ScientiFika

The birth of string theory or how to build a theory without knowing the Lagrangian

2026-10-16T00:00:00+02:00

I will start describing how the Veneziano 4-point amplitude and its generalisation to N-point, called Dual Resonance Model (DRM), were constructed using the basic properties of S-matrix theory. This procedure is opposite to the usual one where one constructs the S-matrix starting from a Lagrangian. In this case the S-matrix was constructed without knowing the corresponding Lagrangian. Only much later it was shown that the S-matrix followed from the string Lagrangian.

Then I will discuss how the scattering amplitude was rewritten in terms of an infinite set of harmonic oscillators that allowed to determine the spectrum of physical states and their scattering amplitudes. Absence of negative norm states, required by unitarity, restricts the intercept of the Regge trajectory to be equal to 1.

Already in 1970 Nambu, Nielsen and Susskind proposed that the underlying theory was a string theory, but it took few more years, by quantising the Nambu-Goto action in the light-cone gauge, to show that the spectrum of physical states coincided with the spectrum extracted from the DRM with $\alpha_0=1$. Later it was shown that also the scattering amplitudes at tree and multiloop level were the same.

I will conclude discussing the attempt of writing the scattering amplitude for pions that brought instead to superstring. A string theory for pions is still absent. In modern language this will require to construct a string extension of the non-linear sigma-model that is the low-energy effective Lagrangian of QCD, but all attempts in this direction generated scattering amplitudes with negative norm states violating unitarity.

The only theories that allow for a string extension are the gauge theories and gravity and no string theory exists with one of the two without the other. In conclusion, one started with the idea of writing an S-matrix for the mesons and one ended up in writing instead a theory unifying gauge theories with gravity.

What is * ******?

2026-10-09T00:00:00+02:00

Typically we talk about space and time as the most fundamental notions in physics. But, if you really think about it, at least operationally, ******* are more fundamental. But what are ****? And how do we know about ****? And perhaps even more importantly, how thinking about the emergence of space and time I, and hopefully you, came to realize that for the longest time I was simply not thinking about such a fundamental notion! Anyways, hope you come to wonder together about how to dramatically rethink our understanding of the world (like, really) together.

Jobs Outside Academia

2026-10-02T00:00:00+02:00

I defended my PhD in astrophysics at KTH in 2021. Afterwards, I did two years as a Data Scientist at Handelsbanken, resigned to try some startups that failed, and accidentally ended up day trading instead.

I will introduce myself, talk a little bit about my research and things I’ve done since, thoughts about transitioning out of academia, and then I’ll open up for questions/discussion. The idea is for this format to be more informal and interactive. (So ideally, it should not just be me talking :)

Hunting for strongly lensed supernovae with the Vera Rubin Observatory

2026-09-25T00:00:00+02:00

When a supernova explodes behind a massive galaxy, its light can be gravitationally lensed into multiple images. Such a strongly lensed supernova is a rare and powerful event that can magnify distant stellar explosions, map out dark matter in galaxies, and even measure how fast the universe expands. While only a handful of lensed supernovae have been discovered to date, the Legacy Survey of Space and Time (LSST) at the Vera Rubin Observatory has promised to discover orders of magnitude more. And after years of anticipation, LSST has just begun full survey operations! Over the next decade, it will scan the entire southern sky every few nights, generating petabytes of data and catching anything that moves, flares, or explodes. Somewhere in all that data, there should be lensed supernovae… but can we find them? In this ScientiFika talk, I will take you along with the Rubin strong lensing team in our hunt for the first strongly lensed supernovae in LSST — including unexpected snowstorms, help from the Euclid telescope, and machine learning troubles.

Why butterflies vary in their colors

2026-05-22T00:00:00+02:00

Butterflies are amazing in many ways, one of which is being incredibly colorful. Why does color vary so much across species and sometimes even between the sexes, or among individuals of the same sex? To get deep insights into these questions, my lab explores color variation in butterflies in diverse ways. We study how color has evolved across deep time, investigating color change across all of Europes butterflies. We also study these dynamics in more recent time, trying to understand the dynamics behind color variation within a butterflies species. Come to my talk if you want to learn about how some of the latest advances in biology are being used in Stockholm to reveal the mysteries of the butterflies in our backyards.

Breaking into venture capital

2026-05-15T00:00:00+02:00

Have you ever bought a stock, a mutual fund, or paid into a retirement account? Then you are already an investor.

Venture capital is one spectacular corner of the investing world, both the same and wildly different from how you invest as an individual. Together, we will dive into how the fastest-growing startups get funded. We will look at how a venture fund actually works, how the ecosystem around it operates, and what makes a company worth investing in and truly exceptional.

Many of Sweden’s great startups come from research and deep industry expertise. If you have ever had an idea and want to see how ideas become companies, this talk is for you.

Send in any questions before the talk that you want answered using this form.

Water’s molecular dance

2026-05-08T00:00:00+02:00

Water has a series of unique properties that make it completely irreplaceable as the matrix of life. The oceans help maintain the climate through its high heat capacity. Water’s density maximum at 4 degrees Celsius makes ice float, allowing for the existence of marine life. Its complex structural network drives the formation of biological assemblies. To fully understand the cause of its strange behaviour, we must investigate liquid water when its anomalies are at their peak - when water is cooled far below its freezing point.

In this talk, I will give a summary of our explorations of deeply supercooled water. I will show the different ways in which we probe how water molecules assemble and move. I will discuss how the different structures that water molecules can form, and how these evolve and rearrange, give rise to water’s unique abilities.

Deep Meditation - practice, theory & science

2026-04-23T00:00:00+02:00

In this scientifika lecture you’ll learn and experience Deep Meditation, and find out about its remarkable long-term benefits and what science has to say about it.

If you’re only interested in the theory & science part and don’t want to meditate, please arrive 30 min late, and only enter the room after the “Do not disturb”-sign on the door is removed.

Meditation when practiced regularly (every day over months and years) leads to astounding changes in the subjective experience of every day life, the perception and relationship to one’s thoughts, emotions and sense of self. This generally goes along with improved physical and mental health, well-being, creativity and contentment.

After dropping out of academia I had the opportunity to dive deep into meditation practices, and I will teach you the one practice that I currently consider to be the most effective and time-efficient for gradually increasing one’s life quality, and which can be incorporated into a busy life.

Ask each other Anything

2026-04-17T00:00:00+02:00

The semester is in full swing, and you might have questions about academia, job applications, research hurdles, or what lies ahead in your career. The good news? You’re not alone—many around you have faced similar challenges and can share valuable insights. This ScientiFika brings together bachelor’s, master’s, and PhD students, as well as postdocs, to create an open and welcoming space for discussing all aspects of academic life. Whether you’re curious about career paths, want to swap practical tips, or need advice on balancing work and life, this session is all about informal, honest conversations. You can submit questions in advance or ask them anonymously during the event using the form (or visit slido.com with code 5405239).

The recommended city: AI, democracy, and urban visibility

2026-04-10T00:00:00+02:00

How does AI shape the city before we even arrive in it? Generative AI is becoming part of how people discover places and decide what matters in a city. What AI makes visible can gain attention and value. What stays in the background can become easier to overlook. These shifts are already influencing how cities are valued and approached, reshaping democracy, diversity, and social equality along the way. In this talk, Ingrid Campo-Ruiz explores how AI is reshaping how people understand cities and public space. Drawing on research in architecture and AI, she examines how AI-generated recommendations and images influence what people see as worth visiting and protecting. Bringing together architecture, responsible AI, and social justice, this talk invites the audience to see AI in a new way: as a force already editing the city, its meanings, and its futures.