Interview with Daniela Saadeh: winner of the IOP Gravitational Physics Group (GPG) thesis prize

Daniela Saadeh

Daniela Saadeh – UCL Astrophysics Group

CQG is proud to sponsor the IOP Gravitational Physics Group (GPG) thesis prize. This year the prize was awarded to Daniela Saadeh, who we have interviewed below. Congratulations Daniela!

Can you tell us a little bit about the work in your thesis?

A fundamental assumption of the standard model of cosmology is that the large-scale Universe is isotropic – i.e. that its properties are independent of direction. Historically, this concept stemmed from the Copernican Principle, the philosophical statement that we do not occupy a ‘special’ place in the Universe. In physical terms, this idea is converted into the assumption that all positions and directions in the Universe are equivalent, so that no observer is ‘privileged’.

However, assumptions must be tested, especially foundational ones. General relativity – our standard theory of gravity – allows for many ways in which spacetime could be anisotropic: directional symmetry is not fundamentally required. If the Universe were indeed to be anisotropic, we would actually need to carefully revise our understanding (for instance, calculations about its history or content). Making this health check is very important!

Previous work had addressed the question, but only restricted to the specific subcase of rotating universes. Nothing could be said about the remaining degrees of freedom: anisotropy could sit unseen where people had not looked.

We developed a framework that allowed us to advantage of the full constraining power of state-of-the-art data, with the goal of making a general test. The Planck satellite had delivered exquisite measurements of the temperature and polarization of the cosmic microwave background (a relic radiation from the Big Bang), creating a golden opportunity for this check. These data, in fact, are extremely sensitive to anisotropy.

After completing our analysis, we discovered that the Universe likes all its directions just the same: our work was able to disfavour anisotropic expansion of the Universe with odds 121,000:1 against.

What motivated you to pursue physics and this particular field of research?

I chose my job when I was 9! At the time, I was hearing a lot about astronomy, and studying the Universe seemed to be the most exciting thing in the world. Eventually, I met my first astronomer at an outreach event, and almost at the same time I saw a famous female astrophysicist on TV. These two events convinced me that pursuing astronomy was actually possible, something I could do. The rest follows!

I chose this particular research field because I’m interested in addressing general problems, and this was a fantastic opportunity to do just that! Additionally, I believe it’s crucial to test the foundational assumptions underlying our models and methods.

What do you find most interesting about this subject?

The fact we can finally answer quantitatively questions that used to be only the realm of philosophy. Nature is often more surprising that what humans can conceive in their wildest imagination, so being able to compare theory of the universe(s) with data is extremely exciting.

What have you gone on to do since completing your thesis?

I am still interested in testing our fundamental assumptions, and I am now turning my attention to tests of gravity. I will join a wide effort to establish if general relativity is the correct theory of gravity (as assumed in the standard model of cosmology), or if there is evidence favouring departures from it.

What advice would give to young scientists?

Look beyond the boundaries of your department, and avoid falling in the trap of thinking it is your whole world. As good and international your institution may be, there are many other institutions in the world. Having the opportunity to attend conferences and meetings early was instrumental for me.

As a female researcher, and winner of the IOP GPG thesis prize, what advice would you give to women in the field or women who are looking to start a career in physics?

Recognise the stereotypes that are holding you back. I look forward to the day when it will cause no sensation to represent ‘the scientist’, in the media, as a black transgender woman with a disability. Until then, I believe it is important to recognise the impact that being part of a minority has on yourself and others. Having female role models was instrumental for me, as well as attending biweekly “Physics Women’s Lunch” meetings at UCL.

And finally, what interests you outside of science?

Too many things for one lifetime! First and foremost, I have a lifelong passion for music (all of it!): I have a diploma in piano. I pretty much enjoy every other art form too, particularly visual arts. Then I love travelling, because I am extremely curious about all the world and the people in it. Then I like languages. And food. And…

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