Interviewing ASTRID EICHHORN: Inspiration Among The Stars



Astrid Eichhorn is an Emmy Noether Junior Research Group leader at the Institute for Theoretical Physics at the University of Heidelberg, Germany. She is also an Emmy Noether Visiting Fellow at the Perimeter Institute for Theoretical Physics. Previously, she was a Junior Research Fellow at Imperial College London and a postdoctoral researcher at the Perimeter Institute for Theoretical Physics. She did her PhD in the group of Holger Gies at the TPI Jena. PBS Nova Next featured her opinion in their report on “A Radical Reinterpretation of Einstein’s Theory”. The online newspaper of the University of Graz mentioned her a “shooting star” among young academics in Physics.

Pratyasha Saha, on behalf of DUSS, spoke with Dr. Eichhorn for a long Q&A session to hear about her research and her view on how to get more people involved in hardcore science, especially women. Her answers are presented below (edited for clarity and brevity).

1. When did you first become interested in science? Why did you particularly choose physics in your bachelor study?

Well, actually it’s difficult to pin out the exact time when I started to become interested in science. But I think it was at some point in high school. That was the time when a lot of amazing pictures from Hubble Space Telescope came out. I just looked at those and thought that it was so wonderful that these beautiful things are out there in the universe, and I thought, “I want to understand more about them! I want to learn all about them!” So that’s sort of how I got interested in physics with this idea that I would like to understand more of astrophysics. And then when I started with it, what I found even more interesting is particle physics because that, in some sense, underlies what goes on in astrophysics. And then I got more and more interested in particle physics and theoretical physics. Eventually I realized there is something even more fundamental that we can try to understand which is quantum gravity. Research on quantum gravity is really trying to understand our universe at the most fundamental level. So that’s how I ended up doing what I do now.

2. You’re working with asymptotic safety and quantum gravity. How are these two phenomena interrelated?

The main idea of quantum gravity is to understand the fundamental building blocks of our universe. It tries to unify the two major pillars of twentieth century physics. These are general relativity, discovered by Albert Einstein, which describes gravity in terms of spacetime curvature, on the one hand, and on the other hand, quantum field theory, which is the framework in which the standard model of particle physics, describing all elementary particles, is formulated. These are the two major pillars on which physics is based nowadays. What we don’t really understand is how to bring the two of them together and accomplishing that is the goal of quantum gravity.

So what is the problem? In particle physics, we treat particles as the excitations of underlying quantum fields. As these have quantum properties, they undergo quantum fluctuations, because of the Heisenberg uncertainty principle. This means, that so called virtual pairs of particles and antiparticles can appear out of the vacuum for a very short time, and then disappear again. The problem of quantum gravity is trying to understand how the gravitational field reacts to these quantum fluctuations. The major problem of quantum gravity is that if we try to treat gravity with the standard quantum field theoretic tools that work well for all other interactions, such as, the electromagnetic force, the strong and the weak force, and then we realize that it doesn’t really work. We come to the conclusion that quantum fluctuations of the gravitational field lead to a breakdown of the model at very high energies, or conversely tiny length scales. Let me explain in a bit more detail what happens in some of the other interactions, where the model doesn’t break down at high energies: These become asymptotically free. Asymptotic freedom is a property that determines the behavior of the strong interaction in the standard model at very high energies. Asymptotic freedom is a consequence of the presence of quantum fluctuations: If you “zoom in” to observe a strongly interacting particle more closely, you will see a cloud of virtual particles and antiparticles that surround it. This virtual cloud shields the so-called color charge of the strongly interacting particle, and the effect becomes stronger, the further we zoom in. Ultimately, we see the strongly interacting particle has having no color charge at all, and it behaves just like a free particle. For quantum gravity, this does not work, as quantum fluctuations lead to a growth of the gravitational coupling, so gravity seems to become stronger, not weaker, as we zoom in, and it cannot become asymptotically free. However, this does not mean that the model must break down as we zoom in to tiny length scales: Steven Weinberg, who is a Nobel prize winner in theoretical physics, for some of his other groundbreaking ideas in quantum field theory, realized that asymptotic freedom can be generalized to asymptotic safety. Asymptotic safety means that quantum fluctuations trigger a growth of the gravitational coupling as we zoom in to small scales, until the coupling reaches a special value, at which scale invariance sets in and the growth of the gravitational coupling is stopped: Scale invariance means that quantum fluctuations follow a delicate balance, where you zoom in further, but the gravitational coupling stays constant. In some sense, this means that in quantum gravity, spacetime becomes a fractal: A fractal is a scale-invariant object, which means, it looks the same, no matter how far you zoom in. If quantum spacetime has similar properties, then it means that we can construct a quantum field theory of gravity which holds up to arbitrarily small scales and provides us with an understanding of the microscopic structure of spacetime.

Now in our universe, you have to consider not only spacetime, but also matter. So one of the biggest questions is, “If we have a consistent model of quantum spacetime itself, would that model still work if we add all the other degrees of freedom, namely the matter fields of the particles in the standard model to it?” And if a model of quantum spacetime doesn’t work if we add matter, it is not a viable model of quantum spacetime for our universe. Thus, what happens to quantum gravity when we add matter is a very important question. So specifically what I and my research group work on is considering asymptotically safe quantum gravity and adding the matter fields of the standard model. Then, quantum fluctuations of matter could destroy the delicate balance that we need to achieve scale-invariance, which makes the model asymptotically safe. We ask whether the asymptotic safety paradigm can provide us with a microscopic model of gravity and matter.

3. How is the influence of experiments in theoretical physics or physics in general?

I think, what distinguishes physics from mathematics is that it’s not just about building mathematically consistent models, it’s about building models of our world. And for that, the existence of experiments is absolutely crucial. In physics the development of theory and the development of experiments always should go hand in hand. When one area makes a big step forward then it can also trigger the progress of the other area. In general, you can’t really think about theoretical physics as being separate from experimental physics. They always have to go together to be successful.

But in high energy physics, we currently have the problem that the energy scales we would ideally like to probe experimentally, like the scale of quantum gravity, are actually much higher than we can reach with our current technology. The highest energies that we can reach experimentally are reached by the Large Hadron Collider at CERN. The Large Hadron Collider is doing a great job, it has delivered really exciting results about the Higgs particle, but it cannot easily help to answer our questions about quantum gravity. So this is one of the very big challenges of quantum gravity that we don’t have the situation where theoretical development and experiments can go hand in hand. This is one of the reasons why we actually have to work much much harder in quantum gravity because we don’t have nature showing us the way toward the right model.

4. So at the moment there are several possible untested quantum theory of gravity. What experiments are going on to test them?

Well, this is really a big challenge of this research field that quantum gravity is expected to set in at an energy of about 10^19 giga electron volts, which is known as the Planck scale. Let’s compare that to the energies that we can reach in experiments: The LHC can reach 10^4 giga electron volts. So there are fifteen orders of magnitude between energies that we can currently reach really well and energy scales that we would like to reach. And so therefore, in quantum gravity we are facing the challenge that we don’t really have a lot of experimental guidance in order to help us shape our models. There’s actually a small community of people who are working on what is called quantum gravity phenomenology. They are trying to face that really challenging question of connecting quantum gravity to experiments. And actually there are some observations, in particular in astrophysics, where you can do that. One idea that works very well, for instance, is trying to understand whether Lorentz symmetry, which underlies Special Relativity, holds at much higher energy or not. Lorentz symmetry tells us that light of different colors, which correspond to different wavelengths, travels at the same speed. Testing whether this holds at high energies, where quantum gravity plays a role, can be done using gamma ray bursts. They are really really bright high energetic bursts of gamma rays, which are high-energetic photons, out there in the universe. For them, the light travels a really really far distance until it reaches us. Now imagine that Lorentz symmetry is broken even very very slightly, for instance, the blue photons travel a little quicker than red photons. Since you have huge distances over which the photons travel to reach us, this effect can build up and then you would actually be able to detect it here. For this particular observation, the Fermi satellite which is observing gamma ray bursts, has actually allowed us to rule out certain types of Lorentz symmetry violation up to the Planck scale. Thus, we can already constrain the properties of quantum gravity models from these astrophysical observations.

We’re trying to probe physics at the quantum gravity scale but in general it’s really very very difficult to do that. So one idea that I’m trying to develop further, is the idea of not trying to build experiments that try to meet the Planck scale. Instead, I’m trying to rule out models of quantum gravity by testing whether they are compatible with everything that we know about the world at lower energies.

To give you a simple analogy of what I’m trying to do, imagine that the question you’d be interested in is trying to understand what the microscopic structure of, let’s say, honey is. But you couldn’t actually probe honey at molecular scales, you could only probe the properties of honey at large scales. Then the ‘honey theorists’ would go ahead and would build models of the fundamental structure of honey and then they would predict macroscopic properties, for instance, the viscosity of honey from their microscopic models. The viscosity of honey is clearly something that you can test at a much much bigger scale than the molecular scale of honey. So you’d have these different ‘honey theorists’ coming up with their different models of what honey is like microscopically and they calculate the viscosity in the different models. Then you can compare that to an experiment to clearly rule out very many different models of the microscopic structure of honey because they give you the wrong value of the viscosity.

In quantum gravity you can try to do something similar, particularly by asking the question of what properties of matter are compatible with quantum gravity. For instance, one of the properties of matter that we observe is that all the matter particles (electrons, quarks and so on) are light compared to the Planck scale. This is a property that’s technically known as the chiral nature of fermions and it is not necessarily easy to include in a quantum gravity model. So just like the different models of honey give you different viscosities, different model of gravity will tell you whether they are compatible with the existence of fermions or not. So if you check all different quantum gravity models that we have and ask which of them is compatible with the properties of matters at low energy scales, then this will actually allow us to rule out a number of quantum gravity models. To summarize, as it’s difficult to probe quantum gravity at the Planck scale directly, we can try to perform indirect observational consistency test that ask which quantum models of space and time are compatible with the properties of matter at large scales.

5. Is there anything in your research field you want to change to improve how science in your field is done?

One thing I would like to change about my research field is to have a closer connection to experiments and to have some experiments that help us in developing models of quantum gravity. Since there are hardly any experiments that allows us to shed light on the question “What is the quantum nature of spacetime?”, a lot of research is founded on assumptions that people make for different models and then they fight with each other about these assumptions. That can potentially become nothing but a waste of time. So one thing I would like to imagine for a change is that someone would have an inspired idea about experiments that will help us understand quantum gravity better. So then we can give up the fight between different quantum gravity models and instead focus on trying to make sense out of the experimental results together.

6. What do you think an ideal science curriculum should contain in school level?

It’s difficult to say that very generally but I think children are really curious about the world around us. So every child is asking questions like, “What is this? How does it work? Why is it this way?” I think a good science curriculum should exploit this natural curiosity. It should encourage children and help them answer the questions they have. It should not be so much about learning predefined things by heart, rather it needs to follow the children’s natural curiosity, and ask each child, “What is that interests you in particular? What would you like to understand?” And then just help them along the way of proper understanding, for instance, explaining to them what experiments are, how to set up an experiment, why we do experiments and then follow them along the particular area they want to explore more. I think that would be an amazing science curriculum.

7. Was your school curriculum perfect for you? How did you deal with that?

My school curriculum in physics was not that good, at least during the early part of high school. To me, science is about understanding, but my curriculum was nothing like that. It was just about memorizing facts. Doing that without having any idea what it actually means or where it comes from, that’s just the opposite of what science is.

This changed about two years before the final high school year when I got a really really good teacher. He was trying to teach us how to do science. He used to say, “Well, here we have an experiment, here’s the question that we have, here’s the open problem. So do you have any idea how to address this problem?” And then he made us develop the ideas to solve the problems. He really showed me that doing physics is a lot of fun and you can just follow your curiosity. So thanks to him, I actually ended up understanding physics.

8. What contents should we add to make students feel motivated to do fundamental science?

I think it is not really that difficult to inspire people about fundamental science. Because at some level we all have the curiosity to understand the world around us. For instance, I think everybody has had that experience of staring up at the night sky seeing the stars and thinking, “Wow! Where has this come from? How did it become so amazing!?”

So the one challenge is to show people what we are actually doing in fundamental science. In theoretical physics, everything might look abstract and mathematical. It is challenging to make people understand that this seemingly very dry subject is exactly trying to answer the questions they naturally have. So the main challenge is to connect the abstract research results to the curiosity that everybody has, the questions that everybody asks at some point in their lives, in particular as a child.

9. What would be your advice to young people trying to pursue physics? Any special advice for to-be theorists?

Well, I think in general it’s always a challenge to give advice because people are very different. Things that might have worked well for me will probably not work well for everybody else. But in general, if you want to pursue physics, it can be a hard subject so what you just need is a great deal of motivation. So, I think what you should do in physics is just following where your curiosity takes you, because these are the topics you’ll be most motivated to explore. Follow what interests you and what you would like to understand. Particularly, in theoretical physics, you need a high degree of motivation because one thing you’d definitely have to do is work hard.

For young students in physics, I think one really good way to get in touch with researchers is summer school programs. For instance, CERN has a summer school program and also DESY, which is a particle accelerator in Germany. Many of the big experiments all over the world have a summer school program. These typically consist of a series of lectures followed by a period of time, where one is involved in a specific experiment. Many of the programs offer scholarships and they place an emphasis on having not only students from western countries but also students from all over the world. At these programs you can talk to the researchers giving the lectures, and you can also work with somebody on her or his specific research topic. This is a very good way to get an idea what research is really like, and to get to know people who might be able to give you a PhD position in the future, if you’re interested in that. So one advice from me would be, apply to these programs.

10. Unfortunately, lots of girls are not encouraged to pursue science in future. Any particular advice from you towards the society addressing this important issue?

Well, it’s an advice to young women first, “Don’t listen when people tell you that you can’t do that, or that’s not the right thing for you, or you will not be interested in it.” I myself faced the situation when I was finishing high school. Some of my teachers in high school, not physics teachers but teachers of other subjects, were telling me, “You know, I don’t think that physics is the right thing for you. You are a person who is more interested in humanities but physics will not interest you.” And really, you see, they were proven wrong. Now I’ve been doing physics for a while and I am still really enthusiastic about it. I think, everybody knows best for themselves, what they’re interested in and what they want to do. So if somebody tells you that something’s not for you or you can’t do that, don’t listen to that. If it’s what you want to do, then just go ahead and do it. As a women, you’ll probably encounter a certain measure of comments that can be discouraging. Try not to take them personally. Just think, “I’m gonna show you”, and don’t be discouraged by them.

One thing to society in general, I think people need to realize that our gender is not the thing that defines who we are. What defines who we are, are general characteristics and they are not tied to specific genders. So whether you are a man or woman shouldn’t determine which jobs you should take or which way you lead your life. This is something that we all need to understand: The idea that our gender is the main thing that determines who we will become and who we will not, what we can do and what we can’t, which roles we are fit for and which roles we are not, that idea is just wrong. Probably we all have certain biases about men and women and their abilities but we need to think about them consciously and avoid categorizing people by their gender. This is something that will not be solved today or tomorrow, but it will take a while. We all should try to be concerned about it and stop ourselves when thinking, “So this is a guy, he can’t be a good parent”, or, “This is a girl, she can’t be a good physicist”. Gender has nothing to do with these questions of what we can achieve in our life or what role we are fit for.

11. Probably this problem is more acute in this part of the world compared to the western world. So what would be your advice to the girls here?

I think it’s a very tough problem obviously and it always takes time to have significant changes in a society. It needs persistence and courage to be different and I think it’s important to stand up for your rights and for what you want to do. Obviously that is much harder when you are the first generation really trying to do that. In western countries, we already had feminist movements in the 60’s and the 70’s so I am now part of the second and third generation following their footsteps. And so when we are facing discrimination misogyny, it’s easier for us to fight them, because we can look up to examples of women who have successfully overcome these in our society. For you, this is probably harder, but don’t give up. Even if change is slow, future generations will be grateful that you did the first hard steps towards gender equality.

One thing I think is very important, to trigger this change in society, is having role models, people who’ve already done or achieved what you want to achieve. Just to give you a concrete example in physics: A female astrophysicist who had a huge impact is Vera Rubin. She measured rotation curves of galaxies and collected the first evidence for the existence of dark matter. And today understanding the nature of dark matter is recognized as one of the most pressing open problems in particle physics. There are a large number of experiments trying to detect dark matter and there are many theorists who are developing theoretical models of dark matter. It’s a huge research field. Role models are important because when people tell you that as a women you can’t do a particular job, then you can give them the examples of women who have done that and who had a huge impact. Show them by naming examples how women are as smart as men. Discuss with people, contradict them when they say women can’t be good scientists and tell them clearly that they are wrong. Probably for anyone in your country it will be more challenging because you are the generation who will become the role models for future generations. But never let anybody else tell you what you should do or what is best for you. You know best what you want to do and what you can’t do. Just keep up your inner strength and do what you can do and want to do.

12. Is balancing life and career a challenge to do science?

Yes, I think in general research in science isn’t very family friendly. That holds for both men and women. It’s a tough and very competitive environment which forces you to travel a lot, for instances to conferences and meetings, to work hard and to spend a lot of time on research. There’s also the idea that as a postdoctoral researcher after your PhD you need to move around and spend two or three years in different universities. This whole system is not at all family friendly. I think that’s a problem for both men and women. In countries like France and Germany people are becoming more aspiring of being a parent a successful researcher at the same time and they also like to spend a significant amount of time with their family. But the current system in science is difficult to reconcile with that. Some universities are trying to be family friendly but these are […] small steps and it will take time until the system is better adapted. But I would like to emphasize that this is a problem for both men and women in science.

13. Back to the education sector in general, what qualities should teachers have to get to the maximum output from the students?

I think it’s certainly difficult to say something about this topic that holds in general. As you know, teachers can be very different people and they have very many different ways which are good ways of teaching. It also depends on the type of students that you have. But in general, I think a good teacher is somebody who is able to make his/her students enthusiastic about the subject so that the students are also motivated and enthusiastic about it. Then success in teaching follows nearly automatically. So I think it is important for a teacher to encourage students and show them that the subject is exciting and interesting. That’s what for me defines a good teacher.

14. Do you have any influential figure for you in research? Any inspiration?

Throughout my career, I’ve had the privilege to meet and also work with a number of people whom I find very inspiring. These are scientists who are very curious and enthusiastic about what they do and whose main goal is to understand things better. They are driven by the desire to learn more about nature, not by their ego. They are not eager to show that they are actually bright or they understand better than other people and so they don’t have a problem with admitting if they were wrong about something. I am always impressed when researchers who have made important discoveries stay humble and do not feel the need to show that they are smarter or better. They try to judge new ideas by their scientific merit, and not by who the idea came from. In particular, they never think that their own ideas are necessarily better than other people’s ideas, they stay open to new suggestions. I had the luck to get to know a number of researchers like that and for me they define what a good scientist is and what I’m also striving to become if I can.

15. What do you think is the importance of fundamental science for a society or a country or the whole world?

I think the answer to that has two parts. First, I think being really curious about the world around us is really an important aspect of our humanity. That is what distinguish us from most animals, they don’t seem to be that curious about the world. We really want to understand our world, how everything works and what the world is made of. Trying to answer these questions is an expression of our culture, our humanity.

Now for many people it maybe isn’t justified to invest a lot of money into fundamental science because they say, “Well, we have so many more pressing problems. First we have to lift everybody out of poverty, provide sufficient nutrition, provide a good education, combat deadly illnesses and when we’ve done all that, we can try to care about the nature of the universe.” But there’s also an answer to that. We don’t yet know what the basis of new technologies will be that will actually help us to solve these pressing problems. There are a number of historical examples in physics where people were thinking that they would do purely foundational science with no application whatsoever and just a short while later their research actually became the basis for technology. A significant example is when Hertz discovered electromagnetic waves: he was thinking that he was doing purely foundational research. But a short while later people started inventing radios and other communication devices using electromagnetic waves. Thus, even the people working on a particular topic aren’t always able to predict that it can become the basis of future technologies. Another example is the GPS which nowadays many people use on their mobile phone to find their way around. In order to really be able to calculate the position of somebody with an accuracy of a few metres using the data from satellites, you must take into accounts the effects of general relativity. Otherwise you just don’t get the accuracy necessary to make GPS actually useful. But


when general relativity was invented by Einstein, he obviously didn’t think about mobile apps and the GPS. He was trying to understand the nature of gravity and spacetime.

So these examples show you that when we do fundamental science it can become a basis for technologies much quicker than we could actually envision. And clearly as long as we haven’t understood that particular area of fundamental science and we don’t know what the discoveries will be, we cannot predict what technologies we’ll be able to use that for. So even if you say that you there are many other pressing problems to solve in the world before one should focus on fundamental science, you have to keep in mind that actually doing fundamental science could allow you to develop new technologies to address these important problems that you want to solve. So I think we can’t really overestimate the importance of fundamental science.

Bonus Question: Any inspiration what gets you up in the morning?


“What are the fundamental building blocks of the universe?”, “How does the world work?”, “What is the world like at the smallest imaginable length scales?” – these are the questions I always had and still have! And as soon as we’ll be able to answer one question, more new questions will come up.

So this is what makes me get up in the morning. I follow my curiosity, do what I think the most exciting thing for me and do not give up, even if people try their best to discourage me.


Pratyasha Saha is a freelance science writer and current undergraduate student in Physics from Dhaka University, Bangladesh. 


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© 2017 Pratyasha Saha| Astrid Eichhorn

7 thoughts on “Interviewing ASTRID EICHHORN: Inspiration Among The Stars

  1. Jc Fortney

    Howdy! This post couldn’t be written any better! Reading through this post reminds me of my good old room mate! He always kept talking about this. I will forward this post to him. Pretty sure he will have a good read. Thanks for sharing!


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