Tuesday, January 9, 2018

Happy New Year!

It's 2018! This summer it will be ten years since I received my PhD from Cornell University.  I used to think of 2018 as being in the very far future. Growing up, movies portrayed this the far future by involving flying cars and robots. David is talking to his phone in the other room asking "what will the weather be". So, while car-flying is still unsafe, we search the web constantly for advice. We consult the world wide web instead of simply looking at the sky or asking the neighbor next door for an opinion. The future from old movies is not very far off. As cars become self-driving they will be tracked precisely and perhaps made to fly. Machine learning is teaching robots to be human, and will progress in time.

My future so far is with my children. James is one, Edward is seven and David is ten. This month marks the first year when I have not been working since I started to work at 18. Yet with three children, I have had less time than ever before. I have often felt like a failure. My house is never clean. The children don't have very good grades. My yard and garden are a big mess, and I have been screaming and complaining to and of the aforementioned children way more often than I should. I have two shirts and two pairs of pants that I have been wearing day after day and a dress for when it's really warm in the summer. Most of my clothes are impractical for home-life and stay in my closet or in various bags. Nobody really cares how I look. It does not make an impression on the children or on the animals. Although, one of the roosters attacks me more when I wear my red pants. Most houses in the neighborhood are empty or populated by older people without children or with grown children elsewhere. Oh, and in the first week of the year I managed to lose my mother's purse with her driver's license, ID and car documents in the short distance of taking it from the car to the house. However, everyone is healthy and plenty of things happened this year.
    David and Edward on Mars

  • Some of the men in my life and Marcel
    The year started and ended in Lugoj because it's where the children go to school. Both Edward and David passed their examinations and are now firmly in third and sixth grade. They have learned a lot, and will continue to do so. Many of the subjects they study in school are not interesting enough for them. So, their grades are far from perfect, but then perfection is for heaven if there is such a place. If I ever I get there,  I want the saints to remember that I spend most of my time this year when I was not putting James on his potty doing homework with either Edward and David. Even though most of it is in German (they attend school in German for continuity's sake after coming from Switzerland), I still don't speak German well, which gets me back to being a failure. 
  • I submitted the paper on measuring planetary spin from space-craft tracking After constructive interaction with referees, it was published in the Frontiers journal.
  • We spent February in Tenerife and celebrated one year after the first gravitational wave detection and David's tenth birthday. I wanted the children to see the ocean again, and get a bit of sunlight in midwinter. Edward, David and Andy climbed their third volcano. Mount Teide is the third highest volcano on Earth with a summit at over 3700 meters.  Its caldera was formed some 180 000 years ago through movement of the tectonic plates that caused a gap. Mount
    Teide grew in response.   The children loved the Mars-like territory and the pumice rocks that still had air trapped in them. They float and were warm to the touch. I mostly stayed 'home' with James and my parents in our rental from Icod de los Vinos. We saw what they claimed is the oldest tree in the world,  some plants from the same family as the dandelion that grow into trees, and lots of chicken living by the road-site and in a Cactus garden near the house. In Galapagos, similar trees grow to be hundreds of meters tall, and bring moisture from the clouds to the islands.
  • Sometimes you can buy love -- animals are quite easy to purchase and they love us almost unconditionally. In June we bought Lady Edward (or Edwina Cleverbrain), Lady David (Davina Cleverbrain) and Lady James (Jamesina Cleverbrain) from the village of Tormac. They can open doors, untie knots and even eat with a fork. They avoid mud puddles, which makes them cleaner than my children, and unlike James, they do not eat food after it falls on the ground. Our guest for the holidays is Marcel -- a male goat. He stinks (most male goats do), but is very friendly. He is, however, not as smart as our ladies. He belongs to the director of the hospital here. He even has eagles and vietnamese pigs and more goats than us, which shows that I am not the only educated person in the area with animals. Today Andy went to the veterinary Farmacy and asked for preventive worm medicine for farm animals. They gave him some for cows because as an American they thought he must be a cowboy. It made no sense to explain he was a professor somewhere and so instead he said "no, I only care about goats. Does it work for goats?" (note that Andy is almost always very serious when he speaks and this was no exception). So, the person at the counter wrote in black the goat dosage: 10 ml/goat.
  • I am the editor of a new topic in Frontiers that is trying to attract more women to publish in its pages. 
  • We went hiking with Ed, Gab and Werner

  • Mihai and I gave invited seminars in Majorca at the Einstein Toolkit Meeting & Ed fest. Edward Seidel was my first advisor. He turned 60 this year and he and Gab remain persons I deeply admire. Ed still climbs mountains better than me and is responsible for connecting science and industry for universities in Illinois. It was fun to see physicists again. James took his first steps there, and has had his picture taken with Bernard Schutz, Gabrielle Allen, and other world-famous scientists who shaped my understanding of the world once-upon-a-time. 
  • I gave a seminar in Southampton in November. James and I also attempted to help Andy settle in his new reader position at Portsmouth. Andy's new apartment has lots of steps, and before he turned one, James learned to go up and down steps there. The departments at Southampton and Portsmouth are still largely intact after our visit. We are planing a second visit to Portsmouth in February.
  • I submitted a fellowship applications to be able to join Andy in England. If I pass the first phase, I will have to go for an interview. It will break my heart to leave Lugoj again, and tear all the little roots the children have built here. This year is marks the first time when Edward wants to go to school because he has friends there. On the other hand, we will have to spend some of the year there, and we cannot do so without health insurance. It's easiest to get if I work. 
  • the 3D boson star code from 2006 works on modern computers. While Gregory Daues, Jayashree Balakrishna and Christine Corbett-Moran and I are still debugging, we are aiming to produce a paper by the end of February and release the code so that other people can build on it by the end of April. My first physics project involved boson stars. Much of what I have done recently is to go back and try to revive old houses. I am now trying the same with technology/code. The equations have not changed and so it should not be too difficult if I can find the time to work, which is very challenging for me.
  • In December, Edward, David and I published our third book for children: You, me and the dinosaurs. This book is more theirs than mine. Mihai criticizes it for not being deep enough, but depth comes with age and the children and I like it the way it is -- for now.
Somehow I still feel the need to motivate my choices so that if I am not around to tell them or if I forget, my children understand why I made them. Also, plenty of people ask these questions and it's only fair to provide answers now and then.

Have I always lived like this when in Romania?
No, my parents are doctors. We've had cats and dogs when I was growing up, but but no farm animals. My grandparents had a few chicken. My grandmother and great aunt were mathematicians. My grandfather was a silvic engineer. They lived in this house before me. In fact, I've never had a goat myself before finishing my second postdoctoral position.

Ok, so are all Cornell graduates crazy? Cornell is in the US and after all and that country has a "very stable genius" for president. No, while I do not guarantee everyone's mental faculties, my former classmates from Cornell are goat-free and chicken-free. I know this from Facebook. Some have faculty positions, some have positions in industry and some teach at other levels. 

So, what's wrong with me?
I am using these animals to connect my children to the real world. When I go to school for updates on their behavior, we are told that children today are three years ahead of us. Teeth grow faster, puberty happens faster, and I backed up a bit in an attempt to slow down this time I have with them. Once we moved to Lugoj, Edward's teeth stopped falling. In Zurich, before he turned six he had changed both upper and lower teeth. We still eat food from the store, but some comes from the market (at least in spring and summer) and some from the trees in our back yard. The eggs are from our chicken and the milk from our goats. I hope that they will grow up to be healthy and have the courage to change the world. To prepare for this we travel, do math, read, and take care of things-- animals, plants, etc. They are children, and so my mother and I do close to all the work (David does milk Devina and Edwina twice a day), and I always worry we strive for too much, but somehow I am not able to stop. I also worry about their future in world where our leaders are too old to lead and cannot adapt and understand or support new technology. They destroy to stay in charge, plunge countries into pointless wars and take decisions that affect us all.

Saturday, November 25, 2017

New Topic in Frontiers: Women in Science!!!

From 'You, me and the dancing black holes' by Edward & David


Frontiers has launched a special topic to attract women in science to publish in its pages. 


The requirement is that either the lead author is a woman or the corresponding author. Articles that appear in this topic are free of charge. I am one of the editors and I wholeheartedly support the idea of promoting science done by women. In the academic community we lose talent too easily in both genders and lose opportunities for progress because of vast bureaucracy. I strongly believe we have reached a point where we cannot afford to let go of our best people if we want humanity to survive and continue to thrive. 

From 'You, me and the dancing black holes' by  Edward & David
Women are a minority in physics, chemistry, astronomy and computer science. I have witnessed physics at top institutions, and it is unfortunately still 'a boys club', where graduate students and postdocs are almost invisible even though they do most of the work and have preciously few rights. There is also no support for the families of graduate students and postdoctoral scholars. Little miracles have to happen in each individual case to make things work. My contract ended when I was eight month pregnant with my second son. As an immigrant, I could have chosen to extend my visa for three months to look for other work -- while 8 months pregnant -- and pay the living costs for myself and three children (I also have a foster son) from my savings or move back with my parents. I chose the latter. My advisor/department said that they cannot cover maternity for a contract that would have ended on that date anyhow. When I contacted Human Resources (HR), I have been told that they might have been able to work something out for my case if I had contacted them at an earlier stage, but that departments are under no obligations to report the pregnancies of their employees to HR. I was the second unreported pregnancy in my office and the first woman to use that office space. 

Most of my colleagues who have children and PhDs have stories that are hard to hear.  The Frontiers topic is, however, not focusing on hardships, but aims to celebrate the work done by talented scientists who happen to be women and are leaders in their field or are likely to become leaders in the years to come.

Why I enjoy publishing in Frontiers?

1) It's a more modern journal that opens an interactive forum with the referees, which is less intimidating and more prone towards constructive communication. After the review process the name of the referees are made public unless explicitly requested otherwise.

2) Its rules include that articles can only be rejected based on scientific arguments and not on personal opinions of the form 'this paper is not interesting enough. so, I reject it or I let you as an editor do as you please' (and no this is not made up. I've seen referee responses of this form. They also do not bother to use capital letters.)

3) Frontiers has a presence in social media, which targets a younger audience that uses social media effectively.

4) Frontiers counts the impact of each paper more thoroughly -- they go beyond the number of citations. You can see the number of views, social buzz, and the demographics of your audience.

And the only down side is ...
It is generally not free publish in frontiers. Note that it is free to publish as part of this topic and also that many journals cost money including Physical Review Letters and the Astrophysical Journal. I have been lucky enough to be supported by universities that pay these fees.

My last two technical articles are in Frontiers:

1. Explicit equations for a self-gravitating stellar collapse (note that all three authors are women and that this is my most mathematical paper to date). See my blog post on stellar collapse and time travel.

2.  general relativity as a tool to measure planetary spin in space-craft timing signals. See the planetary spin blog post on this paper to learn that planets spin faster than black holes.

Note: I opted to use my children's drawings to illustrate this post because it's what I have. Edward drew these women/girls with excitement that is visible on their faces. It's how scientists are. The words are allegoric. Women do shake the fields they are in (of course, we all shake the space-time when we dance), and some of their energy is sucked by the hardships faced, which are amplified by the gender gap. Marie Curie is the most famous example of a woman scientist, but there are so many other talented women out-there who shine today. I hope to see some of them publish in this topic in Frontiers.

Sunday, November 19, 2017

A belated introduction of Mrs. Edwina Cleverbrain, Mrs. Davina Cleverbrain and Ms. Jemsina Cleverbrain

From left to right: Snow, Lady David, Edward, and Lady Edward
This summer we spent the equivalent of $80 on ... goats. Mihai purchased them at my request from the village of Tormac. Their family had gone to work in Italy and was dismantling their farm. So, In June 2017, Snow White (the Lady James or Jemsina Cleverbrain), Snow White Five Years later (the mother of Snow White; also known the Fairest of them all or as the Lady David, Mrs. Devina Cleverbrain), and the genius goat (the Lady Edward or Ms. Edwina Cleverbrain) have joined our family.

Lady Edward and Lady David are like most mothers: friendly, highly intelligent and provide the best milk I have ever tasted. David milks them twice (and sometimes three times) a day. They are too amazing for words -- when one considers my writing ability. They are, however, described in almost every sentence Edward writes for his homework. 

My phone's collage of Edward (at a petting zoo & this summer)
Andy is not too happy with our naming scheme or with my latest acquisition. He said that he will leave me and never return if I buy a cow. This summer he spent his time helping the children milk the goats -- during and in-between gravitational wave detections -- AND claiming not to remember which one is Lady Edward and which one is Lady David (He also does not know whether he/LIGO is seeing black holes or boson stars; nobody knows that yet for sure.) His job was to hold the goats still, but before running to catch them he always asked us to tell him the colour of the goat he was after. Their colours are really very plain. One is white and the other is grey. In his school writing Edward  refers to his goat as 'Edward -- the goat' or 'Goat Edward'.  He mostly has to write in German and told me 'Frau Edward' would sound too strange for school, and I solemnly agreed.

The Genius Goat can open knots with her mouth and use a fork. She was observed to steal David's cup with left-over rice pudding, which had extra sugar and cacao in it. She put it gently on a a box, and started to take stuff out of the cup with David's fork. The door did not close well and to prevent the goats from coming inside and eating the grain (or sitting on my bed) we tied it with a knot. After I closed the gate as I was driving out with the children, we saw Lady Edward climb on her hind legs and gently open the knot with her mouth. Lady David is bigger, and very strong. She mostly pushes stuff with her head. Snow White climbs everywhere -- it's because she is the lightest. She can even climb on the car.

Edward turned seven this summer. David is ten, and little James just turned one. I stopped writing dedicated birthday posts. The children and our animals take so much care that I have not had the energy to write much before today, but tonight I could not sleep.  So, today after re-lighting the fire, I felt the need to write and not for useful, precise, science writing. I should, however, try to get some sleep to have the strength to wake up soon enough to take on the new day with school, animals and a one-year old AND people coming to install central heating (this time it's gas based). I promise to write more later ... after I do some work on boson stars and take some better pictures of David and his goat/the goats. I will first re-check the fire.

Update: The goats have new names so that they can enrol in school if they desire to or so Edward says. He also said his goat seemed so familiar when he first saw her at the farm because he had known  her from a previous life. She was his sister then and they immediately recognized each other. In the previous weeks he had thought he was a tortoise who lived very long and was too heavy to be taken and eaten by humans, but he is now certain he was a goat.

The former Lady Edward is now Mrs. Edwina Cleverbrain, the former Lady David is Mrs. Davina Cleverbrain, and the former Lady James is Ms. Jemsina Cleverbrain. I asked what grade they would be in, and he said they cannot be confined in a grade and they ought to be free to roam the whole school area. I can talk to the principal about enrolling them, but then I'd have to be responsible for taking more beings to school and it would get even harder to get everyone ready in the morning. I have, however, updated this post accordingly. I hope it is not too confusing. Those of you who find the naming scheme confusing would I am sure sympathize with Andy --- and perhaps prefer to seeing the ladies unglamourously referred to as 'the grey goat' and 'the white goat'.

Thursday, November 9, 2017

Measuring Planetary Spin from Spacecraft Timing

Exploring spacetime with general relativity


The trajectory of NASA's Juno Mission
General relativity is slowly becoming a tool that teaches us about the objects that curve spacetime instead of a hindrance to be corrected for. Planets are heavy and bend the fabric of spacetime affecting the orbits of satellites that go around them and the paths of light sent. Knowing very precisely when the light arrived, and when it was sent is part of space-craft timing. For Juno and Cassini this timing is already sensitive to higher order general relativistic effects like frame dragging. In the future, such measurements could be used to determine the spin of planets to within a percent, which can tell us about their interior. For missions in eccentric orbits relativistic effects are kick-like and can only be observed when the satellite is within a few hours of its pericentre.  We argue that instead of performing cumulative frame dragging measurements over many orbits as was done for Earth, high eccentricity missions like Juno and Cassini need the specific time dependence of each relativistic effect to aid in recovery.

A few words about gravity...

Bent spacetime affecting the orbit of a satellite & the light it sends
General relativity is the theory of gravitation. It says we live in four dimensions -- 3 spatial and 1 temporal -- and that space and time are connected. Gravitation itself is a consequence of the curvature of the spacetime. A planet is heavy and curves the spacetime around it causing it to seem like it pulls objects towards/around it.  This is gravity.

Redshift contribution from frame dragging for Juno. Zoom in.
Looking at relativistic effects
Missions like Juno and Cassini present new possibilities for measuring relativistic effects around the giant planets in our solar system. Relativistic effects are amplified if the orbit of the satellite is eccentric because the spacecraft moves faster and the satellite passes by the planet very closely where the gravitational field is stronger.  This coupled to the larger size of the planet causes frame dragging accelerations that are a few hundred times larger than those near Earth. Since the effects are larger, they might be easier to detect than around Earth.

Most planets have higher spins than black holes. The angular momentum per unit mass for black holes is less than 1, whereas for planets it can be of order hundreds. Earth has a spin on about 800 while Saturn's is about 1000. Precise frame dragging measurements can constrain planetary spin providing an independent estimate of the internal structure of the planet. This structure is relatively uncertain for the gas giants, which are believed to have an internal core of unknown size that rotates at a different rate than the surface.

 We simulate the trajectory of a satellite in a curved spacetime and find the path of the light it sends to receiving stations on Earth. Both follow 'straight lines' in their spacetime also called geodesics. The dynamics of a satellite orbiting a planet can largely be described by Newtonian physics with general relativity providing only small contributions.  The equations of motion are expanded in velocity orders to separate Newtonian and relativistic effects.

The biggest general relativistic effect is time dilation. GPS satellites are sensitive to time dilation and correct for it -- if they would not, the GPS would be off by about 10 km every day. Moving clocks tick slower than stationary clocks. So do clocks in a gravitational field. The ground station has its own time dilation and the difference between its tick signals and those arriving from the satellite are known as the redshift. We compute this redshift for satellites around Earth (Galileo and a proposed mission in an eccentric orbit) and for eccentric orbits around Jupiter (Juno) and Saturn (Cassini). Galileo satellites and the Atomic Clock Ensemble in space -- an ensemble of two atomic clocks that will be placed on the International space station in 2018 -- provide an even better measurements of time dilation, which tests the equivalence principle.

We are interested in higher order relativistic effects like frame dragging in which a spinning mass drags the spacetime in its vicinity affecting any orbiting satellite. The orbital plane of the satellite precesses about the spin axis of the planet. Historically, this effect was first predicted by in 1918 by Einstein, Lense and Thirring. They studied Amalthea, the third moon of Jupiter, and found that it precesses by 1'53'' per century.

Existent Measurements of frame dragging 
Orbital perturbations due to frame dragging have been measured using laser ranging by LARES and LAGEOS. Gravity Probe B measured the effects of frame dragging on the orientation of onboard gyroscopes. The effect is typically averaged over multiple orbits. It is then buried in much larger non-relativistic precession making it very hard to identify the relativistic contribution. E.g., Mercury's observed precession is mostly due to Newtonian planetary perturbations with the relativistic contribution being only about 7% of the total.

Relativistic effects for the Juno orbiter
Instead of averaging we compute each higher order relativistic effect as a function of time and find that they alter the orbit in a kick-like manner at the pericentre. For Juno the kick due to frame dragging could be measured for about two hours. We argue that technology has advanced enough so that we might be able to filter out these effects if we knew their specific time dependence.



This post summarizes results of:

Andreas Schaerer, Ruxandra Bondarescu, Prasenjit Saha, Raymond Angelil,  Ravit Helled and Philippe Jetzer, "Prospects for measuring Planetary Spin and Frame dragging in Spacecraft Timing Signals", Frontiers in Astronomy 4, 11 (2017).

Please read our article for more details.