: Children explore the invisible journey of water during the third science talk “Explain it like I’m 5”

4 January 2026, 10 a.m. – “What is radiation used for?” – Joana Madureira (C2TN)

News published on the Técnico website: “Explain it like I’m 5” kicked off in 2026 with a session dedicated to radiation (which ‘we [human beings] also transmit’)

6 February 2026, 10 a.m. – “Did you know that there are cities where every drop of water counts… and others where every drop is wasted?” – Filipa Ferreira (CERIS)

News published on the Técnico website: “Every drop has a path”: a journey through the water cycle explained to children at Técnico

18 March 2026, 10 a.m. – “Where do the things we use to make other things come from?” – Amélia Dionísio (CERENA)

News published on the Técnico website: “From rocks to everyday objects: children discover the origins of raw materials at Técnico”