Chaos, Clocks, and Cries: A Scientific Journey from East Germany

In this interview, Professor Hans-Peter Herzel takes us on a unique journey through the hidden rhythms of life, from the chaotic oscillations found in newborn cries to the intricate clockwork of circadian biology.
Starting in the world of statistical physics and chaos theory, and shaped by the scientific landscape of East Germany, Herzel explores how physical principles reveal themselves in biological systems.

We discuss:
• The transition from noise to chaos in living systems
• The nonlinear dynamics of voice production and newborn vocalizations
• Chronobiology and the genetic clocks that govern life
• Science across borders during the Cold War in East Germany and Russia through history
• The philosophy of finding order within apparent randomness

This conversation connects physics, biology, and history and reveals how chaos theory continues to shape our understanding of life itself.

Timestamps:
0:00 Intro
1:23 What is the meaning of life according to a physicist?
2:50 From Hardcore Physics to Theoretical Biology
4:01 Study background
5:55 Voice production
7:38 PhD thesis and deterministic chaos in newborn cries
9:49 Theory of limit cycles and analysis of voice
11:28 Campus of Humboldt
12:41 Chaos theory vs chaos in movies
13:11 Research collaboration with singers
14:05 The story of Leonor Michaelis
15:11 Summary of Herzel’s research history
17:36 Science in the 70s and 80s in East Germany
19:33 Research limitations under the GDR
20:18 Political bans on communication
21:17 Struggles with copy machines
22:08 East West scientific exchange
23:41 Wartburg conference and fractals
25:05 Sängerwettstreit and cultural symbolism
25:37 Future research and plan B in academia

#Chaos #ChaosTheory #Chronobiology #CircadianRhythms #HanspeterHerzel
#Biophysics #TheoreticalBiology #MolecularMedicine #VoiceScience
#VocalFolds #NewbornCries #Oscillations #NonlinearDynamics
#ScientificInterview #ScienceDocumentary #ScienceHistory
#EastGermany #ColdWarScience #AcademicJourney #PhysicsToBiology
#Neuroscience #Genetics #TimeSeriesAnalysis #ScienceCommunication
#ScienceYouTube #StudentInterviews #MasterStudent #ScientificStorytelling #Planetarymotion
#ComplexSystems #RhythmsOfLife #CoupledOscillators #ScientificFilm

The voice is produced by vocal folds 
and vocal folds are nothing but a constriction in our larynx. They were able to 
generate normal cries but also chaotic cries, all these crazy sounds. This was just 
a small example how crazy East German politics was even in 88. I recommend that you 
make a photograph of this. I will do my best. Let’s start with the current status, right now I’m 
a professor of theoretical biology at Charity and Humboldt University. I started a while ago with 
physics studying physics at Humboldt University before I was grown up in northern Germany in 
Güstrow and now I have two children i’m married 40 years or so and I live now in Berlin for 
many decades and I teach i love to play beach volleyball or volleyball in general i have four 
grandchildren that’s about me. In my eyes biology, medicine has to fulfill the laws of physics and 
chemistry so it’s not out of natural sciences. That’s why all the laws of physics and chemistry 
are valid and relevant and interesting but there is something special about life and one aspect is 
a high complexity so it’s extremely complex and that’s why the rules of physics and chemistry have 
limited applicability, this is one major effect. The other point is that life is in some sense 
a mixture of natural science and of history since life evolved over billions of years 
and and it only makes sense to understand the current life as a view to the evolution of 
of life so that’s why many other forms of life many other decisions might be possible that’s 
why you you have to add the historic aspect to to life if you want to understand biology or 
medicine and this is different from physics where at least most people believe that the laws 
of physics are valid at any time and everywhere in our accessible universe. That’s why I 
studied physics but while studying physics I realized that other areas like biology are 
even more exciting and I moved slowly from hardcore statistical physics to interesting 
complex biological systems. Werner Ebeling, he established a group at Humboldt University 
where interdicciplinary research was the topic so he was interested in self-organization dissipative 
structures second law of thermodynamics, energetics all these interesting topics and 
both students in the group had different topics like stochastics or non-linear dynamics pattern 
formation and I became interested in stochastics and random noise and then deterministic chaos 
and then I had all the freedom to explore what I found interesting but I was also inspired by my 
colleagues working on artificial neural networks or pattern formation so I was surrounded 
by interesting young people with a broad range of interests and that’s why the switch from 
physics to biology was at the end quite natural. So I finished my diploma studies in 84 and 
since I continued with a similar topic, I could start right away with my PhD studies in 
the same group of Werner Ebeling and I finished it in 86 so two years later. In the 80s people 
became interested in complex systems and if data are very complex like brain data or climate 
data biological data then there are at least two alternative explanations so everything is random 
it’s stochastic or there might be something called deterministic chaos this was a new development in 
the 80s that the deterministic chaos can explain complex behavior the butterfly effect is the most 
popular example and in my diploma thesis and PhD I was interested “can you distinguish between 
stoastic process or noise and deterministic chaos from data”. So it was clear that the theory 
of deterministic chaos was finished in 84 to 90% that’s why it was hard to improve the theory 
but the applications were still not clear and in particular in biology and biomedicine people 
claimed a lot that heart rate data are chaotic or brain data are chaotic but it was never proven 
that’s why my main interest became to apply the well-established theory of dynamical systems of 
chaos theory to real data to answer the question “can we learn something from say the concepts 
to to the real world to biological or medical data”. So including circadian rhythms so 
the night rhythms or heart dynamics but perhaps my earliest first interest was voice 
production. So we all know that the voice is generated in the larynx here and it’s it’s 
interesting important and but not so easy to understand from a physical point of view so 
it’s relatively easy to explain a sustained vowel aaaa That’s a sound that is periodic regular 
but requires already an interplay of mechanical oscillations of the vocal folds and aerodynamics 
the air flow from the lungs to the mouth and this brings together an aaa and this was clear in the 
70s 80s this was not new no but many speakers also speak like AaAaAa and this sounds strange and 
it’s not so rare so in singing Louis Armstrong [Louis Armstrong singing] or in patients it’s 
common observation that the clear voice might be interrupted by a rough voice and this 
was widespreadly found but never very well explained and this became my niche since I 
learned irregular voices might be related to nonlinear dynamics to chaos theory this was 
the starting point say in 87 or so to switch from hardcore physics to the first biomedical 
application. Let’s go back to my own PhD thesis in ‘ 86 so I realized deterministic chaos is 
interesting but the theory is well-developed and I can only make minor contributions no but 
then I encountered by chance Kathleen Wermke i was surprised excited how relevant deterministic 
chaos can be in in acoustics and it was told to me by Werner earlier that newborn cries might be 
an application of of chaos theory but this was abstract and I ignored it but then I had to go 
to another building to another in Berlin Pankow since our own computer was broken it was a Hewlett-Packard (HP) computer 9835 or 9845 I don’t recall I used both types and and getting reasonable computers in 
East Germany was not so easy and we were happy to have such a unit packet computer and but since 
I had to do some plots some graphics I had to go to Berlin Pankow and then Werner organized 
that I met by chance Kathleen Wermke and she showed me her thesis PhD thesis and it was full of 
recordings and spectrograms of newborn cries and I was excited to see that newborn cries did what we 
had in labs they were able to generate say normal cries but also chaotic cries all these crazy 
sounds and uh people might used to it and it’s very common and but to me it was a breakthrough 
that say in the real life non phenomena happen all the time and that’s why I started to change my 
topic so I learned acoustics I went to biomedical applications of nonliner dynamics and so 
I realized that I can contribute to this field and not only for newborn cries also for 
patients for singers and later for animal voices in biology. Starting point is that these phenomena 
are not rare in normal languages in patient data in newborn cries and in animal vocalizations 
this is the starting point since if you have a theory about something nobody cares this is 
not very exciting and the next step is that the terminology was confusing mostly voice analysis 
has been done by engineers and medical doctors and they were very strong in linear systems and 
in anatomy and physiology but my education in linear dynamics was distinct. In medicine they had 
many many terms diplophonic dichotic hoarse rough all these terms describing chaotic voices and I 
could provide a relatively simple theory that this is all related to limit cycles period doubling 
deterministic chaos and it can be analyzed with phase space analysis with spectrograms bifurcation 
theory and so on so it was at the end the kind of simplification of of the data with a common theory 
and this was the starting point and then we went to experimental work with exercised larynx studies 
we did computer simulations we developed the theory and in in fact this was indeed together 
with colleagues from where i was doing thesis starting point of a new research field and 
that’s why in 1990 I decided this will be my main research topic in the next 10 years perhaps 
in my whole career. So this is the this beautiful campus here in the middle of town was originally 
the veterinary campus of Humboldt University so it’s older than the university itself and just 30 
years ago you had pigs and horses here on campus but now the veterinary medicine moved to the 
south of Berlin and now these buildings are used mainly by biology and medicine and still 
students like it a lot we like it as teachers we have beautiful lecture halls offices 
and a good atmosphere to relax in between. So there was a debate whether or not languages 
are allowed to enter the campus or biology and there was even a vote in the academic senate 
of Humboldt University and there were two options languages or biology is allowed to 
join the campus and there was a I guess 13 to 12 voting that biology is allowed to join 
the campus and this was very nice for us so we could reconstruct many of these buildings and 
and our biology is here in the center of Berlin. So chaos is a word that is used for everything 
but deterministic chaos is part of a well-defined theory termed non-linear dynamics and it’s 
described mathematically in a strict sense and many people confuse it with everyday chaos 
that’s why if a movie uses the word chaos it’s not implying that it’s non-linear dynamics 
or deterministic chaos or chaos theory. So I mentioned Louis Armstrong we had 
also collaboration with Michael Edgerton and we compiled many many data sets with 
chaos in the voice from modern singers but frankly speaking I’m more interested in 
classical or regular singing and sometimes in Jazz and the Rhythm in Jazz is also 
exciting but really chaotic right now we submitted a paper on a heavy metal singer 
and he is using a lot of chaos but I’m not really interested in his music but I’m more 
interested in his the mechanisms of such voice production and that’s why there’s a gap 
between my research and my musical interests. Our immune system is quite essential but there 
was an old wrong theory by Emil Abderhalden about so-called Abwehrfermente (defensive 
enzymes) and this theory was adopted by Leonor Michaelis but he was politically so strong 
in 1910s or so that Leonor Michaelis had to leave the country to continue his scientific career 
nevertheless Leonor Michaelis became famous due to the discovery of the Michaelis-Menten law 
and Abderhalden is forgotten and nevertheless this old building was named after Abderhalden 
until the ’90s but we changed it now to the Leonor Michaelis house and the whole story is 
written here it’s about the old wrong theory of Abderhalden and the correct uh explanation 
of of our immune system by Leonor Michaelis. You see the traces (on the blackboard)? So my 
research is focused on rhythms so I was trained as a physicist to describe planetary motion 
with the planets oscillating around the sun then as I discussed earlier I became interested 
in voice production you see the voice is produced by vocal folds and vocal folds are nothing but 
a constriction in our larynx and driven by air flow coming from the lungs to the mouth and these 
vibrations are again mechanical oscillators so if I say say Aaa this implies that I have a sound 
of 100 hertz roughly and the period of the vocal fold vibrations is just 10 milliseconds so very 
very fast but later in the 90s mid 90s I became also interested in heart rhythms since also 
heartbeats and respiration are quite important and complicated and here the period is more 
on the order of 1 second so we have about 1 second per heartbeat or 60 beats per minute 
as we might know and later after 2005 or so I started to become interested in chronobiology 
so the chronobiology or the circadian clock is a theory about rhythms that are close to 24 
hours so the period is now much longer about one day and this implies that these rhythms also 
control sleepwake cycles if you go to bed in the evening this is part of the rhythmicity 
if we are active in the morning that’s part of such rhymicity and it’s interesting to that we 
realize these rhythms are generated in our bodies autonomously so without external drive for example 
from the clock or from alarm clocks or from lecture series we have an intrinsic rhythm and the 
generation of these rhythms and the coordination with the sun this is part of our research interest 
and after all I was doing all the time ryhtms even by changing topics from planetary motion to 
circadian clock. So it’s it’s hard to imagine the situation in the 70s and 80s so you might have 
learned that the rules were quite strict there were many hopes but but the situation was very 
bureaucratic and old man more or less dictated what was allowed to say what’s happening how the 
economy develops and the problems were obvious but there were many dogmas in the political world. 
Gorbachev was the first one in about perhaps 85 or so frankly speaking about the problems this 
was already a major change of politics that the problems are named properly and that’s why we were 
reading all the articles published on Gorbachev all his speeches and we were really excited by the 
openness by Glasnost and Perestroika and Glasnost more or less means openness of the discussion and 
Perestroika means let’s change the society and these were really key words in the late 80s and we 
were all optimistic that something will change but it took a while it took a few years until things 
changed also in East Germany. Science in East Germany was good since we had at least libraries 
we had some computers and we had a lot lot of freedom at universities since basic science was 
not so much influenced by old-fashioned politics that’s why personally I felt in a good environment 
at Humboldt University in the 80s in the group of Werner Ebeling and I could do interesting 
topics the there were still limitations so the computers were not up to date and copy machines 
were rare but the main limitation of research in East Germany was the daily exchange with 
colleagues from all over the world so we were rarely allowed to join conferences and that’s why 
we were bit behind from the latest developments and this was not so much a concern of mine since 
I was still young about 30 years old that’s why I couldn’t say that my career was strongly limited 
by the East German situation but after the wall came down I was traveling immediately to Denmark 
to the US to all countries to all conferences and I enjoyed it a lot. This was a strange situation 
it was still at Moscow University but it was not allowed for East German students to have contacts 
to other people than Soviet Union students and East German students and this was to me so much 
outdated that I ignored the rule totally but at a meeting of all East German students I learned that 
it’s forbidden and in particular a female student had an African friend and this was punished by 
authorities and this was so ill so crazy that we were not allowed to have say have a friend 
from Africa that I was shocked at these days this was just a small example how crazy East 
German politics was even in 88. Interestingly copy machines were rare and there were different 
reasons first of all the economy was weak and it was hard to produce high quality copy machines 
but the second reason might be that the government was afraid that people copy socialist or other 
critical books and that’s why when I read that we needed three copies to submit a paper to physics 
letters I had a problem i went to the library and the library said we are not allowed to make 
private copies and then I went to the ministry since my aunt she was working in a ministry 
building and she was able to do some copies that I could submit the paper to a physics letter this 
was later accepted and published we had economic and political problems but we found in many cases 
some ways to solve them the exchange between east and western scientists was complicated but not 
impossible first of all we attended all meetings in Budapest or Eisenach some western colleagues 
attended and this was one option to get to know them personally another option were so-called 
cards we asked for cards on cards to send us reprints so if we realized in some databases that 
there is an interesting paper then we could send a a card to the colleagues typically written 
could you please us send us a latest paper in physics and related papers and these the 
colleagues were so kind that they sent us all their papers at the end in in big thick envelopes 
this was exciting since we got modern preprints early enough to use them for our own science and 
and I sent also such cards around the world and was proud if Jack Hudson a colleague from Virginia 
replied and sent me his papers and and greetings later he became a good friend of mine and this 
was funny since he lived in West Berlin and then he visited us in East Berlin and then he had 
to to get money out who had to exchange western currency to eastern currency and that’s why he 
was happy to spend the beer in in a restaurant and later he became a reviewer of my second 
thesis so this was fun to to have an American friend even before the wall came down. While I was 
still a diploma students I was allowed to give a talk at an international conference it was on the 
Wartburg castle about chaos and in addition to our colleagues from Berlin and other cities in East 
Germany there were also good friends from Bremen. Peitgen, Richter,  Plath and so we had a nice conference 
on chaos and fractals but in addition there was a German history to have a singers contest on the 
Wartburg and since East Germans and Russians love to sing at meetings so we also celebrated the 
singing at the Wartburg Castle and at the very end there was even a prize for the best singer 
and the funny coincidence was that Peter Richter he gave a lecture on fractals and some of you might have 
heard about fractals and that there are these apple trees that look like a fractal like 
a very strange geometric picture and that’s why we decided to give the first prize to Peter Richter
and the first prize was an apple-man so it was it reminded his talk on on fractals but on the other 
hand it was just a combination of three apples on top of each other so it was a nice coincidence 
of food delivery and price and fractals. Germany was not a large strong country before 
say 1871 since there were so many small countries like Saxony and Bavaria and Prussia and they only 
united in 1871 and that’s why such a meeting of people singing together on the Wartburg was already 
influential to have a kind of unification of different small countries where they spoke 
German. Before you go to the real challenges like epigenetics and genetics or immune system and 
circadian clock these are of course hot topics if you combine circadian clock with the immune 
system and chemotherapy this is a perhaps the most important connection I see at this stage but it’s 
also perhaps the most difficult area of research. Problems exist at any time so for the problem of 
socialism falling walls and so on and there are problems of complicated science there are problems 
of positions in academia at the end you have to be positive you have to enjoy science but it’s 
also important to have a plan B since there are not enough positions in academia and that’s 
why also other positions in society are quite important and why not to go to industry to 
artificial intelligence or to social issues that these are also interesting topics. In the mid  90s I realized that I’m no longer a physicist and I’m not really a biological or biomedical 
researcher and I became a bit nervous but then I realized I published enough papers that’s why I 
I might even get a position in the US at a medium university and this was at the end my plan B if I 
cannot make it in Germany then I would go with my family to the United States there is a hierarchy of universities and that’s why I was quite optimistic that I get positions in perhaps 
in at the teaching university at least to enjoy teaching and to enjoy the disciplinary research 
in fact I got a couple of letters that people said okay aren’t you interested to come to Utah 
or to Montreal but at this point I got already my position here in Berlin. Stay optimistic enjoy science and you can also the contribute to science.